Yr 11 - SCB - B2.4 - DNA replication

Question 1

define nucleus

Answer 1

Organelle found in eukaryotic cells. Inside contains the majority of the cell’s genetic material.

Question 2

define nucleolus

Answer 2

where ribosomes are made, and it is made of proteins and RNA

Question 3

4 nitrogen bases

Answer 3

adenine (A), thymine (T), guanine (G) and cytosine (C)

Question 4

The stages of DNA replication

Answer 4

1. double strand helix unwinds
2. Hydrogen bonds between bases separates
3. This exposes the bases of the nucleotides
4. As the bases are exposed, new nucleotides containing the complementary bases attach
5. A new hydrogen bond forms and and the strands recoil

This produces two identical molecules of DNA.
Called semi conservative because half the original strand is used in the new strand.

Question 5

How is DNA replication made accurate

Answer 5

• building 1 new strand off the old strand and using complimentary base pairing
• DNA polymerase also checks for errors

Question 6

What is a nucleotide?

Answer 6

Phosphate group (circle) connected to pentose sugar (pentagon) connected to nitrogenous base (hexagon)

Question 7

Enzymes involved DNA replication

Answer 7

• Helicase unwinds and separates the DNA strands by breaking hydrogen bonds
• Polymerase bonds the new nucleotides together to form the new strand.
• ligase joins the Okazaki fragments together after polymerase has built them

Question 8

How does polymerase join 5 to 3 fragments and 3 to 5 fragments

Answer 8

polymerase only reads in one direction. One strand is read in 5 to 3 direction whereas
polymerase only reads in 3 to 5. The 3 to 5 strand is synthesised continuously and is called the leading strand. The 5 to 3 strand is synthesised in Okazaki fragments (about 1000 base pairs long) and is called the lagging strand.

Question 9

Mitosis steps

Answer 9

.

Question 10

Purpose of mitosis

Answer 10

Mitosis occurs for growth and
repair – so the organism can grow
bigger or replace damaged or worn
out cells.

Question 11

Process of mitosis

Answer 11

1. PROPHASE Chromosomes (2 chromatids joined) condense and nuclear membrane breaks down.
   Centrioles move to cell poles, and spindle fibres form.
2. METAPHASE Spindle fibres attach to centromeres and cause chromosomes to line up along the cell
   equator
3. ANAPHASE Chromatids are separated to opposite poles of cell when centromeres break and spindle
   fibres pull them to the poles
4. TELOPHASE New nuclear membrane forms around chromosomes and cell membrane pinches in
5. 2 new daughter cells form identical to each other and the parent cell