Cell Cycle

what are the stages of the cell cycle in eukaryotes

G1 phase

S phase

G2 phase

M phase

which stages are interphase

G1 + S + G2 = Interphase

What is G0 phase

some cells enter a resting phase where they aren’t in any stages of the cell cycle e.g neurones

explain the G1 phase and how much of the time it takes

around 45%

cell volume increases

protein synthesis

explain the G2 phase and how long it takes

30% of cell cycle time

rapid increase in volume

checking and repairing DNA before cell division

explain the S phase and how long it takes

20% of the time

DNA replication takes place

DNA helicase and DNA polymerase allow semi-conservative DNA replication to take place

dna is only replicated DNA content doubles but the number of chromosomes stays the same- at the end of the S phase chromosomes are in their replicated form

explain the M phase and how long it takes

5%

mitosis and cytokinesis

how does the DNA content of a cell change over the cell cycle

G1 stays the same

S it double

G2 stays at double

Mitosis stays at 2 then halves during mitosis

explain how the volume of the cell changes of the cell cycle

G1 it increases

S stays teh same

G2 increases again

Mitosis stays the same and then halves back to origional

What are the phases of mitosis

Prophase

Metaphase

Anaphase

Telophase

PMAT

Explain the process of interphase

• the cell has 2 pairs of chromosomes (more in real life but just for this example)

• individual chromosomes are not visible

• g, S G2 takes place

explain the process of prophase-3

• the chromosmes condense to become visible

• the nuclear envelope breaks down

• cetrioles migrate to opposite poles of the cell

explain the process of metaphase

spindle fibers made by the centrioles attach to the centromeres of each chromosome

the chromosomes are moved to the equator as a single line/layer

explain the process of anaphase

the spindle fibres are retracted , the centromeres split and the chromatids (now chromosmes)are pulled to opposite poles

explain the process of telophase-3

the chromosmes decondense

nuclear membrane reforms

whilst telophase happens cytokinesis takes place to produce idenitcal daughter cell (splitting of the cytoplasm)

describe the strucutre of a replicated chromosme

2 identical sister chromatids held together by a centromere in the centre - this is one chromosome

How can you identify the different stages of the cell cycle on a picture

Metaphase- lining up in the middle, should look like a big clump mascara eye

Anaphase- two clumps being split apart

Telophase-two clear sections with no connection

Prophase- can see individual chromosomes not just a black circle

Put these vents in order

A chromatids separate

B nuclear envelope disappears

C cytoplasm divides

D chromosomes condense and become visible

E chromosomes on the equator of the spindle

D B E A C

Name the phase in which DNA replication occurs

Interphase/ S phase

Describe the role of the spindle during mitosis

Attaches to the centromeres of chromosomes positions on the equator/ retract and separate chromatids

In which stages would the chromosomes be visible and would consist of a pair chromatids joined together

Prophase and metaphase

Give two reasons that when done on another day the garlic root tip has a different results

Warmer day/ different time of day

Different plant

Anaphase is a stage in mitosis describe how anaphase results in identical cells being produced- 3

Identical chromatids are pulled to their opposite poles by spindle fibres by their centromeres

Describe the changes that occur from early prophase to late prophase

• nuclear membrane breaks down

• Chromosomes condense Into visible chromosomes

• Centrioles move to opposite poles

• Spindle fibres form

Explain why the S-phase is faster at 25 degrees than at lower temperatures-3

Increased temp increases kinetic energy

DNA helicase and DNA polymerase have the required activation energy

Nucleotides are diffusing faster

DNA replication is faster

How do you calculate the mitotic index

(Number of cells in mitosis/total number of cells) X 100

Describe how you can tell from a micrograph what stage of mitosis cells are in

Anaphase- chromosomes are being pulled to opposite poles

There is a lack of DNA at the equator

prophase- the individual chromosomes can now be seen

Interphase- no visible chromosomes can be seen

Metaphase- mascara eye the chromosomes are trying to occupy the equator as a single line

Explain cell division in plant cells

A new cell wall forms down the centre

2 identical daughter cells are produced but the 2 cells stay attached

Binary fission

Label each diagram

Prophase anaphase metaphase telophase interphase

Explain animal cell division

Why is the prokaryotic cell cycle faster

They are smaller so have a larger surface area to volume ration so gain nutrients faster e.g make nucleotides for DNA replication

When observing stem cells that are dividing too quickly and therefore forming a tumour the cells often appear smaller than normal and large nuclei are common, suggest an explanation for these 2 features

Smaller as one of the growth phases is missed out therefore when cytokinesis halves the cell is it going to be smaller than it began as

Larger nuclei more likely to have been through s phase therefore dna is replicated

Explain why the s phase and the m phase take the same amount of time for a tumour cell and a normal cell

S phase is when dna is replicated, tumour/ normal cells have their same amount of DNA to replicate

M phase mitosis takes the same time.g same number of chromosomes to move in the cell

A drug has been developed to prevent anaphase , it is readily absorbed by cells in the ileum , evaluate the drug as a potential treatment for tumours forming in the human ileum

For:

It is absorbed by the cells we want to treat

Stops anaphase so prevents cell division

Against:

Data is for mice not human- human cells may react differently

Side effects as all cells in the ileum not just tumour cells would be effected

Suggest why the mitoitc index is a useful metric to record

The data can be compared to e.g normal range

The data can be plotted

Statistical work can be carried out

Explain a method to see root tips under the microscope

1. Cut 1 cm of a garlic root tip with scissors, make sure you know which end is the tip

2. Using a scalpel, cut around 2mm from the growing root tips on the tile and discard the rest as the tip is where most cell division occurs

3. Put 6 drops of 50:50 HCl and ethanol into a staining block, place the root tips i and cover with a watch glass for 10 minutes

4. Use a mounted needle to transfer the root tips to a second the root tip to a second staining block containing 6 drops of 45% glacial acetic acid and cover with a watch glass, eave for 5 mins

5. Put onto glass slide

6. Add one drop of toluidine blue stain make the DNA visible

7. Tap the tissue on the slide 20 times with a glass rod to form a single layer of cells allowing the light to pass through and then cover with a coverslip

8. Fold a paper towel over the slide and squash

9. Look under the microscope