Cell Division Flashcards
What are the two stages of the
cell cycle in eukaryotes?
- Interphase (growth and replication)
- Mitosis (cell division)
What are the 3 separate growth sstages of interphase?
- Growth phase 1- the cell grows, increase in the number of organelles, proteins are made and ATP is synthesised
- Synthesis of the DNA - semi conservative replication takes place
- Growth phase 2 - cell keeps growing, proteins are made, ATP synthesised
Interphase is the ……. phase of the cycle, normally ……than the whole phase of mitosis, unless the cell is ……. ………
Interphase is the longest phase of the cycle, normally longerthan the whole phase of mitosis, unless the cell is rapidly dividing
What are homologous chromosomes?
Pairs of chromosomes that contain the same genes in the same loci(position of that gene) but not necessarily the same alleles (not genetically identical).
What do homologous chromosomes consist of?
One pair of chromosomes is maternal
One pair of chromosomes is paternal
They are the same size and shape and the centromere is in the same place
How many chromosomes do all somatic cells contain?
46 chromosomes in 23 homologous pairs
Therefore when a new daughter cell is produced it will also contain 46 chromosomes
MATHS QUESTION:
A scientist observes a section of growing tissue under the microscope. He counts 100 cells undergoing mitosis. Of those, 10 cells are in mitosis
One cell cycle last 15 hours. How long do the cells spend in mitosis? Give your answer in minutes
Step 1: find the percentage of the number of cells undergoing mitosis
10/100 x 100 = 10%
Step 2: find 15 hours in mins
15x60 = 900 mins
Step 3: find the time the cells spent in mitosis
10% of 900 = 90 mins
What 4 things occur during interphase?
1) DNA replicates
2) ATP synthesised to provide energy for cellular processes
3) organelles synthesised including centrioles to carry out cellular functions, centrioles take part in separation of chromosomes
4) proteins synthesises to carry out cellular functions
How does DNA replicate in interphase?
• chromosomal DNA is replicated exactly and the two pieces of DNA are held together by the centromere
• if the copies are not done accurately, mutations may occur and daughter cells will not receive identical genetic material
• following mitosis the two new cells will contain one of each sister chromatids
What are 5 things mitosis is important for?
- All organisms need to produce genetically identical daughter cells
- Asexual reproduction
- Growth - grow by producing new cells genetically identical to each other and the parent cell
- Repair - damaged cells need to be replaced by new ones that perform the same donation so must be identical
- Replacement - red blood cells and skin cells need to be replaced
What are the 4 stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
PMAT
What is prophase?
• replicated chromosomes shorten and thicken (supercoil)
• each chromosome consists of a pair of sister chromatids.
• Nuclear envelope breaks down and disappears
• centriole divides into two and each daughter centriole moves to opposite ends of the cell to form a spindle (protein threads)
What is metaphase?
• replicated chromatome line up down the equator (middle) of the cell
• each chromosome is attached to a different spindle fibre by its centromere
Remmeber Middle for Metaphase
What is anaphase?
• Identical sister cheomatids are pulled to different poles by the shortening of the spindle fibres
• centrometres divide
Remember Apart for Anaphase
What is telophase?
• Two new nuclei are formed
• sister chromatids reach poles and are now chromosomes
• spindle breaks down and disappears
• Chromosomes uncoil and can’t be seen in a light microscope anymore
Remember Two for Telophase
What is cytokinesis?
Division of the cytoplasm - when the cell divides
It occurs between telophase and interphase. Each new daughter cell in identical to the parent cell and to each other
What is cytokinesis in animal cells?
Microfibres from a “draw string” just inside the membrane which then fuses as it is pinched in
What is cytokinesis in plant cells?
Microfibres direct vesicles to the middle of the cell to form a cell plate, which forms a new cell wall. New cell surface membrane is made on either side to enclose the two cells
Look at the graph and answer the following:
- When does synthesis take place
- When does mitosis take place
- How many cell divisions age shown
- Between 12 -16 and 36-40 hours because mass of DNA doubles
- 24 hours - mass returns to original mass
- 2
What are mitosis and cell cycle controlled by?
Genes
What is uncontrolled cell division?
When there’s a mutation ( change in base sequence of DNA) in a gene that controls cell division, so the cells grow out of control.
This can lead to the formation of tumours
Where are tumours commonly found?
Can develop in any organ in the body but most commonly found in lungs, prostate, breast and ovaries, large intestine, stomach, oesophagus and pancreas
A tumour can become cancerous if it changes from benign to malignant
How is cancer treated?
• Involves killing dividing cells by blocking part of the cell cycle. If cell cycle is disrupted cancer growth stops.
• these treatments do NOT distinguish tumour cells from normal cells however tumour cells divide more frequently than normal cells so the treatment is more likely to kill tumour cells
• normal body cells that divide rapidly are also vulnerable (explaining frequent hair loss seen in patients undergoing cancer treatment)
How do drugs that treat cancer disrupt the cell cycle?
• prevent DNA from replicating. Radiation and some drugs damage DNA. If severe DNA damage is detected the cell with kill itself
• inhibiting metaphase stage of mitosis by interfering with spindle formation
• preventing the synthesis of enzymes needed for DNA replication
Who is Henrietta lacks and was are some ethical issues of HeLa cells?
