The Cell Cycle (UNIT 2)

Question 1

What are the two main stages of cell division?

Answer 1

Nuclear division- The process by which the nucleus divides.

Two types- mitosis and meiosis.

Cell division- follows nuclear division and is process by which whole cell divides.

Question 2

Before a nucleus divides its DNA it must be… to ensure…

Answer 2

REPLICATED to ensure that all the daughter cells have the genetic info to produce the enzymes and other proteins that they need.

Question 3

What are the four requirements for semi-conservative replication to take place?

Answer 3

• The four types of nucleotide, each with their bases of adenine, guanine, cytosine and thymine, must be present
• Both strands of the DNA molecule must act as a template for the attachment of these nucleotides
• The enzyme DNA polymerase is needed to catalyse the reaction
• A source of chemical energy is required to drive the process.

Question 4

Describe the process of semi-conservative replication.

Answer 4

• The enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA.
• As a result the double helix separates into its two strands and unwinds.
• Each exposed polynucleotide strand then acts as a template to which complementary nucleotides are attracted.
• Energy is used to activate these (free) nucleotides.
• The activated nucleotides are joined together by the enzyme DNA polymerase to form the ‘missing’ polynucleotide strand on each of the two original polynucleotide strands of DNA.
• Each of the new DNA molecules contains one of the original DNA strands i.e. half the original DNA has been saved and built into each new DNA molecule. SEMI CONSERVATIVE REPLICATION.

Question 5

What does mitosis produce?

Answer 5

Two daughter cells that have the same number of chromosomes as the parent cell and each other.

Question 6

What does meiosis produce?

Answer 6

4 daughter nuclei, each with half the number of chromosomes of the parent cell.

Question 7

What is mitosis?

Answer 7

The division of the nucleus of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell.

Except in the rare event of a mutation, the genetic make-up of the two daughter nuclei is also identical to that of the parent nucleus.

Question 8

MUTATION

Answer 8

a sudden change in the amount or arrangement of genetic material in the cell.

Question 9

INTERPHASE

Answer 9

Mitosis is preceded by a phase where the cell is not dividing- interphase.

Period of considerable cellular activity that includes a very important event- replication of DNA.

Question 10

What are the four stage of mitosis?

Answer 10

PROPHASE

METAPHASE

ANAPHASE

TELOPHASE

Question 11

PROPHASE

Answer 11

In which the chromosomes become visible and the nuclear envelope disappears.

Nucleolus disappears.

Question 12

METAPHASE

Answer 12

Spindle fibres form.

In which the chromosomes arrange themselves at the centre of the cell.

Question 13

ANAPHASE

Answer 13

Spindle fibres attached to chromatids contract.

Each of the two threads of a chromosome (chromatid) migrates to an opposite pole.

Question 14

TELOPHASE

Answer 14

Chromatid reaches poles and becomes indistinct.

In which the nuclear envelope reforms.

Nucleolus reforms.

Spindle disintegrates.

Question 15

Why is mitosis important for growth?

Answer 15

When two haploid cells (e.g. sperm and ovum) fuse together to form a diploid cell, this diploid cell has all the genetic info needed to form the new organism.

If the new organism is to resemble its parents, all the cells that grow from this original cell must posses this same set of genetic info.

Mitosis ensures this happens.

The cell firstly divides to give a group of identical cells.

Question 16

Why is mitosis important for differentiation?

Answer 16

Group of identical cells (originating from single diploid cell fused from sperm and egg) change, or differentiate, to give groups of specialised cells.

These different cell types each divide by mitosis to give tissues made up of identical cells which perform a particular function.

This is essential as the tissue can only function efficiently if all its cells have the same structure and perform the same function.

Question 17

Why is mitosis important in repair?

Answer 17

If cells are damaged or die it is important that the new cells produced have an identical structure and function to the ones that have been lost.

If they were not exact copies the tissue would not function as effectively as before. Mitosis is therefore the means by which new cells replace damaged dead ones.

Question 18

Describe simply the process of the cell cycle

Answer 18

Cells do not divide continuously, but undergo a regular cycle of division separated by periods of cell growth.

Question 19

What are the 3 stages of the cell cycle?

Answer 19

INTERPHASE

NUCLEAR DIVISION

CELL DIVISION

Question 20

What are the 3 parts of interphase?

Answer 20

Occupies most of the cell cycle, sometimes known as resting phase because no division takes place.

1. First growth (G1) phase, when the proteins from which cell organelles are synthesised are produced.
2. Synthesis (S) phase, when DNA is replicated.
3. Second growth (G2) phase, when organelles grow and divide and energy stores are increased.

Question 21

What happens during nuclear division?

Answer 21

When the nucleus divides either in two (mitosis) or four (meiosis)

Question 22

What happens in cell division?

Answer 22

Follows nuclear division an is the process by which the whole cell divides into two(mitosis) or four (meiosis).

Question 23

What is cancer?

Answer 23

A group of diseases

Question 24

What causes cancer?

Answer 24

Growth disorder in cells.

Result of damage to genes that regulate mitosis and cell cycle.

Leads to uncontrollable growth of cells.

As a consequence, a group of abnormal cells, called a tumour, develops and constantly expands in size.

Question 25

How do drugs to treat cancer disrupt the cell cycle?

Answer 25

• prevent DNA from replicating.
• inhibiting the metaphase stage of mitosis by interfering with spindle formation.