Lecture 10: cell division and cancer Flashcards
why do somatic cells divide
growth and development, tissue renewal
What somatic cells don’t divide after maturity
muscle, nerve, brain cells. They just stay in interphase.
What are the 4 parts of the eukaryotic cell cycle
G (growth/gap) 1 , S, G2 and Mitotic (M) phase = mitosis + cytokinesis.
describe G1; whats happening and duration
cell metabolically active. duplication of organelles and cytostolic components. centrosome replication begins.
Where can nondividing cells exit the Cell cycle for G 0
from G1
describe S phase
Synthesis for DNA where DNA replication occurs by DNA polymerase, strands are separated at the H bonds holding nucleotides together, new strand of DNA synthesised opposite each of the old strands.
describe G2
Checks for correct DNA synthesis, preparing for Mitotic phase (synthesis of the proteins and enzymes required, gathering of reactants) replication of centrosomes is completed
What are the 5 steps of Mitosis in order
Prophase, metaphase, anaphase, telophase
What happens in prophase
Mitotic spindle forming, chromatin condensing to chromosomes. PM: The nuclear envelope breaks, chromosomes attach to microtubules
What happens in metaphase
Chromosomes line up in a metaphase plate
What happens in anaphase
sister chromatids separate (at the centromere) and over as the new chromosomes to pole
What happens in telophase
the cell nuclei form, spindles disappear, cleavage furrow
Cytokinesis is the process of
partitioning the cytoplasm into two daughter cells
Chromosomes are
two identical chromatids held together by a centromere.
we have 23 chromosomes from mum and 23 chromosomes from dad which mean that we are (haploid/diploid)
diploid
Where are the mitotic cycle checkpoints
G1/S transition, G2/M transition and M checkpoint
How does the regulation at G2 happen to make a mitotic clock?
MPF phosphorylates other proteins allowing mitosis to commence. However MPF can only form when enough cyclin has accumulated, which happens by the G2 phase which activates Cdk.
What is M-phase promoting factor made of
cyclin + cyclin dependent kinase
What does the G1 checkpoint check for and what happens if it doesn’t pass
undamaged DNA, cell size, nutrition and other signals (cyclins). If it doesn’t pass it may exit for G0 or stay rested at G1
What does the M checkpoint check during mitosis
that all the chromosomes are appropriately attached to spindles
Checkpoints rely on …
external signals such as growth factor via signal transduction pathways
IF checkpoints didn’t work
could result in uncontrolled growth - tumours, -> cancer
What causes cancer
acquired changes (effecting specific cells) and inherited DNA changes- increased susceptibility that alters protein function which can result in loss of cell cycle control.
What mutations in what genes result in cancer
mutations in Proto-oncogenes that stimulate cell proliferation render them active in the absence of growth factors.
The mutation of tumour suppressor genes makes them lose their ability to inhibit cell division
acquired change in DNA is from
viruses, UV damage, toxins, drugs
What are some tumor suppressing genes
TP53
3 different ways that proto-oncogene can be turned to an oncogene
mutation within gene results in hyperactive growth stimulating protein. Multiple copies of the gene at normal strength. Gene moved to new position produced under different control so excess produced.
Two examples of proto-oncogenes
Ras and Myc
how many somatic mutations are typically required for the generation of a cancer cell. Do these occur in both types
Multiple, yes
Describe the first meiosis
prophase (crossing over between homologous chromosomes) metaphase (tetrads line up) anaphase (homologous chromosomes separate, sister chromatids remain attached). Telophase (each cell has one of the replicated chromosomes)
meiosis II occurs in the daughter cells of meiosis I and forms
4 daughter cells with haploid number of chromosomes
Whats the difference between the meiosis and mitosis
It doesn’t occur in mitosis, in meiosis it occurs during prophase 1 along with crossing between non sister chromatids.
What are the sources of variations
independent assortment at metaphase, crossing over a prophase and fusion between two gametes.
