DNA REPLICATION

Question 1

what makes up the backbone of nucleotides?

Answer 1

sugar and phosphate

Question 2

Which nucleotide bonds are easier to break ?

Answer 2

G-C is harder to break due to 3 hydrogen bonds whereas A-T is easier to break due to 2 hydrogen bonds

Question 3

what bonds hold the nitrogenous bases together ?

Answer 3

hydrogen bonds

Question 4

where and how does initiation begin ?

Answer 4

begins at the origin of replication (ori) when certain inititor proteins binds and trigger unwinding of DNA

Question 5

when does DNA replication occurs?

Answer 5

During the S phase of interphase each original strand seves as a template for the formation of a complementary new strand

Question 6

How does RNA synthesis start ?

Answer 6

a short fragment of RNA primer must be created and paired with the template of the DNA strand

Question 7

In what direction does DNA forms and how does it start ?

Answer 7

DNA strand will always be from 5’ to 3’
needs a primer to kickstart the DNA replication
DNA polymerase III attaches new nucleotides in the 5’ to 3’ direction

Question 8

What is the second step of DNA Replication

Answer 8

Elongation

Question 9

what keeps the single-strand from re-joining?

Answer 9

Helicase, Topoisomerase and single strand binding protein

Question 10

direction of synsthesis of DNA ?

Answer 10

5’ to 3’

Question 11

function of ligase ?

Answer 11

joins adjacent DNA strands; fixes the nicks

Question 12

function of DNA polymerase ?

Answer 12

matches the correct nucleotides then joins adjacent nucleotides to each other

Question 13

function of primase ?

Answer 13

provides an RNA primer to start polymerization; forming new strand of DNA

Question 14

function of helicase and how does it happen ?

Answer 14

unwind the DNA by breaking the hydrogen bond between complementary base pair

Question 15

What are the basic requirements for DNA Replication?

Answer 15

Substrates - 4 deoxynucleoside triphosphates; cleavage of the high energy phosphate bond provides the energy for the addition of the nucleotide Template - each strand of parental DNA serves as a template strand Replication Enzymes - Helicase , primase , DNA polymerase , Ligase

Question 16

what are the key events in Interphase (s phase)

Answer 16

DNA has replicated but has not formed condense structure of chromosome - remain as loosely coiled chromatin

Question 17

functions of DNA and RNA ?

Answer 17

DNA : stores genetic information

RNA : make proteins and help out in DNA replication

Question 18

Phosphate groups are bond together by ?

Answer 18

phosphoanhydride bonds which are high energy bonds

Question 19

Last step of DNA replication ?

Answer 19

Termination

Question 20

what are the two causes of DNA damage and the effect ?

Answer 20

ENDOGENOUS CAUSE : reactive oxygen species produced from normal metabolic by-product
EXOGENUOS CAUSE : Radiation, UV light, plant toxins, virus, high energy radiation, mutagenic chemicals
-due to environmental factors and normal metabolic processes inside the cell
-Single/double stranded breaks in the DNA sugar-phosphate backbone
-nucleotide bases have been modified chemically
-DNA-cross-links ; a covalent linkage between two nulceotides of DNA
- can occur within the same strand or opposite strands od double stranded DNA (INTRASTRAND VS INTERSTRAND)

Question 20

Accuracy of replication

Answer 20

1 mistake every 10^8 bases

Question 21

what is leading and lagging strand ?

Answer 21

leading strand : runs in the 3’ to 5’ ; strand that is replicated continuously towards the replication fork
lagging strand : runs in the 5’ to 3’ ; strand that is replicated discontinuosly away from the replication fork

Question 22

what are new segments of DNA called

Answer 22

Okazaki Fragments

Question 23

what happens after new Okazaki fragments are formed

Answer 23

RNA primers are replaced by DNA with the help of DNA polymerase
In which it specifically removes the RNA primers via its 5’ to 3’ exonuclease activity
and fill up the gaps with new deoxyribonucleotides by the 5’ to 3’ DNA polymerase activity
Ligase helps to join new adjacent DNA fragments together by breaking the sugar-phosphate backbone between the new adjacent DNA fragments

Question 25

what are the two classes of checkpoints genes?

Answer 25

PROTO-ONCOGENS : code for proteins that promote the cell cycle and prevent apoptosis
TUMOUR SUPPRESSOR GENES : code for proteins that inhibit the cell cycle and promote apoptosis
Mutation in these checkpoints can cause the cell to lose control of the cell cycle hence cancer - uncontrolled cell growth

Question 26

At what point during normal DNA replication is genetic material lost from the telomeres?

Answer 26

Joining of Okazaki Fragments