cell cycle, mitosis, binary fission, cancer Flashcards
What is a chromatin?
unravelled and condensed structure of DNA associated with a histone. Found in the interphase this can be actively transcribed
(Unravelled DNA on a histone)
What’s a chromatid?
One of two strands of copied chromosome, referred to as sister chromatids.
genetically identical
(2 identical chromosomes still make 1 chromosome)
What’s a chromosome
A long DNA molecule associated with a protein
What’s a homologous pair
A pair of chromosomes not identical but contain the same alleles
why is mitosis important in eukaryotic cells
required for growth, repair of tissues and replacement of old cells
What are the stages of the cell cycle
growth 1 = G1
synthesis = S
growth 2 = G2
mitosis = M
what happens in G1
cell grows and performs normal pro
new organelles are synthesised
What happens in S
DNA is replicated. Chromosomes are now compromised of 2 sister chromatids
What happens in G2
Cell continues to grow, genes are transcribed and energy stores are are built up in preparations for mitosis
What happens in M
The nucleus divides in 4 main phases
What is interphase
interphase is the first stage in mitosis which is G1,S and G2 in the cell cycle
what happens in prophase of mitosis
- chromosomes condense and coil becoming visible
- centrioles move to opposite ends/poles of the cell
- centrioles begin to form the spindle
- nucleolus disappears and the nuclear envelope breaks down
chromosomes are comprised of 2 chromatids at this point
what is the metaphase in mitosis
- The spindle fibres attach to the centromere of the chromosomes
- The chromosomes are pulled and are lined up along the equator
what happens in Anaphase of mitosis
- microtubules that make up the spindle are pulled back towards the centrioles
- centromeres divide and sister chromatids are pulled to opposite sides
- each chromatid is now referred to as a singular chromosome
What happens in the telophase stage of mitosis
Events of prophase are reversed
- 2 new nuclear envelopes form
- spindle breaks down
- DNA uncoils and chromosomes ‘disappears’
What happens in cytokinesis
cell divides
genetically identical daughter cells, receiving half of the organelles.
( Diploid cells )
What is a tumour
A mass of cells caused by uncontrolled mitosis. They usually have a low blood supply
what is a benine and malignant tumor
benine - slow growing. Don’t spread, less harmful but no necessarily harmless
malignant - Fast growing, can spread ( metastasis ). Generally more harmful than benine, referred to as cancer
what are proto- oncogenes
Encode proteins that stimulate cell division, inhibit differentiation and halt cell death
results in the normal growth of cells
Can mutate to form oncogenes
What are oncogenes
They cause uncontrolled cell division by triggering DNA replication when not needed
can cause growth factors to become abnormally high, causing uncontrolled division
what are tumour suppressor genes
what happens if mutations occur
encode proteins that stop cell division. may stimulate apoptosis if DNA becomes damaged
if mutations occur it will prevent the genes from stopping cell division
What does chemotherapy do to treat cancer
- interrupts DNA replication
- inhibits metaphase by interfering with the spindle formation
What happens in binary fission?
and what to
Happens to bacterial cells who have no nucleus but still divide.
- Copying of DNA on the circular chromosome at the origin of replication. Plasmids are also being replicated
- 2 origins move to separate ends of the cell
- The cell gets longer and the two newly formed chromosomes are now separated
- Once the chromosomes are at opposite ends the cytoplasm divides and produces 2 daughter cells
How do you work out the mitotic index
. Count cells in mitosis in field of view
. Divide this by the total number of cells in field of view
. Repeat 5 times
What is the mitotic index and what is the equation?
Mitotic index = measure of cellular proliferation (to make more of)
number of cells with visible chromosomes/total number of cells
must be a decimal
what is the fixed position of a gene on a DNA molecule
locus or loci
what are carcinogens
Any agent that may cause cancer e.g. tobacco, UV light
