Chapter 17x2

Question 1

What is the process of translation?

Answer 1

How genetic info flows from mRNA to protein. A cell reads a genetic message and builds a polypeptide accordingly.

Includes the processes of initation, elogation and termination.

Question 2

Transfer RNA (tRNA)

Answer 2

Translates codons on a mRNA molecule Transfers an amino acid from cytoplasmic pool of amino acids to growing polypeptide in a ribosome

Question 3

Anticodon

Answer 3

The particular nucleotide triplet that base pairs to a specific mRNA codon

Question 4

Aminoacyl-tRNA synthetases

Answer 4

A family of related enzymes that match up tRNA and amino acids

Question 5

Wobble

Answer 5

Flexible base pairing

Question 6

P site

Answer 6

Peptidyl-tRNA binding site Holds tRNA carrying the growing polypeptide chain

Question 7

A site

Answer 7

Aminoacyl- tRNA binding site Holds the tRNA carrying the next amino acid to be added to the chain

Question 8

E site

Answer 8

Exit site Discharged tRNAs leave the ribosome

Question 9

What happened during initiation of translation?

Answer 9

In Eukaryotes, the small ribo subunit binds to the 5’ cap and moves to AUG where translation starts. Then the large subunit attaches with the help of protien initation factors which creates a tranlation initation complex. This required GTP. The tRNA sits in the P site and the A site is empty.

N-> C terminus

Question 10

What is the translation Initiation complex?

Answer 10

A small ribosomal subunit which attaches to mRNA and tRNA then attaches a large ribosomal subunit. Proteins called initiation factors bring all of this together, the cell also using GTP to bring all of this together

Question 11

What happens during elongation of translation?

Answer 11

Amino acids are added one by one to the previous amino acid at the c terminus. Each addition involves several proteins called elongation factors

1. Codon recognition. GTP is used
2. Peptide bond forms between amino acids in P and A sites, then detaches from tRNA in P site
3. tRNA moves from P to E site where it is released. Uses GTP

Question 12

What happens in the termination stage of translation?

Answer 12

When the stop codon (UAG, UAA, UGA) in the mRNA reaches the A site a release factor binds to the A site. This causes an addition of a water molecule which breaks the bond releasing the polypeptide through exit tunnel. Requires 2 more GTPs

Question 13

Signal peptide

Answer 13

Marks polypeptides destined for ER or secretion. Adds a sequence of 20 amino acids @ or near N terminus

Question 14

Signal recognition particle (SRP)

Answer 14

Protien RNA complex which recognizes the signal peptide and escorts the ribosome to a receptor protien built into ER membrane

1. SRP recognises signal peptide and attaches to ribosome
2. Escorts ribosome to ER
3. Binds to protein complex that forms a pore on ER
4. SRP detaches and polypeptide grows into ER
5. Signal peptide is cleaved
6. Polypeptide goes into ER and the ribsome detaches

Question 15

Polyribosomes

Answer 15

Strings of ribosomes trailing along mRNA Enable a cell to rapidly make many copies of a polypeptide

Question 16

Point mutations

Answer 16

Changes in single nucleotide pair of a gene

Question 17

Nucleotide pair substitution

Answer 17

The replacement of one nucleotide and its partner with another pair of nucleotides

Question 18

Silent mutation

Answer 18

When a nucleotide pair changes into another nucleotide pair that is translated into same amino acid

Question 19

Missense mutations

Answer 19

Substitutions that change one amino acid to another

Question 20

Insertions or deletions

Answer 20

Additions or losses of nucleotide pairs in a gene

Question 21

Frameshift mutation

Answer 21

Occurs when the number of nucleotides inserted or deleted is not a multiple of 3

Question 22

Mutagens

Answer 22

Physical and chemical agents that interact with DNA in ways that cause mutations

Question 23

What are some post translational modifications?

Answer 23

attachement of sugars, lipids, phosphates or others

my remove 1 or more amino acids.

polypeptide may be cleaved into 2 pieces

2 seperate polypeptides may be joined together

Question 24

What are the types of mutations?

Answer 24

Point mutations

Nucleotide pair mutations

Silent mutations

Missense mutations

nonsense mutations

frameshift mutations