Lecture 12 Flashcards Preview

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Flashcards in Lecture 12 Deck (60)
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1

Multiple ribosomes can bind to the same mRNA, T or F

T – this is referred to as a polysome

2

Why do proteins fold of their own accord

Proteins often contain hydrophobic regions which need to be hidden in the centre of the structure to achieve a low energy state

3

What is the other term used to describe aminoacyl tRNAs

Charged tRNA

4

How many amino acids are there

20

5

What adapter molecule is required for translation

Transfer RNA (tRNA)

6

What is meant by the abbreviation ORF

Open reading frame

7

eIF-4G, eIF-4E, small ribosomal complex binds to the polyA tail of the mRNA strand, T or F

F – the complex binds the capped head of the mRNA

8

Describe how the process of translation is initiated

Initiator tRNA carrying methionine is loaded into the small ribosomal subunit with eIF-2. Met-charged tRNA is the only aminoacyl tRNA molecule capable of binding directly to the small ribosomal subunit and the only charged tRNA that can bind directly to the P site of the ribosome leading the A site vacant. The small ribosomal subunit then binds to the capped 5’ end of the mRNA and begins progressing along the strand until the met start codon AUG is reached. Once this AUG is reached the eIF’s dissociate and the large ribosomal subunit fully assembles

9

The large ribosomal complex contains the peptidyl transferase enzyme, T or F

T

10

What is meant by the P site of the ribosome

Peptidyl tRNA site

11

What is meant by a molten globule

A molten globule is the structure formed from the initial folding of the protein that achieves a roughly correct conformation

12

How specifically does elongation factor-1, EF-1 improve the accuracy of translation

After the anticodon has bound it causes two delays before the peptidyl transferase can act. Firstly it ensures that it must have hydrolysed its bound GTP and then it must have dissociated from the tRNA. These lags allow time for incorrect tRNAs to fall off.

13

Describe chemically, how amino acids are added to the 3’ end of the tRNA

Ester bond forms between the carboxyl group of the amino acid and the ribose group of the last nucleotide

14

What is meant by there being three possible reading frames

Within a codon there are three different points which can act as different starts points and determine different amino acid sequences

15

Give an example of a disease caused by a misfolded protein

Creutzfeldt–Jakob disease is caused by misfolded pathogenic proteins knowns as prions that enter the brain and convert normal proteins into misfolded ones. This seeds new cross-? filaments of protein aggregates.

16

New amino acids are added to the N-terminus of growing polypeptide chains, T or F

F – they are added to the C-terminus

17

Which end of the tRNA strand contains the bound amino acid

The 3’ end

18

Release of eIF-2 initiates translation, T or F

T

19

How does codon-anticodon complementation impact GTP hydrolysis by EF-1

The hydrolysis of GTP by EF-1 occurs more rapidly if the codon and anticodon are correctly matched

20

There are over 50 possible modifications of the bases in tRNAs, what is meant by psi and D bases

psi corresponds to pseudouridine and D is dihydrouridine

21

How many different human codons are there

61

22

How far apart can ribosomes bind to RNA sequences

80 base pairs

23

Which class of molecular chaperone acts directly on the proteins as they leave the ribosome and bind to hydrophobic residues

Hsp 70 class

24

What is meant by the genetic code being degenerate

Some amino acid acids are specified by more than one different codon

25

Describe the propagation of translation after the ribosome has fully assembled

Once this AUG has been reach and eIF’s have dissociated another aminoacyl tRNA bound to Elongation Factor-Tu binds to the vacant A site of the ribosome. If the anticodon of this aminoacyl tRNA doesn’t match the mRNA codon then this tRNA is ejected/falls off. Once the tRNA with the correct anticodon binds to the A site, EF-Tu hydrolyses its bound GTP and dissociates. The ribosome then catalyses formation of a peptide bond between the two amino acids. Following this the ribosome undergoes a conformational change that shifts the initiator tRNA into the E site of the ribosome. The now vacant P site is filled by the newly bound tRNA and EF-G binds to the ribosome. GTP hydrolysis by EF-G switches the ribosome back to being able to accept the next incoming rRNA. This process repeats until a stop codon is reached.

26

What can be said about the expression of molecular chaperones at high temperatures

Expression of hsps is elevated when the temperature is raised above normal. This is because high temperatures can cause properly folded proteins to become misfolded

27

Only the Met-tRNA with eIF-4A can bind to the P site of the small ribosomal subunit alone, T or F

F – met-tRNA is the only aminoacyl tRNA with eIF-2 bound that can bind the small ribosomal subunit alone

28

What accounts for the similar structure seen in all tRNA molecules

Internal base pairing

29

Explain how the action of eIF-4G and eIF-4E act as a checkpoint in translation

eIF-4E and eIF-4G only bind to mRNA that is capped and has a polyA tail. This acts as a checkpoint for broken mRNA

30

Correct tRNAs once bound to the complimentary mRNA codon, don’t fall off, T or F

F – correct tRNAs do also fall off but at a much slower rate