Mitosis Flashcards
When does mitosis not produce 2 genetically identical daughter cells
If mutations occur in DNA replication
Describe prophase
- chromosomes coil and condense, grow shorter and fatter, become visible; they are no longer diffuse (enables then to be moved easily and not become entangled)
- DNA becomes inactive
- animals -> centrioles move to opposite poles of the cell
- microtubules develop from the centrioles to form the spindle apparatus
- plants -> do not have centrioles, still form spindle fibres
- the nucleolus and envelope disappear (nucleus disintegrates) so that chromosomes are free within the cytoplasm so that they can go to opposite poles of the cell
interphase basics
- aka resting phase
- when DNA replication takes place (need double the amount of DNA for the daughter cells to be genetically identical)- attaches new proteins to DNA
- part of cell cycle but not mitosis
- cell grows, carriers out its functions
- 90% of cell cycle
What are MTOCs?
- microtubules organising centers
- where the centrioles are
- contains 2/3 centrioles
Describe metaphase
- chromosomes are seen as two chromatids, each being an identical copy from the parent cell (no alleles)
- the sister chromatids are joined by the centromere, which is where the microtubules from the poles attach to, allowing the chromosomes to be pulled along the spindle apparatus to the equator
Describe anaphase
- centromeres divide into two and microtubules pull individual chromatids apart (chromosome is separated)
- chromatids move to opposite poles of the cell; now referred to as daughter chromosomes
- microtubules which have a chromosome attached shorten and ones which don’t lengthen, causes the cell to elongate and the chromosomes move to opposite poles
- active process- energy comes from mitochondria which circle around microtubules
Describe telophase and cytokinesis
- chromosomes become longer and thinner until they disappear
- microtubules disintegrate, nucleolus and envelope reform
- cytoplasm divides
What happens when cytokinesis does not occur?
- when nucleus divides but no new cell if formed, coenocytes are formed (e.g. skeletal muscles)
- animals -> cleavage furrow pinches the cell in two
Describe cytokinesis in plants
- membrane-enclosed vesicles containing cell wall materials collect at the middle of the parent cell
- vesicles join to form a cell plate
- cell plate grows outwards and fuses with the cell surface membrane so two cell walls can form
What is mitotic index?
- amount of cells in a population that are undergoing mitosis at a certain time
- has no unit because it is a ratio
- cells in mitosis/total number of cells
Describe prokaryotes
- binary fission
- circular DNA replicated and both copies attach to cell membrane
- plasmids also replicate
- cell membrane grows between two DNA molecules and pinches inwards, dividing the cytoplasm in two
- new cell wall forms between the two DNA molecules
- new cells are identical daughter cells each with the same copy of circular DNA but a variable number of plasmids
Describe plasmids
- circular pieces of bacterial DNA
- often contain genes not related to basic life functions
- often contain antibiotic resistance genes
- involved in genetic modification- we cut open plasmids, attach a desired gene and reinsert the plasmid into the bacteria so that the bacteria contains a new gene to create a desired protein
Describe viral replication
- not alive; cannot replicate independently
- attach to a host cell using attachment proteins on their surface
- object their nucleic acid into the host cell
- genetic info from the injected viral nucleic acid provides the instructions for the host cells’ metabolic processes to start producing viral components (e.g. nucleic acids, enzymes, structural proteins) which can be assembled into a new virus
What are the 3 main causes for cell division?
1) growth
2) repair
3) reproduction
Describe cell cycle
- not all cells retain the ability to divide (liver cells, nerve cells) - lose the ability to form spindle fibres
- interphase, nuclear division, cytokinesis
- the sequence of events that occurs between one cell division and the next
- length varies massively- 24hrs for mammals
- RBCs divide at 2.5mill/sec
Describe cancer
- caused by mutations/damage to the genes that regulate mitosis and cell cycle
- results in uncontrolled cell growth and replication, which forms a tumour
- if untreated, the rumour continues to grow depending on where it is in the body
- tumours become cancerous if it changes from benign to malignant
What is a tumour?
• a group of abnormal cells
What is the difference between a benign and a malignant rumour?
- benign -> static
* malignant -> moves
Describe cancer cells
- do not divide normally- they divide at a normal rate, but the divisions are uncontrolled
- do not respond to crowding; loss of contact inhibition leads to a disorganised mass; cels may have extensions
What is metastasis
• when a tumour spreads and becomes a malignant cancer
How does cancer spread?
- cancer cells break away from their home tissue
- metastasising cells become attached to the wall of a blood or lymph vessel; they secrete enzymes that break down part of the wall and enter the vessel
- creep or tumble along inside blood vessels then leave the bloodstream the same way they fit in- start new tumours in new tissues
How are cancers caused?
1) oncogene -> may alter control of cell division
2) faulty tumour suppressor gene -> fails to halt runaway cell division
3) viral infection -> switches pronto-oncogene to oncogene it’s inserts an oncogene into the host cell DNA
4) carcinogens or radiation -> damages DNA
5) faulty immunity -> fails to tag cancer cells for destruction
Describe the treatment of cancer
- involves killing dividing cells by blocking parts of the cell cycle; ceasing the growth of the cancer because cell division stops
- chemotherapy or radiotherapy
- also kills healthy cells- but cancer cells are damaged more
- causes loss of hair and poor immune system
Describe radiation therapy
- used when cancer is small or has not spread
* uses radioisotopes
How do drugs that treat cancer work?
- prevent DNA from replicating (cisplatin)
* interfere with spindle formation- inhibit metaphase (vinca, alkaloids)
The basics of mitosis:
- one division
- 2 genetically identical daughter cells (unless mutations occur)
- used for cell repair, cell growth and asexual reproduction
Nuclear division
- occurs during mitosis
* sister chromatids are separated and redistributed as chromosomes in the nucleus of daughter cells
Cytokinesis
Cytoplasm divides time form daughter cells
Interphase specifics
- G1 -> the cell is very active, growing and carrying out its metabolic reactions
- S -> DNA replicates & two sister chromatids form from each chromosome
- G2 -> organelles replicate (mitochondria, chloroplasts) - cell continues to grow until mitosis begin
