Genetic Control Of Proteins

Question 1

Describe features of RNA compared to DNA

Answer 1

• has bases AGUC
• sugar is ribose
• is single polynucleotide chain
• mRNA is less stable
• mRNA and tRNA are smaller

Question 2

Give structure of tRNA

Answer 2

• clover shaped molecule
• one end of chain extends further than the other, where amino acids can attach
• has anticodon loop at opposite end; specific to each amino acid

Question 3

Define transcription

Answer 3

Process by which pre-mRNA is made, using part of DNA as a template

Question 4

Describe process of transcription

Answer 4

1. DNA helicase breaks H bonds between bases on DNA strand, exposing bases
2. RNA polymerase moves along region, joining complimentary bases to template strand
3. DNA strands rejoin behind RNA polymerase, only 12 base pairs are exposed
4. When RNA polymerase reaches stop codon, it detaches

Question 5

What is splicing?

Answer 5

Removal of non-coding introns, to leave functional exons

Question 6

How are many different proteins made from 1 pre-mRNA molecule?

Answer 6

After splicing, the exons can be rejoined in a variety of combinations

Question 7

Define translation

Answer 7

Process by which codons on mRNA are translated into a sequence of amino acids that make up a polypeptide

Question 8

Where does protein synthesis occur?

Answer 8

In cytoplasm

Question 9

Describe process of translation

Answer 9

1. Ribosome attaches to mRNA, tRNA molecule (carrying amino acid)with complimentary anticodon to 1st 3 bases, joins to mRNA
2. tRNA molecule with anticodon comp to next codon joins, peptide bond forms between amino acids (requires enzyme and ATP), 1st tRNA molecule is released
3. Process continues, many ribosomes can pass behind first

Question 10

What happens after translation?

Answer 10

Protein is assembled according to function;

• folded into secondary, then tertiary structure
• joined with other chains and groups to form quaternary structure

Question 11

Define mutation

Answer 11

Change in quantity or structure of DNA

Question 12

Are mutations passed on to the next generation?

Answer 12

Only if they are in the sex cells

Question 13

What does a ‘deletion mutation’ cause?

Answer 13

• a base is deleted, which causes a ‘frame shift’ and the gene is read in wrong 3-base groups
• has bigger impact if deletion occur near start of chain

Question 14

What is a ‘missense mutation’?

Answer 14

• mutation which involves a different amino acid being coded for
• different polypeptide will be coded for; difference depends on role of specific amino acid

Question 15

What is a ‘nonsense mutation’?

Answer 15

• mutation which involves a stop codon being coded for

- chain is stopped prematurely, protein will be non-functional

Question 16

Why are ‘silent mutations’ inconsequential?

Answer 16

• result in same amino acid being coded for

- due to degenerate nature of amino acids

Question 17

What are mutagens?

Answer 17

• outside factors that increase rate of mutation

Question 18

Give 2 mutagens

Answer 18

• chemicals that alter DNA structure

- high energy radiation

Question 19

What is role of proto-oncogenes?

Answer 19

• stimulate cell division

Question 20

How do proto-oncogenes work?

Answer 20

• growth factors attach to receptors on membrane, cause replication genes to be switched on

Question 21

How do once-genes affect cell division?

Answer 21

• receptor protein on membrane is permanently activated, cell division occurs even in absence of growth factors
• may code for growth factor which stimulates excessive cell division

Question 22

What happens if a tumour suppressor gene is mutated?

Answer 22

• it is inactivated; meaning cell division is not controlled