1.6 Cell division Flashcards
what is the point of mitosis and what happens as “prep”
nucleus of a eukaryote divides to form two genetically identical nuclei.
before - DNA is replicated in interphase
used - embryonic developement, growth, tissue repair, asexual reproduction
what is the difference between a sister chromatid and a chromosome?
what is interphase?
- longest period and very active - most metabolic processes occur here
- DNA replication and protein synthesis only happens during interphase
- number of mitochondria increase and choloplasts
- cell walls expands as cellulose is synthesized
3 parts
- G1 - growth and organelle replication
- S - dna replication
- G2 -more growth, increase energy storage, DNA checked for errors
- G0 - leave cell cycle, can be temporary or permant e.g. specialised cells, damaged DNA
checkpoint here as to if cell is large enough to replicate
how are chromosomes’ size reduced
supercoling or condensing occurs during the first stage of mitosis using repeated coiling
in eukaryotes histone proteins become assosciated with the DNA using enzymes
what is prophase?
- chromosome begin to fatten and coil
- supercoiling
- nucleolus breaks down
- MTOC microtubule organising center grows microtubules which form a spindle shape aray that links the poles to their centre
- end of prophase nuclear envelope breaks down
what is metaphase?
- microtubules grow and attach to centromeres on chromosomes
- two attachment areas on each centromere
- microtubules put under tension to see if attachment is correct so microtubules are shortened at the centromere
- if attachment is correct chromosomes remain on equator of cell
what is the order of the phases?
what is anaphase?
- centromere divides so sister chromatids are formed
- spindle microtubules pull these towards the cell’s poles and they are now called daughter chromosomes
what is telophase
- chromatids have reached poles and are now called chromosomes
- pulled into tight group around the MTOC
- spindles disintegrates
- nuclear membrane reforms
- chromosomes uncoil and nucelolus forms
–> now cytokinesis
what is the mitotic index
used to work out how rapidly tissue is dividing e.g. is it a tumour
formula is
number of cells in mitosis/total number of cells
cytokinesis in animals
the plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow. A contractile ring of protein inside the plasma membrane accomplishes this.
teh proteins are actin and myosin - similar to the protein used to contract a muscle
when furrow reachs centre the two cells pinch apart
cytokinesis in plants
vesicles are moved to the equator where they fuse and form a tubular structure along the membrane. With the fusion of more vesciles these tubular structures fuse together. They form two layers of membrane along the equator. They connect to teh cell walls of the cell.
the plant then deposits pectin etc by exocytosis between the double membrane. The middle lamella is formed which links the new cell walls. Both cells then bring cellulose to the equator and deposit it next to the middle lamella. Each cell therefore is building a cell wall.
what are cyclins?
a group of proteins that ensure that the cell completes each stage of the cycle at the correct time and moves on only when appropriate.
the bind to enzymes called cyclin-dependent kinases which then become active and attach phosphate groups to other proteins in the cell. This attachment of phosphate triggers teh other proteins to become active and carry out tasks as required by that stage in the cell cycle.
4 main cyclins
- if cell does not have a threshold conc of the cyclin the cell will not progress –> CONTROLS CELL CYCLE
in image
- G1 cyclin - move from G0to G1 and G1 to S phase
- cyclin E or G1/ cyclin preps DNa for replication in S phase
- cyclin A / S cyclin activates DNA replication
- cyclin B /Mcyclin promtoes teh assembly of the mitotic spindles / preps cytoplasm for mitosis
what are tumors?
tumors are abnormal cells that can grow anywhere at any times. sometimes the cells adhere to each other and do not invade other cells or move to other parts fo the body. –> benign
others become detached and devlop secondary tumors - malignant - cause the disease cancer - carnimoas are malignant tumours
carinogens
- some viruses
- mutagens e.g
- chemical
- radiation e.g. xrays
oncogenes are genes that can become cancer causing after mutations. they are involved in regulating cell cycle. Therefore cancer divide uncontrollabley
need many mutations in one cell for it to be a tumour cell. have a primary tumour - first cells. Metastatis is the movement of the primary tumour cells to set up the secondary tumour in other boyd parts.
smoking and cancer how do they relate
correlation - the more cigs per day teh higher risk of cancer
even if you stop, still high death rate
cancers of
- mouth
- pharynx
- larynx
- lung
- esophagus
- stomach
- kidneys
- bladder
- pancrease
- cervix
20 of chemicals in cigs are proven carcinogens
