Mitosis Flashcards
Why is cell growth and division so important?
Critical for growth and maintaining body function.
Cell cycle ensures newly formed cells are genetically identical to the parent cells.
How many stem cells in you bone marrow are produced per second?
2 million stem cells. This is to maintain a constant number of red blood cells in the bloodstream.
What is the cell cycle broken down into?
Growth (Interphase: has 3 stages)
Division (Mitosis + Cytokinesis)
What is the general description of Interphase?
Growth phase between cell divisions.
During this period, DNA content duplicates as well as organelles.
What generally happens in the G1 phase?
- Prepares for DNA chromosome replication
- Length of G1 varies
- Decision is made whether to divide again or not. If not, then cells go into G0
- Most nerve cells are in the G0 state where they will never divide again.
What happens during the S phase?
- DNA and chromosome replication takes place
- Sister chromatids are synthesized
Finally, what typically occurs during the G2 phase?
- Prepares for cell division
- Checks duplicated genetic material for errors
- Generally shorter than G1
- Known as the postsynthesis gap
What is characterized as the M phase?
The M phase involves the nuclear division (mitosis) and cytoplasmic division (cytokinesis)
What typically happens during the M phase?
- Sister chromatids are separated and partitioned into daughter cells
- Relatively short phase
- Accounts for 3-5% of the cell cycle
How many stages is mitosis divided into?
5 stages
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What happens just before the start of prophase?
The newly formed chromatin fibres condence into compacted folded structures which makes cell division much easier.
Describe prophase in general terms.
- Nuclear envelope begins to fragment (allows mitotic spindle to attach to the centromeres of the chromosomes.)
- Individual chromosome have condensed to the point they are visible.
Describe what is seen during metaphase
- Chromosomes are fully condensed
- Chromosomes align along the centre of the cell, called the metaphase plate
What occurs during anaphase?
- Sister chromatids are separated and moved towards opposite ends of the cells by the spindle fibre
Finally what occurs during the telophase stage?
- In telophase, the daughter chromosomes have arrived at the poles of the spindle.
- The chromosomes uncoil and extend and nuclear envelopes form around the two groups of daughter chromosomes.
- During the same period, the cell usually undergoes cytokinesis, which divides the cell into two daughter cells.
Which impotant organelle in the prophase allows the spinlde fibre to form?
The centrosome which contains a centriole which is duplicated in the S phase.
What is known as the MTOC?
Microtubule Organizing Centre. Centriole contain the microtubules that allows the sister chromatids to be pulled apart during the rest of the mitotic cycle.
What is an importqant difference between animal and plkant cells when it comes to centrioles?
Centrioles are absent in the majority of plant cells.
What distinguishes between the prophase and prometaphase?
- Breakdown of nuclear envelope
- Centriole reach opposite sides of the nucleus
What is a karyotype?
The number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
Which agent interferes with spindle formation so that the cells can be arrested at metaphase?
Colchicine. Chromosome that are fully condensed can be seen through microscopic examination.
In anaphase, what occurs during its late phase?
Cytokinesis begins as the two sets of daughter chromosomes approach the poles.
What causes the daughter chromosomes to be pulled towards the opposite poles?
Shortening microtubules that are attached to the centromeres.
Which ends of the microtubules are postive/negative? (+/-)
The end that is attached to the centrosome is negative.
The end that is furthest away from the centrosome is positive.
Growth occurs in the positive direction so this is how the tubulin subunits meet the end of the centromeres.
Why is the kinetochore microtubule defined as it is?
This is because this is when the microtubule from the centriole attaches to the kinetochore molecule on the sister chromatid.
What are the 3 types of microtubles involved in mitosis?
- Astral (forms asters at each pole)
- Kinetochore microtubules (attach to chromosome)
- Overlap microtubules (interact with microtubule at opposite pole)
In kinetochores, why are the nucleosomes specialised for attachment of the microtubule.
- Kinetochores associate with specialised nucleosomes (in which H3 is replaced by centromere protein A, CENP-A) at the centromeres.
Which protein helps move the chromosome to the poles?
Motor proteins
- Motor proteins use energy from ATP to change shape so that they exert a force and cause attached structures to move
In plant cells, what happens during cytokinesis?
- Little constriction down the middle
- New cell membrane and cell wall assembled down the middle of the cell.
When cytokinesis begins in early anaphase, what causes the cleavage furrow to occur?
The contractile ring
- actin/myosin microfilament make up the ring.
- Ring tightens around cytoplasm as cytokinesis progresses.
What is the membrane-enclosed disc?
In pkant cells, it is known to form the cell wall to divide a cell into two as it grows outwards.
