Nucleosides and Nucleotides

Question 1

What is the difference between nucleosides and nucleotides?

Answer 1

Nucleotides have a phosphate group

Question 2

What is the structure of a nucleoside?

Answer 2

A pentose sugar linked by N-glycosidic bond to a nitrogenous base

Question 3

How is a phosphate added to a nucleoside to become a nucleotide?

Answer 3

Via a condensation reaction

Question 4

What are the 2 options for pentose sugar?

Answer 4

Ribose or Deoxyribose

Question 5

What is the difference between a deoxyribose and a ribose sugar?

Answer 5

Deoxyribose has one less - OH group

Question 6

What bases are purine?

Answer 6

Adenine and Guanine

Question 7

What bases are pyrimidine?

Answer 7

Uracil, Thymine and Cytosine

Question 8

How are base sequences labelled?

Answer 8

From 5’ to 3’

Question 9

How many bonds are between G-C bonds?

Answer 9

3 Hydrogen bonds

Question 10

How many bonds are between A-T bonds?

Answer 10

2 Hydrogen bonds

Question 11

What is Chargaff’s Rule?

Answer 11

%A=%T and %G=%C

Question 12

How do the 2 strands of DNA run?

Answer 12

Anti-parallel

Question 13

Why does 1 purine match with 1 pyrimidine?

Answer 13

There is only space for one of each in the double helix

Question 14

What are the stabilising forces of the DNA double helix?

Answer 14

H bonding - Large number of weak H bond
Electrostatic interactions - phospho-diester group of the DNA backbone and cation
Hydrophobic effect - nitrogen base rings move away from aqueous solvents to the interior of the helix
Stacking interaction - stacked base pairs from weak Van der Waals attractions. These forces are additive so more bases=more stable

Question 15

What is ribosomal RNA?

Answer 15

Combines with series of proteins to form complex structures called ribosomes

Question 16

What is mRNA?

Answer 16

Messenger RNA which carries genetic instructions for protein synthesis from DNA to ribosomes

Question 17

What is tRNA?

Answer 17

Transfer DNA delivers specific individual amino acids to the ribosomes for protein synthesis

Question 18

What is the process of polymerisation?

Answer 18

Addition to free nucleoside triphosphate, strands unwind and separate, each strand acts as a template for a complementary strand to be built

Question 19

How is DNA replication controlled?

Answer 19

DNA polymerase builds new double helices, polymerase lines up nucleotides in the right order, polymerase bonds to the double helix to the double bond by wrapping round it, enzyme pulls helix apart and nucleotides brought in to build new DNA strand

Question 20

What does PCR do?

Answer 20

Mimics rapid production of multiple copies of DNA nucleotide sequences.

Question 21

How many PCR cycles does it take for DNA to be amplified a billion fold?

Answer 21

30 cycles

Question 22

What are the applications of PCR?

Answer 22

Detection of infectious organisms, detection of genetic variation, and amplification of DNA in crime scenes

Question 23

How is DNA affected by anticancer drugs?

Answer 23

They inhibit cell division