DNA Structure and Replication

Question 1

What is the molecular basis for genes?

Answer 1

The molecular basis for genes is deoxyribonucleic acid (DNA)

Question 2

The transfer of genetic information :

Answer 2

The central dogma of biology

Question 3

What is DNA composed of?

Answer 3

DNA is composed of a chain of nucleotides of which there are four types : adenine (A), cytosine (c), guanine (G), and thymine (T)

Question 4

DNA exists in a…

Answer 4

double strand molecule

Question 5

Describe the strands of the double helix.

Answer 5

The strands of the double helix are anti-parallel with one being 5’ to 3’, and the opposite strand 3’ to 5’.

Question 6

What is the Deoxyribonucleic Acid?

Answer 6

Deoxyribonucleic Acid is a string of nucleotides

Question 7

Nucleotides are made up of three parts, namely :

Answer 7

• A sugar - deoxyribose
• Phosphate
• Cyclic amine[base]

Question 8

The sequence of DNA is the…

Answer 8

order of bases attached to the backbone

Question 9

The sugar - phosphate backbone is…

Answer 9

negatively charged

Question 10

Where is the sugar-phosphate backbone located?

Answer 10

Sugar-Phosphate backbone is on outside

Question 11

Where are the bases located?

Answer 11

Bases are inside - Hydrogen-bonding to opposing base on opposite strand

Question 12

What does the double helix form?

Answer 12

Base pairs

Question 13

How does each nucleotide in DNA pair with its partner nucleotide on the opposite strand?

Answer 13

Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G

Question 14

What do replication processes permit?

Answer 14

Replication processespermit the copying of a single DNA double helix into twoDNA helices,which are divided into the daughter cells at mitosis.

Question 15

DNA replication proceeds in three steps, namely :

Answer 15

• Initiation
• Elongation
• Termination

Question 16

State what takes place during the initiation step.

Answer 16

• The first major step responsible for breaking of hydrogen bonds between bases of the two antiparallel strands
• The splitting happens in places of the chains that are rich in A-T.
• Helicaseis the enzyme that splits the two strands
• The initiation point where the splitting starts is called “origin of replication”.
• The structure that is created is known as “Replication Fork
• ThenRNA Primasebinds in the initiation point of the 3’-5’ parent chain.RNA Primaseattract primer which bind to the DNA nucleotides of the 3’-5’

Question 17

Why does the splitting[in the initiation step] happen in places of the chains that are rich in A-T?

Answer 17

The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine (there are three hydrogen bonds between Cytosine and Guanine)

Question 18

State what happens in the elongation step - The difference between the 5’-3’ and 3’-5’ strand templates.

Answer 18

• Theelongationprocess is different for
• 5’-3’ Template: The 5’-3’ produces a 3’-5’ daughter strand, which is calledleading strandbecauseDNA Polymerase reads the template and continuously adds nucleotide

-3’-5’ Template: The3’-5’ templatecannot be “read” by DNA Polymerase continuously. The replication of this template is complicated and the new strand is calledlagging strand.

Question 19

State what occurs in the elongation step.

Answer 19

• In the lagging strand the RNA Primase adds more RNA Primers.
• DNA polymerase reads the template and stops. The gap between two RNA primers is called “Okazaki Fragments”.
• In the lagging strand theDNA Pol I-exonuclease- reads the fragments and removes the RNA Primers.
• The gaps are closed with the action of DNA Polymerase and DNA Ligase
• Each new double helix is consisted of one old and one new chain.

Question 20

State what takes place in the termination step.

Answer 20

• The laststep of DNA Replicationis theTermination
• This process happens when the DNA Polymerase reaches to an end of the template strands
• The DNA Replication is not completed before amechanism of repairfixes possible errors caused during the replication.
• Enzymes likenucleasesremove the wrong nucleotides and the DNA Polymerase fills the gaps.