Translation and The Genetic Code

Question 1

Explain how RNA is translated to a protein

Answer 1

The mRNA message is decoded by ribosomes

These are some of the largest and most complex structures in the cell

A Eukaryotic ribosome adds about 2 amino acids to a polypeptide chain each second, bacterial ribosomes operate faster, adding 20 amino acids per second

Question 2

What are the 3 main steps of translation called?

Answer 2

Initiation

Elongation

Termination

Question 3

What is always the start codon?

Answer 3

AUG - Methionine

Question 4

Explain the process of translation initiation in eukaryotes

Answer 4

Once the small ribosomal subunit stops at the AUG the large ribosomal subunit binds, completing the ribosome

Initiator: t-RNA occupies the P site so the second t-RNA will occupy the A site. Peptide synthesis begins

Question 5

Name the 3 sites used in translation in order

Answer 5

A site - aminoacyl site

P site - peptidyl site

E site - exit site

Question 6

Explain how the elongation of a new peptide works in the process of translation

Answer 6

P and A sites are occupied, E site is empty

tRNA carrying the next amino acid in the chain binds to the ribosomal A site by forming base pairs with the mRNA codon positioned there

A new peptide bond is formed

Question 7

Explain how termination works in the process of translation

Answer 7

Proteins known as release factors bind to any ribosome with a stop codon positioned in the A site

The peptide transferase is forced to catalyze the addition of a water molecule rather than an amino acid to the peptidyl-tRNA

The C-terminus of the new peptide is released from the tRNA

The completed protein is released

mRNA is released

The ribosome separates into its subunits

Question 8

Name the 3 groups amino acids are classified into briefly explain each of the groups and give examples

Answer 8

Essential amino acids - cannot be made by the body, and must come from food (e.g methionine, leucine, lysine)

Nonessential amino acids - the body produces these amino acids, even if we do not get them from the food we eat (alanine, aspartic acid, glutamic acid)

Conditional amino acids - usually not essential, except in times of illness and stress. (glycine, ornithine,serine,proline)

Question 9

Explain what a codon is

Answer 9

Consists of 3 consecutive bases that specify a single amino acid

Question 10

How many amino acids are there, and how many codons are there

Answer 10

Amino acids - 20

Codons - 64

Question 11

Give the 3 stops codons

Answer 11

UAG

UGA

UAA

Question 12

What is a mutation?

Answer 12

A mutation is a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene

Question 13

Explain what a missense mutation is

Answer 13

DNA change that results in different amino acids being encoded at a particular position in the resulting protein.

Question 14

Explain what a nonsense mutation is

Answer 14

Change in DNA that causes a protein to terminate or end its translation earlier than expected.

Question 15

Explain what a frameshift mutation is and give the 2 types of frameshifts that can happen

Answer 15

Deletion and Insertion

Change in DNA that causes a protein to terminate or end its translation earlier than expected.

Question 16

What is the consequence of a missense mutation?

Answer 16

Different amino acid is produced

Question 17

What is the consequence of a frameshift mutation?

Answer 17

From the point that a base (0r 2) is inserted or deleted the amino acid produced will be different

Question 18

What is the consequence of a nonsense mutation?

Answer 18

No more amino acids are inserted into the growing peptide chain

Production of a truncated protein

Protein synthesis stops

Question 19

Explain what PKU is (Phenylketonuria)

Answer 19

PKU is a genetic disorder in which there is a build-up of phenylalanine in the body. Phenylalanine is an essential amino acid, it is contained in a lot of different foods

Question 20

What happens to a person who has PKU?

Answer 20

A person with PKU lacks a gene that codes to the genetic information on how to synthesize the enzyme phenylalanine hydroxylase (PAH0. Therefore, one should avoid foods containing high amounts of phenylalanine for their entire life