Each cell of a multicellular organism contain the same genetic material, but the expression of the gene is different in different type of cell group. On the basis of expression requirement they are grouped in to
Structural Gene- Mostly expressed once in a life
Vital Gene- Involved in of vital biochemical processes such as respiration and need to be expressed all the time
Functional Gene- Genes are not expressed all the time. They are switched on an off at need
The regulation of Gene required in case of functional gene and its explained by Francois Jacob, Jacques Monod and Andre Lwoff (Nobal Prize in 1961)
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
Introduction
Cre-lox recombination
Cre-lox system- Cre recombinase , loxP site
FLP-FRT recombination
FLP-FRT system- FLP recombinase , FRT site
Mechanism of Cre-lox and FLP-FRT recombination
Binding
Synapsis , cleavage and strand exchange
Three type of arrangement
Inversion
Translocation/ Insersion
Deletion
Application of Cre-lox and FLP-FRT recombination
Disadvantage of FLP-FRT
Advantage and disadvantage of Cre-lox
Conclusion
References
Most bacteria are free-living organisms that grow by increasing
in mass and then divide by binary fission.
Growth and division are controlled by genes, the expression
of which must be regulated appropriately. Genes
whose activity is controlled in response to the needs of a
cell or organism are called regulated genes. All organisms
also have a large number of genes whose products
are essential to the normal functioning of a growing and
dividing cell, no matter what the conditions are. These
genes are always active in growing cells and are known as
constitutive genes or housekeeping genes; examples include
genes that code for the enzymes needed for protein
synthesis and glucose metabolism. Note that all genes are
regulated on some level. If normal cell function is impaired
for some reason, the expression of all genes, including
constitutive genes, is reduced by regulatory
mechanisms. Thus, the distinction between regulated
and constitutive genes is somewhat arbitrary.
Imagine a situation when a cell starts producing enzymes required for metabolism and those required for cell death (apoptosis) at the same time. The cell will be in a confused state and will not know which function to perform first. The needs of the body keep changing with time and cell has to tune itself to perform the desired set of activities. Gene regulation helps a unicellular organism to adapt well to the environment.
Introduction
Cre-lox recombination
Cre-lox system- Cre recombinase , loxP site
FLP-FRT recombination
FLP-FRT system- FLP recombinase , FRT site
Mechanism of Cre-lox and FLP-FRT recombination
Binding
Synapsis , cleavage and strand exchange
Three type of arrangement
Inversion
Translocation/ Insersion
Deletion
Application of Cre-lox and FLP-FRT recombination
Disadvantage of FLP-FRT
Advantage and disadvantage of Cre-lox
Conclusion
References
Most bacteria are free-living organisms that grow by increasing
in mass and then divide by binary fission.
Growth and division are controlled by genes, the expression
of which must be regulated appropriately. Genes
whose activity is controlled in response to the needs of a
cell or organism are called regulated genes. All organisms
also have a large number of genes whose products
are essential to the normal functioning of a growing and
dividing cell, no matter what the conditions are. These
genes are always active in growing cells and are known as
constitutive genes or housekeeping genes; examples include
genes that code for the enzymes needed for protein
synthesis and glucose metabolism. Note that all genes are
regulated on some level. If normal cell function is impaired
for some reason, the expression of all genes, including
constitutive genes, is reduced by regulatory
mechanisms. Thus, the distinction between regulated
and constitutive genes is somewhat arbitrary.
Imagine a situation when a cell starts producing enzymes required for metabolism and those required for cell death (apoptosis) at the same time. The cell will be in a confused state and will not know which function to perform first. The needs of the body keep changing with time and cell has to tune itself to perform the desired set of activities. Gene regulation helps a unicellular organism to adapt well to the environment.
Transcription and the control of gene expression [Autosaved].pptxAbdullahAli647576
The first genetic maps, constructed in the organisms
such as the fruit fly, used genes as markers.
• The only genes that could be studied were those
specifying phenotypes that were distinguishable by
visual examination. Eg. Eye color, height.
• Some organisms have very few visual characteristics
so gene mapping with these organisms has to rely on
biochemical phenotypes
Includes definition, discovery.Enzyme induction is a process in which a molecule (e.g., a drug) induces (i.e., initiates or enhances) the expression of an enzyme.
The induction of heat shock proteins in the fruit fly Drosophila melanogaster.
The Lac operon is an interesting example of how gene expression can be regulated.
Viruses, despite having only a few genes, possess mechanisms to regulate their gene expression, typically into an early and late phase, using collinear systems regulated by anti-terminators (lambda phage) or splicing modulators (HIV).
Gal4 is a transcriptional activator that controls the expression of GAL1, GAL7, and GAL10 (all of which code for the metabolic of galactose in yeast). The GAL4/UAS system has been used in a variety of organisms across various phyla to study gene expression.
The control of gene expression or protein synthesis is called gene regulation or it is the process of turning genes on and off
Gene regulation in prokaryotes is most extensively observed at the initiation of transcription.
Most genes are controlled by extracellular signals- present in medium.
Repressor, a negative regulatory molecule, binds to the operator gene and interferes with the expression of genes. Activator, a positive regulatory molecule, enhances the expression of the genes.
Operon : a group or cluster of structural genes under a single promoter; bacterial operons are polycistronic transcripts that are able to produce multiple proteins from one mRNA
Francois Jacob and Jacques Monod in 1961
“Lac operon is an operon or a group of genes with a single promoter that encode genes for the transport and metabolism of lactose in E.coli and other bacteria.”
Lac operon concept is an example of prokaryotic gene regulation.
A chart showing the fate of each part of an early embryo, in a particular blastula stage is called fate maps. It is done because the correct interpretation of gastrulation is impossible without the knowledge of the position which are the presumptive germinal layers (Ectoderm, Mesoderm and Endoderm) occupy in blastula.
Fate mapping is a method used in developmental biology to study the embryonic origin of various adult tissues and structures. The "fate" of each cell or group of cells is mapped onto the embryo, showing which parts of the embryo will develop into which tissue. When carried out at single-cell resolution, this process is called cell lineage tracing. It is also used to trace the development of tumors.
DNA sequencing is the process of determining the sequence of nucleotides (A, T, G, and C) in the DNA. It includes method or technology that is used to determine the order of the four bases: adenine, thymine, guanine and cytosine.
The chain-termination method developed by Frederick Sanger and coworkers in 1977. This method used fewer toxic chemicals and lower amounts of radioactivity than the Maxam and Gilbert method. Because of its comparative ease, the Sanger method was soon automated and was the method used in the first generation of DNA sequencers.
published a DNA sequencing method in 1977 based on chemical modification of DNA and subsequent cleavage at specific bases. Also known as chemical sequencing, this method allowed purified samples of double-stranded DNA to be used without further cloning.
Maxam-Gilbert sequencing requires radioactive labeling at one 5' end of the DNA and purification of the DNA fragment to be sequenced. Chemical treatment then generates breaks at a small proportion of one or two of the four nucleotide bases in each of four reactions (G, A+G, C, C+T). The concentration of the modifying chemicals is controlled to introduce on average one modification per DNA molecule. Thus a series of labeled fragments is generated, from the radiolabeled end to the first "cut" site in each molecule. The fragments in the four reactions are electrophoresed side by side in denaturing acrylamide gels for size separation. To visualize the fragments, the gel is exposed to X-ray film for autoradiography, yielding a series of dark bands each corresponding to a radiolabeled DNA fragment, from which the sequence may be inferred.
Cloning is the process of producing genetically identical individuals of an organism either naturally or artificially.
It is the process of taking genetic information from one living thing and creating identical copies of it. The copied material is called a clone.
Nature has been doing it for millions of years. For example, identical twins have almost identical DNA, and asexual reproduction in some plants and organisms can produce genetically identical offspring.
Cloning in biotechnology refers to the process of creating clones of organisms or copies of cells or DNA fragments (molecular cloning).
Bacteriophage- types, structure and morphology of t4 phage, morphogenesisDr. Dinesh C. Sharma
Escherichia virus T4 is a species of bacteriophages that infect Escherichia coli bacteria. It is a member of virus subfamily Tevenvirinae (not to be confused with T-even bacteriophages, which is an alternate name of the species). T4 is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle.
From studies and predictions such as Dreyer and Bennett's, it shows that the light chains and heavy chains are encoded by separate multigene families on different chromosomes. They are referred to as gene segments and are separated by non-coding regions. The rearrangement and organization of these gene segments during the maturation of B cells produce functional proteins. The entire process of rearrangement and organization of these gene segments is the vital source where our body immune system gets its capabilities to recognize and respond to variety of antigens.
The cells of the B line synthesize immunoglobulins. They are either produced at a membrane (on the surface of the B-lymphocytes) or are secreted (by the plasmocytes)
Theory of preformation,
Epigenetic theory,
Theory of pengenesis,
Recapitulation theory,
Germplasm theory,
Mosaic theory,
Regulated theory,
Gradient theory
Theory of organizers.
Sericulture is the cultivation of silkworms to produce silk. Bombyx mori (the caterpillar of the domesticated silk moth) is the most widely used species of silkworms.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
NVBDCP.pptx Nation vector borne disease control programSapna Thakur
NVBDCP was launched in 2003-2004 . Vector-Borne Disease: Disease that results from an infection transmitted to humans and other animals by blood-feeding arthropods, such as mosquitoes, ticks, and fleas. Examples of vector-borne diseases include Dengue fever, West Nile Virus, Lyme disease, and malaria.
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
- Video recording of this lecture in Arabic language: https://youtu.be/Ve4P0COk9OI
- Link to download the book free: https://nephrotube.blogspot.com/p/nephrotube-nephrology-books.html
- Link to NephroTube website: www.NephroTube.com
- Link to NephroTube social media accounts: https://nephrotube.blogspot.com/p/join-nephrotube-on-social-media.html
Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?
Operon Modal of Gene Regulation
1.
2. OPERONS
An operon is a group of genes that are transcribed at the
same time.
They usually control an important biochemical process.
They are only found in prokaryotes.
3. The control of gene expression
or
Regulation of Gene
Each cell of multicellular organism contain same
genetic material, but the expression of gene is
different in different type of cell group. On the basis
of expression requirement they are grouped in to
Structural Gene- Mostly expressed once in a life
Vital Gene- Involved in of vital biochemical
processes such as respiration and need to be
expressed all the time
Functional Gene- Genes are not expressed all
the time. They are switched on an off at need
The regulation of Gene required in case of
functional gene and its explained by Francois
Jacob, Jacques Monod and Andre Lwoff (Nobal
Prize in 1961)
4. An operon is a cluster of coordinately
regulated genes. It includes
• structural genes (generally encoding
enzymes),
• regulatory genes (encoding, e.g.
activators or repressors) and
• regulatory sites (such as promoters
and operators).
5.
6. The lactose operon (lac operon) is an operon required for
the transport and metabolism of lactose in humans and
many other enteric bacteria. Although glucose is the
preferred carbon source for most bacteria, the lac
operon allows for the effective digestion of lactose when
glucose is not available through the activity of beta-
galactosidase
The lac operon consists of three genes each involved in
processing the sugar lactose
One of them is the gene for the enzyme β-galactosidase
One of them is the gene for the enzyme Lipase
One of them is the gene for the enzyme Transacteylase
• β-galactosidase hydrolyses lactose into glucose and galactose
• Permease increase the permeability of Cell membrane for
Lactose
The lac Operon
7. ADAPTING TO THE ENVIRONMENT
E. coli can use either glucose, which is a
monosaccharide, or lactose, which is a
disaccharide
However, lactose needs to be hydrolysed
(digested) first
So the bacterium prefers to use glucose when
it can
8. FOUR SITUATIONS ARE POSSIBLE
1. When glucose is present and lactose is absent the E. coli does not produce β-galactosidase.
2. When glucose is present and lactose is present the E. coli does not produce β-galactosidase.
3. When glucose is absent and lactose is absent the E. coli does not produce β-galactosidase.
4. When glucose is absent and lactose is present the E. coli does produce β-galactosidase
10. 1. WHEN LACTOSE IS ABSENT
A repressor protein is continuously
synthesised. It sits on a sequence of DNA just
in front of the lac operon, the Operator site
The repressor protein blocks the Promoter site
where the RNA polymerase settles before it
starts transcribing
Regulator
gene
lac operonOperator
site
z y a
DNA
I
O
Repressor
protein
RNA
polymeraseBlocked
11. 2. WHEN LACTOSE IS PRESENT
A small amount of a sugar allolactose is
formed within the bacterial cell. This fits onto
the repressor protein at another active site
(allosteric site)
This causes the repressor protein to change
its shape (a conformational change). It can no
longer sit on the operator site. RNA
polymerase can now reach its promoter site
z y a
DNA
I O
12. A small amount of a sugar allolactose is
formed within the bacterial cell. This fits onto
the repressor protein at another active site
(allosteric site)
This causes the repressor protein to change
its shape (a conformational change). It can no
longer sit on the operator site. RNA
polymerase can now reach its promoter site
Promotor site
z y a
DNA
I O
13. 3. WHEN BOTH GLUCOSE AND
LACTOSE ARE PRESENT
This explains how the lac operon is
transcribed only when lactose is
present.
BUT….. this does not explain why the
operon is not transcribed when both
glucose and lactose are present.
14. When glucose and lactose are present RNA
polymerase can sit on the promoter site
but it is unstable and it keeps falling off
Promotor site
z y a
DNA
I O
Repressor protein
removed
RNA polymerase
15. 4. WHEN GLUCOSE IS ABSENT
AND LACTOSE IS PRESENT
Another protein is needed, an activator
protein. This stabilises RNA polymerase.
The activator protein only works when glucose
is absent
In this way E. coli only makes enzymes to
metabolise other sugars in the absence of
glucose
Promotor site
z y a
DNA
I O
Transcription
Activator
protein steadies
the RNA
polymerase
16.
17. The trp operon is an operon—a group of genes that is used, or transcribed,
together—that codes for the components for production of tryptophan. The trp
operon is present in many bacteria, but was first characterized in Escherichia coli.
The operon is regulated so that when tryptophan is present in the environment, the
genes for tryptophan synthesis are not expressed. It was an important experimental
system for learning about gene regulation, and is commonly used to teach gene
regulation.
Trp operon contains five structural genes: trpE, trpD, trpC, trpB, and trpA, which
encode enzymatic parts of the pathway. It also contains a repressive regulator gene
called trpR. trpR has a promoter where RNA polymerase binds and synthesizes
mRNA for a regulatory protein. The protein that is synthesized by trpR then binds to
the operator which then causes the transcription to be blocked. In the trp operon,
tryptophan binds to the repressor protein effectively blocking gene transcription. In
this situation, repression is that of RNA polymerase transcribing the genes in the
operon. Also unlike the lac operon, the trp operon contains a leader peptide and an
attenuator sequence which allows for graded regulation.
It is an example of repressible negative regulation of gene expression. Within the
operon's regulatory sequence, the operator is bound to the repressor protein in the
presence of tryptophan (thereby preventing transcription) and is liberated in
tryptophan's absence (thereby allowing transcription).
18.
19. Genes
Trp operon contains five structural genes. Their roles are:
• TrpE (P00895): Anthranilate synthase produces anthranilate.
• TrpD (P00904): Cooperates with TrpE.
• TrpC (P00909): Phosphoribosylanthranilate isomerase domain
first turns N-(5-phospho-β-D-ribosyl)anthranilate into 1-(2-
carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate. The
Indole-3-glycerol-phosphate synthase on the same protein
then turns the product into (1S,2R)-1-C-(indol-3-yl)glycerol 3-
phosphate.
• TrpA (P0A877), TrpB (P0A879): two subunits of tryptophan
synthetase. Combines TrpC's product with serine to produce
tryptophan.
• TrpE & TrpD- Anthranilate synthase
• TrpC- Phosphoribosylanthranilate isomerase
• TrpB & TrpA- tryptophan synthetase
20.
21.
22. L-arabinose operon
The L-arabinose operon, also called the ara or araBAD operon, is an operon
required for the breakdown of the five-carbon sugar L-arabinose in Escherichia
coli. The L-arabinose operon contains three structural genes: araB, araA, araD
(collectively known as araBAD), which encode for three metabolic enzymes that
are required for the metabolism of L-arabinose. AraB (ribulokinase), AraA (an
isomerase), AraD (an epimerase) produced by these genes catalyse conversion
of L-arabinose to an intermediate of the pentose phosphate pathway, D-xylulose-
5-phosphate.
The structural genes of the L-arabinose operon are transcribed from a common
promoter into a single transcript, a mRNA. The expression of the L-arabinose
operon is controlled as a single unit by the product of regulatory gene araC and
the catabolite activator protein (CAP)-cAMP complex. The regulator protein AraC
is sensitive to the level of arabinose and plays a dual role as both an activator in
the presence of arabinose and a repressor in the absence of arabinose to
regulate the expression of araBAD. AraC protein not only controls the expression
of araBAD but also auto-regulates its own expression at high AraC levels.
23. Structure
L-arabinose operon is composed of structural genes and regulatory
regions including the operator region (araO1, araO2) and the
initiator region (araI1, araI2). The structural genes, araB, araA and
araD, encode enzymes for L-arabinose catabolism. There is also a
CAP binding site where CAP-cAMP complex binds to and facilitates
catabolite repression, and results in positive regulation of araBAD
when the cell is starved of glucose
24. Function
• araA encodes L-arabinose isomerase, which catalyses
isomerization between L-arabinose and L-ribulose.
• araB encodes ribulokinase, which catalyses phosphorylation of
L-ribulose to form L-ribulose-5-phosphate.
• araD encodes L-ribulose-5-phosphate 4-epimerase, which
catalyses epimerization between L-ribulose 5-phosphate and D-
xylulose-5-phosphate.
Catabolism of arabinose in E. coli
Substrate Enzyme(s) Function Reversible Product
L-arabinose AraA Isomerase Yes L-ribulose
L-ribulose AraB
Ribulokinas
e
No
L-ribulose-5-
phosphate
L-ribulose-5-
phosphate
AraD Epimerase Yes
D-xylulose-
5-phosphate
25. Regulation
The L-arabinose system is not only under the control of CAP-
cAMP activator, but also positively or negatively regulated
through binding of AraC protein. AraC functions as a homodimer,
which can control transcription of araBAD through interaction
with the operator and the initiator region on L-arabinose operon.
Each AraC monomer is composed of two domains including a
DNA binding domain and a dimerisation domain. The
dimerisation domain is responsible for arabinose-binding. AraC
undergoes conformational change upon arabinose-binding, in
which, it has two distinct conformations.[6] The conformation is
purely determined by the binding of allosteric inducer arabinose.
AraC can also negatively autoregulate its own expression when
the concentration of AraC becomes too high. AraC synthesis is
repressed through binding of dimeric AraC to the operator
region (araO1).
26. Negative regulation of araBAD
When arabinose is absent, cells do not need the araBAD products
for breaking down arabinose. Therefore, dimeric AraC acts as a
repressor: one monomer binds to the operator of the araBAD gene
(araO2), another monomer binds to a distant DNA half site known
as araI1. This leads to the formation of a DNA loop. This
orientation blocks RNA polymerase from binding to the araBAD
promoter. Therefore, transcription of structural gene araBAD is
inhibited
27. Positive regulation of araBAD
Expression of the araBAD operon is activated in the absence
of glucose and in the presence of arabinose. When arabinose
is present, both AraC and CAP work together and function as
activators
28. Via CAP/cAMP (catabolite repression)
CAP act as a transcriptional activator only in the absence of
E. coli's preferred sugar, glucose. When glucose is absent,
high level of CAP protein/cAMP complex bind to CAP binding
site, a site between araI1 and araO1. Binding of CAP/cAMP
is responsible for opening up the DNA loop between araI1
and araO2, increasing the binding affinity of AraC protein for
araI2 and thereby promoting RNA polymerase to bind to
araBAD promoter to switch on the expression of the araBAD
required for metabolising L-arabinose.
29. Autoregulation of AraC
The expression of araC is negatively regulated by its own
protein product, AraC. The excess AraC binds to the
operator of the araC gene, araO1, at high AraC levels, which
physically blocks the RNA polymerase from accessing
the araC promoter.Therefore, the AraC protein inhibits its
own expression at high concentrations