Lecture 4

Question 1

genetic code is – with very few exceptions (e.g. mitochondria) the same codons specify the same amino acids in all organisms.

Answer 1

universal

Question 2

genetic code is – as there are 61 triplets coding for only 20 amino acids, so more than one codon can specify the same amino acid.

Answer 2

degenerate or redundant

Question 3

genetic code is – as each codon specifies only one aa

Answer 3

unambiguous

Question 4

genetic code is almost always read –

Answer 4

linearly and continuously

Question 5

The linear order of codons specifying the order of amino acids in a protein is referred to as the –

Answer 5

reading frame

Question 6

Synthesis of all proteins in eukaryotic and prokaryotic cells begins with methionine. The codon specifying this methionine is the Start codon and is usually –

Answer 6

AUG

Question 7

The reading frame proceeds continuously as triplets to the –

Answer 7

STOP codon.

Question 8

Mutations in the DNA can alter the coding sequence either directly or by–

Answer 8

affecting splicing

Question 9

mutations that alter coding sequence can cause inherited or – (e.g. cancer) disease.

Answer 9

spontaneous

Question 10

TTT to TTC mutation in DNA results in UUU to UUC codon change in mRNA but both encode phenylalanine so the protein would be the same.

Answer 10

silent mutation

Question 11

a change from GAA to GTA in the b-globin gene results in the 6th codon specifying valine (GUA) instead of glutamate (GAA). This mutation causes sickle cell disease

Answer 11

missense mutation

Question 12

TTG to TAG change in the DNA results in UUG (leucine) to UAG (STOP).

Answer 12

nonsense mutation

Question 13

nonsense mutation – the protein

Answer 13

shortens

Question 14

Insertion or deletion, in-frame: insertions or deletions of multiples of 3 nucleotides will result –

Answer 14

in addition or deletion of amino acids

Question 15

most common deletion in frame causes –

Answer 15

cystic fibrosis

Question 16

deletion of the codon specifying the phenylalanine at position 508. AT[C TT]T GGT to ATT GTT in DNA results in AUC UUU GGU (ile phe gly) to AUU GGU (ile gly)

Answer 16

deletion, in frame

Question 17

Frameshift: insertion or deletion of nucleotides not divisible by 3 changes the reading frame – of the mutation

Answer 17

downstream

Question 18

TTG GAA TTT to TTG [C]GA ATT T in DNA results in UUG GAA UUU (leu glu phe…) to UUG CGA AUU U (leu arg ile…)

Answer 18

frameshift

Question 19

encodes the amino acid sequence

Answer 19

mRNA

Question 20

tRNA serves as the – that matches the appropriate amino acid to a codon

Answer 20

adaptor (translator)

Question 21

rRNA is a key structural component of ribosomes and –

Answer 21

catalyzes formation of the peptide bond

Question 22

Translation also requires amino acids, ribosomal proteins, –, and other protein factors.

Answer 22

energy in the form of ATP and GTP

Question 23

The mRNA contains several elements particularly important for translation – the START codon, the coding region, and the STOP codon.

Answer 23

the 5’ cap,

Question 24

Although distinct in –, all tRNAs have common structural characteristics:

Answer 24

sequence

Question 25

tRNAs: -- at the 3’ end where the amino acid attaches in a high energy bond.

Answer 25

CCA sequence

Question 26

tRNAs: An -- containing a 3 nucleotide anticodon that base-pairs with the cognate codon in mRNA

Answer 26

anticodon loop

Question 27

T/F: tRNAs have many bases other than A, C, U and G.

Answer 27

true

Question 28

tRNAs: An L-shaped 3-dimensional structure formed by --.

Answer 28

RNA double helices

Question 29

-- “charge” tRNAs with amino acids

Answer 29

Aminoacyl tRNA synthetases

Question 30

charging tRNA with aa is a 2 step process that requires --

Answer 30

ATP

Question 31

In the first step of charging a tRNA, the tRNA synthetase uses ATP to catalyze addition of -- of an amino acid to form the high energy intermediate aminoacyl-AMP.

Answer 31

AMP to the a-carboxy group

Question 32

in the second step of charing a tRNA, he amino acid is transferred to the -- of the tRNA to generate aminoacyl-tRNA

Answer 32

3’ or 2’ OH

Question 33

Each tRNA synthetase is specific for one amino acid and --

Answer 33

one or a few tRNAs.

Question 34

Some tRNA synthetases have proof-reading mechanisms for --amino acids from tRNA. Mistakes occur about once every 104 to 105 reactions.

Answer 34

removing incorrect

Question 35

Charged tRNA recognizes the appropriate codon in mRNA because the anti-codon is -- to the codon specifying the amino acid carried by that tRNA

Answer 35

complementary

Question 36

Anti-codon and codon interact through--

Answer 36

base-pairing

Question 37

Interaction of codons and anticodons follows the normal base-pairing rules (A:U, G:C) in the first 2 nucleotides of the codon but has -- in the third position

Answer 37

“wobble”

Question 38

wobble in 3rd position allows -- of the code so that a single tRNA can base-pair with multiple codons specifying an amino acid.

Answer 38

degeneracy

Question 39

-- are the translation machine

Answer 39

Ribosomes

Question 40

T/F: Ribosomes of eukaryotes and prokaryotes are similar but not identical

Answer 40

true

Question 41

Mitochondrial ribosomes are more closely related to -- ribosomes

Answer 41

bacterial

Question 42

All ribosomes are -- made up of 2 subunits, one small and one large.

Answer 42

ribonucleoprotein particles (both RNA and proteins)

Question 43

Translation proceeds in the 5’ to 3’ direction on mRNA and synthesizes proteins from the --

Answer 43

amino-terminus to the carboxy-terminus

Question 44

GTP hydrolyzing proteins which cycle between active and inactive states

Answer 44

GTPases

Question 45

GTP hydrolysis is --, providing time for the active form to function

Answer 45

slow

Question 46

The protein assumes a different -- in the two states, providing a molecular switch that can control a process or pathway

Answer 46

3-dimensional conformation

Question 47

GTPase switches are called --

Answer 47

G protein

Question 48

Initiation involves association of tRNAi-Met, mRNA and the small (40S) subunit so that tRNAi-Met base-pairs with the --

Answer 48

Start codon

Question 49

after the tRNAi-Met base pairs with the start codon, the -- associates to generate translationally competent complex

Answer 49

large subunit

Question 50

Initiation is regulated by other proteins called --

Answer 50

initiation factors (eIF)

Question 51

tRNAi is a special tRNA for initiation – it is specific for methionine, is recognized by eIF and uniquely binds to the -- in the ribosome

Answer 51

P site

Question 52

tRNAimet binding to 40S subunit regulated by --

Answer 52

GTPase switch protein

Question 53

-- brings mRNA to 40S subunit

Answer 53

Cap-binding factor

Question 54

Cap-binding factor binds to 5' cap of mRNA and brings mRNA to the tRNAi-Met/40s complex which then scans for --

Answer 54

AUG

Question 55

When tRNAi-met base-pairs with AUG then GTP is -- and 60S large subunit associates.

Answer 55

hydrolyzed

Question 56

Elongation involves entry of a new aa-tRNA, peptide bond formation, and -- of the ribosome to the next codon. Involves elongation factors.

Answer 56

translocation

Question 57

-- base-pairs with 2nd codon, regulated by GTPase switch

Answer 57

aa2-tRNA

Question 58

Peptide bond formation catalyzed by --

Answer 58

28S RNA. (ribozyme)

Question 59

Elongation: -- translocates along mRNA to bring 3rd codon into place for next aa-tRNa

Answer 59

Ribosome

Question 60

Termination involves recognition of the STOP codon, -- from the tRNA, and dissociation of the mRNA and ribosomal subunits

Answer 60

cleavage of the polypeptide

Question 61

-- are proteins that bind to STOP codon

Answer 61

Release factors

Question 62

Peptide is released by -- activity of 28S rRNA

Answer 62

peptidyl transferase

Question 63

Termination: Dissociation of tRNA, -- and ribosomal subunits.

Answer 63

mRNA

Question 64

Multiple individual ribosomes can translate mRNA at the same time, increasing the efficiency of translation.

Answer 64

polysomes

Question 65

Inhibitors of translation cause -- .

Answer 65

cell death

Question 66

Since bacterial and eukaryotic ribosomes are distinct, bacterial ribosome inhibitors can be useful --

Answer 66

antibiotics