Gene Expression & Control (Transcription & Translation)

Question 1

What is the genetic code?

Answer 1

The sequence of bases on the mRNA which is transcribed from sections of DNA

Question 2

What are the main features of the genetic code?

Answer 2

1) Each aa is coded for by a sequence of 3 bases known as a codon
2) Code is degenerate- some aa are coded for by more than one codon
3) 3 stop codons
4) Universal code that works for all organisms

Question 3

What are the structural features of RNA?

Answer 3

1) Single stranded
2) Uracil
3) Ribose sugar

Question 4

What is the structure of tRNA?

Answer 4

1) Single stranded chain folded into a clover leaf shape

2) Has an anticodon region which pairs to complementary codons on the mRNA

Question 5

What are the stages of transcription?

Answer 5

1) DNA Helicase breaks the H bonds in a specific region of the DNA molecule
2) Free RNA nucleotides line up in a complementary fashion
3) RNA polymerase moves along the template strand causing the nucleotides to bind together
4) RNA polymerase reaches a stop codon and detaches itself leaving the pre-mRNA
5) pre-mRNA is spliced to remove introns and combine exon sections
6) mRNA formed leaves the nuclear pores into the cytoplasm to the ribosome.

Question 6

What are the stages of translation?

Answer 6

1) mRNA arrives at ribosome, attaching at starting codon
2) A tRNA molecule with a complementary anti-codon binds with the mRNA whilst having an aa attached to it
3) Another tRNA molecule with a complementary anti-codon will bind to the next codon on mRNA whilst carrying another aa
4) Enzymes and ATP join the first 2 aa together
5) The ribosome moves along to codon 3 and links the aa’s on the 2nd and 3rd tRNA together
6) At the same time the 1st tRNA is released and free to collect another aa
7) Synthesis continues until the ribosome reaches a stop codon

Question 7

What are the types of genetic mutations?

Answer 7

1) Addition
2) Deletion
3) Substitution

Question 8

What are the 3 types of substitution mutations?

Answer 8

1) Non-sense- the substitution results in a stop codon being transcribed onto mRNA
2) Mis-sense- substitution results in a different aa being coded for
3) Silenced- there is no aa change (degenerate)

Question 9

What happens in deletion mutations?

Answer 9

Frame shift, occurs when a nucleotide is lost.

Question 10

What happens in addition mutations?

Answer 10

Frame shift, occurs when a nucleotide is added.

Question 11

How do mutations arise?

Answer 11

1) Radiation
2) Chemicals
3) Genetic inheritance
4) Spontaneous

Question 12

Which genes control the rate of cell division?

Answer 12

1) Tumour suppressor genes

2) Proto-oncogenes

Question 13

How do tumour suppressor genes function?

Answer 13

Inhibit cell division

Question 14

How do proto-oncogenes function?

Answer 14

1) Stimulate cell division

2) Mutations can turn proto-oncogenes into oncogenes

Question 15

What are totipotent cells?

Answer 15

Cells that can differentiate into any cell in the body.

Question 16

How are genes prevented from expressing themselves?

Answer 16

1) Prevent transcription thus the production of mRNA

2) Breaking down mRNA before translation

Question 17

Where can totipotent be found in the mature adult?

Answer 17

1) Inner lining of the intestine
2) Bone marrow
3) Skin

Question 18

What is required for transcription to start?

Answer 18

A transcriptional factor moves from the cytoplasm into the nucleus and binds to a specific region of DNA

Question 19

How is transcription prevented?

Answer 19

An inhibitor molecule can bind to a transcription factor and block the site at which it would usually bind to of DNA

Question 20

How is mRNA broken down before translation?

Answer 20

By siRNA

Question 21

How does siRNA work?

Answer 21

1) An enzyme cuts the siRNA into 2 smaller sections
2) One of the smaller stands combines with an enzyme
3) siRNA enzyme complex binds to a complementary section of mRNA and cuts it into smaller sections which cannot be translated