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Cellular Genetics and the Cell Cycle > Gene Products and Protein Synthesis > Flashcards

Gene Products and Protein Synthesis Flashcards

1
Q

Definition of wobble mechanism

A

Last base on codon loop forms non Watson Crick base pairs

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2
Q

Definition of initiation

A

Formation of initiation complex comprising of ribosomes, mRNA, initiator, tRNA, IF1, IF2, IF3, GTP nucleotide

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3
Q

Definition of the Shine-Dalgarno sequence

A

Upstream of start AUG, binds to 16s RNA sequence, ensures inframe translation

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4
Q

Definition of elongation

A

Activated AA binds to elongation factor, enters A site of ribosome
Energy for proof reading provided by GTP hydrolysis to GDP
Peptide bonds formed between AA in P and A site
EF-G binds and ribosome translocates so A site is free again

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5
Q

Definition of termination

A 
Stop codon of mRNA presented to A site
Release factor 1, 2 binds
Hydrolysis of protein from tRNA
Ribosome complex disassembled
Needs IF3, ribosomal recycling factor, GTP hydrolysis
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6
Q

How many combinations of codon triplets are there?

A

4 to the 3 = 64 combinations

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7
Q

How many stop codons are there

A

3
UAA
UAG
UGA

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8
Q

How many start codons are there

A

1 AUG

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9
Q

Important components to translation and their roles

A

mRNA,
carries sequence info to make protein at ribosome
tRNA,
bring inidivual AA to protein synthesis sites
Ribosomes,
contain rRNA and ribosomal proteins
Machinery of protein synthesis bind mRNA, tRNA

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10
Q

Describe the structure of tRNA

A 
5'
D loop
Anticodon loop
T loop
Acceptor stem
Attached AA at 3'

Extensive internal base pairing
Contains unusual modified base pairing

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11
Q

Describe the tRNA anticodon

A

Triplet of complementary bases to codon
3 unpaired bases, available for HB
tRNA can recognize more than 1 codon due to wobble pairing

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12
Q

What is the wobble mechanism

A

Last base on codon loop forms non Watson Crick base pairs
Does not alter AA sequence of protein
Allows single tRNA species to recognize more than 1 codon

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13
Q

How do AA attach to the 3’ end of tRNA

A

Specific aminoacyl - tRNA - synthetases load tRNA with specific AA
Each tRNA can accept only 1 AA appropriate for the anticodon sequence

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14
Q

Equation for activated AA

A

AA + tRNA + ATP => PPi + AMP + aminoacyl - tRNA

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15
Q

What bond forms between the AA and the tRNA

A

High energy ester linkage

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16
Q

Structure of the ribosome

A

70S complex
Large subunit 50S, 23S rRNA, 5S rRNA, 34 proteins
Small subunit 30S, 16S rRNA, 21 proteins

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17
Q

Internal structure of ribosomes

A

E= exit site
P= polymérisation site
A= acceptor site
mRNA binding site

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18
Q

Steps in translation

A

Initiation
Elongation
Termination

19
Q

Steps in initiation

A

30S binds to Initiation Factor 1, 3
mRNA, fMet (start codon) and IF2 - GTP enter P site
fMet - tRNA anticodon loop lines up with start codon
50S binds to 30S, GDP and Pi released

20
Q

What precedes the start codon?

A

Shine Dalgarno sequence in prokaryotes

21
Q

What is elongation

A

Activated AA binds to elongation factor (EF - Tu GTP), enters A site of ribosome
Energy for proof reading provided by GTP hydrolysis to GDP
Peptide bonds formed between AA in P and A site (no additional energy needed)
EF-G binds, ribosome translocates (GTP hydrolysis) so A site is free

22
Q

Steps of elongation

A

fMet in P site
EF-Tu GTP binds to AA, both enter A site
Pause for proof reading via GTP hydrolysis, EF-Tu GTP leaves AA
Peptide transferase catalyses the formation of peptide bonds so fMet AA2 is a dipeptidyl- tRNA
Another EF-G-GTP is hydrolyses to EF-G-GDP + Pi, so ribosome translocates, A site is free
tRNA is released and discharged and leaves via exit site
Delivery of AA starts meet round of peptide bond synthesis

23
Q

What is termination

A 
Stop codon of mRNA presented to A site
Release factor RF1/RF2 binds
Hydrolysis of protein from tRNA
Ribosome complex diseases,bled
Requires IF3, ribosomal recycling factor and GTP hydrlysis
24
Q

Steps in termination

A

Binding of release factor to A site
Termination of AA chain by hydrolysis, release factor and tRNA move up one position so A site is free
Ribosome complex disassembled, needs IF3, ribosomal recycling factor and GTP hydrolysis

25
Q

Differences between prokaryotic and eukaryotic transcription and translation
Modification of mRNA

A

Unmodified mRNA, translated ASAP/whilst being synthesized

mRNA modified by capping, poly A tailed, splicing before being exported from nucleus for translation

26
Q

Differences between prokaryotic and eukaryotic transcription and translation
Types of ribosomes and subunits

A

30S + 50S = 70S

40S + 60S = 80S

27
Q

Differences between prokaryotic and eukaryotic transcription and translation
How the start codon is found

A

Shine-Dalgarno sequence interacts with 16S rRNA in 30S for RNA binding to ribosome

Interaction between cap at 5’ end of mRNA and ribosome. How start codon found unclear

28
Q

Differences between prokaryotic and eukaryotic transcription and translation
Initiators

A

tRNA = fMet-tRNA fmet

tRNA = met-tRNA met

29
Q

Differences between prokaryotic and eukaryotic transcription and translation
How many proteins are coded by 1 mRNA strand

A

Polycistronic, more than 1 protein

1 protein

30
Q

Differences between prokaryotic and eukaryotic transcription and translation
Location of polyribosomes

A

Free in cytoplasm

Free in cytoplasm and bound to RER

31
Q

How do antibiotics function?

A

Some kill bacteria by distinguishing between eukaryotic and prokaryotic transcription and translation

32
Q

Function of actinomycin

A

Binding DNA at transcription initiation complex, prevents elongation by RNA polymerase

33
Q

Function of rifamycin

A

Inhibition of DNA dependent RNA synthesis through binding to prokaryotic RNA polymerase

34
Q

Function of streptomycin

A

Affects initiation 30S, causes codon misreading

35
Q

Function of erythromycin

A

Binds to 50S, prevents translocation

Inhibits peptidyl transferase

36
Q

Function of chloramphenicol

A

Inhibits peptidyl transferase by binding on 50S

37
Q

Function of tetracyclines

A

Inhibit binding of aminoacyl-tRNA to ribosome

38
Q

Function of puromycin

A

Causes premature chain termination during both translations

39
Q

Function of alpha-aminitin

A

Inhibitor of RNA polymerase II

40
Q

Function of cylcoheximide

A

Inhibits protein biosynthesis in eukaryotic organisms, interfering with translocation (elongation)

41
Q

Function of diphtheria toxins

A

RNA translational inhibitor, inactivating elongation F2

42
Q

Effect of antibiotics on mitochondria

A

In vitro = :)
In vivo = minimal
Few drugs cross inner mitochondrial membrane
Mitochondria have v low rates of transcription

43
Q

Where is peptidyl transferase found

A

On ribosomes

Cellular Genetics and the Cell Cycle (8 decks)

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