Unit 4 - Topic 1 - DNA Structure and Replication

Question 1

What are nucleic acids?

Answer 1

• Basic unit of inheritance
• consititute all genetic material of living things

Question 2

What are the two main types of nucleic acids?

Answer 2

DNA and RNA

Question 3

What does DNA stand for and who discovered the structure?

Answer 3

• Deoxyribonucleic acid
• Watson and Crick, hence it’s called the Watson-Crick model

Question 4

Describe the structure of DNA

Answer 4

• consists of 3 parts - this forms a nucleotide
  1. phosphate group (head)
  2. pentose sugar (in DNA it is deoxyribose sugar)
  3. nitrogenous base
• the nucleotides joined together (stacked) to form long strands
• there are two antiparallel strands (linked by complementary nitrogenous bases) twisted into a double helix shape

Question 5

Why is the antiparallel double helix structure important?

Answer 5

This allows for the bases to face each other and thus be able to pair

Question 6

How are nucleotides linked together? add more detail regarding 5’ and 3’?

Answer 6

• linked in a process called polymerisation, where a phosphodiester bond forms between the pentose sugar and phosphate group (this is the polymerisation of nucleotides)
• results in a long single strand formed
• DNA & RNA - always synthesised in a 5’ to 3’ direction

Question 7

What are the complementary base pairs and how many “something” bonds occur between each?

Answer 7

Adenine and Thymine (with 2 hydrogen bonds)

Cytosine and Guanine (with 3 hydrogen bonds)

Question 8

What are differences between prokaryotic and eukaryotic DNA? (3)

Answer 8

Eukaryotes
- Double stranded - double helix shape
- Bound to histone proteins
- Found in nucleus

Prokaryotes
- Circular DNA
- Naked and unbound
- Free floating in cytosol

Question 9

Where is DNA stored in Eukaryotic cells

Answer 9

stored in nucleus (bound to proteins)

Question 10

Explain how DNA is stored within the nucleus in eukaryotic cells? (what makes it effective?)

Answer 10

• the double helix is initially wrapped around 8 histones (proteins) to form nucleosomes
• packed nucleosomes = chromatin
• chromatin - then tightly coiled into long, thin, thread like structures - called chromosomes

Question 11

What does RNA stand for?

Answer 11

Ribonucleic aid

Question 12

How does RNA structurally differ from DNA?

Answer 12

1. Single stranded
   2.Nitrogenous base Thymine replaced with Uracil
2. Ribose sugar instead of deoxyribose

Question 13

List the 3 types of RNA and explain main function

Answer 13

1. Messenger RNA (mRNA)
   - Copy of the gene from DNA that is carried from the nucleus to the ribosome for protein synthesis
2. Transfer RNA (tRNA)
   - Carries amino acids to ribosome for protein synethsis
3. Ribosomal RNA (rRNA)
   - Primary component of the ribosome