Cell cycle, growth and division Flashcards
Why is the cell cycle important?
It maintains the integrity of the genetic information in the cell progeny by containing multiple checkpoints so that replication and segregation do not introduce any damaging mutations, or occur in an uncontrolled manner
What is the checkpoint in G1 that commits the cell to entering S phase known as?
The restriction point - important decision as it is irreversible and once passed, the cell is committed to cell division.
Gives cell the option of entering G0, which is a resting state that can be temporary or permanent
Outline the central molecular components of the cell-cycle control system in determining progression through the different phases of the cell cycle
Protein kinase family known as cyclin-dependant kinases (CdKs) whose activities rise and fall throughout cell-cycle dependant on cyclin levels.
(Cyclins were named after their constant cyclical formation and degradation in cells)
When levels of cyclin are high, it forms cyclin-CdK complexes which activate CdK
G1/S-cyclins activate CdKs which stimulate progression past restriction point
S-cyclins activate CdKs which stimulate chromosome duplication
M-cyclins activate CdKs which stimulate entry into mitosis (G2 to M)
Describe the phases of interphase
G1 - cell growth, high metabolic activity, commitment to cell division at restriction point
S - DNA replication
G2 - chromosome packaging and checking, synthesis of mitotic proteins
Describe the sequence of mitosis
Prophase - chromosomes begin to condense, nuclear envelope broken down, spindle migrates to poles
Metaphase - chromosomes aligned along equator of nuclear spindle
Anaphase - chromosomes separate into two separate but identical clusters, moving down spindle
Telophase - chromosomes in two clusters, in position to form daughter cell
What is the spindle composed of?
Microtubules, attached to kinetochore that links it to the centromere of each chromosome
What are asters?
Microtubules that are not associated with kinetochores that radiate from the centrioles as astral rays, and are key to correct positioning and orientation of the mitotic spindle apparatus
What is neoplasia?
Loss of cell-cycle checkpoints, leading to an accumulation of DNA damage and disorganisation
This will lead to heightened progression through the cell cycle and thus the proliferation of neoplastic cells
Fill out types of tumour sheet
Notability–>Revision–>biochem and med gen–>types of tumour
Describe the steps in meiosis 1
Normal S-phase, to create sister chromatids in diploid cell
In prophase, homologous chromosomes pair up (e.g. Chromosome 17 from mother and father) to form bivalents. Genetic recombination then occurs as segments of each homologue cross over and exchange genetic material
In metaphase, the bivalents line up along the equator of the spindle, and each chromosome is attached to one kinetochore (not two like in mitosis)
In anaphase, the bivalents are separated randomly
Thus, new gametocytes contain 23 replicated chromosomes (two sister chromatids), each from either the mother or the father in a random arrangement
Describe the steps of meiosis 2
no intervening S-phase, follows straight on from meiosis 1
sister chromatids are simply divided, a bit like in mitosis, although there are only 23 pairs of sister chromatids, not 46
Give examples of chromosome faults that can occur in meiosis
Non-disjunction event: where bivalents don’t separate in meiosis 1 or sister chromatids don’t separate in meiosis 2, leading to one of the daughter cells containing two copies of a chromosome and another containing none. If the former cell is fused with another gamete, the resulting zygote will have three copies of that chromosome (triploid). If the latter cell is fused with another gamete, the resulting zygote will have one copy of that chromosome (haploid)
Translocations + deletions during crossing over
Give examples of tissues which:
- continually grow after birth
- grow only to repair damage
- do not grow
- skin, gut epithelium - contain continually dividing stem cells as cells in these tissues are constantly dying/being damaged
- liver - cells only proliferate to regenerate liver when it is damaged
- neurons - they form new connections, but there is limited proliferation
What are the three routes by which growth factors can arrive at a cell?
Autocrine: GF produced by the cell to act on the same cell
Paracrine: GF produced by a cell in the same tissue as the cell it acts on, in other words, in close proximity
Endocrine: GF produced by a cell very far from the cell it is acting on. GF will travel through the blood stream to reach that cell.
Outline the general mechanism of action of a growth factor and explain how it leads to cell growth
- GF binds to transmembrane cell surface receptor by complimentary binding
- Membrane protein either has an intrinsic enzyme (e.g. kinase) domain intracellularly or is a G-protein coupled receptor linked to a secondary messenger with this enzyme domain
- Sets off a signal transduction cascade which reaches the nucleus, where transcription regulation factors are activated.
- Transcription activators will bind to enhancer sequences which will upregulate the expression of certain protein coding genes
- The proteins will stimulate the cell to pass into (from G0) or continue through (G1) the cell cycle
