Cell division Flashcards
4 phases in the cell cycle
G1 , S , G2 , Mitosis + cytokineses
What happens at the G1 checkpoint
- Growth phase
- Check for following :
cell size, nutrients, growth factors and DNA damage
What happens during G1?
- First growth phase
- Organelles synthesised and produced
- Organelles replicate
- Cell grows in size
What happens at the G2 checkpoint?
- Checks DNA replication and damage
- Check cell size
- Cell initiates molecular process that signals the beginning of mitosis
What happens during the synthesis phase?
DNA is replicated in the nucleus
What happens during interphase?
- DNA replicated and checked
- Protein synthesis occurring in cytoplasm
- Mitochondria grow + divide increase amount
- Chloroplasts grow + divide in plant + algal
- Normal metabolic processes of cells occur (respiration)
What happens during G0?
- When cell leaves the cycle temporarily or permanently
Reasons why G0 can happen
- Differentiation : cell differentiated so no longer able to divide
- DNA of cell is damaged : cell enters a period of permanent cell rest (G0) Majority of cells divide limited times until senescent
- Growing number of senescent cells = age related diseases
What is the cell cycle?
- Highly ordered sequence of events resulting in division of cells and formation of two genetically identical daughter cells
Why are checkpoints needed?
Control mechanisms of the cell cycle
Spindle assembly checkpoint (metaphase checkpoint)
- Happens during mitosis where all chromosomes should be attached to spindles
- Mitosis can not pass until this has happened
Copying and separating DNA
- DNA wrapped around proteins called histones (condensed)
- DNA and histone together called chromatin
- Before cell division, DNA of each chromosome must be replicated
What happens during prophase (Mitosis)
- Chromatin fibres coil and condense
- Nuclear membrane begins to break down
- Chromosomes shorten and thicken
- Centrioles divide into two and move to opposite ends of cell - spindle formed
- Nuclear envelope disappears
What happens during Metaphase (Mitosis)
- Chromosomes moved by spindle fibres to form plane in centre of the cell, Metaphase plate
What happens during anaphase (Mitosis)
- Centromeres holding the pair of chromatids in each chromosome divide
- Chromatids moving towards poles, dragged by centromeres the the liquid cytosol
What happens during telophase (Mitosis)
- Chromatids reach poles + now called chromosomes
- Two new sets of chromosomes assemble at each pole, nuclear envelope reforms
- Chromosomes start to uncoil and nucleolus is formed
What happens during cytokinesis?
Actual division of two cells
Cytoplasm and membrane divide
Why is mitosis important?
- Asexual reproduction, offspring produced
- Growth
- Repair (when cells are damaged, replaced)
e.g. red blood cells + skin cells regularly replaced by new cells
What happens during meiosis
- 4 daughter cells which are not identical produced
- Have half the number of chromosomes as parent cell : haploid
Why is meiosis important?
- Takes place in sex organs
- Gametes are produced here
- Important to have genetically different gametes
- Promote genetic variation and allow for Natural Selection to take place
Prophase 11
- Chromosome condense and become visible again
- Nuclear envelope breaks down and spindle formation
Metaphase 11
- Individual chromosomes assemble on metaphase plate
- Independent assortment and more genetic variation
Anaphase 11
- Chromatids of individual chromosomes pulled to opposite poles after division of centromeres
Telophase 11
- As telophase in mitosis
- Chromosome uncoil and form chromatin again
- Nuclear envelope reforms
- Nucleolus becomes visible
What is independent assortment?
- Process where the chromosomes move randomly to separate poles during meiosis
What is crossing over?
- Exchange of DNA between paired homologous chromosomes
What is a homologous chromosome?
- Paired chromosomes
What is an allele?
- Alternative forms of a gene occupying a position on a chromosome
Examples of specialised animal cells
- Erythrocytes (biconcave, no nuclei, flexible)
- Neutrophils (multi-lobed nucleus can squeeze through, many lysosomes)
- Sperm cells (flagella, mitochondria, acrosome containing digestive enzymes)
Examples of specialised plant cells
- Palisade cells (absorb light, packed, vacuole is large turgor pressure, chloroplasts move)
- Root hair cells (at surface, long extensions)
- Guard cells (lose water during day, change shape prevent further water loss)
4 main categories of tissues in animals
- Nervous tissue (transmission of electrical impulses)
- Epithelial cells (cover body surface)
- Muscle tissue (adapted to contract)
- Connective tissue (transport + joining)
Different tissues in plants
- Epidermis tissue (cover plant surfaces)
- Vascular tissue (transport of water + nutrients)
Stem cell potency
- Totipotent (differentiate into any type and may become a whole organism)
- Pluripotent (form all tissue cells not whole organisms)
- Multipotent (range of cells within a certain type of tissue)
