07b: Protein Synthesis

Question 1

How many bases in tRNA for euk? And prok?

Answer 1

Same for both: 75 bases

Question 2

What percent of bases in tRNA are base paired?

Answer 2

50%

Question 3

(X)% of bases in tRNA are modified.

Answer 3

X = 10

Question 4

All tRNA molecules have which base sequence at the (5’/3’) end?

Answer 4

CCA at 3’ end

Question 5

Where on (X) molecule is the site of AA charging?

Answer 5

X = tRNA

at 3’ end

Question 6

Which loops are present in tRNA?

Answer 6

1. D loop
2. Anticodon loop
3. T loop

Question 7

Function of tRNA D loop

Answer 7

Recognized by synthetase enzymes

Question 8

Function of tRNA T loop

Answer 8

Interacts with 5S rRNA (helps position tRNA in ribosome)

Question 9

The (X) sequence always present at the (3’/5’) end of tRNA is (transcribed/added post-transcriptionally).

Answer 9

X = CCA

3’ end

Either encoded or added post-transcriptionally

Question 10

The 3D structure of tRNA shows that it has which shape?

Answer 10

L-shape

Question 11

(Prok/euk) tRNA are multimeric, which means:

Answer 11

Prokaryotic; 2 or more tRNA per transcript

Question 12

T/F: Bacterial tRNA transcripts may be embedded in rRNA transcripts.

Answer 12

True

Question 13

Steps to Bacterial tRNA transcript processing:

Answer 13

1. RNases cleave 5’ then 3’ ends
2. Bases modified
3. CCA added to 3’ end

Question 14

(Prok/euk) tRNA are monomeric, which means:

Answer 14

Eukaryotic;

Only 1 tRNA per transcript

Question 15

What are the key differences, if any, between euk and prok tRNA?

Answer 15

1. Euk monomeric precursor and prok multimeric

2. Intron in anticodon loop of euk tRNA

Question 16

What’s the reason for the (intron/exon) in the (X) loop of (prok/euk) tRNA?

Answer 16

Intron
X = anticodon
Eukaryotic

So that tRNA precursor can’t be used in protein synthesis prematurely

Question 17

Removal of tRNA (X) in anticodon loop, activating the tRNA, involves:

Answer 17

X = intron

1. Endonuclease cleavage
2. ATP-dependent ligation

Question 18

How many precursors does it take to synthesize all 3 bacterial rRNAs?

Answer 18

One large precursor

Question 19

Describe the processing of bacterial rRNA from precursor.

Answer 19

RNase III cleaves double-stranded regions of RNA in an asymmetric manner (leaving 2 base 3’ overhang)

Question 20

Euk rRNA synthesis is done by:

Answer 20

RNA Polymerase I

Question 21

Eukaryotic rRNA precursors are transcribed from (highly/moderately/single)-repetitive sequences.

Answer 21

Moderately

Question 22

Is there post-transcriptional processing of eukaryotic rRNA?

Answer 22

Yes - self-splicing of 45S rRNA precursor

Question 23

T/F: All euk rRNA are transcribed by the same protein.

Answer 23

False - 5S rRNA transcribed by RNA Pol III (rest by Pol I)

Question 24

Where does transcription of 5S rRNA take place?

Answer 24

Nucleus

Question 25

Where does transcription of most euk rRNA take place?

Answer 25

nucleolus (except 5S rRNA)

Question 26

Where does assembly of the individual ribosomal subunits take place in euk?

Answer 26

Nucleolus (5S rRNA and ribosomal proteins go into there to assemble)

Question 27

What are the organelles of protein synthesis?

Answer 27

Ribosomes

Question 28

List the characteristics of the genetic code.

Answer 28

1. Degenerate 2. Non-ambiguous 3. Almost universal (except mitochondria)

Question 29

Genetic code is degenerate means:

Answer 29

more than 1 codon for some AAs

Question 30

Genetic code is non-ambiguous means:

Answer 30

only 1 AA for each codon

Question 31

A point mutation is:

Answer 31

single base change

Question 32

A silent mutation is:

Answer 32

Change that specifies the same AA

Question 33

Missense mutation is:

Answer 33

Change that specific different AA

Question 34

Nonsent mutation is:

Answer 34

Change that produces STOP codon

Question 35

Which changes can cause frameshift?

Answer 35

Addition/deletion of 1 or 2 bases

Question 36

The anticodon on (X) interacts with codon on (Y) in (Z) fashion

Answer 36

``` X = tRNA Y = mRNA Z = antiparallel ```

Question 37

The sequences of (codons/anticodons) are given 5' to 3'.

Answer 37

Both!

Question 38

What's the sequence of the anticodon that would base pair with codon UCA?

Answer 38

UGA

Question 39

Wobble indicates flexibility with:

Answer 39

3' Base Codon

Question 40

According to wobble, (X) can base pair with a number of different (Y).

Answer 40

``` X = 5' base anticodon Y = 3' base codon ```