FUN Quiz 3 Flashcards
What are the 3 Large scale types of genetic variation with a brief description of each.
Aneuploidy: One or more individual chromosomes in extra copy, or missing
Translocations/Inversions/ring chromosomes: Mixed Chromosomes
CNVs Copy Number Variants: Relatively large sections of DNA duplicated or deleted
How are ring chromosomes formed?
2 ends of the same chromosome fuse together
Distinguish briefly between heterochromatin and euchromatin. Also explain how it is shown in a karyoptype
Heterochromatin represent the dark band in karyotypes. They are AT rich yet gene poor
Euchromatin represent the light bands, are GC rich, and hence gene rich.
What are the Classifications of chromosomes based on centromereposition
Metacentric: Centromere in the middle
Submetacentric: Not in the middle nor at the terminal with one arm significantly longer than the other
Acrocentric: Centromere at terminus. Leftover DNA contains no genetic content.
What are the two arms of a chromosome and what differentiates them
Short arm is the P arm and long arm is the q arm
With the banding nomenclature of 1p13.3, where is the approximate location of the gene in question?
1: Chromosome number
p: Short arm of the chromosome
1: Region
3: Band
.3: Sub-band
Define Aneuploid
There is an abnormal chromosome number
What are the two types of chromosome abnormalities?
Numerical aberrations: incorrect number of chromosomes
Structural aberrations:
Involving 1 chromosome: Duplication, deletion, inversion, ring chromosome
Involving 2 chromosomes: Translocations;
Reciprocal translocations
Robertsonian translocations
Define Euploid
Correct number of chromosomes
Distinguish between Reciprocal translocations and Robertsonian translocations
Reciprocal translocations is the change of DNA between two non-homologous chromosomes. (Not normal cross-over)
Robertsonian Translocations: This occurs when two Acrocentric chromosomes fuse together to form one hybrid chromosome
How does Aneuploidy occur?
Chromosomal disjunction
What is Chromosomal disjunction?
It is the failure of chromosomes to separate and segregate normally either in mitosis or meiosis
Compare chromosomal disjunction in mitosis and meiosis.
When chromosomal disjunction occurs in meiosis, non-disjunction results in imbalanced gametes. If any of these gametes fertilise, all cells derived from the resulting embryo will have a chromosome imbalance.
When it occurs in mitosis, non-disjunction produces two cell-lineages derived from a single zygote causing Mosaicism
Individuals who are mosaic for a particular chromosomal aberration usually have less severe symptoms => Mitosis disjunction is less severe than meiosis disjunction. The earlier the disjunction happens during development, the more severe the outcome.
Distinguish between disjunction occurring in the first meiotic division and the second
If disjunction happens in the first division, gametes contain either both parental chromosomes or neither. If it happens in the second division, then gametes will contain two identical copies of the same chromosome.
Give three clinical signs of Down Syndrome
Developmental delay Variable intellectual disability Characteristic facial features Congenital heart defects Premature aging Risk of leukemia
What are the two ways Down syndrome can occur and which is predominant?
Trisomy (predominant), and Robertsonian translocation
What factor affects risk of trisomy 21?
Maternal age, risk increases with age
Give 3 Human Aneuploid Syndromes
Down Syndrome: Trisomy 21
Turner Syndrome: Monosomy X
Kleinefelter syndrome: XXY
Triple X Syndrome: idk
IF you included Edwards syndrome or Patau syndrome then good for you
What are the gametes produced in the following case as well as their viability when paired with a normal gamete:
Chromosome 14 and 21 fuse together by Robertsonian translocation.
Answer should only reflect chromosomes 14 and 21 in terms of gametes.
Full answer in PowerPoint
Trisomy 14 Dead Monosomy 14 Dead Trisomy 21: Down syndrome Monosomy 21: Dead T(14;21): carrier Normal
What are the two different types of structural chromosomal abnormalities and give one difference
Unbalanced abnormalities involves the loss or gain of genetic material. They often have developmental delays
Balanced abnormalities do not involve the gain or loss of genetic material. Heterozygous individuals can be at risk of passing on the abnormality to offspring.
What are the indications for prenatal cytogenetics?
- Abnormal ultrasound
- Advanced maternal age/biochemical test
- Previous birth of child with trisomy
- Infertility, recurrent spontaneous abortion
- Carrier of heritable chromosome abnormality
What are the clinical indications for post-natal Cytogenetics
Dysmorphic features
Developmental delay
Clinical features of chromosomal syndrome
What is a micro deletion syndrome
Syndrome that involves deletions that are often to small to detect by G banding
What are the viable methods for diagnosis?
Molecular cytogenetic methods including Array CHG and FISH
Why would scientists use Array CGH over FISH
Array CGH is a genome-wide detection method whereas FISH is only for a specific region or gene
Autosomal Dominant inherited disease is mostly ____ but can be seen in _________. Patients often die before _______ in heterozygotes and before ______ in homozygotes
Heterozygous
Homozygotes
Maturity
Reproductive maturity
Explain the Inheritance pattern of Autosomal dominant traits
- Pattern is vertical
- Box sexes have an equal chance of being affected
- Both sexes will transmit the mutation
- Approx 50% of the offspring of an affected parent will be affected
What is a vertical inheritance pattern
A disease that is passed from one generation to the next and each affected person has an affected parent
What is penetrance?
It refers to the proportion of individuals with a given genotype who show the associated phenotype.
Give an example of an autosomal dominant disease. Describe the disease and emphasize the the difference in severity between it’s homozygous and heterozygous state.
Familial Hypercholesterolemia is an autosomal dominant disease characterized by its mutation in the LDL receptor. This leads to an increase in levels of plasma LDL which hence increases LDL cholesterol. Individuals with this disease suffer extreme developments of plaques causing cardiovascular diseases such as myocardial infarction
Heterozygotes with this disease are more common yet have less severe levels of plasma LDL than homozygous (2x compared to 10x). Individuals with this disease in the heterozygous form tend to experience life-threatening CVDs later in life (30-40) when compared to it’s homozygous form (childhood/adolescence)
What is the most common autosomal dominant mating type? What is the expected offspring distribution
Heterozygote with dominant mates with normal homozygote. 50% of offspring will have the trait
What are some exceptions to the autosomal dominant inheritance pattern? Give examples or explain briefly
- Mutation: An individual that has no previous family history with the disease can develop a mutation with disease phenotype.
- Variable Expressivity: Some people with the same genotype might have different expressivity such as Polycystic Kidney Disease which has only 50% of patients develop the cysts in their kidney
- Reduced Penetrance: Some people with the genotype do not show any symptoms and still have offspring with that disease shown. This can be due to another gene that suppresses the disease or any other factor.
What is genetic Penetrance?
Penetrance refers to the proportion of individuals with a given genotype who show the associated phenotype.
How does a mutation at a single gene cause a disease phenotype?
- Haploinsufficiency: When a gene is transcribed onto an mRNA, a mutation can prevent the protein from being made or forcing its degredation. When heterozygote, this prevents the gene on one of the two chromosomes from producing a protein and hence there is a loss of 50% of normal activity => disease
- Dominant Negative Effect: Abnormal protein produced similar to above but in this case, the protein is not being degraded but does not function or does not function properly causing disease
- Gain of Function: Function of a mutant protein is enhanced and hence a once regulatory gene becomes permanently switched on. An example is Huntington Disease where a triple repeat makes the protein toxic to nerve cells
- Loss of Heterozygosity: Also known as dominantly inherited cancers, individuals will have an inherited copy of a mutant gene and a random loss of the normal allele. If it even occurs in a few cells, it will cause cancer.
Why are autosomal recessive diseases more common?
Carriers are not at a selective disadvantage. Even if affected individuals do not breed, the mutation can still become widespread as most are carriers.
Can autosomal recessive traits and autosomal dominant traits skip generations?
Recessive can, dominants cannot
What is the most common autosomal recessive mating type? What are the expected offspring
2 carriers mating. 25% fo offspring will have disease where it can only be shown if both gametes with the disease are passed on. There is a 1/2 chance for carriers
What is Consanguinity?
When 2 individuals that are related mate
How does Consanguinity affect recessive inheritance
Increases chances of disease to be present in offspring due to shared ancestral DNA
How are AR diseases identified?
Give 3
- Newborn Screening
- Multiple siblings affected
- Parental Consanguinity: Preferential mating behavior increases incidence of disease.
- Demonstration of a partial defect in obligate heterozygotes where there are some deficiencies present in parents. Ex. 50% enzyme activity. Or sickle cell anemia in parents.
Define Genetic Heterogeneity and define the two types.
Genetic Heterogeneity is where the same clinically diagnosed disease is caused by different DNA sequence defects, producing identical or similar clinical phenotypes.
Allelic Heterogeneity is where different DNA sequences/mutations are on the same gene
Locus Heterogeneity is where different DNA sequences are found on different genes
Explain the nomenclature of a mutation in phenylalanine hydroxylase R408W
R is Argentine => R
408 is the codon number
In this mutation R becomes W (Tryptophan) => W
Hence R408W
Explain the nomenclature of a mutation in the Cystic Fibrosis gene: F508del
Phenylalanine F
Codon 508
This codon is deleted and hence del.
Give an Example of Allelic Heterogeneity. Explain briefly.
Allelic Heterogeneity is defined as different mutations on the same gene. An example is Phenylketonuria (PKU).
PKU is autosomal recessive and occurs due to a mutation of the Phenylalanine Hydroxylase (PAH) gene located on chromosome 12.
PAH converts Phenylalanine (Phe) into Tyrosine (Tyr).
There are hundreds on mutations on the PAH gene that each give different phenotypes (since Phe is changed into multiple different kinds of molecules) but have the same diagnosis of PKU.
This range of enzyme activity can be treated in different ways based on the specific mutation.
Majority are E390G
Give an example of Locus Heterogeneity. Explain Briefly
It is the same clinical disease caused by mutations in different genes. They are often complex pathways or complex structure.
A disease example is Retinitis Pigmentosa which is associated with over 50 genes. It involves several genes that carry instructions for proteins within photoreceptors.
Symptoms of this include Night blindness, Tunnel vision, and blindness
Locus Heterogeneity often has its effects in two different ways. What are they?
Complex pathways or complex structure
The X found in G542X signifies…
Change of Guanine into a stop codon
True or false: Males are Hemizygous for the X chromosome
True
Why do males and Females produce equal amounts of proteins encoded by genes on the X chromosomes? Explain
Females have dosage compensation where quantity of protein product formed is equivalent.
This is called X-chromosome inactivation or Lyonization.
This inactivation occurs in embryonic life and is random between paternal and maternal X. This occurs in every cell (similar to mosaic). This is permanent and all daughter cells from that cell are identical.
The inactive X appears as a dark-staining mass known as a Barr-Body
Are all X-linked mutant genes fully expressed in males?
Yes since they have 1 X chromosome
Learning Outcome: Explain the effects of X inactivation that occurs in females as well as the characterization of XLR vs XLD
X linked traits are variably expressed in females. They may have:
An intermediate effect where they are clinically unaffected but Biochemically abnormal
Skewed X inactivation: Normal phenotype where more than random X chromosomes containing the mutant gene are inactivated
Manifesting Heterozygote: Clinically affected where more than random X chromosomes containing the normal gene inactivated
This means that an X-linked disease may or may not be expressed clinically in a heterozygous female.
Diseases are characterized as XLR and XLD depending on the relative proportions of females who are affected.
Diseases which are rarely expressed clinically in females are said to be X-linked recessive (most) and diseases which are expressed clinically in many females are said to be X-linked dominant (very few)
Briefly describe X-linked recessive inheritance including an example.
X-linked recessive transmission occurs in the complete absence of male-male transmission.
Males are mainly affected in the pedigree and can be born to unaffected parents.
An example of this is Hemophilia A where there is a deficiency in Factor VIII which is an essential clotting factor.
Vertical Transmission
Briefly explain XLD inheritance giving an example.
There is complete absence of male-male transmission since males only give the Y chromosome from the father.
An affected male will have no affected male offspring but all females affected. An affected female has a 50% chance to pass it on to both male and female offspring
Vertical Transmission
An example is Hypophosphatemia (Vitamin D resistant) RICKETS. It involves the inability of kidneys to retain phosphate causing low blood and high urinary phosphate levels. This causes short stature and bony deformities.
Explain Extra-nuclear inheritance giving an example
This involves the transmission of mitochondrial DNA or mtDNA. It is maternally transmitted via the ovum (since the ovum has the cell contents)
An example of this disease is Leber’s Hereditary Optic Atrophy. This involves the loss of central vision in the late 20s.
Transmission affects both sexes. Males will not transmit to offspring and females will transmit to all offspring.
Vertical Transmission
Differentiate between homoplasmy and heteroplasmy
Homoplasmy is where every mt genome contains mutation
Heteroplasmy is where there is a mixed population of normal and mutant mt genome
The greater the proportion of mt genome, the more severe the disease
What type of genetic heterogeneity are Triplet Repeat Disorders characterized as?
Give an example
Allelic Heterogeneity: Same clinically diagnosed disease caused by different DNA sequence defects producing identical or similar clinical phenotypes
PKU
Learning Outcome: Discuss triplet repeat disorders, parent of origin effects and anticipation with examples of Huntington’s disease and Fragile X syndrome
These mutations are unstable or dynamic where they can change as it passes down through a pedigree.
Normally there are a low number of repeats. Some individuals are at the upper limits of normal and are capable of expanding into a disease (permutation stage). A mutation occurs when the repeat number exceeds the limit causing disease
Triple repeat disorders may be classified as dominant, recessive, or X-linked
These disorders May be subtle (subtle disease) or explosive (Fragile X syndrome) at an individual disease.
Parent of Origin Effect: Premutation where expansion occurs. Also known as the origin of where it expands. Male germline through spermatogenesis and female Germaine through oogenesis. For Huntington’s disease, if the gene has been cast from a father to the next generation, it is likely to expand into a disorder but if it is from the mother then it is not likely. For Fragile X syndrome, it is the opposite
When the repeat expands down a pedigree, its associated with more severe and earlier onset also known as ANTICIPATION.
Fragile X syndrome: X-linked disorder and is the most common form of inherited mental disability in males with a characteristic facial appearance. Can also occur in females. The molecular defect is in the FMR1 gene which has a CGG triplet repeat in its 5’ UTR. During meiosis in female oogenesis, the repeat is unstable and can increased in length. This is an example of a modified X-linked inheritance where it expands throughout a pedigree. It is explosive.
Huntington’s disease is an autosomal dominant disorder. It is an example of a paternal parent of origin effect and anticipation where the increase in repeats occurs during meiosis in spermatogenesis. There is an earlier age of onset associated with larger repeat number. One mutated copy can cause the disease (since dominant).
What are drugs?
Substances that have beneficial biological activities
Are Vitamins and other dietary factors considered a drug?
No, unless taken in excess of normal dietary intake
LEARNING OUTCOME: Outline the limitations of using plant extracts as drugs. How are plant-based drugs made now.
Plant extracts contain many substances which increase the likelihood of toxicity
Rather than use plant extracts, we now purify active ingredients. One approach is to take a known herbal remedy and extract the active ingredient. Another approach is to screen plant extracts for biological activity.
Summary: Drugs are no longer derived directly from the plant.
What are the 3 traditional ways drugs are made?
Plant/herbal
Microbes
Animal tissue
What is used in modern drug development?
Conventional pharmacology uses small synthetic molecules to develop drugs
Distinguish between the two drug-discovery approaches
Target-led discovery:
- Choose a drug target (protein)
- Screen chemicals for binding to target
- Mechanism known and effect is predicted
Chemistry-led discovery:
- Select a Chemical
- Screen for biological activity
- Often mechanism unknown but effect is known
What are the problems with small molecule drugs?
- Many interactions are between proteins, and small molecule inhibitors are not possible
- Chemistry is too difficult
What are the current drug approaches in terms of therapy options?
- Recombinant Engineered proteins
- Nuclei acid-based therapeutics
- Gene therapy approaches
- Cell-based therapies
Explain recombinant protein therapy giving an advantage and an example
- Protein-encoding gene is cloned into the cell line (Rather than from the blood by normal protein therapy)
- Cells generate recombinant proteins
- Limited potential for viral contamination
- Insulin, erythropoietin
What is monoclonal antibody therapy? Give a few advantages and a disadvantage
Monoclonal antibody therapy fuses cells from the spleen with myeloma (cancer) cells to immortalize them in the form of releasing antibody-secreting cancer cells.
This basically generates antibodies that would boost immune system function specifically targeting exploits or the ability of the pathogen (or disease) to use the exploits
Advantages:
- Large amount of antibody can be produced
- Can fight cancer through Anti-PD1 genes and anti-PD1-L
- Not necessary to use animals in production
- Single Epitope on a single antigen
Disadvantages:
- Expensive
- Have to be given IV constantly
What is an Epitope?
The part of an antigen molecule to which an antibody attaches itself
What is used to treat snake and spider bites. How is it produced
Antivenin is used to treat them. Horse serum is foreign and hence can trigger immune reactions where anti-horse antibodies can neutralise the anti-venin
How can Nucleic acids be used as drugs?
- Antisense molecules where an mRNA complementary chain can bind and inhibit the OG mRNA chain
- Aptamers are nucleic acid sequences that bind to proteins (same as above)
What are drugs?
Substances that have beneficial biological activities
Are Vitamins and other dietary factors considered a drug?
No, unless taken in excess of normal dietary intake
LEARNING OUTCOME: Outline the limitations of using plant extracts as drugs. How are plant-based drugs made now.
Plant extracts contain many substances which increase the likelihood of toxicity
Rather than use plant extracts, we now purify active ingredients. One approach is to take a known herbal remedy and extract the active ingredient. Another approach is to screen plant extracts for biological activity.
Summary: Drugs are no longer derived directly from the plant.
What are the 3 traditional ways drugs are made?
Plant/herbal
Microbes
Animal tissue
What is used in modern drug development?
Conventional pharmacology uses small synthetic molecules to develop drugs
Distinguish between the two drug-discovery approaches
Target-led discovery:
- Choose a drug target (protein)
- Screen chemicals for binding to target
- Mechanism known and effect is predicted
Chemistry-led discovery:
- Select a Chemical
- Screen for biological activity
- Often mechanism unknown but effect is known
What are the problems with small molecule drugs?
- Many interactions are between proteins, and small molecule inhibitors are not possible
- Chemistry is too difficult
What are the current drug approaches in terms of therapy options?
- Recombinant Engineered proteins
- Nuclei acid-based therapeutics
- Gene therapy approaches
- Cell-based therapies
Explain recombinant protein therapy giving an advantage and an example
- Protein-encoding gene is cloned into the cell line (Rather than from the blood by normal protein therapy)
- Cells generate recombinant proteins
- Limited potential for viral contamination
- Insulin, erythropoietin
What is monoclonal antibody therapy? Give a few advantages and a disadvantage
Monoclonal antibody therapy fuses cells from the spleen with myeloma (cancer) cells to immortalize them in the form of releasing antibody-secreting cancer cells.
This basically generates antibodies that would boost immune system function specifically targeting exploits or the ability of the pathogen (or disease) to use the exploits
Advantages:
- Large amount of antibody can be produced
- Can fight cancer through Anti-PD1 genes and anti-PD1-L
- Not necessary to use animals in production
- Single Epitope on a single antigen
Disadvantages:
- Expensive
- Have to be given IV constantly
What is an Epitope?
The part of an antigen molecule to which an antibody attaches itself
What is used to treat snake and spider bites. How is it produced
Antivenin is used to treat them. Horse serum is foreign and hence can trigger immune reactions where anti-horse antibodies can neutralise the anti-venin
How can Nucleic acids be used as drugs?
- Antisense molecules where an mRNA complementary chain can bind and inhibit the OG mRNA chain
- Aptamers are nucleic acid sequences that bind to proteins (same as above)
Briefly define the two types of cell-based therapy
Cells based therapy can involve:
- Adoptive Cell Transfer Therapy: The introduction of genetically-modified cells to treat disease
Or - Stem Cell Therapy: The application of stem cells to renew existing cell defects of deficits
Explain Adoptive cell transfer therapy using an example
It is the introduction of genetically-modifies cells to treat disease.
Chimeric Antigen receptor (CAR) T-cell therapy: Uses patient’s own T cells being isolated where they are genetically modified to express synthetic receptors on their surface that recognize tumor antigens. This makes the T cells between able to destroy malignant cells
Overall: Using patient cells and modifying them them to perform function better.
Briefly explain Stem Cell Therapy:
Stem cells have the potential to differentiate into an unlimited number of cell-types. This could be used to treat several diseases such as leukemias or can be used to replace damaged or missing tissue.
What are the three different types of receptor ligands?
Ligand
Agonist
Antagonist
What is a Ligand?
A chemical that specifically binds to a receptor
What is an agonist?
A ligand which binds to a receptor and causes a biological response
What is an Antagonist?
Binds to a receptor but has no effect and prevents other ligand from binding
What is a receptor?
Receptors are normally located on a membrane and possesses high affinity for it’s specific endogenous ligand (basically it’s substrate). They are saturable and finite (limited number of binding sites). Binding with the ligand allows for a biochemical event to occur
How do receptors bind specifically to ligands?
How do ligands act in different tissues and environments?
Receptor structure has evolved over time to recognize specific ligands (similar to an enzyme).
One receptor expressed in different tissue can mediate distinct physiological outcomes.
What is the relationship between tissue response and receptor occupation?
What is the name of the curve that shows this?
Dose-response curve
They are proportional => the more occupied receptors (or fraction of occupied receptors), the bigger the signaling response
The curve eventually plateaus when the receptors are saturated.
The EC50 represents the amount of agonists required for 50% effective concentration (50% response).
The Log-dose response curve is used to determine the amount of agonist required for 50% response. Note the X-axis is only logged (agonist).
Explain how to measure drug binding to receptors. Basically discuss the curve.
Bmax: Maximum bounds = maximal drug binding to receptor
Dissociation constant: Kd = Half-maximal drug binding to receptor.
The higher the affinity, the lower the Kd (ie. the lower the amount of agonists needed to be present for binding to occur)
We also log the x axis again (agonist) to measure drug affinity and maximal effect (E max)
How do we calculate drug potency
Potency is a measure of drug activity
It is expressed in terms of the amount required to produce an effect of given intensity.
Potency is related to affinity
We use the same graph as the dose-response curve. When comparing different drugs, the drug that is shifted most to the left (lower log Agonist concentration) is the most potent, has the highest potency, and highest affinity.
What is a partial agonist
how is it displayed on a response vs [Agonist] graph?
how does it compare to agonists and antagonists?
Agonists that never produce maximum response. They have a reduced response and receptors have a reduced conformational change when bound to a partial agonist.
Normal agonists are either fully functional or not functional at all.
Partial agonists exhibit intrinsic activity between 0-1. Agonists have 1 and antagonists have 0
Give an example of a receptor that shows partial agonism, explain briefly, and give an example of an agonist that binds to it
Opioid receptors are important for pain transmission and neurotransmission.
Opioids are agonists for Opioid receptors.
Full agonists include Codeine, Fentanyl, and Methadone
Partial agonists include Buprenorphine, Butorphanol, and Tramadol
OR
Nicotinic Receptors - Nicotine Replacement Therapy
Blocking or desensitizing nicotinic receptors prompts greater receptor expression on neurons
Nicotinic partial agonists relieve craving and withdrawal symptoms
Craving and withdrawal symptoms from nicotine can be relieved by this partial blockage
What are Spare Receptors
Spare receptors are extra receptors which exist when maximum signaling response is observed without full occupancy of available receptors.
Define Intrinsic Activity
Intrinsic activity is the ability to produce a response
Explain the concepts of Kd, Bmax, and EC50
Kd = Half-maximal drug binding to receptor. (Binding % curve)
Bmax = Maximal drug binding to receptor
EC50 = 50% of effective concentration (Found in Response% curve)
Define Antagonists
Antagonists bind to a receptor but they have no effect and prevent other ligands from binding.
What is the Intrinsic activity/efficacy of antagonists compared to agonists and partial agonists
Full agonists have a=1
Partial agonists are anywhere between 0 and 1
Antagonists have 0 efficacy
What is a competitive antagonist and how does it affect effectiveness of an agonist? Mention it’s effect on the Log Dose Response Curve
Competitive antagonists bind to the same site as the agonist.
They compete for the same site
Binding is reversible and is surmountable by excess agonist concentration.
Maximum effect of agonist is unchanged yet the dose required to achieve maximum effect is increased i.e. higher concentration required to reach maximum but maximum is possible.
Shifts Dosage response curve to the right
What is a non-competitive antagonist and how does it affect effectiveness of an agonist? Mention it’s effect on the Log Dose Response Curve
Antagonists that bind to a different site than an agonist. Also known as an allosteric antagonist or inhibitor.
Binding is also reversible but cannot be overcome by increasing agonist concentration. => reducing max response or efficacy (Bmax/Emax). This does not shift the curve but just lowers the maximum.
How are antagonists compared? How is it different from agonist comparison?
Antagonists are compared by their effect on the dose-response curve where its is the dose that inhibits the response by 50% or IC50
Agonists are compared by the dose that causes 50% response or EC50
How is the bonding different in reversible and irreversible antagonists
Reversible antagonists can be displaced by other ligands and bind non-covalently
Irreversible antagonists binds to the receptor covalently.
What is the effect of an inverse agonist?
Inverse agonists binds to a receptor like an agonist, but induces opposite signaling outcome. Basically completely inverses normal function.
Can be partial or full
Regularly taking a drug leads to the buildup of…
Desensitization and tolerance
Desensitization and tolerance build up can be described as refractoriness. This is due to…?
Give examples for brownie points
- Change or loss of receptors (beta receptor agonists)
- Exhaustion of mediators (amphetamine)
- Increased metabolic degradation (alcohol)
- Physiological adaptation (Diuretics)
Due to safety considerations, how do scientists find out the correct dose to be sold among the population?
A response curve is constructed to determine the dose where individuals that take the drug elicit a response. This is taken as all or nothing. This landmark on the graph is known as ED50 which is the dose required to produce a therapeutic effect in 50% of the tested population.
Describe Textured Antagonism
Competitive antagonists are pure antagonists. Just as partial agonists exist, non-competitive antagonists can often direct multiple signaling pathways. => it can inhibit one pathway but activate another ex. Permissive Antagonists
What are permissible Antagonists? Give an example
They are non-competitive antagonists that will block some pathways but continue to produce others.
GPIIB/IIIA is a fibrinogen receptor on platelets. It’s antagonist inhibits platelet aggregation but does not inhibit platelet signaling.
I.e. its goal is to not inhibit necessary pathways yet still inhibit the possibility for thrombosis but inhibiting excessive aggregation
Side note:
It is important to note that drugs target different aspects of the process of response and its not just limited to ligand binding.
Describe the Main structure and components of a G-protein coupled receptor
They are monomeric proteins that pass through the membrane 7 times.
The enzyme is composed of 3 subunits alpha beta and gamma. It is inactive when GDP is bound and active when GTP is bound.
This receptor is not linked to the enzyme but is coupled with it. When the receptor is activated (by ligand-binding), the enzyme acquired high affinity for GTP
They include light, taste, smell receptors, and neurotransmitters.
The activity status of G proteins is determined by which subunit? What is it’s main function
Alpha subunit
It’s main function is to regulate amplifier or effector protein activity
Do beta and gamma subunits (GPCR) have enzymatic activity? If so, what are they?
They dont haha but they can exert signaling activity
What subunits are responsible for anchoring the G-protein?
The alpha and gamma subunits of the G-protein anchor it to the membrane it its inactive or unbound state
When the G-protein is inactive, what is bound to it?
GDP
Learning Outcome: Explain the mechanism of G-coupled protein signaling cascade. I.e. Mechanism or Action
- Receptor and complete G protein are bound to the membrane with the G-protein being GDP-bound
- Receptor ligand binds to GPCR and the occupied receptor couples with the alpha subunit. This causes the G protein to gain a high affinity for GTP where GDP is replaced with GTP
- Since alpha-GTP is the active form of the receptor, it dissociates from the receptor to interact with the Effector Enzyme or Adenylate Cyclase.
- Adenylate cyclase, which is an enzyme that generates cAMP, is activated by G-alphas. cAMP is generated from ATP
- cAMP activates cAMP-dependent protein kinases where it is then metabolized by phosphodiesterase into AMP.
- Signaling is carried out. When GTP is converted to GDP and becomes inactive, the alpha subunit returns back to its original position with the beta and gamma subunits.
What does Adenylate cyclase generate
cAMP
How is Adenylate cyclase activated? How is it Inhibited
It can be activated by G-alphas, or by some GPCRs through beta-adrenergic receptors.
It can be inhibited by alpha-2-Adrenergic receptors
What do cAMP-dependent kinases have as substrates? What are their main functions
Ion channels and metabolic pathways
It’s main function is to add phosphate groups to their substrates which can cause wither activation or inhibition
How is cAMP metabolized during GPCR mechanism of action? What is the product?
Phosphodiesterase breaks down cAMP into AMP
How is cAMP formed?
Adenylate cyclase, activated by alpha-G protein, catalyzes the reaction forming cAMP from ATP
How does G-alpha-i affect GPCR signaling? What role does this play in the regulation of Adenylate cyclase activity?
It is an inhibitor, part of the Galpha subunit, that inhibits Adenylate cyclase in its production of cAMP from ATP.
Gai and Gas subunits counteract each other. The concentration of stimulatory and inhibitory hormones determines the mode of action and extent to which signals are transmitted or lack there of based on the needs of the cell.
How is GPCR signaling switched off?
When an effector protein is bound, the GTPase activity of the alpha sub unit is increased when the effector protein is bound. This causes the hydrolysis of GTP into GDP rendering it inactive.
This causes the alpha subunit to return to its original position with the beta and gamma subunits
What is an alternative G-protein activated effector protein to Adenylate cyclase?
Activation of phospholipase C by GPCR signaling.
Explain the function/mechanism of phospholipase C
- Phospholipase C is activated through G-alpha-q.
- Phospholipase C then hydrolysis PIP from the membrane to produce 2 second messagers which are DAG and IP3.
- IP3 is water soluble and binds to the IP3 receptor in the ER which results in the Ca2+ release enclosed within it
- Signal is terminated by the removal of the terminal phosphate
How is phospholipase C activated? (What subunit)
G-alpha-q
What is the intracellular tyrosine kinase domain responsible for?
It is responsible for transmitting signals when ligand bound
Explain the mechanism of action for the RTK (Receptor Tyrosine Kinase)
- Ligand Binds to receptor (extracellular)
- Dimerization of receptor and auto phosphorylation of tyrosine by Relay Proteins
- GRB2 (adaptor protein) links signaling molecules together without signaling. SH2 recognizes the phosphotyrosine on the active receptor and SH3 recognizes the proline on signaling molecules.
- SOS binds onto SH3 and Ras (small GTPase) binds onto the SoS. SoS acts to convert inactive Ras into active Ras by removing GDP and binding to it instead.
- Ras is required for RTK cell signaling by hydrolysis of ATP. This is done through several cell signaling pathways which cause changes in protein activity and gene expression.
What is the function of relay proteins in RTK mechanism of action?
Autophosphorylation of tyroSine kinase on the activated receptor.
What domains are on the GRB2 growth receptor binding protein? Give their function
SH2: recognizes phosphotyrosine on active receptor
SH3: Recognizes proline on signaling molecules
Function of Ras.
Ras hydrolyses GTP into GDP required to transmit RTK signaling
Function of SoS in RTK
Acts to convert inactive Ras to active Ras by binding to it and removing GDP
What is the mechanism of action for Ligand-gated ion channel linked receptors?
When a hormone binds to a receptor, the channel opens and activates an influx of ions. When the ligand leaves, its inactivated. Tadaaa
Explain the mechanism of action for Intracellular receptor activation/Nuclear receptor.
- Steroid hormones enters via cell membrane
- Receptor in cytosol bound to a molecular chaperone binds to the hormone causing the chaperone to dissociate.
- Steroid hormone bound to receptor can translocate to nucleus once chaperone removed.
- Binds to DNA-associated receptor to initiate gene expression to cause cell changes.
Define Pharmacodynamics
Actions of drug on the body
Define Pharmacokinetics
Effects of body on drug
List the 4 key processes involved in pharmacokinetics
Absorption, distribution, metabolism, and elimination
Describe drug movement in the body
- The drug will be absorbed into the blood through the GI tract or other sites of administration.
- The absorbed drug will then be distributed to different organs such as liver, kidney, sites of action, and other sites.
- Drugs may be metabolised in the liver, kidney, and other sites of action.
- The metabolised drug may be excreted as bile in the liver and as urine from the kidney.
What are the 3 common routes of drug administration
Topical, Enteral, and Parenteral
Describe Topical drug administration
Topical: local effect, where the substance is applied directly where its mode of action is desired
- Applied on epithelial surfaces (i.e. skin, cornea, vaginal, nasal mucosa)
Describe Enteral drug administration
Enteral: systemic effect, where a substance is given via the digestive tract
- Oral (per os) by the mouth
- Sublingual (SL) placed under the tongue
- Rectal (per rectum) through suppositories and enemas
Describe Parenteral Administration
Parenteral: systemic effect, where a substance is given by routes other than the digestive tract
- Inhalation
- Injections
List the 5 different types of injections with a brief statement describing it.
- Intravenous injections given directly into a vein
- Subcutaneous injections given below the dermis and epidermis when a slower and more prolonged effect is desired (i.e. insulin, immunizations, heparin)
- Intramuscular injections given in large muscle masses such as deltoids or gluteals. This is best for larger volumes and when faster absorption is desired (i.e. antibiotics)
- Intrathecal injections are given into subarachnoid space via a lumbar puncture needle to access cerebrospinal fluid (CSF)
- Intradermal injections given into the dermis just below the epidermis, which gives the longest absorption time of all the parenteral routes used for allergy tests and local anaesthesia
What are the 4 factors influencing Drug absorption
Drug structure, formulation, gastric emptying (stomach and eating with food), first pas metabolism
Explain the process of First Pass Metabolism
- First pass metabolism (Presystemic Metabolism)
o Drugs are absorbed from GI tract and passes into the liver via the portal vein, where drugs are metabolized with multiple enzymes such as CYP350
Propanolol, lignocaine, glyceryl trinitrate (GTN)
o Results in a proportion of drugs reaching the systemic circulation
o Occurs in:
Gut (benzylpenicillin and insulin)
• Intestinal lumen (digestive and bacterial enzymes)
• Intestinal wall (MAO)
Lung (MAO, peptidase)
o Alternative routes of administration avoid the first pass effect:
Intravenous
Intramuscular
Sublingual
What is the route of administration of a drug determined by?
Route of administration is determined by:
- Physical characteristics of drugs
- Speed which the drug is absorbed and/or released
- The need to bypass hepatic metabolism and achieve higher concentrations at particular sites
What does the area under the curve of Drug Plasma vs. Time Plots
It is a measure of the total amount of drug that enters the body after administration.
Define Drug distribution
Drug Distribution: process by which a drug reversibly leaves the blood stream and enters the extracellular fluids and/or intracellular fluids (cells of the tissue)
What is a more effective way of administering a drug? IV or oral? Explain why.
IV since 100% of what is injected into the blood is in the blood lol but not all what is given orally is absorbed and allowed into the blood stream
