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MCBG > Gene Expression > Flashcards

Gene Expression Flashcards

1
Q

What is a gene?

A 
Stretch of DNA, chromosomal locus
Code+regulation of protein 
2x 25,000 alleles per cell
"Unit of inheritance"
"Unit of transcription"
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2
Q

Which direction is the antisense strand of DNA read during transcription?

A

3’ to 5’

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3
Q

Which direction is mRNA synthesised during transcription?

A

5’ to 3’

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4
Q

Which direction are proteins synthesised?

A

N to C

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5
Q

What is needed to synthesise a polynucleotide or polypeptide?

A

Enzyme
Activated substrates
Needs a template

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6
Q

What are the stages in making a polynucleotide or polypeptide?

A

Initiation
Elongation
Termination

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7
Q

What is needed to synthesise RNA?

A

Enzyme - RNA polymerase
Activated substrates - NTPs
Templates - DNA

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8
Q

What are the stages in making RNA?

A

Initiation
Elongation
Termination

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9
Q

What is needed to make a polypeptide?

A

Enzyme - ribosome
Activated substrates - amino acids
Template - mRNA

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10
Q

What are the 3 stages in making a polypeptide?

A

Initiation
Elongation
Termination

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11
Q

Describe the 3 stages in DNA replication

A

Initiation - recognition origin of replication, initiation proteins, DNA polymerase

Elongation - 5’ to 3’ chain growth

Termination - when replication forks meet

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12
Q

Describe the 3 stages in transcription

A

Initiation - promoter recognition, transcription initiation factors, RNA polymerase

Elongation - 5’ to 3’ chain growth

Termination - sequence dependent

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13
Q

Give a general equation to denote making an mRNA polynucleotide

A

(rNMP)n + rNTP —-> (rNMP)n+1 + PPi

NMP = nucleotide monophosphate 
NTP = nucleotide triphosphate
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14
Q

What is a promoter sequence?

A

Upstream sequence - regulates gene expression

Define where the transcription of a gene by RNA polymerase begins

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15
Q

What is a TATA box?

A

A DNA sequence that indicates where a genetic sequence can be read and decoded. It is a type of promoter sequence which specifies to other molecules where transcription begins.

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16
Q

Why is RNA processing necessary

A

Turn pre-mRNA into mature mRNA

mRNA is prone to degradation

17
Q

What is capping?

A

Cap added at the 5’ end - protection against degradation
A 5’ - 5’ linkage is created
Plays a role in translation

18
Q

What is tailing?

A

aka polyadenylation
PolyA tail added at the 3’ end - protection against degradation
Signal for termination is AAUAA. The mRNA is cut a but later
PolyA polymerase adds up to 200 A nucleotides to the 3’ end
This uses ATP

19
Q

What is splicing?

A

Introns in the middle removed, sequence dependent

20
Q

Describe prokaryotic ribosomes

A

3 rRNAs + 56 proteins
30S + 50S subunits
70S ribosome

21
Q

Describe eukaryotic ribosomes

A

4 rRNAs + 82 proteins
40S + 60S subunits
80S ribosome

22
Q

Name 5 types of RNA

A
  • rRNA (ribosomal RNA) - RNA polymerase I - few kinds, many copies of each, >80%
  • mRNA (messenger RNA) - RNA polymerase II - 100,000s of kinds, few copies of each, ~2%
  • tRNA (transfer RNA) - RNA polymerase III - ~100 kinds, very many copies of each, ~15%
  • miRNA (microRNA)
  • noncoding RNA
23
Q

Briefly describe the genetic code

A

Triplet code, degenerate
Non-overlapping, no gaps
“Changing the language” from 4-letter DNA to 20 letter protein “language” results in 5’ to 3’ template producing N to C polypeptide chain extension
Adaptor molecule needed is tRNA

24
Q

What is needed for translation?

A

Enzyme - ribosome
Activated substrates - amino acids
Template - mRNA

25
Q

Describe the structure of tRNA

A

Clover model
3 stem loops - hydrogen bonds are formed between antiparallel complementary sequences
Has an anticodon loop which binds to mRNA - e.g. tRNA 5’CAU recognises mRNA 5’AUG (methionyl tRNA)
CCA terminus at 3’ end (OH) which binds correct amino acid

26
Q

What are wobble bases?

A

5’ base of anticodon has I base - this is the wobble position (3’ base of codon)
This allows a single tRNA to recognise more than one codon

27
Q

Describe the 3 steps in translation

A

Initiation - AUG codon recognition, “special” methionyl tRNA ribosome
Elongation - N to C chain growth, aminoacyl tRNAs
Termination - stop codons

28
Q

Describe initiation of translation

A

Cap recognised by cap binding proteins, initiation factors, methionyl tRNA binds, GTP needed
Downstream, AUG recognised methionyl tRNA binds, initiation factors, cap binding proteins, GDP

29
Q

Describe elongation in translation

A

60S subunit
2 sites of ribosome, P site and A site
Methionyl tRNA on P site, binding of aminoacyl-tRNA to A site
Peptide bond formation between AAs (now attached to tRNA in A site)- peptidyl tRNA
Translocation of this tRNA to P site using GTP (ribosome “moves along”) - enzyme peptidyl transferase ensures peptide is transformed and growing chain on correct side
A site now empty for another tRNA to bind

30
Q

Describe termination of translation

A

Stop codon reached, water added to peptidyl tRNA to give the peptide and tRNA

MCBG (18 decks)

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