Mitosis Flashcards
what is the purpose of cell division?
- cell maintenance, growth and development requires cell division
- repair also requires cell division
- cell division is also required for replication
what is a genome?
the cell’s DNA is called the cells genome (all genetic material)
what is the difference between nuclear division and DNA replication?
nuclear division is mitosis- the process of dividing the nucleus into 2 daughter nuclei
DNA replication is the process of replicating the DNA completely
what are the necessary requirements for DNA replication/mitosis to be considered successful?
for it to be successful the DNA needs to be replicated
1. faithfully
2. carefully
3. accurately
4. each daughter cell must have identical DNA/genome to each other
what are the phases of cell division in eukaryotes?
G1
Synthesis
G2
Interphase
describe interphase
Interphase is the period between when cells are undergoing division
a period where normal molecules required by the cell and DNA is present and being synthesised
DNA exists as chromatin not chromosomes
describe G1
first gap phase
cell grows in preparation for cell division
the commitment to G1 prompts the rest of the cell cycle to commence
describe the synthesis phase
DNA replication occurs
describe the G2 phase
cell grows again in preparation for cell division
organelle synthesis
what are the steps in mitosis?
prophase
prometaphase
metaphase
anaphase
telophase
how do prokaryotes undergo cell division/cell cycle and what is its purpose?
-cell division in prokaryotic cells does not involve mitosis
- prokaryotes do not have DNA in the nucleus but are loosely coiled in the nucleoid.
they have a gap phase and then replication occurs (similar to s phase). It then goes immediately into division.
Gap phase:
- No DNA replication in the gap phase
- in replication less then 60 minutes, there is no gap phase
Replication:
- as shown below
Division:
- FtsZ protein (filament temperature sensitive protein) similar to tubulin
- constricts the cell and allows for the pinching that divides the two cells
- also involved in the division of chloroplasts and mitochondria
- homologue of eukaryotic cytoskeleton protein tubulin
binary fission: division in half, refers to the process and to the asexual reproduction of the single-celled eukaryotes, such as the ameoba
what are the steps of DNA replication in eukaryotes?
multiple origins of replication
it is being copied at multiple sites at the same time
- Origin replication complexes (ORCs) identify and bind to the point of replication
- Helicases unwind the DNA, producing a replication bubble with 2 replication forks
- two forks move in opposite directions and eventually disrupt the nucleosomes ahead of them
- nucleosomes then reassemble along the daughter strand, maintaining the chromatin structure
- DNA gyrase relieves tension from unwinding
- SSB’s bond to prevent recoiling and hair pin loop formation
- DNA primase adds RNA primers to the DNA to elongate the leading strand or the okazaki fragments of the lagging strand
lagging strand
- DNA polymerase III extends the primers until they reach the other primer
- Rnase enzymes remove the primase enzyme
- DNA polymerase I replaces the primers with DNA
- DNA ligase- joins okazaki fragments together through adding covalent bonds
leading strand
- DNA polymerase III extends the primer continuously
- Rnase enzymes remove the primer
to finish:
- As the last primer is removed, it produced an overhanging stretch of DNA (gDNA overhang) on the leading strand.
- telomerase extends the overhanging stretch with non-coding DNA to prevent the loss of coding DNA during subsequent replication cycles
- the replication bubbles merge as replication continues, until the whole chromosome is duplicated
what is the difference between the leading and lagging strand?
leading strand is continuously replicated, however, the lagging strand isn’t because it is antiparallel and DNA can only be synthesised in the 5’ to 3’ direction
what does semiconservative mean?
That the new strand of DNA conserves half of the DNA and creates a new strand. Therefore conserving some of the original DNA.
how does prokatyotic DNA replicate?
circular double stranded genome
1. DnaA binds to ATP to become activated and binds to OriC to begin replication
2. Helicase unwinds and forms replication bubble, supercoiling DNA
3. Replication bubble stabilised by SSB
4. Replication bubble now has two replication forks on either side of the bubble
5. At each fork, the multi-protein complex synthesises DNA. Simultaneously synthesising teh leading and laggin strand
6. Type 1 topoisomerase relieves torsional strain from supercoiling by creating nicks and reforming the bonds (ligating)
7. 2 forks meet at termination point where the DNA replication completes
what is cytokinesis and its steps
division of cytoplasm, producing two daughter cells
each daughter cell can start a new cell cycle
cell membrane/wall formation
what are cyclin CDK’s and how do they work?
cyclin and CDK (cyclin dependent kinases)
cyclin-CDK’s interact with other signalling molecules to prevent the progression of the cell cycle if certain triggers are not met (checkpoint triggers)
restriction points/checkpoints
they do this through phosphorylation and dephosphorylation and through interacting with signalling molecules
the restriction points are:
- G1 (DNA damage)
- S cyclin (incomplete replication of DNA damage)
- G2-M cyclin (DNA damage)
- M cyclin (Chromosomes unattached to spindle)
what is prophase?
condensation of chromosomes
spindle assembly
what is anaphase?
seperation of chromatids
migration of sister chromatids to poles
what is metaphase?
alignment of chromosomes at metaphase plate
what is telophase?
chromosomes decondense
nuclear envelopes re-forms
what is prometaphase?
nuclear envelope breakdown
chromosome attachment to spindle
compare the cytokinesis of animal and plant cells
animal: contractile ring
plant: cell plate formation
Explain DNA replication forks
DNA replication fork begins at specific points, called the origin of replication
DNA helicase binds and moved along the DNA unwinding and seperating DNA into a Y shape known as the DNA replication fork
what are microtubules
- largest
- long, hollow, unbranched cylinders
- 25nm
- spindle fibres
roles
1. rigid internal skeleton for some cells
2. framework along which motor proteins can move structures within the cell
assemlbed from two dimers
- tubulin a and b
what are microfilaments
- smallest
- single, bundles or networks
- 7nm
roles
1. help the entire cell or parts of the cell move
2. determine and stabilise shape
made from: actin
cytoplasmic streaming and muscle contraction
what are intermediate filaments
- medium
- lots of different kinds
- 8-12nm
roles
1. anchor cell structures in place
2. help maintain position of nucleus
3. resist tension
4. maintain rigidity
What is DNAA and how is it regulated?
- initiation factor
- promotes unwinding at OriC
- The initiation of DNA is determined by teh concentration of DNAA which is bound to ATP
- This is the active form of DNAA
- During normal growth this accumulates, and when it reaches a threshold replication will be initiated
- DNAA in its active form has a high affinity for binding ‘boxes’, which are section of DNA that are upstream of oriC
- They are 9 base pair regions that are specific for the binding of DNAA in its active form
- This causes a separation in the oriC region of 13 base pair repeats, forming DNA loops
- This allows preparation for melting open by a helicase enzyme, DNA B
- Although ATP is required to be bound to DNAA to make it active there is no ATP hydrolysis necessary for the binding to ori C or the unwinding process
- During replication DNAA-ATP, the bound form of the DNA initiator protein, is converted into DNA-ADP by DNA polymerase and other factors, releasing energy
- This is done during DNA replication and provides the energy that allows it to proceed
- It also lowers the concentration of DNAA-ATP so that DNA replication doesn’t just continue on forever when the threshold is reached
