Unit 1 Biological Molecules - DNA,RNA. DNA Replication

Question 1

Describe the basic structure of a nucleotide

Answer 1

• Pentose sugar
• Phorsphate group
• Nitrogen containing organic base

Question 2

Describe the functions of DNA.

Answer 2

DEOXYRIBONUCLEIC ACID

• Holds/Stores genetic information
• Codes for sequence of amino acids in primary structure of protein

Question 3

Describe the structure of a DNA nucleotide.

Answer 3

The monomer that makes up DNA is called a nucleotide
- Deoxyribose(Pentose sugar)
- Phosphate group
- Nitrogenous base
ADENINE, THYMINE, CYTOSINE, GUANINE
- form polymers of nucleotides, nucleotides joined by phosphodiester bonds

Question 4

Describe the functions of RNA.

Answer 4

RIBONUCLEIC ACID
- Transfers genetic information from DNA to ribosomes
- Formed from RNA & proteins
- mRNA = copy of a gene created in nucleus
- tRNA = found in cyptoplasm

Question 5

Describe the structure of a RNA nucleotide.

Answer 5

• Ribose(Pentose sugar)
• Phosphate group
• Nitrogenous base
  ADENINE, URACIL, CYTOSINE, GUANINE

Question 6

Describe how a polynucleotide strand is formed.

Answer 6

• Condensation reaction between deoxyribose sugar and phosphate group creating a phosphodiester bond

Question 7

Describe how a DNA molecule is made

Answer 7

• Double helix structure with 2 polynucleotide chains held together by hydrogen bonds
  (Between complementary bases)
  ADENINE & THYMINE - 2 hydrogen bonds
  CYTOSINE & GUANINE - 3 hydrogen bonds

Question 8

Describe how a RNA molecule is made

Answer 8

• Single polynucleotide chain which is relatively short

Question 9

Why is DNA replication described as semi conservative

Answer 9

• Strands from original DNA molecule acts as template

- New DNA molecule contains 1 old strand and 1 new strand

Question 10

Outline the processes involved in semi conservative replication,

Answer 10

1. DNA helicase breaks hydrogen bonds between DNA stands and causes double helix to unwind to form 2 single strands
2. Each original strand acts as a template
3. Free-floating DNA nucleotdies within nucleus attach to complementary base pair
4. DNA polymerase catalyses the condensation
   reaction
   & joins adjacent DNA nucleotides forming phosphodiester bonds
   - Forming 2 sets of DAUGHTER DNA
   1 stand = parental DNA
   1 strand = newly synthesised DNA
   - Hydrogen bonds reform

Question 11

Describe the evidence for DNA replication.

Answer 11

• Meselon & Stahl conducted an experiment that proved DNA replication must be semi conservative
  1. if replication was conservative HEAVY DNA would still be together at bottom and LIGHT DNA would be together at the top
  2. if replication was semi conservative new bacterial DNA molecules would contain 1 strand of old DNA(heavy) and 1 strand of new DNA(light) & would settle in the middle
  3. which is what happened