14.2: Lamaze International Childbirth Education
By the end of this section, you will be able to:
- Discuss the history of Lamaze International childbirth education
- Verbalize the six evidence-based healthy birth practices that encompass the Lamaze International childbirth education practices
- Summarize the importance of shared decision making within the Lamaze International childbirth education program
- Summarize the importance of understanding the process of physiologic birth when educating birthing persons and their partners
- Discuss the education that is provided to birthing persons and their families regarding the postpartum period
Becoming educated in the process of pregnancy, labor, birth, and postpartum and newborn care is called childbirth education . It is a significant nursing intervention that can improve birth outcomes and the birth experience for the entire family. Lamaze is an educational platform that families have used to improve their confidence by preparing for birth. Lamaze is taught in many different birth settings.
History of Lamaze Childbirth Education
The Lamaze method was introduced in 1951 in France by Dr. Fernand Lamaze, who developed a technique for childbirth that consisted of relaxation, childbirth education classes, continuous emotional support, breathing techniques, and specially trained nurses who helped birthing people manage the intensity of birth (Lamaze International, n.d.). In the late 1950s, the Lamaze technique started to be used in the United States. Over time, Lamaze teachings shifted from childbirth education only to an evidence-based practice that supports physiologic birth and prepares birthing people to have confidence in their ability to birth and parent.
Evidence-Based Lamaze Childbirth Education
Research shows that labor care provided by a Lamaze-informed nurse increases rates of vaginal birth, shortens lengths of labor, and reduces pain and postpartum bleeding in first-time birthing patients (Wu et al., 2021). Moreover, birthing people have increased knowledge of pregnancy, nutrition needs, and exercise needs after completing Lamaze education (Mahalakshmi et al., 2018). Research has identified no risks associated with Lamaze childbirth education. These significant benefits should be discussed with hospitals and health-care providers and should be offered to families in their pregnancy care. The drawbacks to this method for patients include lack of access to the education, cost of the education, and inability to attend the necessary 8 weeks of sessions to complete the education. These factors can be a significant barrier to improved outcomes, especially in populations at higher risk who may want these resources but be unable to obtain them.
The WHO recommends four care practices, which were built into the Lamaze philosophy:
- Let labor begin on its own.
- Continuous labor support should be provided.
- Persons should avoid giving birth lying on their back.
- Birthing person/newborn couplets should stay together.
Two additional practices, position changes and avoidance of interventions, were added later. These recommendations are echoed in many other childbirth-education models as foundational practices that improve the experience and outcomes of birthing people (Lothian & Devries, 2017).
Let Labor Begin on Its Own
Spontaneous labor occurs by multiple avenues that are explored in Chapter 15 Process of Labor and Birth. Supporting the process is crucial to reducing interventions. Labor often begins in dark, calm, comfortable environments. If the environment is disrupted, this can stall or disrupt the process. Lamaze teaching includes a preference for the baby to come on their own when ready, to have early labor undisturbed in a comfortable or familiar environment, and to avoid the risks of induction of labor except for medical indications (Lothian & Devries, 2017).
Traditions and Culture Surrounding Birth
Birthing traditions are oftentimes associated with culture or religion. For example, in Cambodia and Lebanon, female relatives are in the room for birth; husbands are not in the room. However, fathers in India are more likely to be present during the birth. In Iran, pregnant persons many times attend Lamaze classes. Nurses must ask patients their preferences and respect their cultural values.
(Boules, n.d.)
Position Changes
The weeks leading to birth can prepare the body for labor. Lamaze teachings recommend that as labor nears, pregnant people should avoid semireclined positions like propped positioning in bed and reclined chairs to avoid undesirable fetal positions. Frequent position changes during labor, especially a balance of upright and restful positions, can encourage labor progression and prevent fatigue (see 17.1 Nonpharmacological Pain Management). The American College of Obstetricians and Gynecologists (ACOG; 2019) suggests frequent position changes during labor to increase comfort and assist in fetal positioning. Research has shown that labor can be shortened by more than an hour for persons laboring in an upright position (Ondeck, 2019). Freedom of movement is one of the core principles of a healthy birth (Lothian & Devries, 2017).
Continuous Labor Support
People typically deal better with stress when surrounded by people who love and respect them. Labor support goes much further than reviewing monitor strips and changing intravenous (IV) fluids. Labor support includes respecting the person’s space and providing reassurance that they are capable of birth. Quality labor support can be provided by a labor nurse offering heat or ice for comfort, assisting with position changes, providing words of encouragement, or holding space without discomfort in the silence, when words may be disruptive (Lothian & Devries, 2017). A loved one or doula can also provide excellent labor support, especially when nurses have additional responsibilities and are caring for more than one patient.
Avoid Unnecessary Interventions
Lamaze teaching cautions against the use of continuous fetal monitoring, restricted eating or drinking, intravenous fluids, epidural anesthesia, artificial rupture of membranes, induction or augmentation with oxytocin ( Pitocin ), or episiotomy (Lothian & Devries, 2017). These interventions are not done unless they are medically necessary. ACOG (2019) suggests individualized labor management according to pregnancy risk factors. Lamaze stresses the importance of shared decision making between the couple and health-care provider. ACOG also notes that intermittent auscultation, noncoached pushing, not artificially rupturing the membranes, and family-centered care are safe for low-risk persons and help limit interventions in labor.
Push in Your Own Position
When allowed to choose, most laboring persons prefer to push in the upright position (Huang et al., 2019). This position allows gravity to assist in the descent of the fetus. The majority of laboring persons in hospitals in the United States are placed in a supine position, which does not encourage spontaneous pushing efforts. Lamaze teaching recommends pushing how and where it feels right to the birthing person because their body and instincts know the exact movements that are necessary for the fetus to navigate the pelvis (Lothian & Devries, 2017).
Couplets Should Stay Together
Birthing people and their newborns should remain together, as shown in Figure 14.2. This idea is a constant theme throughout most childbirth-education programs and even part of the Baby-Friendly Initiative (BFI) in the United States. The BFI was developed by the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) as a global program to implement the “Ten Steps to Successful Breastfeeding” (Baby-Friendly USA, 2024). Lamaze teachings include couplets staying together to improve their bond, assist with breast-feeding, and assist with newborn transition to extrauterine life (Lothian & Devries, 2017).
Shared Decision Making
Shared decision making improves patient autonomy, satisfaction, and safety and reduces health-care costs (Vanderlaan & Givens, n.d.). Because evidence supports shared decision making, Lamaze International has added this to its advocacy resources and recommendations for health-care providers (Vanderlaan & Givens, n.d.). Research shows that the most confounding factor for use of shared decision making is the short duration of a prenatal visit (Vanderlaan & Givens, n.d.). Childbirth education like Lamaze can fill the gap and provide time for questions and answers so that patients have the knowledge to make informed decisions and develop a written birth plan to share with their health-care provider and birthing facility.
Rights of Childbearing Persons
Knowing the rights of birthing people is crucial for nurses. Not all people are provided the same rights for birth as others. For example, Black people have been denied equal rights in birth through overt decisions and systemic racism. Lamaze points out that it is not the job of the Black person to fight for equal rights in the health-care system during labor. Instead, it is the responsibility of the nurse and health-care provider to provide care that is equal and nonbiased (Terreri, 2020). The nurse advocates for the birthing person and family, and if that advocacy is not deeply engrained in the nurse, it may not be possible for them to provide safe, equitable, and quality care. Lamaze education includes an extensive list of patient rights with which all obstetric nurses should become familiar (Terreri, 2020).
Communication and Negotiation Skills
Lamaze teachings include educating the pregnant person or couple on how to communicate a preference for nonintervention of the health-care provider into the labor progress and birthing process when a low-risk labor and birth are expected. The strategies taught include alertness, informed basis for decision making, confidence in the knowledge gained, and communication through requests for explanations and more information as well as available alternatives. This allows the patient and family time to weigh the risks and benefits of each option (Lothian & DeVries, 2017).
When and How to Connect with the Health-Care Provider
As previously discussed, the biggest risk for having a cesarean birth is the birth setting . Lamaze teaches families to find the environment in which the patient is most comfortable. Patients should research the type of health-care provider that mirrors their philosophy of birth, whether that is an OB, a midwife, or a family practitioner. Lamaze also teaches patients to trust their instincts and change providers if they no longer feel comfortable or sense their provider is no longer using shared decision making (Grauer, n.d.).
Physiologic Birth Process
When a birth occurs vaginally and without medical intervention, it is considered a physiologic birth (International Childbirth Education Association [ICEA], 2015). Factors that increase the success of physiologic birth are the pregnant person’s health and childbirth education (ICEA, 2015). Factors that interrupt physiologic labor are artificial rupture of membranes prior to active labor, induction of labor, augmentation of labor, and epidural anesthesia. Lamaze education identifies the normal processes of birth and the few alterations from normal that indicate the need for intervention. These teachings also include lists of basic care, screening options, and interventions categorized by their balance of risks to benefits, including effectiveness (Lothian & DeVries, 2017). Lamaze supports the American College of Nurse Midwives , Midwives Alliance of North American , and the National Association of Certified Professional Midwives ’ joint statement, titled “Supporting Health and Normal Physiologic Childbirth: A Consensus Statement by ACNM, MANA, and NACPM” (Muza, 2012). The principles taught in Lamaze give patients the opportunity to make informed choices that allow for physiologic birth to occur.
Read this article that discusses the consensus statement by ACNM, MANA, and NACPM supporting normal physiologic childbirth.
Birth Is Normal
Lamaze teachings include the following six healthy practices for birthing persons that promote normal birth:
- Let labor begin on its own.
- Walk, move around, and change position throughout labor.
- Bring a loved one, friend, or doula for continuous support.
- Avoid interventions that are not medically necessary.
- Avoid giving birth on your back and follow your body’s urges to push.
-
Keep birthing person and baby together; it is best for both and for chest-feeding.
( What is a safe and healthy birth? n.d.)
The Lamaze teachings also include references from the Cochrane Database of Systematic Reviews as evidence that birth is normal (Lothian & DeVries, 2017). Lamaze International attempted to define “normal birth” and found that 36 percent of polled persons assigned female at birth felt that “normal birth” meant they had had a vaginal birth; 63 percent of Lamaze instructors defined it as any birth without interventions (Prusky, 2010). No consensus exists of what constitutes a “normal birth,” but Lamaze teaches that avoiding unnecessary interventions and following evidence-based practice will lead to a successful, satisfying birth experience.
Physical and Emotional Responses to Birth
Preparing for birth includes exploring expectations about and tools needed to navigate the intensity of labor. Lamaze teachings include how to view birth as a task instead of a trial, as pain with a purpose; how to create a comfortable environment, reduce pain perception, find a rhythm in the ebb and flow of labor; and how to acknowledge the realities of labor pain (Lothian & DeVries, 2017). Patients taking Lamaze classes learn that labor is normal and that preparing emotionally with their partner is an important part of birth preparation. They are also taught exercises to prepare their body for birth; these are summarized in (Table 14.1).
| Trimester | Exercise* |
|---|---|
| Every trimester |
Walking
Swimming Yoga Kegels |
| First trimester |
Can continue to perform the same workouts as prior to pregnancy
Taking a break when needed Staying hydrated |
| Second and third trimesters |
Focus on low-impact exercises
Yoga Strengthening muscles for labor Taking breaks when needed Avoid lying on back during exercises |
|
*The pregnant person should always check with their provider before starting an exercise routine. |
Last Weeks of Pregnancy
Preparing for labor takes months, even though the process itself may take only hours or days. The weeks leading up to birth can be physically and emotionally taxing. Lamaze teachings review the meanings behind these late-pregnancy discomforts and how to ease through them to prepare for a positive birth (Lothian & DeVries, 2017). Lamaze teaches that many pregnant persons will have backaches, insomnia, hip pain, and discomforts of pregnancy in the third trimester. Their recommendations consist of the following:
- Remember the person will not be pregnant forever.
- Take time to sit and feel the baby inside.
- Take naps and rest.
- Take a bath.
-
Stretch, do yoga.
(Terreri, 2020)
Postpartum Life and Parenting
The transition into parenthood or the addition of a new child to a previously smaller family unit is an adjustment. Lamaze teachings include information on the transition to extrauterine life for the newborn, bonding with the birthing parent, overview of newborn procedures and feeding, adjusting to life with a newborn, and postpartum recovery. Distinguishing between expected physical and emotional changes and those that can be warning signs of pathologic processes is crucial for birthing people and their nurses to understand. Lamaze teachings help identify when to seek for help when trouble arises (Lothian & DeVries, 2017).
Nurse:
Courtney W., MS, APRN, CNM
Years in practice:
6
Clinical setting:
Labor and birth unit
Geographic location:
Dallas, Texas
As a new nurse, I was fascinated by people who were able to give birth without an epidural, in part because it happened so infrequently on the unit where I worked. Most of those who did not have the epidural experienced quickly progressing labors without time to administer the anesthetic before birth, and they were clearly suffering. This all changed when I witnessed my first patient with a planned and well-prepared-for unmedicated birth. She was calm and focused. She listened to her body. She had a doula who supported her and her partner. They worked together beautifully.  I went on to study childbirth education, doula support in labor, and finally went to graduate school to become a midwife after seeing the difference quality prenatal care with education can have on birth outcomes and experiences.


11.3: Unit C- What to Do When Injuries and Emergencies Happen
While Home Health Aides/Personal Care Aides work to keep their patient and their home safe, there are situations where an accident may occur. It is important that Home Health Aides/Personal Care Aides are aware of their agency’s policies regarding incidents. Most agencies will have provided them with training in how to deal with emergency situations. This will include the agency’s policies and procedures and an emergency contact list.If Home Health Aides/Personal Care Aides have not been informed about their agency’s policies and procedures, they should speak with their supervisor to find out what the procedures are in dealing with emergencies. Whenever in doubt, call a supervisor.


5.4: Population Growth and Consumption?
Until about 150 years ago, the rate of human population growth in Africa had been relatively slow, with the birth rate only slightly exceeding the death rate. Modern medical achievements and more reliable food supplies have changed this balance; they have reduced mortality rates while birth rates remain high. Consequently, Sub-Saharan Africa’s human population has exploded to 1 billion people over the past decade (World Bank, 2019). Today, Sub-Saharan Africa is leading the world in human population growth, projected to increase by four-fold over the next century. Population growth rates for individual countries are similar, if not higher. For example, Ethiopia’s human population has grown from 48 million in 1990—when the region experienced a famine crisis—to nearly 100 million in 2015; current projections forecast a population of 172 million by 2050. The human population of Tanzania’s Dar es Salaam, a coastal city particularly vulnerable to sea level rise (Section 6.3.2), is expected to increase from 4 million to 21 million between 2015 and 2050, while Lagos in Nigeria is expected to grow from 21 million to 39 million people over the same time.
Simple math suggests that more people leads to less space for biodiversity (Figure 5.8), because humans and wildlife compete for the same resources, broadly speaking. With many countries in Africa already facing social, economic, and developmental challenges such as malnutrition, crime, and unemployment, one can almost understand why politicians prioritise socio-economic upliftment over biodiversity conservation. This is a grave mistake; as discussed in Chapter 4, biodiversity and human well-being are intricately linked. It is one of conservation biologists’ most important tasks: to make the link between conservation and human welfare clear to policy scholars and politicians.
In recent years, there has been an increasing tendency of economists, scientists, and politicians to shift the focus from population growth to consumption as the more important underlying driver of biodiversity loss. For many, the emphasis on consumption avoids politically charged topics, such as population control, which most people oppose on ethical or moral grounds, and because it is associated with divisive topics such as xenophobia, racism, and eugenics (Kolbert and Roberts, 2017). Others highlight that it is not the number of people per se, but how natural resources are consumed that is the main cause of environmental decline. Indeed, affluent people and affluent countries have a disproportionate impact on the natural environment because they consume a disproportionately large share of the world’s natural resources. To use one example, the USA accommodates only 5% of the world’s human population but uses 25% of the world’s harvested natural resources each year (WRI, 2019). In fact, decorative Christmas lights in the USA alone use more energy than the annual energy usage of the entirety of Ethiopia or Tanzania (Moss and Agyapong, 2015). And yet, the average USA citizen uses less than half of the energy (measured as carbon emissions) that an average citizen of Qatar uses (World Bank, 2019; see also Figure 5.9), Qatar being a small but wealthy Middle Eastern country.
The major threats to biodiversity are all rooted in expanding human populations and unsustainable consumption patterns.
The global demand for natural resources such as coffee, cacao, palm oil, and timber is helping fuel habitat loss in Africa.
Another important aspect to consider in the consumption argument is that, through increased globalisation , the impacts of consumption in industrialized countries are felt over much greater distances than before (Moran and Kanemoto, 2017). For instance, chocolate consumed in Europe was most likely made with cacao produced in West Africa (Gockowski and Sonwa, 2011); other crops, such as coffee and tea, produced in Africa are similarly enjoyed all over the world. In the best-case scenario, African farmers are satisfying a demand in a global market; at worst, foreign companies are establishing croplands with little benefit trickling down to local people. Supporters of the consumption argument rightfully point out that it would be very unjust to blame the local farmers for cleared forests when they simply produce commodity crops that the international market demands.
As with many other complex challenges, both sides of the population-consumption debate are correct. One method to link the impact (\(I\)) of a human population on the environment is through the formula
\(I = P × A × T\]
This is the IPAT in short, where \(P\) is population size, \(A\) is Affluence (e.g. per capita GPD), and \(T\) is technology (e.g. per capita energy use) (Ehrlich and Goulder, 2007). The IPAT equation is similar in concept to the ecological footprint (Figure 5.9): both illustrate that human populations and consumption patterns interact to exacerbate human impacts on the environment. In other words, many poor Africans can have the same impact on the environment as just a few wealthy Americans, and vice versa.
Both the IPAT equation and ecological footprint concept are insightful as to the challenges facing Africa’s ecosystems and people. Today, Africans are increasingly aspiring to attain the same levels of high consumption as industrial countries. These patterns generally lead to an inefficient, wasteful, and unsustainable use of natural resources (i.e. overconsumption). Population growth rates in many industrial countries are currently slowing; some countries are even experiencing long-term population declines, which allow conservation-minded individuals in those countries to focus their efforts on addressing consumption patterns. The situation is quite different in Africa, where we are faced with increasing per capita consumption and the fastest growing human population on Earth. In the face of the resulting increased competition for space, African conservation biologists must adopt a holistic approach to ensure that welfare standards are upheld or improved while our natural heritage is protected. One of the most important strategies involves championing sustainable economic development over unsustainable economic growth (Section 15.1). While conservation biologists differ in terms of how strongly they argue for addressing the population size issue, most also agree that conservation goals benefit from education, the empowerment of women, and wider access to family planning and reproductive health services.


5.7: Gene Regulation and Operon Theory
- Compare inducible operons and repressible operons
- Describe why regulation of operons is important
Genomic DNA contains both structural genes, which encode products that serve as cellular structures or enzymes, and regulatory genes, which encode products that regulate gene expression. The expression of a gene is a highly regulated process. Whereas regulating gene expression in multicellular organisms allows for cellular differentiation, in single-celled organisms like prokaryotes, it primarily ensures that a cell’s resources are not wasted making proteins (especially enzymes- which use up energy as they are synthesized and as they are speeding up chemical reactions) that the cell does not need at that time.
Each nucleated cell in a multicellular organism contains copies of the same DNA. Similarly, all cells in two pure bacterial cultures inoculated from the same starting colony contain the same DNA, with the exception of changes that arise from spontaneous mutations. If each cell in a multicellular organism has the same DNA, then how is it that cells in different parts of the organism’s body exhibit different characteristics? Similarly, how is it that the same bacterial cells within two pure cultures exposed to different environmental conditions can exhibit different phenotypes? In both cases, each genetically identical cell does not turn on, or express, the same set of genes. Only a subset of proteins in a cell at a given time is expressed.
Elucidating the mechanisms controlling gene expression is important to the understanding of human health. Malfunctions in this process in humans lead to the development of cancer and other diseases. Understanding the interaction between the gene expression of a pathogen and that of its human host is important for the understanding of a particular infectious disease. Gene regulation involves a complex web of interactions within a given cell among signals from the cell’s environment, signaling molecules within the cell, and the cell’s DNA. These interactions lead to the expression of some genes and the suppression of others, depending on circumstances.
Prokaryotes and eukaryotes share some similarities in their mechanisms to regulate gene expression; however, gene expression in eukaryotes is more complicated because of the temporal and spatial separation between the processes of transcription and translation. Thus, although most regulation of gene expression occurs through transcriptional control in prokaryotes, regulation of gene expression in eukaryotes occurs at the transcriptional level and post-transcriptionally (after the primary transcript has been made).
Prokaryotic Gene Regulation
In bacteria and archaea, structural proteins with related functions are usually encoded together within the genome in a block called an operon and are transcribed together under the control of a single promoter, resulting in the formation of a polycistronic transcript (Figure \(\PageIndex{1}\)). In this way, regulation of the transcription of all of the structural genes encoding the enzymes that catalyze the many steps in a single biochemical pathway can be controlled simultaneously, because they will either all be needed at the same time, or none will be needed. For example, in E. coli , all of the structural genes that encode enzymes needed to use lactose as an energy source lie next to each other in the lactose (or lac ) operon under the control of a single promoter, the lac promoter. French scientists François Jacob (1920–2013) and Jacques Monod at the Pasteur Institute were the first to show the organization of bacterial genes into operons, through their studies on the lac operon of E. coli . For this work, they won the Nobel Prize in Physiology or Medicine in 1965. Although eukaryotic genes are not organized into operons, prokaryotic operons are excellent models for learning about gene regulation generally. There are some gene clusters in eukaryotes that function similar to operons. Many of the principles can be applied to eukaryotic systems and contribute to our understanding of changes in gene expression in eukaryotes that can result pathological changes such as cancer.
Each operon includes DNA sequences that influence its own transcription; these are located in a region called the regulatory region. The regulatory region includes the promoter and the region surrounding the promoter, to which transcription factors, proteins encoded by regulatory genes, can bind. Transcription factors influence the binding of RNA polymerase to the promoter and allow its progression to transcribe structural genes. A repressor is a transcription factor that suppresses transcription of a gene in response to an external stimulus by binding to a DNA sequence within the regulatory region called the operator, which is located between the RNA polymerase binding site of the promoter and the transcriptional start site of the first structural gene. Repressor binding physically blocks RNA polymerase from transcribing structural genes. Conversely, an activator is a transcription factor that increases the transcription of a gene in response to an external stimulus by facilitating RNA polymerase binding to the promoter. An inducer, a third type of regulatory molecule, is a small molecule that either activates or represses transcription by interacting with a repressor or an activator.
In prokaryotes, there are examples of operons whose gene products are required rather consistently and whose expression, therefore, is unregulated. Such operons are constitutively expressed, meaning they are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products. Such genes encode enzymes involved in housekeeping functions required for cellular maintenance, including DNA replication, repair, and expression, as well as enzymes involved in core metabolism. In contrast, there are other prokaryotic operons that are expressed only when needed and are regulated by repressors, activators, and inducers.
- What are the parts in the DNA sequence of an operon?
- What types of regulatory molecules are there?
Regulation by Repression and Induction
Prokaryotic operons are commonly controlled by the binding of repressors to operator regions, thereby preventing the transcription of the structural genes. Such operons are classified as either repressible operons or inducible operons. Repressible operons, like the tryptophan ( trp ) operon, typically contain genes encoding enzymes required for a biosynthetic pathway. As long as the product of the pathway, like tryptophan, continues to be required by the cell, a repressible operon will continue to be expressed. However, when the product of the biosynthetic pathway begins to accumulate in the cell, removing the need for the cell to continue to make more, the expression of the operon is repressed. Conversely, inducible operons , like the lac operon of E. coli , often contain genes encoding enzymes in a pathway involved in the metabolism of a specific substrate like lactose. These enzymes are only required when that substrate is available, thus expression of the operons is typically induced only in the presence of the substrate.
The trp Operon: A Repressible Operon
E. coli can synthesize tryptophan using enzymes that are encoded by five structural genes located next to each other in the trp operon (Figure \(\PageIndex{2}\)). When environmental tryptophan is low, the operon is turned on. This means that transcription is initiated, the genes are expressed, and tryptophan is synthesized. However, if tryptophan is present in the environment, the trp operon is turned off. Transcription does not occur and tryptophan is not synthesized.
When tryptophan is not present in the cell, the repressor by itself does not bind to the operator; therefore, the operon is active and tryptophan is synthesized. However, when tryptophan accumulates in the cell, two tryptophan molecules bind to the trp repressor molecule, which changes its shape, allowing it to bind to the trp operator. This binding of the active form of the trp repressor to the operator blocks RNA polymerase from transcribing the structural genes, stopping expression of the operon. Thus, the actual product of the biosynthetic pathway controlled by the operon regulates the expression of the operon.
Watch this video to learn more about the trp operon.
The lac Operon: An Inducible Operon
The lac operon is an example of an inducible operon that is also subject to activation in the absence of glucose (Figure \(\PageIndex{3}\)). The lac operon encodes three structural genes necessary to acquire and process the disaccharide lactose from the environment, breaking it down into the simple sugars glucose and galactose. For the lac operon to be expressed, lactose must be present. This makes sense for the cell because it would be energetically wasteful to create the enzymes to process lactose if lactose was not available.
In the absence of lactose, the lac repressor is bound to the operator region of the lac operon, physically preventing RNA polymerase from transcribing the structural genes. However, when lactose is present, the lactose inside the cell is converted to allolactose. Allolactose serves as an inducer molecule, binding to the repressor and changing its shape so that it is no longer able to bind to the operator DNA. Removal of the repressor in the presence of lactose allows RNA polymerase to move through the operator region and begin transcription of the lac structural genes.
The lac Operon: Activation by Catabolite Activator Protein
Bacteria typically have the ability to use a variety of substrates as carbon sources. However, because glucose is usually preferable to other substrates, bacteria have mechanisms to ensure that alternative substrates are only used when glucose has been depleted. Additionally, bacteria have mechanisms to ensure that the genes encoding enzymes for using alternative substrates are expressed only when the alternative substrate is available. In the 1940s, Jacques Monod was the first to demonstrate the preference for certain substrates over others through his studies of E. coli ’s growth when cultured in the presence of two different substrates simultaneously. Such studies generated diauxic growth curves, like the one shown in Figure \(\PageIndex{4}\). Although the preferred substrate glucose is used first, E. coli grows quickly and the enzymes for lactose metabolism are absent. However, once glucose levels are depleted, growth rates slow, inducing the expression of the enzymes needed for the metabolism of the second substrate, lactose. Notice how the growth rate in lactose is slower, as indicated by the lower steepness of the growth curve.
The ability to switch from glucose use to another substrate like lactose is a consequence of the activity of an enzyme called Enzyme IIA (EIIA). When glucose levels drop, cells produce less ATP from catabolism, and EIIA becomes phosphorylated. Phosphorylated EIIA activates adenylyl cyclase, an enzyme that converts some of the remaining ATP to cyclic AMP (cAMP), a cyclic derivative of AMP and important signaling molecule involved in glucose and energy metabolism in E. coli . As a result, cAMP levels begin to rise in the cell (Figure \(\PageIndex{5}\)).The lac operon also plays a role in this switch from using glucose to using lactose. When glucose is scarce, the accumulating cAMP caused by increased adenylyl cyclase activity binds to catabolite activator protein (CAP), also known as cAMP receptor protein (CRP). The complex binds to the promoter region of the lac operon (Figure \(\PageIndex{6}\)). In the regulatory regions of these operons, a CAP binding site is located upstream of the RNA polymerase binding site in the promoter. Binding of the CAP-cAMP complex to this site increases the binding ability of RNA polymerase to the promoter region to initiate the transcription of the structural genes. Thus, in the case of the lac operon, for transcription to occur, lactose must be present (removing the lac repressor protein) and glucose levels must be depleted (allowing binding of an activating protein). When glucose levels are high, there is catabolite repression of operons encoding enzymes for the metabolism of alternative substrates. Because of low cAMP levels under these conditions, there is an insufficient amount of the CAP-cAMP complex to activate transcription of these operons. See Table \(\PageIndex{1}\) for a summary of the regulation of the lac operon.
| Glucose | CAP binds | Lactose | Repressor binds | Transcription |
|---|---|---|---|---|
| + | – | – | + | No |
| + | – | + | – | Some |
| – | + | – | + | No |
| – | + | + | – | Yes |
Watch an animated tutorial about the workings of lac operon here.
- What affects the binding of the trp operon repressor to the operator?
- How and when is the behavior of the lac repressor protein altered?
- In addition to being repressible, how else is the lac operon regulated?
Global Responses of Prokaryotes
In prokaryotes, there are also several higher levels of gene regulation that have the ability to control the transcription of many related operons simultaneously in response to an environmental signal. A group of operons all controlled simultaneously is called a regulon.
Alarmones
When sensing impending stress, prokaryotes alter the expression of a wide variety of operons to respond in coordination. They do this through the production of alarmones, which are small intracellular nucleotide derivatives. Alarmones change which genes are expressed and stimulate the expression of specific stress-response genes. The use of alarmones to alter gene expression in response to stress appears to be important in pathogenic bacteria. On encountering host defense mechanisms and other harsh conditions during infection, many operons encoding virulence genes are upregulated in response to alarmone signaling. Knowledge of these responses is key to being able to fully understand the infection process of many pathogens and to the development of therapies to counter this process.
Alternate σ Factors
Since the σ subunit of bacterial RNA polymerase confers specificity as to which promoters should be transcribed, altering the σ factor used is another way for bacteria to quickly and globally change what regulons are transcribed at a given time. The σ factor recognizes sequences within a bacterial promoter, so different σ factors will each recognize slightly different promoter sequences. In this way, when the cell senses specific environmental conditions, it may respond by changing which σ factor it expresses, degrading the old one and producing a new one to transcribe the operons encoding genes whose products will be useful under the new environmental condition. For example, in sporulating bacteria of the genera Bacillus and Clostridium (which include many pathogens), a group of σ factors controls the expression of the many genes needed for sporulation in response to sporulation-stimulating signals.
- What is the name given to a collection of operons that can be regulated as a group?
- What type of stimulus would trigger the transcription of a different σ factor?
Other Factors Affecting Gene Expression in Prokaryotes and Eukaryotes
Although most gene expression is regulated at the level of transcription initiation in prokaryotes, there are also mechanisms to control both the completion of transcription as well as translation concurrently. Since their discovery, these mechanisms have been shown to control the completion of transcription and translation of many prokaryotic operons. Because these mechanisms link the regulation of transcription and translation directly, they are specific to prokaryotes, because these processes are physically separated in eukaryotes.
Although the focus on our discussion of transcriptional control used prokaryotic operons as examples, eukaryotic transcriptional control is similar in many ways. As in prokaryotes, eukaryotic transcription can be controlled through the binding of transcription factors including repressors and activators. Interestingly, eukaryotic transcription can be influenced by the binding of proteins to regions of DNA, called enhancers, rather far away from the gene, through DNA looping facilitated between the enhancer and the promoter (Figure \(\PageIndex{7}\)). Overall, regulating transcription is a highly effective way to control gene expression in both prokaryotes and eukaryotes. However, the control of gene expression in eukaryotes in response to environmental and cellular stresses can be accomplished in additional ways without the binding of transcription factors to regulatory regions.
DNA-Level Control
In eukaryotes, the DNA molecules or associated histones can be chemically modified in such a way as to influence transcription; this is called epigenetic regulation. Methylation of certain cytosine nucleotides in DNA in response to environmental factors has been shown to influence use of such DNA for transcription, with DNA methylation commonly correlating to lowered levels of gene expression. Additionally, in response to environmental factors, histone proteins for packaging DNA can also be chemically modified in multiple ways, including acetylation and deacetylation, influencing the packaging state of DNA and thus affecting the availability of loosely wound DNA for transcription. These chemical modifications can sometimes be maintained through multiple rounds of cell division, making at least some of these epigenetic changes heritable.
Because different regions of DNA are packaged differently, some regions of chromosomal DNA are more accessible to enzymes and thus may be used more readily as templates for gene expression. Interestingly, several bacteria, including Helicobacter pylori and Shigella flexneri , have been shown to induce epigenetic changes in their hosts upon infection, leading to chromatin remodeling that may cause long-term effects on host immunity. 1
Noncoding DNA
In addition to genes, a genome also contains many regions of noncoding DNA that do not encode proteins or stable RNA products. Noncoding DNA is commonly found in areas prior to the start of coding sequences of genes as well as in intergenic regions (i.e., DNA sequences located between genes) Figure \(\PageIndex{8}\).
Prokaryotes appear to use their genomes very efficiently, with only an average of 12% of the genome being taken up by noncoding sequences. In contrast, noncoding DNA can represent about 98% of the genome in eukaryotes, as seen in humans, but the percentage of noncoding DNA varies between species. 2 These noncoding DNA regions were once referred to as “junk DNA”; however, this terminology is no longer widely accepted because scientists have since found roles for some of these regions, many of which contribute to the regulation of transcription or translation through the production of small noncoding RNA molecules, DNA packaging, and chromosomal stability. Although scientists may not fully understand the roles of all noncoding regions of DNA, it is generally believed that they do have purposes within the cell.
This video describes how epigenetic regulation controls gene expression.
- Describe the function of an enhancer.
- Describe two mechanisms of epigenetic regulation in eukaryotes.
- What is the role of noncoding DNA?
Key Concepts and Summary
- Gene expression is a tightly regulated process.
- Gene expression in prokaryotes is largely regulated at the point of transcription. Gene expression in eukaryotes is additionally regulated post-transcriptionally.
- Prokaryotic structural genes of related function are often organized into operons , all controlled by transcription from a single promoter. The regulatory region of an operon includes the promoter itself and the region surrounding the promoter to which transcription factors can bind to influence transcription.
- Although some operons are constitutively expressed , most are subject to regulation through the use of transcription factors (repressors and activators). A repressor binds to an operator , a DNA sequence within the regulatory region between the RNA polymerase binding site in the promoter and first structural gene, thereby physically blocking transcription of these operons. An activator binds within the regulatory region of an operon, helping RNA polymerase bind to the promoter, thereby enhancing the transcription of this operon. An inducer influences transcription through interacting with a repressor or activator.
- The trp operon is a classic example of a repressible operon . When tryptophan accumulates, tryptophan binds to a repressor, which then binds to the operator, preventing further transcription.
- The lac operon is a classic example an inducible operon . When lactose is present in the cell, it is converted to allolactose. Allolactose acts as an inducer, binding to the repressor and preventing the repressor from binding to the operator. This allows transcription of the structural genes.
- The lac operon is also subject to activation. When glucose levels are depleted, some cellular ATP is converted into cAMP, which binds to the catabolite activator protein (CAP) . The cAMP-CAP complex activates transcription of the lac operon. When glucose levels are high, its presence prevents transcription of the lac operon and other operons by catabolite repression .
- Small intracellular molecules called alarmones are made in response to various environmental stresses, allowing bacteria to control the transcription of a group of operons, called a regulon.
- Bacteria have the ability to change which σ factor of RNA polymerase they use in response to environmental conditions to quickly and globally change which regulons are transcribed.
- There are additional points of regulation of gene expression in prokaryotes and eukaryotes. In eukaryotes, epigenetic regulation by chemical modification of DNA or histones, and regulation of RNA processing are two methods.
Footnotes
- H. Bierne et al. “Epigenetics and Bacterial Infections.” Cold Spring Harbor Perspectives in Medicine 2 no. 12 (2012):a010272.
- R.J. Taft et al. “The Relationship between Non-Protein-Coding DNA and Eukaryotic Complexity.” Bioessays 29 no. 3 (2007):288–299.
Contributors and Attributions
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Nina Parker, (Shenandoah University), Mark Schneegurt (Wichita State University), Anh-Hue Thi Tu (Georgia Southwestern State University), Philip Lister (Central New Mexico Community College), and Brian M. Forster (Saint Joseph’s University) with many contributing authors. Original content via Openstax (CC BY 4.0; Access for free at https://openstax.org/books/microbiology/pages/1-introduction )