Cell Structure and Function - Cell Division and Cancer Flashcards
What is a Eukaryotic Cell?
cells that have a nucleus enclosed within membranes
What is Somatic cell division (Mitosis)?
When a diploid cell divides to form two diploid daughter cells (genetically identical to parent cell)
What is Reproductive cell division ( Meiosis)?
When a diploid cell divides to form four haploid cells (genetically DIFFERENT from the parent cell)
What are the reasons for somatic cell division/mitosis?
Growth and development, tissue renewal
Examples in the body were mitosis for cell growth is needed
Skin and blood cells
Examples of cells that do not/require little division
Muscle and Neuron cells
What phase do most cell spend the majority of their time?
G1 of interphase
What is interphase?
Metabolic phase of the cell
The cell obtains nutrients and metabolizes them, grows, reads its DNA, and conducts other “normal” cell functions
What are the three stages of interphase?
G1, S, G2
What is G0?
If cells do not divide they stay in G0 which means they do not progress past G1 of interphase
What is the G1 phase?
The phase of interphase where most cellular activity occurs (cell is metabolically active, duplicated organelles, centrosome replication begins)
How long is G1?
The duration of this phase depends on the cell but usually between 8-10 hours
(Maybe more or even less in some cases)
What is the S phase?
The phase of interphase where DNA is replicated
How long is the S phase?
8 hours
What is the G2 phase?
The phase of interphase where the cell prepares for M phase by synthesising proteins and enzymes, gathers reagents, replicates centrosomes
Also checks for correct DNA synthesis for the mitotic phase
What are the four stages of the mitotic phase?
PMAT
Prophase, metaphase, anaphase, telophase and cytokinesis
(Please make another two CELLS )
What is in the interphase? (Start of cell division images)
Made up of G1, S, G2
Chromosome are un-condensed
DNA exists as chromatin
Nuclear envelope is intact
What is the prophase stage?
Mitotic spindle forms (made of microtubules), chromatin condenses into chromosomes, nuclear envelope disappears and chromosomes begin to line up
What is in the metaphase stage?
Spindles are fully formed and condensed chromosomes align along the equator (M=iddle)
What is the anaphase stage?
Chromosomes (sister chromatids) separate, pulled by microtubules attached at the centromere to either pole of the cell
This is due to the shortening of the mitotic spindle fibres attached to each sister chromatid
What occurs in Telophase and Cytokinesis?
When the nuclear envelope reforms in the two daughter cells and they cleave apart (cleavage furrow forms, the indentation of the cell membrane as cell division occurs)
When two independent nuclei have formed, mitosis is complete.
What are sister chromatids?
refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere
What is the centromere?
Part of chromosome that attaches the two sister chromatids
What does diploid mean?
Full amount of chromosomes in a cell (46 in humans)(2n)
What does haploid mean?
Half the amount of chromosomes in a cell (23 in human gametes)(n)
What are the mitotic cell cycle checkpoints?
G1, G2 and M
What is the G2 checkpoint?
Assesses if the cell is ready to divide
What is the G1 checkpoint
Checkpoint where the DNA is checked for damage, cell size and nutrition are checked, and the cycle proceeds if the appropriate signals are present
What is the M checkpoint?
Checks for the mitotic spindle attachment
Why are cell cycle checkpoints important?
They keep cells in a certain stage or stimulate progression into the next staged if the cells are deemed PERFECT
If not done, could lead to cancer
What is cyclin?
A protein whose levels fluctuate throughout the cell cycle and regulates the mitotic cell cycle
It accumulates towards G2 and degrades after mitosis
What is cyclin dependent kinase (cdk)
An enzyme that is activated when bound to cyclin
It phosphorylates proteins
What is M-phase promoting factor (MPF)?
A cyclin/cdk complex that is key to the G2 checkpoint, phosphorylating proteins and hence allows mitosis to commence
What is MPF made up of?
Cyclin and cdk
What do checkpoints rely on?
Cell signalling (Lots of signals contribute to checkpoints in the profession of the cycle)
What are mutations?
A permanent, random change to the base sequence of DNA
What is translocation
Common type of mutation in cancer
Where a chromosome breaks and a portion of it reattaches to a different chromosome
What are acquired changes in DNA?
Often due to viruses, drugs, treatment of UV damage
Only in certain cells, not every cell in the body
Can occur is a mistake is made as DNA copies itself during cell division
What are inherited changes in DNA?
Are mutations inherited from parents.
Affect all cells and affect susceptibility genes which are genes that are more likely to develop into cancer
What are proto-oncogenes?
Are genes that stimulate cell proliferation/cell division
ACCELERATOR
What is an oncogene?
When a mutation occurs to a proto-oncogenes they turn into an oncogene
This results in the formation of a hyperactive growth stimulating protein
Examples of proto-oncogenes
Ras - GTPase protein that is susceptible to mutations that lead to tumours
Myc - A proto-oncogene that codes for a transcription factor
What are tumour supressor genes?
Produce a normal growth inhibiting protein so that cell division remains under control
What happens to a tumour supressor gene when it is mutated?
Produces a defective/non-functioning protein so cell division goes out of control and causes cancer
Examples of tumour supressor genes
TP53, BRCA 1, BRCA 2
What is a tumour?
Groups of abnormal cells that form lumps or growths
What are polyps?
Small begnign growths that can develop into adenoma
What is an adenoma?
A large begnign tumour formed from glandular structures in epithelial tissues
What is a carcinoma?
A cancer developing from epithelial cells
What is meiosis?
When a diploid cell divides into four haploid cells
Where does meiosis occur?
In the gonads (ovaries and testes)
What is fertilisation?
When two gametes come together to produce a diploid cell
What is Meiosis I?
The pairs of homologous chromosomes are separated, making the cell go from diploid to haploid
What are the stages of Meiosis I?
PMAT 1: Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokinesis
What is prophase 1?
Synapsis occurs
recombination
tetrads form
What is synapsis?
Pairing of homologous chromosomes (they come together)
What is a tetrad?
The four chromatids in a pair of homologous chromosomes
What is Recombination/crossing over?
When non-sister chromatids exchange sections
What is a chiasmata?
The point of contact between 2 chromatids
The point at which genetic material can be exchanged between chromatids
What is metaphase I?
Homologous pairs of chromosomes line up randomly along the metaphase plate
What is anaphase I?
Spindle fibres shorten
Homologous chromes are pulled apart to opposite poles of the cell
Sister chromatids remain attached to each other
What is meiosis II?
Separates sister chromatids in a similar way to mitosis
What is the metaphase plate?
Plane midway between the two poles of the cell, is where chromosomes line up during metaphase
Differences between mitosis and meiosis in the number of divisions?
Mitosis = 1 division (including PMAT) Meiosis = 2 divisions (including PMAT)
Differences between mitosis and meiosis in synapsis of homologous chromosomes?
Does not occur in mitosis
In meiosis occurs in prophase 1
EDIT THIS CARD LATER
Differences between mitosis and meiosis in number of daughter cells and their genetic composition?
Mitosis produces 2, diploid, daughter cells that are genetically identical to the parent cell (both have 46 chromosomes)
Meiosis produces 4, haploid, daughter cells that are genetically different from the parent cell and each other due to crossing over, independent assortment etc
What is independent assortment and how much variation does it produce ?
Homologous pairs line up randomly upon the metaphase plate during metaphase 1.
>8 million combinations possible
When does crossing over occur and how much variation does it produce
At prophase 1
Approximately 1-3 crossover events per pair
How much variation does fertilisation/fusion produce?
> 223 combinations possible
