2.1.2j DNA Replication

Question 1

Why does DNA need to replicate

Answer 1

• DNA copies itself before cell division so that each new cell has the full amount of DNA
  This is important for:
• making new cells fro growth & repair
• for passing genetic info from generation to generation (reproduction)

Question 2

Why must DNA replication be accurate

Answer 2

The DNA replicate must be an exact copy to form 2 sister chromatids, and so the process must be accurate

Question 3

What are enzymes

Answer 3

DNA replication is controlled by enzymes, a class of proteins that act as catalyst for biochemical reactions

Question 4

4 enzymes involved in DNA replication

Answer 4

• DNA ligase
• Helicase
• DNA polymerase
• Single-stranded binding protein

Question 5

What does DNA ligase do

Answer 5

Joins together short sections of the lagging strand

Question 6

What is Helicase also known as

Answer 6

The unzipping enzyme

Question 7

What does Helicase do

Answer 7

• Enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous pairs of bases in DNA molecule.
• The result is 2 single strands of DNA w exposed nucleotide bases

Question 8

What is DNA polymerase also known as

Answer 8

The builder enzyme

Question 9

What does the DNA polymerase do

Answer 9

• Enzyme that catalyses the formation of DNA from activated deoxyribose nucleotides using single stranded DNA as a template
• Catalyses the formation of phosphodiester bonds between the nucleotides.
• This addition of nucleotide bases happens in the 5’ ti 3’ direction

Question 10

What do Single-strand binding proteins do

Answer 10

Separates the 2 DNA strands before replication

Question 11

Process of Semi-conservative replication

Answer 11

1. DNA helicase cause the hydrogen bonds to break, separating strands
2. The double helix structure unwinds
3. Free nucleotides join the complementary unpaired bases
4. Hydrogen bonds form between bases
5. DNA polymerase catalyses the formation of phosphodiester bonds between the nucleotide
6. Half the molecules is old DNA, half is made of new molecules. This is known as semi-conservative replication

Question 12

What is Semi-conservative replication

Answer 12

Each new DNA molecule is formed of one conserved strand from the og molecule, which acts as the template, & one strand of new nucleotides

Question 13

Uses of semi-conservative replication

Answer 13

The loops of DNA in prokaryotes, & inside mitochondria & chloroplast, also replicate semi-conservatively.
A bubble sprouts from the loop & this unwinds and unzips. The complementary nucleotides join to the exposed nucleotides. Eventually, the whole loop is copied

Question 14

Process of Continuous & Discontinuous Replication

Answer 14

1. DNA polymerase always moves along the template strand in the same direction. It can only bind to the 3’ (OH) end, so travels in the direction of 3’ to 5’
2. As DNA only unwinds & unzips in one direction, DNA polymerase has to replicate each of the template strands in opposite directions
3. The strand that is unzipped from the 3’ end can be continuously replicated. This strand is called the leading strand & is said to undergo continuous replication
4. The other strand is unzipped from the 5’ end, so DNA polymerase has to wait until a section of the strand has been unzipped & then work back along.
5. This results in DNA being produced in sections, called Okazaki fragments. These fragments then have to be joined. This strand is called the lagging strand & is said to undergo discontinuous replication

Question 15

see showbie for diagrams