Unit 3.2.5 - DNA Replication and Cell Cycle

Question 1

What type of replication does DNA replicate through?

Answer 1

Semi-conservative replication

Question 2

What are the four steps in DNA replication?

Answer 2

1. ) DNA helicase breaks down the hydrogen bonds between the bases
2. ) The two straps of DNA are unzipped into two single strands
3. ) Free nucleotides from the nucleus attach to the complementary bases
4. ) DNA polymerase makes the hydrogen bonds reform

Question 3

Why is it called semi conservative DNA replication?

Answer 3

Each DNA molecule contains one strand from the original DNA and then one new strand

Question 4

What were the original three ides for how DNA was replicated?

Answer 4

Conservative, dispersive and semi conservative

Question 5

Which experiment proved DNA replication was semi conservative?

Answer 5

Melson’s and Stahl’s experiment

Question 6

Describe how the heavy DNA was formed?

Answer 6

A sample of bacteria was grown in a broth containing heavy nitrogen, as the bacteria grew they took up the heavy nitrogen to make the nucleotides for the new DNA creating the heavy DNA

Question 7

What is heavy nitrogen?

Answer 7

N - 15

Question 8

What is light nitrogen?

Answer 8

N - 14

Question 9

How did Melson’s and Stahl’s experiment prove that DNA replication was semi conservative?

Answer 9

The bacteria grown in heavy nitrogen was transferred to a broth containing light nitrogen and allowed to replicate. A new sample of DNA was taken and spun in a centrifuge and the DNA settles in the middle showing that the sample contained the old heavy nitrogen and the light nitrogen and so it must have replicated semi conservatively

Question 10

What is the difference between DNA containing only heavy nitrogen and the DNA containing only light nitrogen when spun in a centrifuge?

Answer 10

The heavy DNA settled a lot lower than the light nitrogen in the test tube

Question 11

What two sections is the cell cycle split into?

Answer 11

Interphase and mitosis

Question 12

What are the three sections within interphase?

Answer 12

G1 phase, S phase and G2 phase

Question 13

What happens during the G1 phase within interphase?

Answer 13

New proteins and organelles formed whilst the cell grows

Question 14

What happens during the S phase within interphase?

Answer 14

DNA replicated and amount of chromatins doubled

Question 15

What happens during the G2 phase within interphase?

Answer 15

Spindle proteins synthesised ready for mitosis

Question 16

What is mitosis?

Answer 16

A type of cell division that produces two genetically identical daughter cells

Question 17

Give two reasons why mitosis is important?

Answer 17

For cell growth and repair

Question 18

What is cytokinesis?

Answer 18

When the cytoplasm divides after mitosis or meiosis forming two daughter cells

Question 19

What is cell mass continually increasing during the cell cycle?

Answer 19

Because the cell is growing

Question 20

When does the DNA mass double during the cell cycle?

Answer 20

During the S phase

Question 21

Why does the DNA and cell mass all of a sudden half?

Answer 21

When the cell divides during cytokinesis

Question 22

What four stages can mitosis be split into?

Answer 22

Prophase, metaphase, anaphase and telophase

Question 23

What three things happen during prophase?

Answer 23

1. ) Chromosomes condense becoming more visible
2. ) Nuclear membrane breaks down
3. ) Spindle fibres form

Question 24

What two things happens during metaphase?

Answer 24

1. ) Chromosomes line up along the equator

2. ) Spindle fibres attach to the chromosomes

Question 25

What two things happen during anaphase?

Answer 25

1. ) Chromosomes are pulled apart by the spindle fibres

2. ) Sister chromatids move to opposite poles

Question 26

What two three things happen during telophase?

Answer 26

1. ) Chromatids are at opposite ends of the cell
2. ) Nuclear membrane reforms
3. ) Cell divides

Question 27

Describe the structure of a chromosome during mitosis?

Answer 27

Two sister chromatids joined together by a centromere

Question 28

Label the stages within the cell cycle?

Answer 28

See flash card

Question 29

Label the stages within mitosis?

Answer 29

See flash card

Question 30

What is a mutagen?

Answer 30

Anything that causes a mutations

Question 31

What is meant by mutagens are often carcinogenic?

Answer 31

They are cancer causing

Question 32

Give three examples of mutagens?

Answer 32

Ionising radiation, UV radiation and certain chemicals like thalidomide

Question 33

How can a mutation cause a tumour?

Answer 33

If a mutation occurs in a cell that controls cell division it can cause a cell to grow and divide out of control forming a tumour

Question 34

How does chemotherapy kill cancer?

Answer 34

Prevents the synthesis of enzymes needed for DNA replication and so the cell is unable to replicate disrupting the cell cycle causing it to kill itself

Question 35

How does radiation kill cancer?

Answer 35

It damages the DNA so that when it gets to the S phase and checks for damaged DNA it finds damaged DNA and kills itself preventing further growth of the cancerous cells