3.2.2 All Cells Arise From Other Cells

cell cycle

1) mitotic phase - mitosis and cytokinesis

2) G1 phase - cellular contents (excluding the chromosomes) are duplicated

3) S phase - each of the 46 chromosomes are duplicated

4) G2 phase - the cell ‘double checks’ duplicated chromosomes for error, making any needed repairs

mitosis stages -interphase

DNA replication, cell growth, organelles duplicate

-prophase

chromosomes condense and become visible, centrioles migrate to poles, spindle fibres develop, nuclear envelope breaks down and nucleolus disappears, chromosomes appear as 2 chromatids joined at centromere

metaphase

chromosomes attach to spindle fibres at centromere, chromosomes line up along the equator because the spindle fibres shorten

anaphase

centromeres divide, sister chromatids are pulled to opposite poles by spindle fibres - will be V-shaped as being pulled apart at centromeres

telophase

chromosomes unwind/decondense, nuclear envelope reforms, spindle fibres disintegrate

cytokinesis

cytoplasm splits to create 2 separate cells, cell membrane is pulled inwards creating a furrow which deepens and fuses to form 2 individual cells

cell cycle graph

-mass of DNA doubles during interphase

-then when mitosis occurs, mass of DNA halves

-then cell cycle repeats

how is cytokinesis different in plants?

vesicles form membrane structures down the centre of the cell then fuse together to form 2 individual cells

mitotic index formula

number of cells in mitosis / total number of cells in field of view (x 100)

cancer + treatment of it

uncontrollable division of abnormal cells lead to tumours (benign and malignant)

treatment - block part of cell cycle, 1) prevent DNA replication, 2) inhibit metaphase by interfering with spindle formation

binary fission

-in prokaryotic cells

1) circular DNA and plasmids replicate

2) cytoplasm divides to produce 2 daughter cells

3) each daughter cell has a single identical copy of circular DNA and a variable number of copies of plasmids

viral replication

-cannot undergo cell division and replicate using host cells

1) attachment proteins attach to receptors

2) virus injects nucleotides

3) host cell replicates the nucleic acid

4) host cell produces viral components

5) virus is assembled and replicated