AS Level - The Mitotic Cell Cycle

chromosomes

structure made from DNA and histones, found in the nucleus of a eukaryotic cell
made from two identical chromatids held by the centromere
DNA is 2nm wide and 1.8m long

gene

one unit of inheritance coding for one polypeptide

DNA

double helix
antiparallel
complementary base pairing

DNA structure

acidic so interacts with basic histone proteins
nucleosome is formed by a cylindrical core of eight histone molecules with 146 base pairs of DNA (11nm wide and 6nm long)
nucleosomes line up to form a fibre (10nm wide)
fibre is coiled to form chromatin

chromatin

tightly coiled DNA
euchromatin is loose and is transcribed
heterochromatin in tight and contains inactive genes

mitosis

the division of a nucleus so that the two daughter cells have exactly the same number and type of chromosomes as the parent cell
prophase, metaphase, anaphase, telophase

importance of mitosis

production of genetically identical daughter cells
growth
cell replacement
repair of tissues
asexual reproduction

the mitotic cell cycle

interphase, mitosis, cytokinesis

interphase

G1, S phase, G2

G1

gap
cell absorbs nutrients and grows
proteins and organelles are synthesised
ATP stockpiled

S phase

semi-conservative DNA replication

G2

gap
centrioles replicate
cell grows
spindle fibres formed from microtubules

checkpoints

after G1 to ensure sufficient ATP
after G2 to ensure correct DNA replication
after metaphase to ensure enough spindle fibres are attached to each kinetichore

prophase

nuclear envelope disintegrates
chromosomes formed by supercoiling of chromatin
chromosomes appear as sister chromatids
centrosomes move to opposite ends of the cell

metaphase

spindle microtubules attach to chromosomes' kinetichores
chromosomes line up across the equator

anaphase

centromeres split
spindle fibres contract
sister chromatids pulled centromere first to opposite poles
spindle fibres detach

telophase

daughter chromosomes unwind
spindle fibre remains break down
new nuclear membranes form

cytokinesis

cytoplasm divides
in animal cells, the cleavage furrow seals off the plasma membrane
in plant cells, the Golgi body produces a cell plate between the nuclei which becomes the cell wall

telomeres

repeated DNA sequences at the ends of chromosomes that shorten with each round of cell division
rich in guanine and cytosine
telomerase adds extra bases during each cycle to allow for continued replication

stem cells

a cell that can divide an unlimited number of times by mitosis and has the potential to differentiate or remain a stem cell

stem cell uses

cell replacement and tissue repair
totipotent, pluripotent or multipotent
treat disease or injury

tumours

uncontrolled cell division forms a mass

cancer

disease caused by dysfunctioning control mechanisms regulating cell divisions so abnormal cells proliferate

mechanism of cancer

mutations to proto-oncogenes and tumour suppressor genes
uncontrolled cell division
growth of cell mass
blood capillaries grow
no apoptosis
metastasis occurs as tumour cells spread

causes of cancer

carcinogens
hereditary
lifestyle
ionising radiation

mitosis photomicrograph

prophase photomicrograph

metaphase photomicrograph

anaphase photomicrograph

telophase photomicrograph