3b. MITOSIS Flashcards
Describe what mitosis is
Mitosis is the production of identical daughter cells for growth and repair.
Describe the importance of mitosis
Mitosis is needed for growth, repair of damaged cells and replacement of worn out cells.
State the number of daughter cells mitosis produces.
2
Why might some tissues have a faster rate of mitosis / shorter cell cycle?
Because cells are damaged / lost faster, e.g. in the small intestine
State how long it takes for a mammalian cell to complete a cell cycle
24 hours
Define what the cell cycle is
The cell cycle includes all the stages that take place that cause one cell to divide into two daughter cells
Recall all the stages of the cell cycle
Interphase, Prophase, Metaphase, Anaphase, Telophase and Cytokinesis
Name the stages of interphase, and what happens at each stage
- G1 (cell growth & organelle replication)
- S (DNA replication)
- G2 (cell growth and organelle replication)
Define mitosis
The splitting of the nucleus
Which stages of the cell cycle are part of mitosis?
Prophase, metaphase, anaphase, telophase
Which stages of the cell cycle are not part of mitosis?
Interphase and cytokinesis
What percentage of the whole cell cycle is interphase?
90%
Total length of the cell cycle = 25 hours.
Total cells in the cell cycle = 60.
Cells in anaphase = 10.
Calculate the length of anaphase.
10 / 50 = 0.2
25 x 0.2 = 5 hours
What are sister chromatids?
Two identical copies of a chromosome produced during DNA replication
What is a centromere?
Centromeres are the binding sites on the sister chromatids for the spindle fibres
What are centrioles?
Centrioles are organelles where the spindle fibres develop from
What are spindle fibres?
These connect the centrioles and centromeres, and pull the chromosomes to the poles of the cell
Describe what happens during interphase
The cell grows and organelles replicate.
DNA replication occurs.
G1 (cell growth), S (DNA replication) & G2 (cell growth)
Why are mutations more likely to occur during interphase?
DNA replication occurs in interphase
Why are the cells produced in mitosis called clones?
Because they are genetically identical
Describe what happens during prophase
Chromosomes condense and become visible. They are now two sister chromatids, joined at the centromere.
Describe what happens during metaphase
Chromatids attach to spindle fibres by their centromeres. Chromosomes line up on the equator of the cell.
Describe what happens during anaphase
The centromeres spilt and sister chromatids are pulled to the opposite poles of the cell. They are now referred to as chromosomes again. This stage requires ATP.
Describe what happens during telophase
Chromosomes uncoil. Two nuclear envelopes reform.
Describe what happens during cytokinesis.
The cytoplasm divides to form two daughter cells.
Recall the equation to calculate mitotic index
Mitotic index = number of cells with visible chromosomes / total number of cells observed
Recall the percentage the cell is in interphase
90%
What is a tumour?
A mass of undifferentiated cells formed from uncontrolled cell division
How is uncontrolled cell division caused?
Mutations
Name the two types of tumours
Benign and Malignant
Which type of tumour is classed as cancer?
Malignant
Why are benign tumours not cancerous?
Because they do not mestastisise, so pieces that break off cannot start new tumours elsewhere in the body
Why are malignant tumours cancerous?
Because they mestastasise. Therefore they can spread to other parts of the body and form new, secondary tumours.
Describe three ways tumours can cause damage to the body
Damaging the organ concerned, causing blockages or obstructions, exerting pressure on other organs
Why are mutagenic agents dangerous?
They increase the rate / chance of mutations occuring
Name mutagenic agents
Radiation, X-Rays, UV rays, cigarette tar (any carcinogen)
The chance of developing cancer is a combination of which two things?
Genes and exposure to mutagenic agents
Why are people with a family history of cancer at a greater risk of developing cancer?
Because cancer has a genetic component which can be inherited. These genes give a predisposition to cancer
Define what a risk factor is
A factor that increases the rate of a disease (in a population)
Name a risk factor for lung cancer
Smoking
Name a risk factor for liver cancer
Alcohol
Name a risk factor for cervical cancer
HPV
Name a risk factor for stomach / bowel cancer
High fat diet
Name a risk factor for skin cancer
UV Rays
Why are darker skinned people at a lower risk of developing skin cancer than lighter skinned people?
Darker skinned people have more melanin, which absorbs more UV Rays and prevents burning.
State the two things cancer drugs inhibit
DNA polymerase and spindle fibre formation / function
Describe how inhibiting DNA polymerase would treat cancer
It would prevent DNA replication by preventing the formation of phosphodiester bonds in the new DNA strand
What would a cell look like once a drug that inhibits DNA Polymerase had taken effect?
The chromosomes would be visible but not fully condensed, so you wouldn’t see individual chromosomes.
Describe how inhibiting spindle fibre formation would treat cancer
It would prevent sister chromatids from being pulled to the opposite poles of the cell
What would a cell look like once a drug that inhibits spindle fibre formation had taken effect?
The chromosome would be fully condensed and visible as sister chromatids, but unable to line up on the equator
What would a cell look like once a drug that inhibits spindle fibre function had taken effect?
The chromosomes would be lined up on the equator, but unable to be pulled to the poles of the cell
Why might using drugs that inhibit DNA replication be problematic?
Because healthy cells also undergo mitosis
Why would using drugs that inhibit DNA replication affect cancer cells more than healthy cells?
Because cancer cells undergo mitosis at a faster rate, therefore more cancer cells are killed.
Why is mitosis important in single-celled organisms?
Single celled organisms reproduce by making genetically identical copies of themselves
Name the process by which prokaryotic cells divide
Binary Fission
Describe the process of binary fission
The circular DNA replicates, the cytoplasm divides to produce two identical daughter cells.
Why can viruses only replicate inside a host cell?
They are non-living
How do viruses attach to host cells before injecting their genetic material?
Using attachment proteins
Once a virus has injected its genetic material into a host cell, how does the host cell produce the viral components?
Transcription and translation
Once the viral components have been assembled inside the host cell, how do they exit the host cell?
By budding off
Describe the process of budding off
When a new virus leaves a host cell, part of the host cell’s membrane forms an envelope around the virus and detaches, forming the new virus cell membrane
When preparing to look at onion cells under the microscope to calculate mitotic index, why must only the very ends of the roots be used?
Because this is the meristem, where cells are undergoing mitosis
What two processes do you carry out to ensure you end up with one layer of cells?
Separate the cells using a mounted needle, and squash the roots using the side of your fist
Why is it important to end up with one layer of cells?
So light can pass through so you can view the chromosomes
In which order do you use the focus knobs when focussing the image?
Coarse, then fine
How do you calculate mitotic index?
Number of cells in mitosis / Total number of cells
