Genetic Variation Flashcards
In which direction does RNA polymerase move?
And therefore in which direction is mRNA made?
3’ –> 5’
mRNA made from 5’ –> 3’
What are the stages of the cell growth cycle?
G1 –> Cell prepares for cell growth
S-Phase –> DNA replicated/synthesised
G2 –> Cell prepares for division
M-Phase –> Mitosis, spindle formation and cell division
How is Cortisol secreted in the body?
Stimuli cause Corticotrophin Releasing Hormone (CRH) from the hypothalamus
This stimulates the pituitary to release AdrenoCorticoTrophic Hormone (ACTH) –> This causes the adrenals to secrete cortisol
Why can chemotherapy cause damage to our own cells, but not always the tumour cells?
Because our own cells have p53 (pro-apoptopic) and so the chemo will damage our cells enough to induce apoptosis
However the mutated tumour cells will probably not have any p53, so apoptosis will not be induced!!
Explain X-linked recessive Alleles?
The allele is on te X chromosome, so is more prevelent in females (more likely to be carriers as they have to X chromosomes)
Males only need 1 copy of the allele to be a suffer (as they only have one X-chromosome)
Explain the anti-inflammatory effects of glucocorticoids
Inhibits not the innate and adaptive immune systems
Decrease the production of inflammatory mediators (ROS, leukotrienes, complement, histamine and prostanoids)
Inhibit Th cells activation –> As well as IL-2 and clonal expansion
Decrease vasodialtion –> Preventing wbc to get to the site of infection
What are the 4 normal control mechanisms of the body to prevent loss of function from mutations?
Hetrozygosity –> 2 versions of the same gene, as there’s less chance that both will get mutated
Apoptosis –> Regulated cell death to prevent the transmission of mutated genes
Cell Cycle Control –> Checkpoints during cell division ensures thats no damaged cells become fully grown (but killed by apoptosis)
Regulation of Gene Transcription –> There is a requirement for certain activation signals for gene transcription
Describe the characteristics of Adult (Somatic) Stem Cells
They can proliferate….but not indefinitely
Multipotent/unipotent cells
Located in stem cell niches
Replace worn out/dead cells –> so important for homeostasis
What is the difference between Homodimers and Heterodimers?
Homodimers –> Cytoplasmic and nuclear loacalisation
Each subunit binds one repeat as an inverted dimer, and as a palindrome
Heterodimer –> Activated by ligands binding in the nucleus
RXR forms a dimer with either…
Vitamin D receptor (VDR) –> 3 base pair spacing
Retionic Acid receptor (RAR) –> 4bp
Tridothyronine receptor (T3R) –> 5bp
Bind direct repeat half sites
What will a mutation in the gene IL36RN do?
Cause pustular psoriasis
IL36RN usually helps regulate inflammation by suppressing cytokines like IL-1
Explain two reasons for Atopic Eczema?
A change in the Filaggrin gene that encodes for a structual protein in the skin
Genetic tendencies can cause more IgEs to be produced when exposed to certain allergens
What is an allele?
Different forms of the same gene
Can be dominant or reccesive
Can predispose to disease –> usually mutated versions (eg, CF)
What is the screening that is done for CF?
Immunoreactive Trypsinogen (IRT) - Guthrie Test –> If positive, trypsingoen will be present in the blood, due to the duct in the pancreas being blocked
Genetic Screening –> For the most common genetic mutations
Sweat Test –> Cl- above 60mM = CF likely
What is the difference between Cyclin/CDKs and CKIs?
Cyclin/CDKs –> Cell growth promoters
CKIs –> Inhibitors…..so cell cycle (growth) suppressors……there are 2 types…..
INK4/p16 –> Inhibit CDK4/6
CIP/Kip (p27) –> Inhibt all CDKs
Name 2 pharmacological approches for fixing the ASL in patients with CF
Calcium-Activated Chloride Channel (CACC) Activators
Blocking ENaC –> Amiloride
How does 3 person IVF work?
The parents embryo is fertilised with the mans sperm
The parents embryo has their nucleus removed, and inserted into a donors embryo that has healthy mitochondria (and no nuclei)
What are Tumour Suppressor Genes?
Genes that exert negative effects on cell growth (eg, p53)
So mutations in these will cause an increase in cell growth!!
Usually recessive, so less likely to have full mutations
Explain how the differentation of embryonic stem cells occurs
ESCs will form embryoid bodies once they have stopped renewing (around 6 days)
These bodies have three germ layers (endoderm/mesoderm/ectoderm)
After another 10 days, with differentation factors, the specific cell is formed (for example a cardiomyocyte for the heart)
Explain siRNA mediated RNA interference
Short dsRNA (siRNA) binds to a specific part of an mRNA coding region –> Causing mRNA cleavage
What’s the difference between Heterochromatin and Euchromatin?
Heterochromatin –> Densely packed (condensed) and deacetylated….so not actively transcribed
Euchromatin –> Beads on a string apprearance and acetylated….so actively transcribed!
What are the 2 types of families of proteins involved in the cell growth cycle?
And where abouts are these used?
Cyclins –> Transcription dependent
Cyclin-Dependent Kinases –> Activation dependent
Usually by phosphorylation
What is a Single Nucelotide Polymorphism (SNP)?
And what criteria needs to be filled for something to be called an SNP?
A varation in a DNA sequence by a single nucleotide, at the same position, in the genome between members of the same species
The variation must occur in at least 1% of the population
Generically speaking…. if a molecule involved in cell growth starts with a p (eg, pRb/P53/P16) what do they do?
They inhibit cell growth (suppress it)
So mutations in these will cause an increase in cell growth
What is NFkB?
Nuclear Factor of Kappa (light chain) in B cells
Causes the activation of inflammatory genes
Inhibited by IKb which binds across the Rel domain
Alkaline phosphotase surface expression is exclusive to what type of stem cell?
Pluripotent embryonic stem cells
How does the CRISPR/Cas system work in bacteira to prevent viral infection?
Viral DNA is cleaved by the Cas complex, producing short spacer regions. These are then inserted into the CRISPR region of the bacterias genome.
The CRISPR is then transcribed and then pairs with TracrRNA to produce a dsRNA that is cleaved by endonuclease III. This produces (crRNA-tracrRNA) dsRNA sequances.
This binds to Cas9. This searches for matching DNA from viruses that matches the spacer regions. If found, it is destroyed.
What’s the difference between miRNA and siRNA?
And their effects?
miRNA –> 21 nucleotides long
Target the 3’ end of mRNA, causing a prevention of translation
siRNA –> 21 nucleotides long and double stranded
Cleaves mRNA in the coding region
Both interfere using the protein AGO 2
Explain what oncogenes are?
And what can they can cause?
They are mutated forms of normal genes needed for growth
They are usually dominant, so only one mutation is needed
Point mutations in RAS cause ligand independence (activation without a ligand) due to constitutive activation of EGFR (Epidermal Growth Factor Receptor)
and overexpression of genes
When are bone-marrow transplants done?
And what are the types?
For people whose bone marrow is destroyed during the treatment of myelomas and lymphomas
Autologus –> Self transplant (most common due to lack of rejection)
Allogenic –> Non-self transplant
How do glucocorticoids work?
Bind to intracellular receptors (as GCs are lipophillic)
Bind to their specific receptor inside of the cell, once the receptor has been activated. It is normally held in an inactivated state by the heat shock protein (HSP90)
The complex then translocates to the nucleus to act as a transcription factor. They must bind as dimers to show biological activity
This can cause the repression of anti-inflammatory genes (by controlling gene transcription)
How does Antisense work?
A single strand of DNA/RNA that is complemetory to the mRNA (15-30 nucleotides long) binds
This causes RNase H to split the mRNA into 2, causing it to degrade
What is a Simple Sequence Repeat (SSR)?
A tandam repeat of between 2-8 base sequences
Eg, TGTGTG
Each person will inherit a different number of these SSRs, which creates a biological fingerprint
Explain the effects of losing the CFTR channel in terms of the Air-Surface Liquid (ASL)
And how can these effects be dampened?
Usually there is a large layer of mucus (ASL), caused by Cl- ions that are moved by the CFTR channel
However when we remove the CFTR channel, we lost lots of Cl-…. causing a much thinner layer of mucus (ASL), which is dehydrated and sticky…. which makes it harder fo cilia to clear pathogens
Can be partially fixed using hypertonic saline
Name 3 new drugs that are being used to treat specific mutations of CF?
Ataluren –> For class I mutations (force through a premature stop codon)
Lumacaftor –> For class II (acts as a chaperone in channel processing) –> Must be with Ivacoftor
Ivacoftor –> For class III (acts as a potentiator)
What is AP-1?
Regulates cell growth as well as early response genes
Made up of a dimer of Fos (needs to be transcribed) and Jun (needs to be phosphorylated)
What is stem cell differentation driven by?
Growth factors and other extracellular mediators
Name the two main things that can move through damaged skin?
Allergens –> Bypass the innate system and directly activate B cells (which create IgE)
Bacteria –> Activate the innate and then adaptive immune systems
What type of inheritance is associated with both huntingtons disease and hypercholesteremia?
Autosomal Dominant
Name a few examples of diseases that are caused by X-linked Recessive alleles?
Haemophillia
Colour Blindness
Muscular Dystrophy
