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Cells, organisms and systems > 3.4 - DNA to protein > Flashcards

3.4 - DNA to protein Flashcards

1
Q

transcription

A

production of messenger RNA using DNA template and ribonucleoside triphosphates as substrates

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2
Q

in which direction does RNA synthesis occur?

A

5’-3’

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3
Q

difference between DNA replication and transcription? (2)

A
  1. replication - identical copies of entire genome
  2. transcription - selective copies of certain parts of genome into RNA
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4
Q

role of RNA polymerase (3)

A
  1. DNA strands separate at active site of enzyme, polymerase transiently unwinds DNA base pairs
  2. ribonucleotides added to 3’ end of new RNA
  3. newly formed RNA forms RNA-DNA double helix (about 12 base pairs in length)
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5
Q

3 phases of transcription (3)

A
  1. initiation
  2. elongation
  3. termination
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6
Q

where does transcription occur?

A

the nucleus

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7
Q

promoters

A

RNA polymerase recognises and binds to promoters to start transcription

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8
Q

promoter in eukaryotes

A

TATA box (binding initiated by TATA-binding protein)

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9
Q

how is the first transcribed nucleotide numbered?

A

+1, regulatory sequences upstream have -ve numbers

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10
Q

terminator sequences (2)

A
  1. palindromic sequences that result in formation of hairpin, causing RNA polymerase to drop off DNA
  2. tell RNA polymerase where to stop
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11
Q

prokaryotic transcription (4)

A
  1. simpler production of mRNA molecules
  2. prokaryotic cells lack nucleus
    3.transcription/translation/degradation take place in common compartment
  3. translation of mRNA can begin before synthesis is completed
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12
Q

mRNA processing (eukaryotes) (3)

A
  1. adding 5’-cap of 7-methylguanosine (protects from degradation by nucleases)
  2. adding 3’-poly(A) tail
  3. splicing out introns and rejoining exons
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13
Q

what performs splicing reactions in the processing of pre-mRNA?

A

spliceosome

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14
Q

alternative splicing

A
  • important means if generating protein diversity in eukaryotes
  • different combinations of exons removed or retained in mature mRNA (can generate 2+ proteins from one gene)
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15
Q

what % of genetic diseases are caused by defects in splicing?

A

15%

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16
Q

how can defects in splicing cause genetic disease?

A

mutation of splice site in gene results in missing exon, giving truncated (missing functional domain) protein

17
Q

retrovirus replication (5)

A
  1. virus enters host cell by binding to a cellular envelope protein
  2. reverse transcriptase makes DNA from RNA
  3. degrades RNA from DNA-RNA hybrid and replaces it with DNA
  4. DNA incorporated into host DNA
  5. host cell machinery transcribes viral genome and new viruses assembled before budding and infecting new cells
18
Q

why does HIV evolve quickly?

A

error-prone reverse transcriptase, high rates of mutation

19
Q

where does translation occur?

A

ribosome

20
Q

codon

A

sequence of 3 nucleotides that encode an amino acid

21
Q

what is the correct frame for most proteins?

A

frame initiated by the most 5’AUG start codon

22
Q

tRNA function

A

adaptor molecule between codon and amino acid

23
Q

how does tRNA bind to mRNA? (2)

A
  1. mRNA codon sequence complementary to tRNA anticodon sequence
  2. codon and anticodon bond via hydrogen bonding (antiparallel allignment)
24
Q

what enzyme attaches amino acids to tRNA

A

aminoacyl tRNA synthase

25
Q

what are the 4 types of mutation? (4)

A
  1. silent - dont change amino acid sequence
  2. missense - change resulting amino acid
  3. nonsense - introduce stop codon
  4. frameshift - insert/delete bases causing ribosome to read “out of frame”, usually will eventually hit stop codon
26
Q

2 major sub-units of ribosomes (2)

A
  1. large subunit - contains peptidyl transferase centre (small subunit containing decoding centre)
  2. catalytic site - for peptide bond formation (is in 23S rRNA, not the protein) - ribozyme
27
Q

3 tRNA binding sites (3)

A
  1. A - for aminoacyl
  2. P - for peptidyl
  3. E - for exit
    (only 2 of which occupied at any one time)
28
Q

which sites of tRNA are base-paired with mRNA?

A

A and P

29
Q

polysome

A

each mRNA can be translated by more than one ribosome (polysome)

30
Q

how many bases can 1 ribosome translate?

A

80

31
Q

rate of translation in bacteria and eukaryotes? (2)

A
  1. bacteria - 20 amino acids/second
  2. eukaryotes - 2-4. amino acids/second
32
Q

role of mRNA

A

encode amino acid sequences of proteins

33
Q

tRNA

A

match their anticodon to mRNA while carrying specific amino acid for protein synthesis

34
Q

rRNA

A

constituent of large and small ribosomal subunits

35
Q

microRNA

A

regulate expression of genes

36
Q

ribozymes

A

catalytic RNA molecules that act as enzymes

37
Q

prions

A
  1. misfolded versions of normal cellular proteins
38
Q

what can prions cause?

A

can cause normal proteins to also misfold (essentially copy themselves), can also be infectious

39
Q

infectious beta sheet structure

A

aggregates and converts cellular prion into infectious prion

Cells, organisms and systems (25 decks)

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