3.8 Nucleic Acids

Question 1

What are nucleic acids?

Answer 1

Polymers of nucleotides

contain C, H, O, N, P.

Store/transfer genetic information

& used in synthesising polypeptides.

Question 2

What is a nucleotide?

Answer 2

Monomers of nucleic acids

made from pentose sugar, nitrogenous base & phosphate group

Question 3

What 3 groups are nucleotides made from?

Answer 3

1. Nitrogenous base
2. Phosphate group
3. Pentose sugar

Question 4

Describe the process by which nucleotides are linked together:

Answer 4

Condensation between hydroxyl (3’) & phosphate (5’)

phosphodiester bonds form sugar-phosphate backbone

Question 5

Polymerase enzymes can only add nucleotides onto the _____ group of the [3’/5’] end of the nucleotide.

Answer 5

hydroxyl

3’

Question 6

What are the different nitrogenous bases?

Answer 6

PURINE - Adenine, Guanine

PYRIMIDINE - Cytosine, Thymine, Uracil

Question 7

What is the difference between pyrimidine & purine nitrogenous bases?

Answer 7

Pyrimidine bases have a single carbon ring structure

Purine bases have a double carbon ring

Question 8

What are the types of purine bases?

Answer 8

Adenine, Guanine

Question 9

What are the types of pyrimidine bases?

Answer 9

Thymine, Cytosine, Uracil

Question 10

In any DNA strand, the number of Adenine bases present is always equal to the number of ____ bases present.

Answer 10

Thymine

Question 11

Purine bases always form hydrogen bonds with ____ bases.

Answer 11

pyrimidine

Question 12

Purine + Pyrimidine complementary base pairing ensures that…

Answer 12

DNA strand width remains consistent

Question 13

By complementary base pairing, adenine forms ___ hydrogen bonds with ___.

Answer 13

2

Thymine

Question 14

By complementary base pairing, Guanine forms ___ hydrogen bonds with _____.

Answer 14

3

Cytosine

Question 15

What is complementary base pairing?

Answer 15

Hydrogen bonding

between specific nitrogenous bases.

Adenine bonds to Thymine, Guanine bonds to Cytosine

Question 16

Describe the structure of DNA:

Answer 16

• SUGAR-PHOSPHATE BACKBONE
• DOUBLE HELIX
  
  • strands twist
• ANTIPARALLEL
  
  • strands run in opposite directions
• DOUBLE STRANDED
  
  • 2 polynucleotide strands held together by hydrogen bonds
• COMPLEMENTARY BASE PAIRING
  
  • specific hydrogen bonding between complementary nitrogenous bases

Question 17

What is RNA?

Answer 17

Polynucleotide

involved in copying & transfer of genetic material from DNA

Question 18

Compare the structures of DNA & RNA:

Answer 18

• SIMILARITIES
  
  • pentose sugar
  • phosphodiester bonds between nucleotides
  • polymer of nucleotides
• DIFFERENCES
  
  • DNA has deoxyribose sugar, RNA has ribose
  • RNA has Uracil base instead of Thymine
  • RNA single stranded, DNA double stranded

Question 19

Why can DNA not be used directly to transfer genetic information to the ribosome?

Answer 19

too large to leave nucleus

also could be damaged in transport, so template (RNA) used

Question 20

Outline the process by which DNA can be extracted from a tissue sample, explaining the reasoning behind the steps:

Answer 20

1. Grind sample
   
   1. Breaks down cell walls & provides large surface area
2. Add detergent
   
   1. Dissolves phospholipid bilayer of membranes
3. Add salt
   
   1. Makes DNA less soluble in water by breaking hydrogen bonds between DNA + H₂O
4. Add protease
   
   1. Breaks down enzymes involved in DNA degradation
5. Add ethanol
   
   1. DNA insoluble in ethanol & salt, ∴ forms precipitate
6. Pick out DNA using hook