DNA Replication

Question 1

What is heterochromatin and what is euchromatin?

Answer 1

Euchromatin is light -uncondensed and not dividing

Heterochromatin is dark and in condensed

Question 2

How Is DNA packaged?

Answer 2

DNA is wrapped around histones forming a nucleosome. These nucleosomes are connected and are called beads on a string. These beads on a string are joined together forming a solenoid (heterochromatin).

Question 3

How are chromosomes packaged and what is their structure?

Answer 3

Solenoids loop around each other forming chromatids. 2 chromatids are joined by a centromere. The top 2 arms are the p arms and the bottom 2 arms are the q arms.

Question 4

What is the difference between nucleotide and nucleoside?

Answer 4

Nucleoside- base+sugar and no phosphate group

Nucleotide- base+sugar+phosphate group

Question 5

Difference between ribonucleotide(RNA) and deoxyneucleotide(DNA)?

Answer 5

Deoxy has H group instead of OH group on 2nd carbon. Both attached to charged phosphate group by phophodiester bond and to a nitrogenous base.

Question 6

Purine vs Pyrimidine

Answer 6

purine = 2 rings (A&G)
Pyrimidine= 1 ring (T&C)

Question 7

How do bases pair?

Answer 7

Hydrogen bonds form between C=O and NH3 on the different bases
C and G form 3 hbonds
A and T form 2 hbonds ( so does AU )

Question 8

How do you write a base sequence?

Answer 8

From 5’ to 3’ from left to right

Question 9

Describe DNA replication

Answer 9

1. Initiation - primase binds to specific sequence before origin of replication and makes little bit of polynucleotide allowing DNA pol to bind
2. Elongation - DNA pol replicates strand from 3’ to 5’. This means 1st complimentary pair to 3’ will be 5’. In opposite direction (5’ side of of strand) called lagging strand. This is because the replication must happen in the opposite direction and in fragments. These fragments are called Okazaki fragments. DNA ligase joins these fragments. 2 new strands joined by helicase.
3. Termination - When 2 replication forks meet DNA joins final fragments = 2 new DNA strands.

Question 10

Structure of DNA in prokaryotes

Answer 10

Circular and naked

Question 11

Chromosomes structure before and after replication

Answer 11

Before - 1 chromatid/chromosome with 1 DNA molecule

After - 2 chromatids joined by centromere, 2 molecules of DNA.