2.1.3 - Nucleotides & Nucleic Acids

Question 1

General structure of a nucleotide

Answer 1

• Nitrogenous base
• Pentose sugar
• Phosphate

Pyrimidine = 1 nitrogenous base
Purine = 2 nitrogenous bases

Question 2

Difference between RNA and DNA nucleotides

Answer 2

Pentose sugar; Ribose in RNA, Deoxyribose in DNA

Nitrogenous base; in RNA U replaces T

Question 3

Formation of a polynucleotide

Answer 3

Condensation reaction between the phosphate group and pentode sugar; forms a 3’ to 5’ phosphodiester bond

• Broken via hydrolysis

Question 4

Structure of ATP

Answer 4

• Adenine base
• 3 Phosphate groups
• Ribose sugar

Question 5

DNA Structure

Answer 5

• Two anti-parallel strands (3’ to 5’ and 5’ to 3’) twist around to form a double helix
• Strands are held together via hydrogen bonds between complementary base pairs

C - G: 3 hydrogen bonds
A - T: 2 hydrogen bonds
- Purine binds with pyrimidine

Question 6

DNA replication: Step 1

Answer 6

• DNA replicates during interphase
• The enzyme helicase breaks hydrogen bond between the bases
• The double helix unwinds/uncoils
• Each strand acts as a template

Question 7

DNA replication: Step 2

Answer 7

• Free nucleotides from the cytoplasm assemble on the template DNA in complementary base pairs

Question 8

DNA replication: Step 3

Answer 8

• Hydrogen bonds reform between bases
• The enzyme DNA polymerase joins the nucleotides, forming a new sugar-phosphate backbone
• Two identical DNA molecules have been produced

Question 9

What does semi-conservative replication mean?

Answer 9

• DNA replication is semi conservative a each new DNA molecule contain one of the old strand and one of the new strands

Question 10

Why is semi-conservative replication useful?

Answer 10

• Accurately conserves genetic material
• Lowers the occurrence of spontaneous mutations

Question 11

What is a gene?

Answer 11

A section of DNA that codes for the sequence of amino acids in a polypeptide

• Alleles are different versions of a gene