Cell Division (Mitosis And The Cell Cycle) Flashcards
How long does the cell cycle take place and what does the duration depend on
It takes a long time and the duration depends on the type of cell.
What does the cell cycle consist of
Two different phases or parts
What are the two different phases
M phase or mitosis phase as well as interphase.
What is M phase or mitotic phase and how long does it take
It is when mitosis takes place and the cell divides in two. And this phase takes up only a relatively short period of time.
What can the cell appear to be during interphase and what occurs during it
The cell may appear to be inactive but lots of different processes are occurring. During interphase the cell is carrying out the functions of that particular cell type.
What are the specific processes that occur during interphase
DNA is replicated and checked for errors in the nucleus.
Protein synthesis occurs in the cytoplasm
Mitochondria grow and divide increasing their number in the cytoplasm.
Chloroplasts grow and divide in plant and algae cells increasing their number in the cytoplasm.
The normal metabolic processes of the cell occur.
What are the 3 different stages of interphase
G1, S, G2
What occurs during G1
The cell replicates organelles such as mitochondria.
Replicating organelles requires lots of proteins, so a high level of transcription and translation take place.
The size of the cell also increases, so that when the cell divides the two daughter cells are the correct size.
What occurs during S phase
All of the chromosomes are replicated
So a large amount of DNA is synthesised.
What occurs during G2 phase
The cell replaces the energy stores that are used up during S phase
The cell also continues to carry out transcription and translation
If any of the chromosomes have been damaged they are repaired too
The cell also continues to grow
What happens once a cell exits G2 phase
It enters the M or mitotic phase.
What can the mitotic phase be divided into and what does each stage do
Mitosis - the chromosomes separate into 2 nuclei
Cytokinesis - the cell divides into two
What is G0 phase
When some cells exit the cell cycle and this is called G0 phase.
What are the three different reasons that cells enter G0 phase
Fully differentiated cells enter G0 and stay there for the rest of their lives.
Overtime the DNA in cells can be damaged and at a certain point will no longer be able to divide, these are called senescent cells and they enter G0 permanently.
Some cells enter G0 temporarily from example B memory cells.
What are checkpoints in the cell cycle
At certain points in the cell cycle the cell checks that the cycle should continue.
What happens if a cell fails at a checkpoint
The cell cycle halts
What is the first checkpoint
Before the S phase the cell must pass through the G1 checkpoint.
What does the cell check for at the first checkpoint and if it is successful what occurs.
The cell checks that it has grown to the correct size
The cells checks for DNA damage
If successful then it enters into S phase
What is the second checkpoint and what does the cell do and what occurs if it is successful
The second checkpoint is at the end of G2 before the cell passes into mitotic phase.
The cell checks for DNA damage and whether it has grown to the correct size
If the checkpoint is passed it moves into the mitotic phase.
What is the last checkpoint what does the cell do and what occurs if it is successful
It is the metaphase checkpoint
This checks that the chromosomes are arranged correctly in the mitotic spindle.
If this occurs the cell completes mitosis and proceeds through cytokinesis.
what are diploid cells
when cells contain chromosomes in pairs they are referred to as diploid cells.
What occurs in terms of diploid cells in mitosis
We start with one diploid cell and end up with two identical diploid daughter cells
When does cell division by mitosis occur and why
It is used in asexual reproduction and in growth and repair as we want identical copies of a cell.
During interphase what can’t you see in the nucleus, and what do you see instead
You can’t see chromosomes as they are not visible as distinct structures instead you see a dark material called chromatin.
In chromatin what is a feature of the structure of DNA
the chromosomes have a loose open structure so that the DNA is accessible for transcription and replication.
What is a chromosome
It is a single long molecule of DNA
In interphase what occurs (chromosome replication)
The chromosomes are replicated so now there are two identical molecules of DNA. And this process occurs for every chromosome.
What are the stages of mitosis
Prophase, metaphase, anaphase and telophase.
What occurs during prophase (1) and what does each chromosome consist of at this stage
The chromosomes condense and become visible in the nucleus.
Each chromosome consists of 2 sister chromatids, joined at the centromere.
The nucleolus becomes disorganised and is no longer visible and the nuclear membrane starts to break down
What occurs during prophase (2)
A pair of centrioles move to either side/pole of the cell
Proteins begin to form spindle fibres attaching to the centromere of each chromosome.
They start to move the chromosomes towards the centre of the cell.
What is metaphase and what occurs during it
The second stage of mitosis
The spindle apparatus has completely formed and the chromosomes are line at the equator of the cell.
What is anaphase and what occurs during it
The chromosomes divide into two and the spindle fibres begin to shorten.
This pulls the sister chromatids towards opposite poles of the cell.
What occurs during telophase
The chromatids reach the poles of the cell and are now referred to as chromosomes again.
The spindle apparatus breaks down and the nuclear membrane reforms.
The chromosomes uncoil back to their chromatin state.
The nucleolus also forms in each nucleus.
The cell finishes nuclear division by mitosis.
What occurs during cytokinesis
The central cell membrane is pulled in by the cytoskeleton
This creates a groove/furrow which gradually deepens
The membranes eventually fuse to form 2 independent cells.
At this stage cell division by mitosis has finished.
How is mitosis different in plant cells (1)
- centrioles don’t play a role in forming the spindle apparatus in plant cells. As plant cells don’t contain centrioles.
- When plant cells undergo cytokinesis the cell membrane can’t form a groove/furrow like in animal cells. Instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell which fuse together to form a central membrane dividing the cytoplasm into 2.
How is mitosis different in plant cells (2)
A new cellulose cell wall also forms down the centre
