Nucleic acids

Question 1

What are nucleic acids?

Answer 1

Macromolecules needed for the storage and expression of genetic information

Question 2

What are the two main types of nucleic acids?

Answer 2

DNA: deoxyribonucleic acid
RNA: ribonucleic acid

Question 3

What subunits are nucleic acids made up of?

Answer 3

Nucleotides

Question 4

What does each nucleotide contain?

Answer 4

A five carbon sugar
A nitrogenous base
A phosphate group

Question 5

In DNA, what is the sugar?

Answer 5

Deoxyribose

Question 6

What four different nitrogenous bases does DNA contain?

Answer 6

Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)

Question 7

Which bases are purines and how many rings does a purine have?

Answer 7

Adenine and guanine are purines

2 rings

Question 8

Which bases are pyrimidines and how many rings does a pyrimidine have?

Answer 8

Cytosine and thymine

1 ring

Question 9

When is a nucleoside formed?

Answer 9

A nucleoside is formed when a base is linked to the 1’ carbon of a deoxyribose (or ribose) molecule

Question 10

What is the difference between nucleotides and nucleosides?

Answer 10

Nucleotides are nucleosides with one or more phosphate groups linked to the 5’ carbon

Question 11

In DNA and RNA, how are the nucleotides linked?

Answer 11

By phosphodiester bonds between the 5’ and 3’ carbons

Question 12

Are nucleic acids negatively or positively charged?

Answer 12

Negatively

Question 13

Is DNA double-stranded or single-stranded in prokaryotes and eukaryotes?

Answer 13

Double-stranded

Question 14

What base does guanine pair with? How many hydrogen bonds is this held together by?

Answer 14

Cytosine

3 hydrogen bonds

Question 15

What base does adenine pair with? How many hydrogen bonds is this held together by?

Answer 15

Thymine

2 hydrogen bonds

Question 16

What are some properties of double stranded DNA?

Answer 16

Right handed 
Sugar-phosphate backbone on the outside
Strands held together by base-pairing and hydrophobic interactions between adjacent base pairs
Bases lie flat inside helix, perpendicular to backbone 
Diameter: 2nm
Height 3.4nm per turn
10 base pairs per turn
Major and minor grooves

Question 17

What are the enzymes that synthesise DNA?

Answer 17

DNA polymerases

Question 18

What is a primer?

Answer 18

A short piece of nucleic acid base-paired to the template
It acts as a start point
Must have a 3’-OH group

Question 19

In what direction is DNA synthesised?

Answer 19

5’ —> 3’ by addition of nucleotides to the 3’ end

Question 20

What happens to DNA when it is unwound?

Answer 20

Unwinding a DNA molecule with fixed ends introduces positive supercoils

Question 21

What are topoisomerases?

Answer 21

Enzymes that introduce or remove supercoils

Question 22

What happens to DNA when it is heated to 70-110 degrees celsius?

Answer 22

Becomes denatured

Question 23

What is the melting temperature?

Answer 23

The temperature needed to denature 50% of the DNA in a sample

Question 24

What is the melting temperature increased by?

Answer 24

DNA with content of GC base-pairs, as there are more H-bonds between the strands
The presence of cations, which reduce repulsion between negatively charged phosphate groups on the two strands