D2.1 cell and nuclear division

Stages of the cell cycle

Interphase - G1, S - replication, G1

Mitosis

Cytokinesis - cell division

Mitosis

P - prophase - chromosomes condense and nucleus dissolves

M - metaphase - chromosomes align on the equator

A - anaphase - chromosomes pulled apart to the poles by spindle fibres

T - telophase - chromosomes are at the poles and nuclei reform

Mitotic index

Number of cells in mitosis / total number of cells

What affects how tightly DNA is bound around histones and controls expression

Acetylation and Methylation

Why do all daughter cells end up with different patterns of mum and dad cell DNA

Random assortment of bivalents (homologous pairs)

What is crossing over

The end sections of adjacent chromosomes can become tangled and can exchange genes meaning that the final version of that chromosome is not the same as the original copy.

How does cytokinesis occur

cells have a ring of contractile actin and myosin proteins that contract forming a cleavage furrow, splitting the cytoplasm, and eventually the fluid mosaic membrane pinches off

What must happen in cytokenisis

both cells must receive roughly equal distribution of organelles, must get at least one mitochondrion

What are examples of unequal cytokinesis

Oogenesis (formation of eggs and ovaries) - one of the cells at each stage fails to mature due to lack of organelles - and budding in yeast

Cell proliferation

Process used to make new cells for growth and repair through mitosis

What is an example of failed meiosis

Down’s syndrome

Cyclins

A group of cell regulatory proteins that control the cell cycle

What do cyclins do

interact with enzymes called cyclin dependent Kinases (CDKs) which trigger a cascade of phosphorylating and activating multiple enzymes

What is required for a cell to pass each checkpoint in the cell cycle

Threshold level of specific cyclin

Role of histones

support the structure of DNA and are responsible for the supercoiling

What is a proto-oncogene

Healthy genes that have the potential to become cancerous

What can cause Porto-oncogenes to turn into cancerous oncogenes

Mutation - gain of function - activated when they shouldn’t be

What can happen if tumour suppressor genes mutate

Uncontrolled cell division and growth of tumours

Benign tumour

Slow growing, non cancerous, non invasive - may be monitored by not always removed/targeted

Malignant tumor

Fats growing, can be invasive, can be surgically removed or targeted with radio/chemotherapy

Metastasis

small groups of cells break off the rapidly growing tumor and move around the body in the bloodstream or lymph.

Primary tumour

First tumour to grow

Secondary tumour

Cells that have metastasised from the primary tumour and settled somewhere else, forming a new tumour