IMEG Flashcards
(38 cards)
What is X - inactivation
One X chromosome in female mammals is inactivated. It is packaged so it becomes transcriptionally inactive (heterochromatin). This is to prevent females from have twice as many x chromosome gene products
What is nonsense mediated mRNA decay?
Surveillance pathway which functions to reduce errors in gene expression by eliminating mRNA transcripts that contain premature STOP codons.
Translation of these could lead to gain/loss of function mutations or dominant negative activity of resulting protein
Transcription factors use a variety of interactions to bind and recognise DNA. Briefly explain how these proteins recognise their specific binding sites.
DNA sequence is recognised by basal machinery which binds and unwinds DNA. The machinery then recruits RNA polymerase II which contains TFIID. TFIID contains TATA Binding Protein (TBP) which binds to the TATA box of the promoter region. It also contains TBP Associated Factors (TAFs) which show selectivity for promotor regions. When TBP binds to DNA it causes a bend in the DNA which allows the subsequent binding of the components of RNA polymerase II.
Which of the following does not occur during meiosis.
a) Physical exchanges (recombination) between two homologous chromosomes.
b) Random assortment of maternal and paternally derived chromosomes.
c) A reduction from 46 to 23 chromosomes.
d) Chromosomal non-disjunction.
e) Zygotic non-disjunction
E
Which of the following will not cause a frameshift mutation
a) In frame deletion of 1bp
b) In frame deletion of 2 base pairs
c) In frame deletion of 3 base pairs
d) In frame deletion of 4 base pairs
e) Insertion of 4 base pairs
C
Cohesive or sticky ends in DNA fragments
a) are caused by shearing of DNA
b) are always the result of cutting DNA
c) can be the result of cutting DNA with restriction enzymes
d) occur mainly in plasmids
e) are caused by DNA ligases
C
rRNA is:
a) The major structural material making up ribosomes
b) The molecule that carries the genetic information from DNA and is used as a template for protein synthesis
c) The major structural component of chromosomes
d) A molecule that incorporates a specific amino acid into the growing protein when it recognizes a specific group of three bases
e) The template for protein synthesis
A
Outline the importance of the invention of PCR in life sciences and how you would carry out a typical PCR experiment, describing the components that you would use and the conditions involved at each step.
Can very rapidly gain millions of copies of DNA from just one strand. Aids in genetic testing- analyse presence of genetic disease mutations, tissue typing before organ transplantation and individualised cancer therapy treatment.
To carry out PCR you mix the template DNA with dNTPs, forward and reverse primers, Taq polymerase and MgCl2 and water to make up reaction volume. Then heat this to 94 to denature DNA into ssDNA. Then cool to 65 so primers can anneal to single strand. Then heated to 72 so Taq polymerase can catalyse the addition of nucleotides to single stranded DNA molecules (5’ to 3’ direction). Repeated cycles (~25) of heat denaturation, hybridisation of primers and DNA synthesis.
Why are all cases of achondroplasia due to the same recurring mutation in the
FGFR3 gene?
Other mutations cause different diseases
Only specific mutation will cause gain of function causing achondroplasia, caused by increase in paternal age.
Mutated nucleotide = one of the most mutable single nucleotides known
Haploinsufficiency is…
Usually only need 50% functionality of protein to express normal phenotype however some genes need both normal alleles to express the desired protein and without you get haploinsufficency and an abnormal phenotype.
Dominant Negative Effect is…
When a non functional mutant polypeptide can interfere with a normal protein from a normal allele to produce a dominant negative effect
What is a missense mutation and what is its effect
When a nucleotide is swapped for another. Can often not have a large effect on protein transcribed however if the mutation is non conservative, a evolutionary conserved amino acid or at a functionally important part of the protein the effects could be much worse.
Are somatic mutations heritable? Explain.
No they’re not heritable because the mutations occur during mitosis. Only germline mutations can be inherited as they are mutations in germ cells. Somatic mutations are likely to cause cancer.
Why are there fewer mutations in coding DNA than non-coding DNA?
Coding regions are generally more conserved because mutations in coding regions tend to be lethal
What is homoplasmy and heteroplasmy in mitochondrial genetics?
Homoplasmy- All mitochondria are the same i.e all mutated or all normal
Heteroplasmy- Mixture of mutated and normal mitochondria
Distinguish between triploidy and trisomy
Triplody is when you have an extra one of every chromosome i.e 69 chromosomes in total. Whereas Trisomy is when you gain one chromosome i.e 47 chromosomes in total.
Allelic heterogeneity is…
Disease can be caused by different mutations in different, independent genes
No heterogeneity in achondroplasia as mutation can only be in transmembrane domain otherwise causes different disease
What is alternative splicing?
Alternative splicing is a regulated process during gene expression that results in a single gene coding for multiple proteins. Can have alternative selection of promotors and cleavage sites so as to have different exons. Can also have exon cassette mode where an exon is either retained or excluded to change protein.
DNA damage in cells.
Sunlight- introduces bends in DNA. DNA repair however if can’t keep up with demand –> cancer
Ionising Radiation- double strand breaks, single strand breaks, crosslinks, multiple damage sites. If can’t repair DNA –> cancer
Smoking- covalently binds to nucleotide to disrupt base-pairing, reopens and can’t be recognised. Must be removed. If not –> cancer
Spontaneous base loss (weak link between sugar backbone and base)
Spontaneous deamination of cytosine
Reactive oxygen species attack DNA bases
Difference in G banded chromosome pairs
Heterochromatic Block at Centromere. i.e 16 dark band under centromere
Satellite Regions Vary in Size i.e 13,14,15,21 (Bits of DNA sticking above chromosome)
Variable size of Y chromosome
Variation in meiosis comes from
Free Assortment of maternal and paternal chromosomes
Presence of crossing over exchange between homologous chromosomes- recombination
Wrong parental origin leads to…
Hydatiform mole- All chromosomes of paternal origin 46XX
Ovarian Terratoma- All chromosomes of maternal origin 46XX
Post- Transcriptional Processing-
Polyadenylation: Poly(A) Tail added to 3’ end
Capping: 7mG Cap added to 5’ end
Splicing: Exons remain, Introns removed
Splice site is highly conserved
Splicing by snRNPs RNA-RNA recognition, forms splicesome to splice out intron
Sickle Cell Anaemia Mutation
Base Change GAG –> GTG i.e Glutamate to Valine
