1.6 Cell Division Flashcards
what is interphase?
the stage in the development of a cell between 2 successive divisions
an active period in the cell cycle when many metabolic reactions occur
what are the 3 stages of interphase?
G1 - first intermediated gap stage in which the cell grows and prepares for DNA replication
S - synthesis stage in which DNA is replicated
G2 - second intermediate gap stage in which the cell finishes growing and prepares for cell division
what is M phase?
the period of the cell cycle in which the cell and contents divide to create 2 genetically identical daughter cells
what are the two broad stages of cell M phase?
mitosis - nuclear division whereby DNA is separated into 2 identical nuclei
cytokinesis - cytoplasmic division, whereby cellular contents are segregated and the cell splits into 2
what events need to occur in interphase to prepare the cell for successful division? (6)
DNA replication - DNA is copied during S phase
Organelle duplication - organelle must be duplicated for twin daughter cells
Cell growth - cytoplasmic volume must increase prior to division
Transcription/translation - key proteins and enzymes must be synthesised
Obtain nutrients - vital cellular materials must be present before division
Respiration (cellular) - ATP production is needed to drive the division process
what are the characteristics of chromatin? (3)
- DNA is loosely packed within the nucleus as unravelled chromatin
- this unravelled form, DNA is accessible to transcriptional machinery and so genetic information can be translated
- DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase
what are the characteristics of chromosomes? (3)
- DNA is temporarily packaged into a tightly wound and condensed chromosome prior to divisions (via supercoiling)
- in the condensed form, the DNA is able to be easily segregated however, is inaccessible to transcriptional machinery
- DNA is organised as chromosomes during the process of mitosis (condensed in prophase, decondensed in telophase)
what are the differences and similarities between chromosomes and chromatins? (4)
- chromosome is condensed form of DNA which is visible during mitosis (via microscopy)
- as the DNA is replicated during the S phase of interphase, the chromosome will initially contain 2 identical DNA strands
- these genetically identical strands are called sister chromatids and are held together by a central region called centromere
- when these chromatids separate during mitosis, they become independent chromosomes each made of a single DNA strand
what is mitosis and the stages?
the process of nuclear division whereby duplicated DNA molecules are arranged into 2 separate nuclei
prophase, metaphase, anaphase, telophase
what occurs in interphase? (4)
- DNA is present as uncondensed chromatin (not visible under microscope)
- DNA is contained within a clearly defined nucleus
- centrosomes and other organelles have been duplicated
- cell division is enlarged in preparation for division
what occurs in prophase? (4)
- DNA supercoils and chromosomes condense (visible under microscope)
- chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
- paired centrosomes move to the opposite poled of the ell and form microtubule spindle fibres
- the nuclear membrane breaks down and the nucleus dissolves
what occurs in metaphase? (3)
- the microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
- microtubules depolymerization causes spindle fibres to shorten in length and contract
- this causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)
what occurs in anaphase? (3)
- continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
- once the chromatids separate, they are considered an individual chromosome
- the genetically identical chromosomes move to the opposite poles of the cell
what occurs in telophase? (4)
- once the two chromosome sets arrive at the poles, spindle fibres dissolve
- chromosomes decondense (no longer visible under light microscope)
- nuclear membrane reform around each chromosome set
- cytokinesis occurs concurrently, splitting the cell into 2
what is cytokinesis? (2)
- the process of cytoplasmic division, whereby the cell splits into 2 identical daughter cells
- cytokinesis occurs concurrently with the final stages of mitosis (telophase) and is different in plant and animal cells
how does cytokinesis occur in animal cells? (4)
- after anaphase, microtubule filaments form a concentric ring around the centre of the cell
- the microfilaments constrict to from a cleavage furrow which deepens from the periphery towards the centre
- when furrow meets in the centre, the cells becomes completely pinched off and two cells are formed
- this separation occurs from the outside and move towards the centre, it is described as centripetal
how does cytokinesis occur in plant cells? (4)
- after anaphase, carbohydrate-rich vesicle form in a row at the centre of the cell (equatorial plane)
- the vesicle fuse together and an early cell plate begins to form within the middle of the cell
- the cell plate extends outwards and fuses with the cell wall, dividing the cell into 2 distinct daughter cells
- because this separation originates into the centre and moves laterally, described as centrifugal
what is mitotic index?
measure of the proliferation status of a cell population
- mitotic index may be elevated during processes that promote division, such as normal growth or cellular repair
what can mitotic index be used for?
can function as an important prognostic tool from predicting the response of cancer cells to chemotherapy
how can mitotic index be calculated?
is the ratio between the number of cells in mitosis and total number of cells
can be determined by analysing micrograph and counting the relative number of mitotic cells vs non-dividing cells
what are cyclins?
a family of regulatory proteins that control the progression of the cell cycle
what do cyclins acivate?
cyclin dependent kinases which control cell cycle processes through phosphorylation
how do cyclins work? (3)
- when a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation
- the phosphorylated target protein will trigger some specific event within the cell cycle
- after the event has occurred, the cyclin is degraded the CDK is rendered inactive again
how are cyclin concentrations tightly regulated in order to ensure that the cell cycle professes in a proper sequence? (2)
- different cyclins specifically bind to, and activate different classes of cyclin dependent kinases
- cyclin levels will peak when their target protein is required for function and remain at lower levels at all other times
what are tumours (or cancers)?
abnormal cell growths resulting from uncontrolled cell divisions and can occur in any tissue organ
what are mutagens?
mutagen is an agent that changes the genetic material of an organism
what three things can mutagens be in origin?
physical - sources of radiation including X-rays (ionising), ultraviolet (UV) and radioactive decay
chemical - DNA interactive substances including reactive oxygen species (RPS) and metals
biological - viruses, certain bacteria and mobile genetic elements
what are mutagens that lead to the formation of cancer called?
carcinogens
what are oncogenes?
a gene that has the potential to cause cancer
what are the 2 basic classes of gene most cancers are caused by?
proto-oncogenes - code for proteins that stimulate the cell cyles and promote cell growth and proliferation
tumour suppressor genes - code for proteins that repress cell cycle progression and promote apoptosis
how can a proto-oncogene become a cancer-causing oncogene?
when a proto-oncogene is mutated or subjected to increased expression
what are tumour suppressor genes normal function?
prevents cancer
what two things may tumour cells be?
benign - remain in original location
malignant - spread and invade neighbouring tissue
what are secondary tumours made of?
made up of the same type of cell as primary tumours
what kind of links between smoking and the incidence of cancers?
strong and contain 4,000 chemical compounds over 60 which are carcinogenic
- strong positive correlation between the frequency of smoking and the development of cancer
increases the risk of ver a dozen other cancers including mouth, stomach, over, pancreas and bowel
