MBG Part Two: Lecture 9

Question 1

What are ribosomes composed of?

Answer 1

Proteins and several different rRNAs

Question 2

What is a Ribosomes main purpose?

Answer 2

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

Question 3

What is the Size of a Prokaryotic Ribosome?

Answer 3

70S

Question 4

What is the Size of a Eukaryotic Ribosome

Answer 4

80S

Question 5

What does each amino acid have?

Answer 5

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

Question 6

What does the tRNA synthetase enzyme do?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What is the first step of the tRNA Synthetase reaction?

Answer 8

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

Question 9

What is the Second Step of the tRNA Synthetase reaction?

Answer 9

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

Question 10

What is the Amino Acid covalently attached to?

Answer 10

The 3’ end of the tRNA.

Question 11

What are tRNAs adapters between?

Answer 11

Amino Acids and the codons in mRNA.

Question 12

What does the anticodon of the tRNA base pair with?

Answer 12

The codon of the mRNA

Question 13

What happens during initiation of Translation?

Answer 13

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)

Question 14

What happens during elongation?

Answer 14

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

Question 15

What happens during termination?

Answer 15

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

Question 16

What is required to form the initiation complex in prokaryotes?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

Near the AUG start codon

Question 19

What is IF-3 required to do?

Answer 19

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

Question 20

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

Answer 20

(f)Met-tRNA over the start codon

Question 21

What makes the 30S initiation complex?

Answer 21

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

Question 22

What happens when GTP is hydrolyzed to GDP?

Answer 22

The remaining IF factors dissociate

Question 23

What does IF-3 dissociating allow for?

Answer 23

The large 50S ribosomal unit to bind.

Question 24

What is the complete complex called?

Answer 24

70S initiation complex

Question 25

What does fMet=tRNA fmet occupy?

Answer 25

The P site of the ribosome

Question 26

What is methionine in eukaryotes?

Answer 26

Not formulated

Question 27

What is the Kozak Sequence?

Answer 27

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

Question 28

What does the Kozak Sequence do?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What happens during elongation?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

EF-G and GTP

Question 33

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

Answer 33

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

Question 34

What happens to the tRNA that occupied the A site?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

P Site

Question 37

How does ribosomes move down the mRNA

Answer 37

5' to 3'

Question 38

What way do polypeptide chains grow?

Answer 38

N terminal to C terminal

Question 39

What site contains the growing polypeptide chain?

Answer 39

P Site

Question 40

How does termination occur?

Answer 40

When a stop codon enters the A site of the ribosome

Question 41

Are there tRNAs that bind to stop codons?

Answer 41

No.

Question 42

What happens when a stop codon is encountered?

Answer 42

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

Question 43

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

Answer 43

UAG and UAA stop codons

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

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

Answer 46

In the dismantling of the entire complex.

Question 47

What are the Six Antibiotics that inhibit Bacterial Protein Synthesis?

Answer 47

Chloromycetin Erythromycin Neomycin Streptomycin Tetracycline Paromomycin

Question 48

What does chloromycetin inhibit?

Answer 48

Formation of peptide bonds

Question 49

What does erythromycin inhibit?

Answer 49

Translocation of mRNA along ribosome

Question 50

What does Neomycin inhibit?

Answer 50

Interactions between tRNA and mRNA

Question 51

What does Streptomycin inhibit?

Answer 51

Initiation of translation

Question 52

What does Tetracycline inhibit?

Answer 52

Binding of tRNA to ribosome

Question 53

What does Paromocycin inhibit?

Answer 53

Validation of mRNA-tRNA match