The Cell Cycle Flashcards
Why do cells need to divide ?
Cells have limited size - if too big SA: V ratio is inefficient
Produce gametes
Multicellular organisms - growth and repair
Asexual reproduction
What is Interphase
Cells do not divide continuously
Long periods of growth and normal working separate divisions
Active phase of the cell cycle - cell is carrying out major functions liek producing enzymes and hormones while actively preparing for cell division
What things happen in interphase speicifically?
Dna is replicates an checked for errors in the nucleus
Protein synthesis occurs in cytoplasm
Mitachondria grow and divide increasing in number in the cytoplasm
Chloroplasts grow and divide, in agal cell cytoplasm
Normal cell metabolic processes occur ( some e.g. reputation also occur throughout cell division ! T
3 phases of interphase
G1- first growth phase , proteins from which organelles are synthesised are produced + organelles replicate , cell increases in size
S- synthesis phase, DNA replicated
G2- 2nd growth the cell continues to increase in size, energy stores increased and the duplicated DNA is checked for errors
The cell cycle
A series of events when a parent cell divides to form 2 daughter cells
Daughter cells can function as parent cells - EXACT copy of dna
G1 phase
Cells grow and increase in size
Transcription for genes to make rna
Organelles duplicate
Making DNA replication enzyme
P53( tumour suppressor) gene helps to control this phase
S phase
Replication of DNA
Chromosomes are unwound and DNA Is replicated
Specific sequence of the replication of genes - these rhat are active in all types of cells are duplicated first
Genes that are normally inactive in specific types of cell are replicated LAST
rapjd and because exposed DNA base pairs are more susceptible to mutagenic agents, reduces chance of spontaneous mutations
G2
Special chemicals ensure the cells are ready for mitosis by stimulating proteins that will be infolved in making chromosomes condense and in formation for be spindle
Cells growth
Miotic phase
MITOSIS
Cytokinesis
Cytoplasm divides and 2 new cells produced
G0
The cell leaves the cycle, temporarily or permenantly
Triggered during early g1 at the restriction point by a checkpoint chemical
Some cells e.g. epithelial in gut DONT have this phase
Reasons for g0
Differentiation
The dna May be damaged - enters period of permenant cell arrest
Control of cell cycle?
Viral to ensure he cell only divides when it has grown to the right size , the replicated dna is error free/ repaired and the Chromosomes are in correct positions during mitosis
This is to ensure fidelity of cell division
Checkpoints are the control mechanisms of the cycle
Monitor or verify whether the processes at each stage of the cell cycle has been accurately completed before cell is allowed to progress into next phase
G1 checkpoint
Check for cell size, nutrients, growth factors and DNA damage
Ensures cell is ready to enter Sphase
If it satisfies requirements - triggered to begin DNA replication , If not it enters G 0
G2 checkpoint
Check for all size , dna replication and damage
if checkpoint is passed, cell initates the molecular process that signal beginning of mitosis
Spindle assembly checkpoint
(metaphase) at the point is mitosis where all the chromosomes should be attatched to spindles and have aligned
mitosis CANNOT proceed until this checkpoint is passed
Importance of mitosis - GROWTH
All cells produced enable a zygote to become an adult
Must be genetically identical
All cells within a tissue must have the same structure and perform the same function
Importance of mitosis- REPAIR
If cells become damaged o lost- repair cells used have to be exact copies otherwise the tissue wouldnt function
Importance of mitosis- ASEXUAL REPRODUCTION
Parents that have survived- well suited to that environemnt,
Genetically identical offspring shoudl also succeed in the same environment
Moat common in plants( vegetitive propagation and natural cloning)
Chromosome
Each DNA molecule is converted into 2 identical DNA molecules called chromatids in interphase
The chromatids are joined at the CENTROMERE - necessary to keep them together so they can be precisely maneuvered and segregated equally = 1 each inot the 2 new daughter cells
prophase
Chromatin fibres coil and condense
nucleolus disappears
Protein microtubules form spindle-shaped structures linked to the poles of the cell. Spindles(fibres forming)are necessary to move chromosomes into correct positions before cell division.
2 centrioles migrate to opposite poles of the cell
spindle fibres attatch to specific areas of centromeres and move chromsomes to centre
Metaphase
Chromsomes align in the middle f the cell
METAPHASE plate
Attatched to spindle by centromere
Metaphase checkpoint
Anaphase
The centromeres holding together the pairs of chromatids in each chromsome divide
- Chromatids seperated and pulled to poles by shortening spindle fibres
- V shape of chromatids, moving towards pole = result in being dragged through liquid cytosol by centromeres
Telophase
Chromatids reach opposite poles- now called CHROMOSOMES
2 new sets of chromosomes assemble around each pole and nuclear envelope reforms around them
chromosomes uncoil adn nucleolus formed
Cytokenisis
Cytoplasm divides
There are now 2 genetically identical daughter cells
Cytokinesis - ANIMALS
Cleavage furrow forms around the middle of the cell, the cell surface mebrane is pulled inwards by the cytoplasm until its close enough to fuse aorund the middle, forming 2 cells
cytokinesis in PLANTS
Vesicles from the golgi begin to assmeble in the same place where the metaphase plate was formed
The vesicles fuse together and the cell surface membrane, dividing the cell in 2
New sections of cell wall then form along hte new sections of the membrane ( if the dividing cell wall were formed before the daughter cells separated , they would immediately undergo osmatic lysis from surrounding water)
