1.6 Cell Cycles Flashcards
What must a cell do before it can divide?
- make new organelles
- copy DNA in DNA replication
- synthesise new proteins
- cell growth
What is a chromosome?
- a long, thin structure of DNA and protein in the nucleus of eukaryotic cells carrying genes
When can you see chromosomes?
- only become visible under a microscope when chromatin condenses prior to division
- sister chromatids attached by the centromere
What is the role of the telomere?
- act as a cap/buffer and prevents DNA degeneration
What are characteristics of supercoiled chromosomes?
- can’t perform usual functions
- easily segregated
- can be easily stained
- increase in size from 30nm to 500nm
What are the 3 stages of interphase?
G1: cell growth and proteins produced
S: synthesis and replication of sister chromatids
G2: more growth and new organelles made
Stages of mitosis
IPMAT + cytokinesis
Explain prophase
- chromosomes in replicated form - 2 sister chromatids joined by centromere and condensed giving a thicker, shorter appearance
- nuclear envelope and nucleolus break down
- centrosomes move to opposite poles of cell and a spindle starts to from
—> spindle fibres made from protein microtubule, tubulin
Explain metaphase
- centrosomes reach a pole
- chromosomes line up on the equator of the cell and attach to spindle fibres by their centromeres
Explain anaphase
- centromeres joining sister chromatids split as motor proteins walk along the spindle, causing chromosomes to be pulled apart as chromatids
- taken to opposite poles of the cell centromere first
Explain telophase
- separated chromosomes reach the opposite poles of the cell
- nuclear envelope forms around the 2 sets of duplicated chromosomes
- 2 identical nuclei form, and once cytokinesis occurs, 2 identical daughter cells are made
What is cytokinesis?
Division of the cytoplasm following divisin
How does cytokinesis occur in animal and plants?
Animal: constriction of the parent cell around the equator from the outside inward - cleavage furrows
Plant: droplets of cell wall material (cellulose deposit) form a cell plate across the equator of a parent cell from the centre outward
Significance of mitosis
Generic stability: 2 GI cells that are exact replicas of parents
Growth + repair: produce new cells, grow repair and replace, in adult mammals tissues (ie skin) are replaced daily
Asexual reproduction: unicellular organisms produce identical offspring - clones.
Explain the significance of mitosis in terms of damage and disease
- uncontrolled CD leads to tumours and therefore cancer ie tumour suppressor and proto-oncogenes
- cell cycle length is controlled by genes, so when they’re damaged the cell cycle is unregulated
- timely replacement of cells + tissue
Role of tumour suppressor and proto-oncogene genes
- tumour suppressor: slow and regulate CD, if mutate then don’t regulate so lead to tumour
- proto-oncogene: encourage cell growth and repair, mutate means don’t regulate so tumour forms
Drugs that treat cancer
Cisplatin: prevents DNA replication to halt tumour growth
Vinca alkaloids: inhibit metaphase by interfering with spindle formation
Ploidy level
The number of complete sets of chromosomes in an organism
- humans are diploid
- 1 = haploid
Explain meiosis 1
- PROPHASE 1: dna condenses and becomes visible, chromosomes arranged in homologous pairs (bivalent). Crossing over of non-sister chromatids may occur (wrap @ chiasmata and lead to genetic variation). Centrioles migrate to poles and spindle is formed as the nucleolus and nuclear envelope break down
- METAPHASE 1: bivalents line up along equator with spindle fibres attached to centromere. Position each other independently- independent assortment (GV)
- ANAPHASE 1: homologous pairs separated as microtubules pull chromosomes to opposite ends of spindle centromere first. Centromeres do not divide.
- TELOPHASE 1: chromosomes arrive at poles. Spindle fibres break down and nuclear envelopes form around 2 groups, and nucleolus reforms. (Some plant cells go to meiosis 2 without reformation)
Explain meiosis 2
- PROPHASE 2: centrioles separate and organise new spindle and right angle to old. Nuclear envelope and nucleolus break down.
- METAPHASE 2: chromosomes line up at equator which chromosomes attach to spindle fibre by centromere. Independent assortment occurs again
- ANAPHASE 2: centromeres divide and individual chromatids pulled to opposite poles centromere first, creating 4 groups of chromosomes with half the number of chromosomes of the parent cell
- TELOPHASE: nuclear membrane and nucleolus reforms around each group of chromosomes. Cytokinesis occurs. 4 gametes are made
Cells produced by meiosis are … and mitosis are …
- haploid
- diploid
What is the significance of producing haploid eggs?
Genetic variation via fertilisation of a zygote and restore diploid number
Explain diff between cells produced in mitosis and cells in meiosis
- 2 v 4
- diploid v haploid
- GI v GD
Importance of meiosis
- genetic variation due to genetically different cells
- restore diploid state as meiosis produce haploid
