Cell Division, Cell Diversity And Cellular Organisation Flashcards
Why is cell division needed?
To grow and repair tissues in the organism
Stages of the cell cycle
interphase
G1=protein synthesis to make proteins that produce organelles then organelles replicate=cell grows
S=DNA is replicated
G2=cell continues to grow+replicated DNA is checked for errors, if there are any they’re repaired+other things needed for cell division are done
G0=cell leaves cell cycle (temporarily/permanently) eg. damaged DNA=x be used, differentiates=x divide again, become senescent=x carry out cell division (have divided too many times)
More senescent cells=link to age related disease arthritis
mitosis=nucleus divides
cytokinesis=cytoplasm divides= cells produced
Checkpoints of the cell cycle
During G1 phase - chromosomes are checked for damage. If damage is detected then the cell does not advance into the S phase until repairs have been made
During S phase - chromosomes are checked to ensure they have been replicated. If all the chromosomes haven’t been successfully replicated then the cell cycle stops
During G2 phase - an additional check for DNA damage occurs after the DNA has been replicated. The cell cycle will be delayed until any necessary repairs are made
During metaphase - the final check determines whether the chromosomes are correctly attached to the spindle fibres prior to anaphase
Why is it important to control the cell cycle?
It is essential that the DNA within new cells is accurate in order for them to carry out their function
When the DNA is replicated (during the S phase) errors can occur
There are several checkpoints throughout the cell cycle where the genetic information contained within the replicated DNA is checked for any possible errors
Specific proof-reading enzymes and repair enzymes are involved in this checking process
When possible enzymes will repair the error but in some cases the cell may destroy itself to prevent passing on harmful mutations
Stages of mitosis
prophase
- Chromosomes condense and are now visible when stained
The chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere
The two centrosomes (replicated in the G2 phase just before prophase) move towards opposite poles
Spindle fibres (protein microtubules) begin to emerge from the centrosomes (consists of two centrioles in animal cells)
The nuclear envelope (nuclear membrane) breaks down into small vesicles
The nucleolus disappears
metaphase
Centrosomes reach opposite poles
Spindle fibres (protein microtubules) continue to extend from centrosomes
Chromosomes line up at the equator of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosome poles
Spindle fibres (protein microtubules) reach the chromosomes and attach to the centromeres
This attachment involves specific proteins called kinetochores
Each sister chromatid is attached to a spindle fibre originating from opposite poles
anaphase
The sister chromatids separate at the centromere (the centromere divides in two)
Spindle fibres (protein microtubules) begin to shorten
The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres (protein microtubules)
telophase
Chromosomes arrive at opposite poles and begin to decondense
Nuclear envelopes (nuclear membranes) begin to reform around each set of chromosomes
The spindle fibres break down
New nucleoli form within each nucleus
