W3 Nucleic Acids & DNA Replication

Question 1

Which of the following related to nucleic acids are correct?
- They are carriers of genetic information
- They are made of nucleotides
- They are represented by DNA and RNA
- They are present in every type of cell

Answer 1

All of the above

Question 2

Structure of a nucleotide

Answer 2

Pentose sugar
Nitrogenous base
Phosphate group (1-3)

Question 3

What bond is between a phosphate group and pentose sugar?

Answer 3

Phosphodiester bond (Phosphoester)

Question 4

What bond is between a pentose sugar and nitrogenous base?

Answer 4

Glycosidic bond

Question 5

What are the bases in RNA?

Answer 5

Adenine, Cytosine, Guanine, URACIL

Question 6

What is a nucleoside?

Answer 6

The part of a nucleotide consisting of only the pentose sugar and nitrogenous base (not phosphate)

Question 7

How can DNA and RNA be distinguished?
(not by base which is easier)

Answer 7

DNA (DEOXYribose) has a H at 2’ whereas RNA (ribose) has an OH at 2’
(deoxy- no oxygen)
And also,Thymine for DNA and Uracil for RNA

Question 8

What bases are pyrimidines?
(hint-pyramid)

Answer 8

Cytosine, Thymine, Uracil

Question 9

Which bases are purines?

Answer 9

Adenine, Guanine

Question 10

Differences between purines and pyrimidines?

Answer 10

Purines are double ring (shorter name=longer)
Pyrimidines are single ring

Question 11

What is the corresponding nucleoside for base Adenine in DNA and RNA?
(nomenclature)

Answer 11

RNA- Adenosine
DNA- Deoxyadenosine

Question 12

What are the functions of nucleotides? (3)

Answer 12

1. Biological energy carriers (ATP, GTP)
2. To form coenzymes
3. Intracellular signalling molecules

Question 13

How can nucleotides link?

Answer 13

Nucleotides can link covalently with each other by phosphodiester bonds and form a polynucleotide strand.
(in condensation reactions)

Question 14

Where is the phosphodiester bond? which C?

Answer 14

The phosphodiester bond links the 5’ end of one sugar with the OH group of the 3’ end of the next.
Thus nucleic acid strands have two ends. The direction is 5’ to 3’

Question 15

How do DNA strands link in prokaryotes?

Answer 15

In prokaryotes, the 5’ and 3’ ends of the DNA strands are linked to give circular DNA. This applies for plasmids and mitochondrial DNA (eukaryotes)

Question 16

What is the DNA double helix structure?

Answer 16

2 anti parallel strands
Sugar Phosphate backbone
DNA bases facing inwards (complementary base pairs)

Question 17

What is DNA reversible denaturation?

Answer 17

DNA double strands can be separated into SINGLE strands by breaking the temporary H bonds (upon heating)

Question 18

What is DNA reversible renaturation?

Answer 18

Renaturation: temp lowered to generate double helix again

Question 19

What is the genome?

Answer 19

It contains the genetic program that instructs a cell how to behave?

Question 20

Where is DNA located in eukaryotes?

Answer 20

Mostly in the nucleus (packaged with histones into chromatin)

Question 21

What is chromatin formed of?

Answer 21

Formed of nucleosomes.
Half DNA and half protein

Question 22

How many pairs of chromosomes do humans have?

Answer 22

22 pairs of chromosomes and 2 sex chromosomes

Question 23

What is DNA replication?

Answer 23

DNA Replication is the process by which DNA makes a copy of itself
Mitosis occurs in the nucleus during interphase.

Question 24

What are the 4 steps of DNA replication?

Answer 24

1. Replication fork formation
2. Initiation
3. Polymerase elongation
4. Termination

Question 25

What is produced in DNA replication?

Answer 25

Two copies of DNA are produced. Containing one original and one new strand.

Question 26

What happens in Replication Fork Formation?

Answer 26

• DNA polymerase needs a short RNA primer (produced by DNA primase) to start (free 3’ -OH)
• DNA polymerase allows the incorporation of nucleotides to 3’ end of a growing DNA strand, using one parental DNA strand as a template.
• It requires nucleotide
• New DNA strands are synthesised from 5’ to 3’
• It forms a phosphodiester bond between the 3’ end of the growing DNA chain and the 5’ phosphate group of the incoming nucleotide (esterification)

Question 27

What happens during Initiation?

Answer 27

• DNA polymerase needs a short RNA primer (produced by DNA primase) to start (free 3’ -OH)
• DNA polymerase allows the incorporation of nucleotides to 3’ end of a growing DNA strand, using one parental DNA strand as a template.
• It requires nucleotide
• New DNA strands are synthesised from 5’ to 3’
• It forms a phosphodiester bond between the 3’ end of the growing DNA chain and the 5’ phosphate group of the incoming nucleotide (esterification)

Question 28

What happens during termination?

Answer 28

• Because the parental strands are antiparallel, the replication fork is asymmetrical.
• Replication of the leading strand is continuous
• Replication of the lagging strand is discontinuous (opposite direction from the fork movement)
• It requires many RNA primers
• Synthesis of small DNA fragment
• RNA primers are degraded and replaced by DNA chain growth from the previous Okazaki fragments
  The enzyme DNA ligase joins adjacent fragments (phosphodiester linkage between DNA stretches)

Question 29

Which enzyme proofreads during DNA replication?

Answer 29

DNA polymerase does, making DNA synthesis an accurate process.

Question 30

What does polymerase do?

Answer 30

Incorporates nucleotides to the growing DNA strand

Question 31

What does helicase do?

Answer 31

It unwinds the parental double helix

Question 32

What does ligase do?

Answer 32

It joins Okazaki fragments and seals breaks in sugar phosphate backbone