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MBG*2040 > MBG Part Two: Lecture 9 > Flashcards

MBG Part Two: Lecture 9 Flashcards

1
Q

What are ribosomes composed of?

A

Proteins and several different rRNAs

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2
Q

What is a Ribosomes main purpose?

A

It is an “RNA machine” with key roles in protein synthesis, including the formation of peptide bonds between amino acids.

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3
Q

What is the Size of a Prokaryotic Ribosome?

A

70S

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4
Q

What is the Size of a Eukaryotic Ribosome

A

80S

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5
Q

What does each amino acid have?

A

Its own aminoacyl tRNA synthetase. This enzyme “charges” the tRNA with its specific amino acid.

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6
Q

What does the tRNA synthetase enzyme do?

A

Attaches its specific amino acid to the 3’ end of the tRNA.

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7
Q

How does the amino acid become attached to the appropriate tRNA by the amino acyl tRNA synthetase?

A

In a Two Step Reaction:
- Addition of AMP
- Addition of the tRNA

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8
Q

What is the first step of the tRNA Synthetase reaction?

A

The amino acid rects with ATP to produce aminoacyl-AMP and PPi

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9
Q

What is the Second Step of the tRNA Synthetase reaction?

A

The Amino Acid is transferred to the tRNA and the AMP is released

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10
Q

What is the Amino Acid covalently attached to?

A

The 3’ end of the tRNA.

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11
Q

What are tRNAs adapters between?

A

Amino Acids and the codons in mRNA.

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12
Q

What does the anticodon of the tRNA base pair with?

A

The codon of the mRNA

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13
Q

What happens during initiation of Translation?

A

The components of the translational apparatus come together with an mRNA and a tRNA carrying the first amino acid (AA1) binds to the start codon (AUG)

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14
Q

What happens during elongation?

A

Amino Acids are Brough to the mRNA by tRNAs and are added, one by one, to a growing polypeptide chain

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15
Q

What happens during termination?

A

A stop codon in the mRNA is recognized by a protein release factor, and the translational apparatus comes apart, releasing a completed polypeptide.

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16
Q

What is required to form the initiation complex in prokaryotes?

A

mRNA, large and small ribosomal subunits, initiation factors (IF1-3) and GTP

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17
Q

What is the 16S rRNA a component of in prokaryotes?

A

The 30S small ribosomal subunit and contains the complement to the Shine-Dalgarno sequence in the mRNA.

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18
Q

What does pairing between the two sequences position the ribosome near in prokaryotes ?

A

Near the AUG start codon

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19
Q

What is IF-3 required to do?

A

Inhibit large (50S) subunit from binding (30S) small subunit.

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20
Q

What does IF-1 and IF-2 position formylate?

A

(f)Met-tRNA over the start codon

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21
Q

What makes the 30S initiation complex?

A

Fmet-tRNA + 30S ribosome + IF2-GTP+IF-3+IF-1

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22
Q

What happens when GTP is hydrolyzed to GDP?

A

The remaining IF factors dissociate

23
Q

What does IF-3 dissociating allow for?

A

The large 50S ribosomal unit to bind.

24
Q

What is the complete complex called?

A

70S initiation complex

25
Q

What does fMet=tRNA fmet occupy?

A

The P site of the ribosome

26
Q

What is methionine in eukaryotes?

A

Not formulated

27
Q

What is the Kozak Sequence?

A

Only found in eukaryotes and is 5’ C[A/G]NCAUGG 3’

28
Q

What does the Kozak Sequence do?

A

Influences the efficiency of which AUG in the vicinity is used to start translation.

29
Q

What does the poly(A) tail of the eukaryotic mRNA interact with?

A

The mRNA 5’ 7-MG cap structure via a cap-binding protein complex (CBC) to promote translation initiation,

30
Q

What happens during elongation?

A

1.) A charge tRNA binds to the A site of the ribosome (requires complex formation between the amino-acyl tRNA, elongation factor Tu plus GTP)

2.) Once in the A site, GTP is hydrolyzed to GDP and is released along with EF-Tu.

3.) rRNA in large subunits catalyzes the formation of the peptide bond between the two amino acids.

4.) Polypeptide chain is transferred to the aa in the A-site

31
Q

What is formed between the amino acids in the P and A sites?

A

A peptide bond and the tRNA in the P site releases its amino acid.

32
Q

What does the ribosome require too move down the mRNA to the next codon (translocation)?

A

EF-G and GTP

33
Q

What happens to the tRNA that was in the P site?

A

Enters the E site, from which it moves into the cytoplasm

34
Q

What happens to the tRNA that occupied the A site?

A

It is now in the P site and the A site is open and ready to receive another tRNA.

35
Q

How do all Amino Acids (other then f-Met or Met) move?

A

From the cytoplasm to the A site to the P site to the E site bak to the cytoplasm.

36
Q

Where does F-Met or the first Met in Eukaryotes start?

A

P Site

37
Q

How does ribosomes move down the mRNA

A

5’ to 3’

38
Q

What way do polypeptide chains grow?

A

N terminal to C terminal

39
Q

What site contains the growing polypeptide chain?

A

P Site

40
Q

How does termination occur?

A

When a stop codon enters the A site of the ribosome

41
Q

Are there tRNAs that bind to stop codons?

A

No.

42
Q

What happens when a stop codon is encountered?

A

A release factor (RF) binds to the A site.

43
Q

What does Release Factor 1 (RF-1) recognize?

A

UAG and UAA stop codons

44
Q

What does Release Factor 2 (RF-2) recognize?

A

Release factor 2 (RF-2) recognizes UAA and UGA stop

45
Q

What does the RF-1 and RF-2 binding promote?

A

Promotes the cleavage of the polypeptide chain from the tRNA, releasing the chain and leading to termination.

46
Q

What does the binding of RF-3 and GTP to the ribosome assist?

A

In the dismantling of the entire complex.

47
Q

What are the Six Antibiotics that inhibit Bacterial Protein Synthesis?

A

Chloromycetin

Erythromycin

Neomycin

Streptomycin

Tetracycline

Paromomycin

48
Q

What does chloromycetin inhibit?

A

Formation of peptide bonds

49
Q

What does erythromycin inhibit?

A

Translocation of mRNA along ribosome

50
Q

What does Neomycin inhibit?

A

Interactions between tRNA and mRNA

51
Q

What does Streptomycin inhibit?

A

Initiation of translation

52
Q

What does Tetracycline inhibit?

A

Binding of tRNA to ribosome

53
Q

What does Paromocycin inhibit?

A

Validation of mRNA-tRNA match

MBG*2040 (26 decks)

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