Topic 2: Nucleic acids

Question 1

What consists of a nucleotide

Answer 1

A pentose sugar: Has five carbon atoms
A phosphate group
A nitrogen-containing base

Question 2

What are the 4 bases of DNA

Answer 2

• Adenine
• Thymine
• Cytosine
• Guanine

Question 3

What holds together the pentose sugar, phosphate group and organic base

Answer 3

Sugar phosphate backbone + condensation reactions

Question 4

What do you call the bond between the phosphate and sugar in DNA

Answer 4

Phosphodiester bond

Question 5

Waht do you call the continued linking of mononucleotides

Answer 5

Polynucelotide

Question 6

What is the pentose sugar in DNA and RNA

Answer 6

DNA - deoxyribose
RNA - ribose

Question 7

What are the bases in RNA

Answer 7

• Adenine
• Uracil
• Cytosine
• Guanine

Question 8

What joins the polynucleotides in DNA

Answer 8

Hydrogen bonds

Question 9

How do the bases pair and how many bonds do they form

Answer 9

• Adenine + Thymine (2 bonds)
• Cytosine and Guanine (3 bonds)

Question 10

Give two reasons DNA is stable

Answer 10

1. The phosphodiester backbone sits on the outside of the molecule, protecting the reactive bases
2. Hydrogen bonds link the organic bases together. One hydrogen bond alone is very weak but because there are so many it creates a very strong structure.

Question 11

How is DNA adapted to its function

(4 different adaptations)

Answer 11

1. Stable structure - rarely mutates
2. Two separate strands - weak H-bonds between strands allow them to separate for protein synthesis and replication
3. Extremely large - can carry alot of genetic information
4. Cylindrical helix - Information is protected from chemical and physical forces

Question 12

Define semi-conservative replication

Answer 12

each strand serves as a template, which means that each new copy of DNA has one strand from the original molecule and one new strand.

Question 13

What does antiparalell mean

Answer 13

The strands are parallel but run in the opposite direction

Question 14

Explain how DNA is antiparalell

Answer 14

One strand runs from the 5 prime (5’) to the 3’ and the other from the 3’ to the 5’

Question 15

What direction does DNA replication occur in

Answer 15

From the 5’ to the 3’

Question 16

What 4 things are needed for semiconservative replication in DNA to occur

Answer 16

1. The 4 types of nucleotide bases (A,T,C,G)
2. 2 complimentary strands of DNA (to act as templates)
3. Enzymes (DNA polymerase and DNA helicase)
4. Chemical energy (from ATP)

Question 17

Explain DNA replication

5 points

Answer 17

• DNA helicase breaks the H-bonds between base pairs and DNA unzips
• Free nucleotides bind to their exposed complimentary base pairs (A+T & C+G)
• DNA polymerase joins the free nucleotides
• The result is two new DNA molecules, both with one new strand and one old strand
• Which is known as semi-conservative replication