2.6 Cell division Flashcards
(46 cards)
1
Q
What is the cell cycle?
A
The sequence of events that cells go through as they grow and divide
2
Q
What are the stages of the cell cycle?
A
1) Mitosis [Then cytokinesis] - division and splitting
2) G1 - the first growth phase
[G0 - optional process that stops the cell from continuing the cell cycle]
{G1, S checkpoint}
3) S phase - DNA replication/synthesis
4) G2 - the second growth phase
{G2, M checkpoint}
3
Q
What are the stages of mitosis?
A
Prophase
Metophase
Anaphase
Telophase
4
Q
What is mitosis?
A
The division of the nucleus
5
Q
What is cytokinesis?
A
Splitting of the cell into two cells
6
Q
What happens in G1 (the growth phase)?
A
- Cells grow
- Transcription
- Translation [New proteins are built]
- Replication of organelles
7
Q
What happens in the S phase (the DNA replication/synthesis phase)?
A
- Semi conservative replication occurs
- By the end of the stage the chromosomes are left in the “X” structure instead of the “I” structure
- This is because the original chromosome has been copied into two identical sister chromatids
8
Q
What happens in G2 (the second growth phase)?
A
- Preparation for mitosis
- Proteins needed for mitosis are produced (For example: Cyclin enzymes are made)
9
Q
Why must the cell cycle be controlled?
A
Prevents the cells dividing too much uncontrollably (Cancer)
10
Q
Why do endothelial cells in the intestine have a short G0 phase?
A
Endothelial cells inside the intestine can’t have a large gap as they have to be continuously replicated to replace the lining in the intestine as food breaks it down
11
Q
Why do neurones have a larger G0 phase?
A
Neurones stop being replicated at a young age so no new ones are made. This is because the neurones stay in the G0 phase
12
Q
What are the two checkpoints in the cell cycle?
A
- The G1 ,S checkpoint
- The G2, M checkpoint
13
Q
What does the G1 ,S checkpoint do?
A
- Checks to see if the DNA is damaged
- Sees if it is safe to proceed
- p53 tumour suppressor gene = makes it less likely for cells to replicate out of control to create a tumour
- p53 could mutate though meaning that tumours could still be caused from the checkpoint not stopping out of control replication
- This checkpoint works like brakes on a car as it works to slow down and stop the cell cycle if something is going wrong
14
Q
What does the G2 M checkpoint do?
A
- Oncogene works to control the cell cycle
- Accelerates the division
- Could mutate though meaning that tumours could be caused from accelerated out of control division due to the mutation
15
Q
Which parts of the cell cycle is considered interphase?
A
- G1, S and G2
- Preparation for mitosis
16
Q
What happens in prophase of mitosis?
A
- Chromosomes condense and become visible
- Chromosomes become present as sister chromatids
- Nuclear envelope breaks down
- Spindle starts to form
17
Q
What is the spindle?
A
The spindle is an arrangement of microtubules made up of tubulin coming out of the centrioles
18
Q
What happens in metaphase of mitosis?
A
- Chromosomes line up in the centre of the cell on the metaphase plate/equator of the cell
- The centromere of the chromosomes attaches to the spindle fibres
19
Q
What happens in anaphase of mitosis?
A
- The sister chromatids are pulled to the poles by spindle fibres coming from the centrioles powered by motor proteins that pull the centromeres of the chromatids with the spindle fibres
- The sister chromatids on each chromosome are split a part and they are now seen as separate chromosomes
20
Q
What happens in telophase of mitosis?
A
- Both sets of individual chromosomes make it to the poles on the different sides of the cell/the poles
- Nuclear envelope begins to re-form around the two sets of chromosomes on the poles
21
Q
What is purpose of mitosis?
A
- Produces two identical daughter cells
- For growth & repair of cells
- Asexual reproduction in multicellular organs (for example plants or yeast) [Called “budding” in yeast cells]
22
Q
What is the splitting of cells in prokaryotes called?
A
- Binary fission (The equivalent of cytokinesis but for prokaryotes)
- The splitting of a bacteria cell
23
Q
What is a mitotic index?
A
- The percentage of cells that are undergoing mitosis in a sample
- A large image of many cells that is used to see which cells are undergoing mitosis
- This is done by seeing if chromosomes are visible
- If the chromosomes can be seen then the cell is undergoing P, M, A or T of mitosis
- If chromosomes are not visible it means that the cell is undergoing interphase
- Done on root tip squash’s for example
24
Q
What is the equation used for a mitotic index?
What is the percentage of cells undergoing mitosis in an image
A
Number of cells undergoing mitosis (PMAT) /
Total number of cells
25
Why is the mitotic index used?
-To see whether cells fall under the normal number of cells undergoing mitosis
-Practical applications: Smear tests, to see if cells are dividing too rapidly
-If the mitotic index number is too high then it could be a sign that the cells are dividing out of control so the woman could be leading to cervical cancer or potentially pre cancerous
[The normal percentage for cells undergoing mitosis is normally 5-10%]
26
What is the purpose of meiosis?
- To produce 4 non-identical haploid (1n) gamete cells
- Each cell ends up with one set of 23 chromosomes
- The process causes the chromosome pairs to be split into single sets, so it goes from two copies of every chromosome to one copy of every chromosome
- The number of single sets of chromosomes in each cell made from meiosis is 23
- Produces gametes for sexual reproduction
27
How are the chromosomes structure at the start of meiosis (During prophase 1 and metaphase 1)
- Chromosomes pair up and form a pair of homologous chromosomes/bivalent (2 "X's) [Paternal and maternal chromosome/homologue]
- Each chromosome ("X") is formed of two sister chromatids ("I's")
28
What happens in prophase 1 of meiosis?
- Chromosomes condense and become visible
- Chromosomes come present as sister chromatids
- Nuclear envelope breaks down
- Spindle starts to form
- Non sister chromatids cross over and wrap around each other (Chiasma) to form a pair of homologous chromosomes joined by the chiasma
29
What happens in metaphase 1 of meiosis?
-Pairs of homologous chromosomes line up in the centre of the cell on the metaphase plate/equator of the cell
-The centromere of both chromosomes in every homologous pair attaches to the spindle fibres
-Independent assortment occurs:
-This happens when the chromosomes line up along the equator.
-All 23 of the paternal and all 23 of the maternal chromosomes have the random chance to line up on the right side or the left side of the
equator before anaphase, this causes genetic variation in the daughter cells
30
What happens in anaphase 1 of meiosis?
- The homologous chromosomes are pulled apart to the poles by spindle fibres coming from the centrioles powered by motor proteins
- The homologous pairs are split a part and they are now seen as separate chromosomes
31
What is the purpose of the crossing over of the non-sister chromatids in prophase 1 of meiosis?
- To exchange genetic material between the paternal and maternal homologue
- This creates genetic variation in the non-identical daughter cells produced at the end of meiosis
32
What happens in telophase 1 of meiosis?
- Both the paternal and maternal chromosomes make it to either poles on the different sides of the cell
- The nuclear envelope begins to re-form around the two poles
33
What happens in prophase 2 of meiosis?
- Centrioles replicate and move to the poles ready to pull the chromosomes apart to the poles for the second time
- Nuclear envelope breaks down
- New spindle fibres form at right angles to the ones present in prophase 1
34
What happens in metaphase 2 of meiosis?
- Chromosomes line up in the centre of the cell on the metaphase plate/equator of the cell
- The centromere of the chromosomes attaches to the spindle fibres
35
What happens in anaphase 2 of meiosis?
- The sister chromatids are pulled to the poles by spindle fibres coming from the centrioles powered by motor proteins
- The sister chromatids on each chromosome are split a part and they are now seen as separate chromatids
36
What happens in telophase 2 of meiosis?
- Both sets of individual chromosomes make it to the poles on the different sides of the cell/poles
- The nuclear envelope begins to re-form around the four poles
- Four haploid gametes are produced all unique due to the crossing over of genetic information in prophase 1
37
How does the amount of DNA in a diploid (animal) cell change over time during mitosis?
-At G1 starts as two as there is two of each
chromosome
-In S phase DNA is copied until there is 4 sets of DNA
-DNA enters G2 with 4 and ends up with 4
-The DNA then splits and returns to diploid cells with 2 chromosomes
38
How does the amount of DNA in a diploid (animal) cell change over time during meiosis?
-There is 4 DNA at the start as there are two pairs of homologous chromosomes (4 chromosomes)
-In meiosis 1 the DNA is halved to 2 in each cell, so the cells are now diploid
-In meiosis 2 the DNA is halved again so it ends with 1 chromosome in each non- identical haploid daughter
cell
39
How are guard cells specialised?
-Guard cells are able to open and close in response to water stress
40
How are leaf cells specialised?
- The palisade mesophyll cells are specialised for photosynthesis as they:
- Contain large amounts of chlorophyll
- They have a long shape that maximises light absorption
- The layer of Spongy Mesophyll beneath has many air spaces to maximise gas circulation.
41
How are root hair cells specialised?
- Root hair cells have a very large surface area due to them being very long and having hair like projections, this increases diffusion rate
- They are also filled with many mitochondria so they are very well specialised for active transport of mineral ions from the soil and into the roots.
42
What are the two key sources of variation in meiosis?
- Crossing over in prophase 1
| - Independent assortment in anaphase/metaphase 1
43
How are sperm and egg cells made?
-Sperm cells are gametes so they are produced in meiosis
44
How do sperm and egg cells have genetic variation?
- As they are made in meiosis they have genetic variation from:
- Crossing over in prophase 1 &
- Independent assortment
45
What is the number of total potential variations, in a gamete produced by meiosis, is made by independent assortment?
2^23 (2 to the power of 23)
46
What type of stem cells are made in the bone marrow?
Bone marrow is home to multipotent stem cells which produce blood cells
