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FBS1 > Gene Products And Protein Synthesis > Flashcards

Gene Products And Protein Synthesis Flashcards

1
Q

Why is the genetic code considered degenerate?

A

64 combinations of nucleotides in a codon possible yet only codes for 20 amino acid - some amino acids are coded for by more than one triplet

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2
Q

What is the start codon

A

AUG, methionine

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3
Q

What are the stop codons

A

UAA, UAG, UGA

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4
Q

What are the types of point mutation?

A

Nonsense: amino acid to stop
Missense: amino acid to a different amino acid
Silent: amino acid doesn’t change (degenerate code)

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5
Q

What is the mutation that causes sickle cell anaemia?

A

Mutation in B-globin gene; amino acid coded for at 6th position changed from glutamate to valine

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6
Q

What is the mutation that causes cystic fibrosis?

A

A mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene

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7
Q

What is tRNAs shape and why?

A

Single stranded RNA molecule with intramolecular double stranded regions which fold it up into a clover leaf shape.

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8
Q

Where on a tRNA molecule will the amino acid attach?

A

To the 3’ end at the - CAA-OH group

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9
Q

What is wobble pairing?

A

The last base on the codon loop can form non-Watson-Crick pairs; this does not change the amino acid sequence, just means that a single tRNA molecule can recognise more than one codon - good for degenerate code when last base in codon won’t effect the the acid called for

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10
Q

What is the enzyme that produces aminoacyl-tRNA

A

Aminoacyl-tRNA-syntheases

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11
Q

What is an aminoacyl-tRNA?

A

What forms when an amino acid bonds to a tRNA molecule

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12
Q

Amino acid + tRNA + ATP (via aminoacyl-tRNA) =

A

= aminoacyl-tRNA + PPi + AMP

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13
Q

What are the subunits (and their compositions) in prokaryotic ribosome?

A

70s complex, made up of a large 50s and a small 30s subunit.
The 50s subunit is made up of 23s RNA + 5s RNA + 34 proteins
The 30s subunit is made up of 16s RNA and 21 proteins

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14
Q

What is a 50s subunit in a prokaryotic ribosome made up of?

A

23s RNA + 5s RNA + 34 proteins

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15
Q

What is a 30s subunit in a prokaryotic ribosome made up of?

A

16s RNA + 21 proteins

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16
Q

What are the three sites in the 30s subunit of a ribosome?

A

E, P, and A

17
Q

Describe the initiation step of translation in prokaryotes.

A

30s subunit binds initiation factors IF1 and IF3

Then the mRNA binds to the 30s subunit; with the AUG start codon binding near the P site (in the middle of E and A). The Shine-Dalgarno Sequence will bind upstream of the start codon to 16s RNA which ensures in-frame translation.

fmet-tRNA^fmet binds IF2-GTP which then enters P site and lines up with start codon.

Then the 50s subunit binds to 30s ribosome, this removes the initiation factors IF1,2,3 and hydrolyses GTP to GDP + Pi - releasing energy.

18
Q

Describe the elongation step of translation in prokaryotes

A

Aminoactyl-tRNA bound to EF-Tu-GTP (EF = elongation factor) binds to A site. Tu is a G-protein so factor complex can be called EF-G-GTP as below.

Pause for proof reading + GTP hydrolysis

Peptidyl transferase moves second amino acid on top of first, fMet will stay in same place as it was at P site. The 3’ end of tRNA hydrolysed to -OH group and moves over to E site at top while staying attached to P site (sitting diagonally) then tRNA to which fMet-AA is attached has top move over to P site while attached to A site (also sitting diagonally).

Then translocation occurs where bottom of tRNA lines up with top so top+bottom of tRNA at A and top+bottom of tRNA at P; leaving A site free. EF-G-GTP hydrolysed to EF-G-GDP + Pi

Then tRNA at E site released

repeats

19
Q

Describe the termination step of translation in prokaryotes

A

When a stop codon (UAA, UAG, UGA) presented to A site it causes the binding of the release factor and then the protein is released and everything dissociates

20
Q

Classes of antibiotics:

A

Chloramphenicol
Actinomycin
Puromycin
Tetracyclines

Alpha-amanitin
Rifomycin
Streptomycin
Erythromycin

Cyclohexamide
Diptheria toxin

21
Q

Chloramphenicol

A

Inhibits peptidyl transferase by binding on 50s subunit

22
Q

Actinomycin

A

Binding DNA at the transcription initiation complex - preventing elongation by RNA polymerase

23
Q

Puromycin

A

Causes premature chain termination during translocation (for both pro- and eukaryotes)

24
Q

Tetracyclines

A

Inhibits binding of aminoacyl-tRNAs to the ribosome

25
Q

Alpha-amanitin

A

Inhibitor of RNA polymerase II

26
Q

Rifomycin

A

Inhibits RNA synthesis by binding to prokaryotic RNA polymerase

27
Q

Streptomycin

A

Affects initiation (30s) causes misreading of codons

28
Q

Erythromycin

A

Binds to 50s subunit and prevents translocation

29
Q

Cyclohexamide

A

Inhibitor of protein biosynthesis in eukaryotes

30
Q

Diptheria toxin

A

RNA translocational inhibitor by inactivating elongation factor 2

FBS1 (74 decks)

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