2.2 All cells arise from other cells Flashcards
What is the role of mitosis and the cell cycle
- To produce identical daughter cells for growth and asexual reproduction.
- This produces 2 daughter cells which are genetically identical to the parent cell, so mitosis does not give rise to genetic variation.
Why is mitosis an important process (3 reasons)
- Growth and repair: All cells produced are identical, so organisms can grow and replace dead tissues using mitosis.
- Reproduction: Can be used as a form of reproduction in some single-celled organisms.
What are the 3 phases of the cell cycle
- Interphase
- Mitosis
- Cytokinesis
What are the 4 phases of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
What are the 3 phases of interphase
G1, S, G2
What happens during each phase of interphase
- G1(growth 1): cell grows and receives a signal to divide.
- S (synthesis): DNA duplicated (semi-conservative replication).
- G2 (growth 2): cell prepares for division and DNA is checked for mutations.
What happens during prophase
- Chromosomes condense and are now visible when stained.
- The chromosomes consists of 2 identical chromatids (sister chromatids) that are joined at the centromere.
- The 2 centromeres (replicated in the G2 phase) move towards opposite poles.
- Spindle fibres (protein microtubules) begin to extend from the poles towards the equator.
- The nuclear envelope (nuclear membrane) breaks down into a small vesicle, leaving the chromosomes free.
What happens during metaphase
- Chromosomes (consisting of 2 identical chromatids) move to the equator.
- Spindle fibres attatch to the centromere, each sister chromatid being attatched to a spindle fibre originating from opposite poles.
What happens during anophase
- Spindle fibres contract which separates the chromosomes into sister chromatids, each being pulled to opposite poles.
- The centromere also divides.
- The energy to move the chromatid (ATP) comes from the mitochondria.
- The cell starts to elongate.
What happens during telophase
- Spindle fibres break down.
- Chromosomes unwind back into chromatin and are no longer visible under a microscope.
- The nuclear membrane starts to reform around each set of chromosomes
Describe the process of binary fission
- The circular DNA replicates and both copies attatch to the cell membrane.
- Plasmids (if present) replicate.
- Cell membrane pinches inwards between the 2 circular DNA molecules, dividing the cytoplasm.
- New cell walls form between the 2 DNA molecules, dividing the original cell into 2 identical daughter cells.
How is cell division controlled
- After a certain amount of time/ a maximum number of cell divisions has occured from that cell, it will enter the G0 phase.
- This means the cell stops dividing (is in a permanent stage of interphase).
What is cancer
- Uncontrolled cell division/ mitosis.
- There is no maximum number of cell divisions that occur.
- Cancer cells don’t stop dividing.
When does uncontrolled cell division become cancerous
When abnormal growths change from benign to malignant.
What is cancer caused by
- Mutations.
- DNA has a natural (very low) rate of mutation.
- 99% of DNA is non-coding (not expressed) and approx. 99% of codding DNA codes for proteins which don’t affect cell division or death.
What is a ‘cause of cancer’
Something that increases the likelihood of mutations.
What are 4 examples of causes of cancer
- Ionising electromagnetic radiation (e.g. x-rays, gamma rays).
- Pathogens (e.g. HPV).
- Mutagenic chemicals (e.g. nicotine, alcohol, air pollutants).
- Lifestyle factors (e.g. diet, lack of exercise).
What are the 2 types of genes that affect cell division/ death
Proto-oncogenes and Tumour suppressor genes.
What do proto-oncogenes usually do
They normally produce proteins which increase the rate of mitosis and decrease the rate of cell death.
What happens when proto-oncogenes mutate
- They mutate to become more functional.
- They further increase the rate of cell division/mitosis and further decrease the rate of cell death.
- This caused cells to be more likely to divide uncontrollably.
What do tumour-suppressor genes usually do
They normally produce proteins which decrease the rate of mitosis/cell division and increase the rate of cell death.
What happens when tumour suppressor genes mutate
- They mutate to become non functional.
- This means they no longer decrease the rate of mitosis and increase the rate of cell death.
- This makes cells more likely to divide uncontrollably as their cell division is no longer being controlled.
