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* Year 2 EMS > GiM week 2 > Flashcards

GiM week 2 Flashcards

1
Q

what is epigenetics?

A

the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself

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2
Q

which end of a DNA strand is the phosphate group found on?

A

5’

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3
Q

what is another name for the coding strand of DNA (ie the one that mRNA is a copy of)?

A

sense strand

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4
Q

what are the small sections of DNA that are synthesised on the lagging strand of replicating DNA called?

and why are such sections only found on the lagging strand and not the leading strand?

A

okazaki fragments

because of the way the original dna is unzipped, the new daughter strand of dna on the leading strand is synthesised from 5’–>3’ in one long section but, on the lagging strand the dna on the daughter strand needs to be synthesised from 3’–>5’ but, since dna can only be synthesised in 5’–>3’ direction, the lagging strand is synthesised in chunks (okazaki fragments)

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5
Q

do all genes code for proteins?

A

no, some are just transcribed into RNA which is then used for other purposes like signalling and structure

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6
Q

what is a well known example of a promoter sequence before a gene?

A

TATA box

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7
Q

what happens after splicing at the 5’ end and the 3’ end of RNA?

A

5’ - guanine cap added

3’ - polyadenylation

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8
Q

what is the difference between an exon and an intron?

A

exons are kept in mature RNA and are translated

introns are removed from RNA by splicing

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9
Q

what is the benefit of alternative splicing?

A

one gene can code for more that one mRNA sequences (and thus more than one protein)

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10
Q

what are the two types of alternative splicing?

A

exon skipping

mutually exclusive exon choice

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11
Q

what are pseudogenes?

A

genes that were once functional, in our evolutionary history, but, due to mutation, are no longer functional

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12
Q

what are processed genes?

A

intronless copies of other genes

(produced by reverse transcription and reintegration [into the dna], for example by retroviruses)

if the processed gene has then undergone mutation, rendering it non-functional, it’s called a pseudo processed gene

occasionally remain functional, most are non-functional

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13
Q

what are the two types of repetitive dna?

A

satellite DNA - large blocks of repetitive DNA sequence

interspersed repeats - scattered around the genome

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14
Q

what does the word heterochromatic mean?

and what are heterochromatic chromosomal regions?

A

“differently staining” - ie they stain differently from most DNA

this is because they contain a lot of repeating sequences (satellite dna)

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15
Q

what is alphoid dna? and what is it used for in the study of genetics?

A

a type of satellite DNA found at centromeres on every chromosome.

but it is slightly different and unique to each chromosome

so if different staining methods are used, you can use the different alphoid DNA to differentiate between chromosomes and identify which is which

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16
Q

what is a SINE?

A

Short Interspersed Nuclear Element

they make up 5% of the genome

are often dispersed by RETROTRANSPOSITION (reverse transcription followed reintegration into the DNA)

have a role in generation of molecular pathology

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17
Q

what can interspersed repeats cause?

A

molecular pathology from unequal crossing over

ie during normal recombination between non-sister chromatids at meiosis, if there are interspersed repeats, the section of DNA that is swapped may be reattached at the wrong point (for example leaving chromatid A with two copies of gene 1 while chromatid B has no copies of said gene)

therefore this can lead to a genetic disorder (or there can be no phenotypic change)

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18
Q

Why is the deletion of an exon which has a number of base pairs that is a multiple of 3 less likely to result in a phenotypic change than if the number of base pairs was not a multiple of 3?

A

if multiple of 3: only causes deletion of whatever amino acids that exon coded for

if not: not only causes deletion of exon but also causes a frame shift for the rest of the gene and possible truncation of the mutated protein (if a premature stop codon is coded for)

19
Q

what is Charcot-Marie-Tooth disease and what causes it?

A

CMT is a group of varied inherited disorders of the peripheral nervous system characterised by progressive loss of muscle tissue and touch sensation across various parts of the body. Currently incurable, this disease is the most commonly inherited neurological disorder

The most common cause of CMT (70-80% of the cases) is the duplication of a large region on the short arm of chromosome 17

20
Q

what is duchenne muscular dystrophy caused by?

A

deletion of the dystrophin gene on the X chromosome

21
Q

what is Haemophilia A caused by?

A

a ‘gross rearrangement’

INTRAchromosomal recombination (instead of INTER) occurs causing a segment of the X chromosome to be inverted

22
Q

why are a lot of point mutations ‘silent’ in the phenotype?

A

because there are more codons than there are amino acids so more than one codon codes for each amino acid

so if the point mutation causes GAC to become GAT then both of these code for Asp so there will be no change in the phenotype

23
Q

why are CG –> TG mutations so common (make up 1/3 of pathogenic mutations)?

A

because one of the ways that DNA is stabilised is that methylation occurs on C residues that are next to G residues.

However methylCytesine is very similar to tyrosine so during the next replication tyrosine can be incorrectly inserted instead of cytesine, thus causing a CG –> TG mutation

24
Q

what can a point mutation at a splice junction cause?

A

mRNA insertion (as splicing occurs at wrong point), deletion and/or frame shift mutation

all –> possible pathology

25
Q

when naming base pairs in a gene, what is number 1 always?

A

the A of the ATG (which codes for the start aa of methionine)

26
Q

what does a * mean when talking about genetic codes?

A

a stop codon

also written as: ter

27
Q

what is an example of a genetic bottleneck?

A

migration

28
Q

The heterochromatic region on chromosome 1 is an example of this type of DNA…

A

satellite dna

29
Q

what types of genes are enriched for CNVs?

A

olfactory receptor genes

huge variation in what things smell like to different people

30
Q

what are most genes examples of?

A

single copy sequences

31
Q

what is the name given to a mutation if it causes a substitution of an amino acid residue in a protein?

A

missense

32
Q

what is the name given to a mutation if it causes a premature stop codon in a polypeptide, resulting in a truncated protein?

A

nonsense

33
Q

As most amino acids have more than one possible three letter base code, the code is said to be…

A

degenerate

34
Q

What is the chemical difference between ribose and deoxyribose sugars?

A

ribose has one more hydroxyl group than deoxyribose

35
Q

what is CNV?

A

People have two copies of most genes, one copy inherited from each parent. In some cases, however, the number of copies varies—meaning that a person can be born with one, three, or more copies of particular genes. Less commonly, one or more genes may be entirely missing. This type of genetic difference is known as copy number variation (CNV).

Copy number variation results from insertions, deletions, and duplications of large segments of DNA. These segments are big enough to include whole genes. Variation in gene copy number can influence the activity of genes and ultimately affect many body functions.

Researchers were surprised to learn that copy number variation accounts for a significant amount of genetic difference between people. More than 10 percent of human DNA appears to contain these differences in gene copy number.

36
Q

Language acquisition in humans is a consequence of variation in which gene?

A

FOXP2 gene

If mutation in this gene –> speech and language difficulties

(able to understand spoken words perfectly, but struggled to string words together in order to form a response.)

The FOXP2 gene is highly conserved between species. This means that the gene has a very similar DNA sequence in different species, suggesting it has not evolved much over time. The FOXP2 protein in the mouse only differs from the human version by three amino acids. The chimpanzee version only differs from the human version by two amino acids. These two changes in amino acids may be key steps in the evolution of language in humans.

scientists have concluded that FOXP2 is involved in the brain’s ability to learn sequences of movements. In humans this has translated into the complex muscle movements needed to produce the sounds for speech, whereas in other species it may have a different role, coordinating other movements.

37
Q

what are the two different types of trinucleotide repeat expansions?

give examples of each

A 
polyglutamine repeats (CAG)
- eg huntingtons

large non-coding repeat expansions

  • eg fragile X syndrome (transcriptional silencing)
  • eg myotonic dystrophy
38
Q

what is the genetic cause of fragile X syndrome?

A

CGG repeat expansion in the Fragile X Mental Retardation 1 gene (FMR1 gene)

if there are too many repeats then the gene cannot be transcribed and so is silenced

39
Q

what general differences are seen between dominant and recessive inherited conditions? 3

(nb there are exceptions though!)

A

recessive - tend to be LOSS of function
dominant - tend to be GAIN (or alteration) of function

recessive - de novo mutations rare
dominant - de novo mutations common

recessive - often caused by lots of slightly different mutations (sufferers are often compound heterozygotes) - genetic testing hard
dominant - narrower mutational spectrum - genetic testing easier

40
Q

what two factors may influence the likelihood of someone being a carrier of CF?

A

consanguinity

caucasian ethnicity more likely

41
Q

what is familial adenomatous polyposis?

A

autosomal dominant

mutation in APC gene (tumour suppressor gene)

gene is 99% penetrant by age 40

lots of benign polyps in bowel
–> cancer (incredibly high colon cancer risk)

42
Q

what are caspases?

A

a group of enzymes which are released when apoptosis is triggered

43
Q

what happens to endothelial cells in acute inflammation?

A

they CONTRACT, thus leaving bigger gaps between them so proteins/cells/etc can get into tissues

* Year 2 EMS (7 decks)

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