1.6 : Cell Division Flashcards
what are the phases of cell division?
G1, S, G2 (interphase) Mitosis, Cytokinesis
what occurs in G1?
the first phase of growth :
- cytoplasm is active
- new organelles are formed (synthesis of new organelles in cytoplasm)
- intense biochemical activity of growing cell
- accumulation of energy store before nuclear division occurs again.
what occurs during the synthesis (S) phase?
synthesis of the DNA :
-chromosomes are replicated –> chromatids formed (two sister chromatids = replica of chromosome)
(chromatids remain attached until they divide again during mitosis).
what occurs in G2?
second phase of growth :
- more growth of cell
- preparation for mitosis
- increase in amount of cytoplasm
what phases are there in mitosis?
- prophase
- metaphase
- anaphase
- telophase
how does cell division occur in bacteria?
-binary fission –> replication starts at specific gene (the one that translates into the replication-triggering enzyme.
what occurs during the interphase? what type of chromosome is dispersed in this phase?
- Chromosomes are actively involved in protein synthesis –> copies of information of a particular gene / group of genes in the form of mRNA –> taken for use in the cytoplasm (ribosomes in cytosol) –> assemble proteins from amino acids –> these are combined in sequences dictated by the information from the gene –> assembled in the form of mRNA.
- compact chromosome - dispersed in interphase = chromatin (only visible during mitosis)
what does the nucleolus contain?
contains proteins & mRNA = site of synthesis of ribosomes, which then are dispersed into sytoplasm.
how is the cell cycle controlled? how?
- regulated by a molecular control system.
- the cell cycle contains many key checkpoints where signals operate –> these have to be overridden for the cell cycle to continue (key checkpoints at G1, G2, M)
what occurs in the G2 checkpoint?
a ‘continue’ signal is received –> allowing the cell to go to M (mitosis) and C (cytokinins)
what are the molecular control substances in the cytoplasm of cells?
Kinase and Cyclin.
what are Kinases? why are they referred to as CDK?
- enzymes that activate or inactivate other proteins
- kinases are activated by specific cyclins = cyclin-dependent kinases (CDK)
what occurs when the cyclin concentration in the cytoplasm increases?
(cyclin concentration changes constantly)
increases –> combine with CDK molecules –> forms a complex –> functions as a mitosis - promoting factor (MPF)
what occurs when MPF accumulates?
MPF accumulates –> it triggers chromosome concentration & fragmentation of the nuclear membrane and spindles
what occurs in mitosis?
- cell division occurs where the nucleus divides first.
- chromosomes (present in the form of chromatids) –> are separated (pulled apart by spindles) –> then they are accurately distributed between two daughter nuclei.
what is metastasis? (cancer)
when the tumor cells break away from the primary tumour, and are carried to other parts of the body causing a secondary tumour to form.
when does cancer arise?
cancer arises when the cell cycle operates without its normal control, causing repeated division of cells by mitosis.
what is a mutation?
a change in the amount or chemical structure of DNA of a chromosome.
what is the name for a ‘cancerous’ and ‘non-cancerous’ tumour?
- malignant (cancerous)
- benign (non cancerous)
what is a benign tumour?
a tumour that absorbs nutrients, enlarges and may compress surrounding tissues but doesn’t spread from the site of initiation.
what is a malignant tumour?
a tumour that consists of cells that secrete signals triggering the growth of blood and lymph vessels to serve the tumour cells at the expense of other tissues.
what are causes of DNA damage?
- ionising radiations.
- non-ionising radiations.
- chemicals (tobacco smoke & asbestos)
- virus infection
- diet.
what are proto-oncogenes?
genes that code for the proteins that stimulate the cell cycle.
what are tumour-suppressing genes?
genes that code for proteins that stop a cell cycle if damaged DNa is copied.
