DNA

Question 1

what does tropoisomerase do?

Answer 1

relieves supercoiling unwinding the double helix

Question 2

what does helicase do?

Answer 2

unzips hydrogen bonds between base pairs and separates strands

Question 3

what does DNA polymerase do?

Answer 3

reads from 3’-5’ and prints DNA 5’-3’ starting at a primer

Question 4

describe the process of transcription.

Answer 4

• topoisomerase relieves super coiling
• helicase unzips DNA
• RNA polymerase binds to a promoter region (usually TATA bos) on the anti-sense strand
• prints mRNA and stops at AUG stop codons

Question 5

why is transcription necessary?

Answer 5

DNA is too big to fit outside of the nuclear membrane so mRNA needs to be produced so gene expression can occur and proteins can be made

Question 6

what is pre-mRNA

Answer 6

it’s made up of exons and introns
exons = useful mRNA
introns =useless mRNA.

Question 7

why does splicing of mRNA take place?

Answer 7

• to generate mature mRNA

- different combinations of exons allow for different proteins to be made

Question 8

describe the process of translation.

Answer 8

• mRNA attaches to a ribosome
• complementary tRNA with an anti-codon bind with a codon of the mRNA
• tRNA have specific amino acids attached to them and primary protein structure is made

Question 9

what are mis-sense and non-sense mutations?

Answer 9

-mis-sense = a point mutation that causes a condon to change causing a new amino acid to be present in an polypeptide chain ie sickle cell
non-sense = point mutation that gives rise to a stop codon resulting in an incomplete non-functional protein

Question 10

what are the stages of the cell cycle?

Answer 10

1. interphase
2. prophase
3. prometaphase
4. metaphase
5. anaphase
6. telophase
7. cytokinese

Question 11

what happens interphase?

Answer 11

3 stages

1. growth phase 1 - growth preparation, cell contents are replicated
2. synthesis phase - DNA is synthesis by semi-conservative replication
3. growth phase 2 - spindle formation and double checking for errors take place and repair

Question 12

what happens in prophase?

Answer 12

• DNA condenses into visible chromosomes = 2 chromatids joined at a centromere
• centromeres separate and start spindle production

Question 13

what happens in prometaphase?

Answer 13

• nucleus membrane totally disappear
• spindles grow towards the center of the cell
• chromosomes attach to microtubules

Question 14

what happens in metaphase?

Answer 14

• chromosomes line up on the equator of the cell

- spindles attach to centromeres

Question 15

what happens in anaphase?

Answer 15

• sister chromatids a pulled apart by the shortening of spindle fibres
• chromatids move towards the poles of the cell

Question 16

what happens in telophase?

Answer 16

• nuclear membrane begins to reform
• a ring of microfilaments form at the center of the cell and tighten
• chromatids unravel to form chromatin

Question 17

what happens in cytokinesis?

Answer 17

• ring of microfilament ring tightens until membranes separate
• cell divides into 2 genetically identical cells

Question 18

what is gonadal mosaicism?

Answer 18

-in germline epithelium you have cells from two lineages