DNA + RNA

Question 1

Where is DNA found in the cell?

Answer 1

Nucleus and mitochondria

Question 2

How is DNA arranged?

Answer 2

In a double helix. There is complementary base pairing. DNA is coiled around histones. DNA is double stranded and these strands run antiparallel.

Question 3

What is the function of DNA?

Answer 3

The template and regulator for transcription and protein synthesis.

Question 4

Which direction is DNA synthesised?

Answer 4

5’ to 3’. There is a phosphate at the 5’ end which is catalysed as activation energy, so synthesis must start at 5’

Question 5

Why is DNA replication semi conservative?

Answer 5

Each resulting DNA molecules retains one strand of the original DNA.

Question 6

Outline the steps of DNA replication.

Answer 6

1. Topoisomerase unwinds the double helix and creates two replication forks.
2. Single-strand binding protein prevents re-annealing
3. DNA helicase separates the DNA and exposes the nucleotides
4. DNA polymerase reads 3’-5’ and synthesises a daughter strand 5’-3’. It causes the binding of complementary base pairs. Starts at a primer
5. Ligase enzymes join short Okazaki fragments (short DNA pieces) together into once continuous strand

Question 7

What is a primer?

Answer 7

A short strand of DNA that is the start point for DNA synthesis. DNA polymerase can only add nucleotides onto an existing strand of DNA.

Question 8

Name 3 types of RNA

Answer 8

mRNA, rRNA, tRNA

Question 9

What is the structure of RNA?

Answer 9

Single stranded. Contains uracil instead of thymine.

Question 10

Name a start codon.

Answer 10

AUG

Question 11

Name 3 stop codons.

Answer 11

UGA, UAG, UAA

Question 12

What is the binding site at the 5’ end called?

Answer 12

Promoter region

Question 13

Outline the steps for transcription and translation of a protein.

Answer 13

1. Topoisomerase unwinds the double helix
2. DNA helicase separates the DNA and exposes the nucleotides
3. RNA polymerase binds free mRNA nucleotides to their complementary bases on the template strand. This forms an antiparallel mRNA strand starting at the promoter.
4. mRNA leaves the nucleus and attaches to a ribosome
5. mRNA binds to complementary tRNA molecules at their anticodon.
6. One codon will code for a particular amino acid. Bases are read 5’-3’
7. Peptide bonds form between adjacent amino acids creating a polypeptide chain

Question 14

Where is mRNA made?

Answer 14

Nucleus. Transcription occurs in nucleus, translation occurs on ribosome.

Question 15

What are the features of the genetic code?

Answer 15

1. Degenerate - more than one codon codes for an amino acid
2. Universal
3. Non overlapping

Question 16

What happens if DNA is methylated?

Answer 16

The gene is silenced

Question 17

What is an out of frame deletion?

Answer 17

One single base is deleted.

Question 18

What is an in frame deletion?

Answer 18

One complete codon is removed.

Question 19

Give an example of a disease caused by an out of frame deletion.

Answer 19

Duchenne muscular dystrophy. Deletion causes absence of dystrophin.

Question 20

What is a mis-sense mutation?

Answer 20

A point mutation where a single nucleotide change results in a codon that codes for a different amino acid.

Question 21

Give an example of a disease caused by a mis-sense mutation.

Answer 21

Sickle cell disease. CAG is replaced with CTG.

Question 22

What is a non-sense mutation?

Answer 22

Point mutation that produces a stop codon. Results in an incomplete, non functional protein.

Question 23

Name a disease caused by expansion of a tri-nucleotide repeat.

Answer 23

Huntington’s disease: CAG. Repeat is >36.

Question 24

What is anticipation?

Answer 24

When repeats get bigger from generation to generation, resulting in earlier symptoms of greater severity.

Question 25

Which reaction synthesises fragments of DNA?

Answer 25

PCR.