Cell Division, Cell Diversity And Cellular Organisation Flashcards
what is the cell cycle
regulated cycle of cell division with intermediate growth phases
what are the stages of the cell cycle
- interphase
- mitosis or meiosis ( nuclear division )
- cytokinesis ( cytoplasmic division )
what happens during interphase
G1 - cell synthesis proteins for replication - tubulin for spindle fibres & cell size doubles, organelles replicate, cell increases in size
S - DNA replicates, chromosomes consist of 2 sister chromatids joined at the centrosome
G2 - cell continues to grow in size, energy stores increases, and duplicated dna is checked for errors
purpose of mitosis
produces two genetically identical daughter cells for
- asexual reproduction
- growth
- tissue repair and replacement
what are the stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase
chromosomes condense, shorten and thicken to become visible - 2 sister chromatids joined at the centrosome in an X shape
centrioles move to opposite poles of the cell in order to form mitotic spindle fibres
nuclear envelope and nucleolus disintegrate so the chromosomes are free in the cytoplasm
What happens during Metaphase
Chromosomes are moves by spindle fibre and align up along the centre of the cell called the metaphase plate and are held in position
What happens during Anaphase
Spindle fibres contract and the centromeres start to divide.
Sister chromatids are pulled to opposite ends of the cell.
Distinct V shape formed due to centromeres being dragged through liquid cytosol by the spindle fibres
Spindle fibres disintegrate
What happens during Telophase
Chromosomes decondense and become invisible again
Nuclear envelope forms around each set of chromosomes
What happens during cytokinesis
cell membrane cleavage furrow forms - the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming 2 separate cells
How are checkpoints used to control the cell cycle
Ensure damaged cells do not progress to the next stages of the cell cycle. Check for DNA damage, if the cell has grown to the right size, whether it has enough nutrients and if chromosomes are in the right position.
G1 Checkpoint
At the end of the G1 Phase, before entering the S phase
Cell checked for: cell size, nutrients, growth factors, and DNA damage
G2 Checkpoint
At the end of the G2 Phase, before entering mitosis.
Cell checked for: Cell size, DNA replication and DNA damage
Spindle Assembly checkpoint/ Metaphase checkpoint
At the point in mitosis where all the spindle fibres should be attached to the centromeres
Check for: spindle fibre attachment to centromeres
What happens during cytokinesis in plants
Plant cells have cell walls so cannot form a cleavage furrow. Vesicles from the golgi apparatus begin to assemble in the same place as where the metaphase plate was formed. Vesicles fuse with eachother and the cell surface membrane, dividing the cell into 2. New section of cell wall then form along the new sections of membrane.
What happens if the cell wall was formed before the daughter cells seperated
They would immediately undergo osmotic lysis from the surrounding water
What are homologous chromosomes
Each chromosome in a homologous pair has the same genes at the same loci
What are Alleles
Different versions of the same gene - gene variants
Prophase 1
Chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and spindle formation begins, HOWEVER the homologous chromosomes pair up forming bivalents.
What is Crossing Over
Chromosomes are large molecules of DNA and moving them through the liquid cytoplasm as they are brought together results in the chromatids entangling
Metaphase 1
Same as Metaphase in mitosis except the homologous pairs of chromosomes assemble along the metaphase instead of the individual chromosomes
What is independent assortment
The orientation of each homologous pair on the metaphase plate is random and independent of any other homologous pair. The maternal or paternal chromosomes can end up facing either pole which results in many different combinations of alleles facing the poles - this results in genetic variation
Anaphase 1
The homologous chromosomes are pulled to the opposite poles and the chromatids stay joined to each other. Sections of DNA on ‘sister’ chromatids which became entangled during crossing over, now break off and rejoin - sometimes resulting in an exchange of DNA.
What is a chiasmata
The point at which the chromatids break and re-join
