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Y1S1- Fundamentals of Medicine > Genetics > Flashcards

Genetics Flashcards

1
Q

how many chromosome do humans have?

A

46

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2
Q

histone core

A

octamers of 8 protein molecules- 2 each of H2A, H2B, H3, H4

  • small positively charged molecules
  • have tails
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3
Q

nucleosome

A

DNA wrapped around 1 histone core

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4
Q

further packaging of DNA chromatin loops

A

folding of long chromatin fibres into loops- some are less condensed that others- tend to be genes that are highly transcribed and so, need to be more accessible

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5
Q

what can accessibility of DNA be controlled by?

A

chromatin remodelling complexes- locally reposition DNA and change configuration eg. tails of histones can be reversibly chemically modified for different DNA accessibilities.

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6
Q

centromere

A

highly repetitive DNA sequence that can stretch over megabases at constriction point of a pair of chromatids, bound by a large pair of protein complexes known as the kinetochore

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7
Q

telomere

A

long repetitive DNA sequence form a T loop where longer stand folds back on itself to bind with complementary strand at point where it initially skipped over
- DNA sequence in telomeres: TTAGGG

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8
Q

function of telomere

A

Protect the end of chromosome from natural cellular exonucleases, maintaining chromosome integrity

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9
Q

purine bases

A

adenine, guanine

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10
Q

pyrimidine bases

A

cytosine, thymine

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11
Q

nucleoside

A

nucleotide without phosphate, ends with -osine

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12
Q

what can DNA strands be separated by?

A
  • Initiator proteins- recognise replication origins and locally open helix to create 2 replication forks for every origin (allows bidirectional replication)
  • DNA helicase
  • Single stranded binding proteins holding them apart
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13
Q

what direction is DNA synthesised in?

A

5’ to 3’ direction, dNTPs are added 3’ ends - the high-

energy phosphate bond is broken to release energy

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14
Q

leading strand replication

A

continuous

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15
Q

lagging strand replication

A

discontinuous, Okazaki fragments created that are joined by DNA ligase

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16
Q

DNA mismatch repair process

A
  1. Localised distortion is made in helix
  2. Detection: mismatch proteins scan this and make nick in new strand
  3. Removal: proteins bind and remove part of DNA with the mismatch
  4. Repair: DNA repair is made by DNA polymerase and ligase
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17
Q

how is DNA damage repair possible?

A

due to redundancy- 2 copies of genetic code because of 2 strands so if 1 is damages, encoded information isn’t lost

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18
Q

PCR process

A
  1. Heated to about 95C for a minute  strands of DNA separate
  2. Cooled to 55C  primer annealing
  3. Heated to 72C  synthesis new DNA strands using thermophilic DNA polymerase
  4. After nth PCR cycle, 2^n double stranded molecules are produced
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19
Q

allele-specific PCR

A

different primers used to determine presence of a mutation as amplification depends on DNA bases

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20
Q

mutations can lead to:

A
  • Loss of function
  • Gain of function
  • Too much gene product
  • Too little gene product
21
Q

point mutation types

A
  • non-frameshift
    Synonymous- same resultant amino acid
    Non synonymous- different resultant amino acid
  • Nonsense- codes for stop codon (UAG, UGA, UAA) [transcription stops at mutation resulting in unstable/truncated protein]
  • Missense- creates amino acids of different chemical properties
  • Splice site- changes order of exons or introns
22
Q

deletion mutation

A
  • Base is removed
  • All later bases move up, changes all downstream- all codons change (FRAMESHIFT)
  • Less likely to make functional protein
23
Q

insertion mutation

A
  • Base added to sequence/ copied
  • Moves all downstream bases down- changes codons (FRAMESHIFT)
  • Less likely to make a functional protein
24
Q

non-allelic homologous recombination

A

alignment may not happen correctly when maternal and paternal genomes switch about

25
Q

copy number pleomorphism

A

changes in number of genes ex. Crohn’s and SLE (systemic lupus erythematosus

26
Q

deaminination

A

changes in base cytosine to uracil via ammonia release

27
Q

PKU mutation

A
  • Mutation in gene encoding liver enzyme phenylalanine hydroxylase- converting phenylalanine to tyrosine  toxic phenylalanine build up  impaired brain development in children
  • Low protein (phenylalanine) diet can prevent toxic build up
28
Q

ribosomal RNA

A
  • Encoded by DNA

- Involved in ribosomal structure

29
Q

messenger RNA

A
  • Encoded by DNA

- Encodes proteins

30
Q

transfer RNA

A
  • Encoded by DNA

- Involved in transferring codons in transcription

31
Q

formation of sense strand

A

using the antisense strand with base pairing to generate a template copy of the sense strand, DNA strands separate to form an open complex and RNA polymerase pair nucleoside triphosphates to partner bases on the antisense strand in 5’ to 3’ direction.

32
Q

promoters

A

sequence immediately upstream (5’ direction) to the section being described, initiate transcription

33
Q

enhancers

A

on nearby genes, can operate over considerable distances, increase transcription

34
Q

2 types of mRNA processing

A
  1. Splicing- removing introns, stitching together exons to form mature transcript for translation
  2. Polyadenylation- when transcription terminates, the 3’ most segment of new transcript is cleaved off and polyA tail is synthesised
    [Alternative polyadenylation- can cleave in different places, producing variety of transcripts]
35
Q

translation process

A
  1. A start codon is recognised- AUG
  2. 2 subunits of ribosome (large & small) assemble at 5’ end of mRNA transcript
  3. Ribosome moves along to find start codon
  4. tRNA has an amino acid attached to 3’ end and an anticodon loop on 5’ end (complementary to codon), tRNAs come and go throughout EPA docking sites to bring amino acids to be linked together according to mRNA code
36
Q

ribsome tRNA docking sites

A
  • aminoacyl site (A)
  • peptidyl site (P)
  • exit site (E)
    EPA- order they sit in
37
Q

tRNA docking process

A
  1. Charged tRNA molecule binds to vacant aminoacyl site (which tRNA that binds is determined by base pairing with the mRNA codon) immediately adjacent to proceeding tRNA, the tRNA which proceeds from before is ejected from the exit site
  2. A new peptide bond forms between two amino acids on the tRNAs in the P&A sites, the amino acid ion the tRNA in the P site unbinds from the tRNA
  3. Bound tRNAs are shifted into the exit and peptidyl sites as the large subunit translocates
  4. Small subunit translocates, resetting the ribosome with a vacant A site so it can reset the cycle
38
Q

stop codons

A

UAA, UAG, UGA

39
Q

epigenetic

A

from non-genetic influences on gene expression

40
Q

ways that histone tails can be reversibly chemically modified:

A
  • Methylation
  • Acetylation
  • Phosphorylation
41
Q

mitosis phases

A
  1. Interphase- late G2 phase, DNA is already copied, sister chromatids are formed and centrosome is copied
  2. Prophase- mitotic spindle fibres start to form, chromosomes start to condense & nucleolus disappears, nuclear envelope breaks down and chromosomes become fully condensed
  3. Metaphase- chromosomes lined up at metaphase plate, microtubules bind to chromosomes at kinetochore on centromere of chromatids
  4. Spindle Checkpoint- checks chromosome alignment and attachment
  5. Anaphase- chromatids separate to become chromosomes, pulled to opposite ends of cell
  6. Telophase- new nuclear membrane forms around each set of chromosomes + chromosomes decondense
    Cytokinesis- division of cytoplasm into 2 cells, overlaps with final stages
42
Q

2 processes that create genetic variation in metaphase 1

A
  1. Crossing over- genetic information can cross over at points called chiasmata between non sister chromatids
  2. Independent assortment- maternal and paternal chromosomes are shuffled and dealt randomly so daughter cells differ from parent cells
43
Q

in cytoplasmic division, which daughter cell goes on to form the egg?

A

there is unequal divison so the daughter cell with the most cytoplasm goes on to form the egg and the other is a polar body that eventually degenerates

44
Q

aneuploidy

A

numerical change in part of chromosome set

45
Q

polyploidy

A

numerical change in whole set of chromosomes

46
Q

what phases can non-disjunction lead to ploidy?

A
  • Anaphase I- sometimes chromosomes don’t separate properly so too many chromosomes may end up in one daughter cell
  • Anaphase II- chromatids may not separate properly alternatively in this phase
47
Q

law of segregation

A

Homologous alleles segregate (during gamete formation) and then unite at random in fertilisation.

48
Q

law of independent assortment

A

Alleles for different traits segregate independently.

Y1S1- Fundamentals of Medicine (11 decks)

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