Cell Structure - Cell Replication

Question 1

What are the three stages of the cell cycle?

Answer 1

• interphase = chromosomal replication and cell growth
• nuclear division = stages of mitosis (or meiosis)
• cytokenises = division of the cytoplasm

Question 2

What does mitosis produce?

Answer 2

Two daughter cells that have the same chromosomes as the parent cell as well as each other

Question 3

What happens at interphase?

Answer 3

• there is de-condensed chromatic in the nucleus
• nucleoli are visible
• the nuclear membrane is visible
• centrioles are present
• the DNA undergoes replication and the two sister chromatids remain joined at the centromere

Question 4

what happens at prophase?

Answer 4

• chromatin condenses and chromosomes become visible
• nucleoli disappears
• the nuclear membrane disappears
• the centrioles move to the poles off the cell and each centriole forms spindle fibres to produce the spindle apparatus
• the chromosomes attach to the spindle fibres at their centromeres

Question 5

In prophase of mitosis, how do you know centrioles are not essential to spindle fibre formation

Answer 5

As plant cells lack centrioles yet still develop the spindle apparatus

Question 6

What happens at metaphase?

Answer 6

• the chromosomes can be seen to be made of two chromatids
• the microtubules of the spindle apparatus are attached to the centromere of each chromosome
• the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell

Question 7

What happens at anaphase?

Answer 7

• the centromeres divide and the spindle fibres begin to shorten
• sister chromatids are pulled to opposite poles by the spindle fibres using energy from ATP
• the separated chromatids are now referred to as individual chromosomes

Question 8

What happens at telophase and cytokinesis ?

Answer 8

• the chromosomes reach the poles and de-condense making them no-longer visible to leave the widely spread chromatin
• the spindle breaks down and the centrioles reappear
• the nuclear membrane and nucleoli reappear
• the cytoplasm divides in cytokinesis to form two identical daughter cells

Question 9

What are the three sub phases of interphase?

Answer 9

• G1 = growth
• S= DNA synthesis
• G2= preparation and growth for mitosis

Question 10

On a graph, how can you determine where the S phase of interphase is happening?

Answer 10

By looking at where the amount of DNA in the cell doubles

Question 11

In what stage of the cell cycle do chromosomes become visible in the cell?

Answer 11

After the DNA has been replicated in interphase so at the start of prophase the chromosomes become visible

Question 12

What is mitotic index?

Answer 12

The % of cells that are in mitosis

Question 13

How do you calculate the mitotic index?

Answer 13

Mitotic index = # of cells in mitosis / # of total cells

Question 14

Around how much of the time a mammals cell cycle takes is interphase?

Answer 14

90%

Question 15

What is cancer? What is it a result of?

Answer 15

A group of diseases (around 200 in total) caused by a growth disorder of cells as a result of damage to the genes that regulate the cell cycle and mitosis

Question 16

When does a tumour become cancerous?

Answer 16

If it changes from benign to malignant

Question 17

Name 4 organs where tumours are most commonly found

Answer 17

Lungs, prostate gland, breast and ovaries and stomach

Question 18

What controls the rate of mitosis and what can meme its uncontrollable?

Answer 18

Two types of gene control mitosis and it can become uncontrollable if there is a mutation to one of these genes

Question 19

What happens to cells after they are mutated?

Answer 19

Most die but the ones that do survive are capable of dividing to form clones of themselves and form tumours.

Question 20

What’s the difference between malignant tumours and benign tumours?

Answer 20

Malignant tumours grow rapidly, are less compact and are more likely to be life threatening while benign tumours are more slow growing, more compact and are less likely to be life threatening

Question 21

How do the drugs used to kill cancer (chemotherapy) usually disrupt the cell cycle?

Answer 21

• by preventing DNA from replicating

- inhibiting the metaphase stage of mitosis by interfering with the spindle formation

Question 22

What is a draw-back of chemotherapy?

Answer 22

Despite the drugs are more effective against rapidly dividing cells, they can also disrupt the cell cycle of normal cells.

Question 23

What is apoptosis and when can it happen?

Answer 23

Apoptosis = programmed cell death

It can happen when there are gene mutations in the genes that control the cell cycle

Question 24

In the core practical, why do you place the plant root tissue in ethanoic alcohol and concentrated HCL?

Answer 24

As this stops cell division and hydrolyses the middle lamella so that the cells can be separated easily

Question 25

In the core practical what stain is used on the plant root tip and why is it used?

Answer 25

Toluidine blue is the stain used that binds to the chromosomes to make them more easily seen

Question 26

In the core practical, why is the stained plant root tip squashed by placing the coverslip in top of the root tip and pressing down gently but firmly in the centre of the coverslip?

Answer 26

In order to produce a single layer of cells so you can see the individual cells when you view the slide under the microscope and to allow better transmission of light through the specimen onto the other side

Question 27

What is binary fission?

Answer 27

The process that prokaryotic cells undergo to divide

Question 28

What are the steps involved in binary fission?

Answer 28

1. The circular DNA molecule replicates and both copies attach to the cell membrane
2. The plasmids also replicate
3. The cell membrane begins to grow between the two DNA molecules and begins to pinch inwards dividing the cytoplasm into two
4. A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids