L20

Question 1

D arm (left)

Answer 1

dihydrouracil

Question 2

TpsiC arm (right)

Answer 2

thymine (normally doesn’t occur in RNA but occur in tRNA)

Question 3

amino acid arm (top)

Answer 3

3’ end of tRNA, CCA always for any tRNA

Question 4

tRNA double helices similar to

Answer 4

A-DNA

Question 5

inosine in tRNA anticodon binds to which third base on codon

Answer 5

A/U/C

Question 6

inosine is deaminated what?

Answer 6

deaminated adenine

Question 7

uracil in tRNA anticodon binds to which third base on codon

Answer 7

A/G

Question 8

guanine in tRNA anticodon binds to which third base on codon

Answer 8

C/U

Question 9

aaRS - aminoacyl tRNA synthetase

Answer 9

1. activation of amino acid
2. formation of charged tRNA

Question 10

activation of amino acid

Answer 10

• adenylation: amino acid nucleophilic attack to phosphate connected to sugar to create mixed anhydride

Question 11

formation of charged tRNA: class 1 vs class 2 aaRS

Answer 11

1. 2’-OH vs 3’-OH of 3’ end of tRNA attacks aminoacyl-AMP
2. transesterification or no transesterification to 3’-OH

Question 12

pyrophosphatase

Answer 12

PPi –> 2Pi + heat

Question 13

charged tRNA

Answer 13

aminoacylated tRNA

Question 14

formation of charged tRNA

Answer 14

adenylated amino acid + tRNA –> AMP + aminoacyl tRNA via tRNA synthetase

Question 15

class 1 aa

Answer 15

2’ OH on tRNA sugar performs nucleophilic attack and release aminoacyl AMP, transesterification to 3’ OH

Question 16

class 2 aa

Answer 16

3’ OH on tRNA sugar performs nucleophilic attack and release aminoacyl AMP

Question 17

3 sources of error in translation

Answer 17

1. aaRS uses wrong aa as substrate
2. aaRS selects wrong tRNA as substrate
3. ribosome selects wrong aa-tRNA for codon

Question 18

why hard to achieve specificity in aaRS

Answer 18

valine and isoleucine differ in only 1 CH3, free energy of methylene binding is only around 12kJ/mol –> synthetic site of Ile has at least 1 Val for every 200 Ile

Question 19

proofreading by aaRS

Answer 19

• either adenylated amino acid or aminoacyl tRNA is undone, futile cycle of ATP

Question 20

Which of the following is true about aminoacyl-tRNA synthetases?
They add an amino acid to the 5′ end of a tRNA.
They recognize only the anticodon arm of tRNAs.
They cannot proofread.
They generate charged tRNAs.

Answer 20

They generate charged tRNAs.

Question 21

What does it mean when the genetic code is described as “degenerate?”
- It means that the translation machinery is prone to making errors.
- It means that more than one codon can specify the same amino acid.
- It means that two or more anticodons can base pair with the same codon.
- It means that there are fewer codons than amino acids.

Answer 21

It means that two or more anticodons can base pair with the same codon.

Question 22

How many amino acids are there in the standard genetic code?
4
16
20
3
64

Answer 22

20

Question 23

Which of the following is not a feature of tRNA molecules?
About half the nucleotides in tRNA are base-paired.
They are synthesized by RNA polymerase II.
They contain many unusual bases.
Each is a single chain between 73 and 93 ribonucleotides.
They are linked to amino acids at their 3’ end.

Answer 23

They are synthesized by RNA polymerase II.

Question 24

Which of the following could not be used as an anticodon in a cell because it would recognize codons of two different amino acids?
(3′) GCI
(3′) CCC
(3′) AAG
(3′) UCI

Answer 24

(3′) UCI

Question 25

In preparation for attachment to the tRNA, amino acids are activated by formylation N-acetylation adenylation methylation

Answer 25

adenylation

Question 26

You synthesize an RNA molecule with U and C nucleotides used at a 3:1 ratio and then use this synthetic RNA for an in vitro translation reaction. What would be the amino acids in this protein in descending quantity from most to least? This poll is locked. A. Leu, Ser, Pro, Phe B. Pro, Ser, Leu, Phe C. Phe, Ser, Leu, Pro D. Phe, Leu, Ser, Pro E. Phe, Leu=Ser, Pro

Answer 26

Phe, Leu = Ser, Pro

Question 27

If Crick’s experiment had revealed that one + mutation could be suppressed by adding 3 or more + mutations to the gene, what would this indicate of the genetic code? - multiples of 2, 3, or 4

Answer 27

4

Question 28

What is the anticodon on a tRNA that carries Trp, written 5' – 3'? Response recorded A. CCA B. ACC C. UGG D. GGU E. None of the above

Answer 28

CCA

Question 29

Degeneracy of code

Answer 29

Some amino acids are specifics by multiple codons, and usually only differ at the third position

Question 30

Which of the following would be a suitable anticodon for the valine tRNA? You can respond once A. 5’-CAI-3' B. 5’-IAC-3' C. 5’-IGC-3' D. 5’-IAU-3' E. none of the above

Answer 30

B. 5’-IAC-3'

Question 31

Which of the following best characterizes the relationship between amino acids and tRNAs? This poll is locked. A. The activation of an amino acid by formation of an aminoacyl-tRNA is coupled to the hydrolysis of ATP to AMP + 2 Pi. B. The conformation of an aminoacyl-tRNA facilitates the direct interaction between the amino acid and its appropriate codon in the mRNA-ribosome complex. C. Formation of the ester linkages between a tRNA and its corresponding amino acid is catalyzed by the tRNA itself. D. A tRNA binds to its appropriate amino acid through a covalent linkage of the amino acid’s side chain to the base of the nucleotide immediately 5’ of the anticodon. E. A tRNA is a six-nucleotide RNA molecule consisting of an anticodon followed by a CCA sequence that accepts amino acids

Answer 31

A. The activation of an amino acid by formation of an aminoacyl-tRNA is coupled to the hydrolysis of ATP to AMP + 2 Pi.

Question 32

Which ONE of the following statements about tRNA is FALSE? Response recorded A. A tRNA may recognize more than one codon. B. All tRNA have a CCA sequence at their 3’ end which is the site of aminoacylation. C. tRNAs can have thymine in their sequence D. An amino acid is added to the end of the tRNA by the nucleophilic attack of the amino acid carboxyl group on the terminal phosphate of the tRNA E. All of the above statements are true

Answer 32

D. An amino acid is added to the end of the tRNA by the nucleophilic attack of the amino acid carboxyl group on the terminal phosphate of the tRNA

Question 33

Which best explains how the valine aaRS is prevented from incorrectly adding isoleucine to the valine tRNA? You can respond once An isoleucine adenylate would be hydrolyzed at the synthesis site of the valine aaRS. An isoleucine adenylate would be hydrolyzed at the editing site of the valine aaRS. A valine adenylate would be hydrolyzed at the editing site of the valine aaRS. Isoleucine is too big to bind to the synthesis site of the valine aaRS. Isoleucine is too big to bind to the editing site of the valine aaRS.

Answer 33

Isoleucine is too big to bind to the synthesis site of the valine aaRS.