Cell Cycle and Mitosis Flashcards
1
Q
Significance of mitosis
A
- Increase in cell number for growth and development of embryo
- Repair of damaged or worn out cells
- Asexual reproduction to produce genetically identical offsprings (have all the advantages of the parents in mastering the same habitat, and any disadvantages too)
2
Q
Explain the need for the production of genetically identical cells.
A
- Genetic stability (each daughter cell produced by mitosis has a full set of chromosomes, identical to those of the parent cell so there is no variation in genetic information)
- In the growth of multicellular organisms, it is essential that all cells carry the same genetic information (the same chromosomes) as the existing cells of the organism
- When repair of damaged tissues or worn out cells occurs, the new cells must be exact copies of the cells being replaced
3
Q
Interphase
A
longest part of cell cycle where DNA replication occurs
3
Q
Prophase
A
- Chromosomes increasingly shorten and thicken by supercoiling to become 2 chromatids held together at the centromere (DNA must become tightly packed for the chromosomes to move about and to separate)
- Nucleolus gradually disappears
- Nuclear envelope breaks down
- In animals, the centrosome (absent in plants) divides and the 2 centrioles replicate (make copies) to form 2 centrosomes
4
Q
Metaphase
A
- 2 centrosome move to opposite ends of the cell
- Microtubules of the cytoplasm start to form into a spindle, radiating out from the centrioles
- Each pair of chromatids is attached to a microtubule of the spindle and is arranged at the equator of the spindle
5
Q
Anaphase
A
- Centromeres separate
- Spindle fibres shorten
- Chromatids are pulled by centromeres to opposite poles (once separated, chromatids are referred to as chromosomes)
- Without spindle fibres, chromosomes cannot be organised and moved → uneven distribution of chromosomes into daughter cells during mitosis, therefore leading to the failure of cells to reproduce by mitosis
6
Q
Telophase
A
- Nuclear envelope reforms around both groups of chromosomes at opposite ends of the cell
- Chromosomes ‘decondense’ by uncoiling becoming chromatin again
- Nucleolus reforms in each nucleus
7
Q
Mitosis = nuclear division
A
- Chromosomes, present as the chromatids formed during interphase, are separated and accurately and precisely distributed to 2 daughter nuclei
- A continuous process with no breaks between the 4 phases: prophase, metaphase, anaphase, and telophase
- Animal mitosis is formed with the help of two centrioles whereas mitotic spindle in plant mitosis is formed without any centrioles
8
Q
Cytokinesis: cytoplasm division
A
- Division of the cytoplasm that follows telophase
- Cell organelles become evenly distributed between the daughter cells
In animal cells
- Cytokinesis occurs by a process known as cleavage
- First sign of cleavage is the appearnace of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate
- The cleavage furrow deepens until the parent cell is pinched into 2, producing 2 completely separated cells
In plant cells
- Golgi apparatus forms vesicles of new cell wall materials which collect along the line of the equator of the spindle = cell plate
- Vesicles will merge, forming the new cell surface membranes and the cellulose cell walls between the 2 cells
9
Q
Carcinogen
A
- any agent that may cause cancer
- Highly likely to cause damage to the DNA molecules of chromosomes, resulting in mutation - a change in the amount or chemical structure of DNA of a chromosome
10
Q
causative factors which can increase the chances of cancerous growth
A
Ionising radiation: x-rays and radiation (gamma rays, α particles, β particles) from various radioactive sources
- May trigger the formation of damaging ions inside the nucleus leading to the break up of DNA
Non-ionising radiation: UV light
- Less penetrating than ionising radiation but is absorbed by the nitrogenous bases of DNA, may modify it - causing adjacent bases on the DNA strand to bind to each other, instead of binding to their partner on the opposite strand
Chemical carcinogens: in tobacco smoke
- Prolonged exposure to asbestos fibres may trigger cancer in the linings of the thorax cavity
11
Q
Mitotic cell cycle
A
- the sequence of events that occur between one division and the next
- 3 stages: interphase, nuclear division (mitosis), cell division (cytokinesis)
- Dysregulation of checkpoints of cell division can result in uncontrolled cell division and cancer (mutations)
12
Q
Describe the development of cancer as a multi-step process that includes accumulation of mutations, angiogenesis and metastasis.
A
- Mutations of different types build up in the DNA of body cells over time due to carcinogens (a single mutation is unlikely to be responsible for triggering cancer)
- Cancer arises when the cell cycle operates without its normal controls - a molecular control system controlled by specific genes
- Rate of cell multiplication is very much faster than the rate of cell death, and a tumor (irregular mass of cells) is formed
Stages of cancer
- Stage I: a tumor grows from a single cancer cell
- Stage II: cancer cells invade neighbouring cells
- Stage III: cancer spreads through lymph and blood vessels to other parts of the body
- Stage IV: a small percentage of cancer cells may survive and establish a new tumor in another part of the body
13
Q
Features of cancer cells
A
- Replicative immortality: can divide many more times than a normal cell of the body
- Metastasis: ability to migrate to other parts of the of the body
- Angiogenesis: ability to promote growth of new blood vessels, which helps provide tumour cells a source of oxygen and nutrients
- Immortal: lost the ability to undergo apoptosis (programmed cell death) under conditions where normal cells would (e.g. due to DNA damage)
- Metabolic changes: cancer cells undergo metabolic changes that support increased cell growth and division
