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All cells arise from other cells - Coggle Diagram
All cells arise from other cells
The cell cycle
The cell cycle is split into two parts: Interphase and Mitosis
Interphase
The cell appears to be relatively inactive
The cell will be carrying out the functions that are important for that cell type
Interphase is the largest segment of the cell cycle
Interphase has around three stages...
G1 Phase
Organelles replicate
Transcription and Translation occur
The size of the cell increases
G2 Phase
Energy stores replaced
Transcription and Translation occur
Chromosomes are repaired
The size of the cell increases
S (synthesis) phase
Chromosomes replicated
DNA is synthesised
Mitotic phase
There are two parts of mitosi
Mitosis - Chromosomes seperate into two nuclei
Cytokinesis - Cell divides in two
Go phase
This mainly happens because:
1.) The cells are fully differentiated
Cells can exit the cell cycle
2.) DNA is damaged (Senescent)
3.) Or they enter the Go phase temporarily
Checkpoints
The cell will constantly pass through 'checkpoints'
They monitor the order, integrity, and fidelity of the major events of the cell cycle.
G1 Checkpoint : The start or restriction checkpoint
G2 Checkpoint : Metaphase to Anaphase transition
If these checkpoints are failed then the cell will enter the Go phase
M Checkpoint Spindle checkpoint
Mitosis
Chromosomes
Starts with a diploid cell that contains only two pairs of chromosomes
Cell division then occurs by mitosis takes place when we want identiacal copies of a cell
Mitosis is also used for asexual reproduction
This produces two diploid cells
Cell cycle
Mitosis is a small part of the cell cycle and its made up of
Cytokinesis
and
Mitosis
Interphase
Energy store increases
Cell grows in size
DNA copied
Organelles replicate
Mitotic phase
The nucleus divides into two nuclei
The cell divides into two daughter cells
Division of the nucleus
Interphase
Although interphase looks like its inactive, functions are occuring
DNA not visible as distinct structures
Cell copies all of its DNA
Theres a material (chromatin), it has an open structure for transcription and translation
DNA + chromosomes
Originally the chromosome exists as a singular strand
Its joined at the centromere where the sister chromatid is also joined up forming a pair of chromosomes (there are 23 pairs in humans)
Cell Fractionation
It is a process used by scientists to allow them to study the functions of organelles seperate from their cell
Homogenising
The actual 'breaking' open of cells
A blender is used
Or a homogeniser: which is a device that contains a glass tube and a plunger esque device
Homogenising steps:
1.) First we place the sample in a glass tube
2.) Then we cover with a
Buffer solution
to maintain pH
3.) An
isotonic solution
is added to maintain the water potential
4.) The homogeniser is placed on
ice
, to slow down the enzyme activity
5.) The plunger is moved up/dpown to break open the cell
6.) We are left with a homogenate
Control variables
Isotonic solution =
This is to keep the water potential the same as inside the cell to prevent water from moving inside it via osmosis
Ice =
The homogeniser is placed on ice, this means that the enzyme activity is slowed and the organelles remain intact
Buffer solution =
To maintain the pH because if it changes the enzyme could denature
Order of Mass
Lysosomes
Mitochondria
Smallest
- Ribosomes
Largest
- Nucleus
Centrifugation
Our samples of homogenate are placed into a device known as a centrifuge, it is then spun
The heavier organelles move to the bottom whilst the lighter orgnalles collect at the top
Initally once its spun, the nuclei will collect at the bottom (pellet)
The remaining homogenate liquid is known as supernatant
This process is repeated at faster speeds to collect lighter organelles
Stages in Mitosis
M
etaphase
A
naphase
P
rophase
T
elophase
Some drugs work by targetting the spindle fibre formation in metaphase to prevent mitosis from happening
Prophase
The chromosomes condense and become visible
In animal cells, the centriioles seperate and move to opposite sides of the cell
The centrioles will then form spindle fibres which are released from both poles, to create a spindle apparatus: these will later attach to the centromere and chromatids on chromosomes.
Plants have a spindle apparatus without centrioles
Metaphase
The spindle fibres are released from the centrioles and attach to the centromere and chromatids on the chromosomes
There is also a spindle assembly checkpoint, where there is a check to ensure that every chromosome has attached to a spindle fibre before mitosis can enter anaphase
The chromosomes align along the equator (centre) of the cell
If the cell fails this then it will enter the 'Go' phase
Anaphase
This causes the centromere to divide into two and the individual chromatids are pulled to each opposite pole
This stage requires ATP, which is provided by respiration from the mitochondria
The spindle fibres begin to shorten and move towards the centrioles and pull the centromere and chromatids that they are bound to towards their respective pole
Chromosomes break at centromeres, and sister chromatids move to opposite ends of the cell
Telophase
The spindle fibre disintergrates and the nuclear membrane reforms
Chromosomes unwind into chromatin and the nuclear membrane reforms
The chromosomes are now at each pole of the cell and they become longer and thinner again
Cytokinesis
The cytoplasm splits into two genetically identical cells
In animals, a cleavage furrow (an indentation in the cells surface) forms in the middle of the cell
In plant cells, the cell membrane splits into two new cells due to the forming of vesicles from the Golgi apparatus. The cell wall forms new sections around the membrane to complete the division into two new cells
The cytoskeleton causes the cell membrane to draw inwards until the cell splits in two