M2 - Chapter 6 - Cell Division Flashcards
what is the cell cycle
a sequence of ordered events that takes place in a cell, resulting in division happening and then the formation of 2 genetically identical daughter cells.
a cell spends most of its time in what stage
Interphase
What happens in interphase
- DNA is replicated and checked for errors.
- Protein synthesis (enzymes and hormones are replicated)
- The number of chloroplasts in plants also divides (it increases in size first and then it splits)
- Mitochondria will also grow and divide (again grows and then splits) This is because mitosis requires a lot of energy, obtained from mitochondria.
Stages in interphase
G1- Growth stage 1 - The protein content and the amount of cell organelles increases (by growing and then splitting), to hold everything together.
S- Synthesis stage - DNA is replicated here
G2- Growth stage 2 - Cells continues to increase in size. The energy stores are also increased (ATP, glucose, fats and oils). The duplicated DNA is checked for errors. If there is damage, it will fix it by using free nucleotides.
Mitotic phase
The actual cell division takes place here.
4 stages here
After this is cytokinesis, which is the actual splitting of the cells into 2 daughter cells.
What is G0
This is called the “resting stage”, where there is no growth that can be caused. The cell will leave the cycle, but this can be temporary or permanent.
- Differentiation (if the cell becomes specialised to carry out a specific task and can no longer divide at all)
- DNA of a cell may be damaged so it can’t differentiate. It can enter a period of Permanent cell arrest.
- As you age, the number of ineffective (called senescent) cells increases, which are related to many age-related diseases.
How does exercise affect the number of senescent cells
As you exercise more, you force your cells to keep being used up and hence they duplicate more. This way there are more cells, and more ATP created, leading to more movement.
What is a checkpoint
Control mechanisms of the cell cycle. It monitors and verifies whether the processes at each phase have been completed accurately, to allow the next phase to occur.
3 checkpoints
- Spindle assembly
- G1
- G2
Explain G1 checkpoint
It looks for: - cell size - nutrients - growth factors - any DNA damage If these criteria aren't met, then it goes to the resting state. It does this before it goes to the S stage.
G2 checkpoint
It looks for: - Cell size - DNA replication - DNA damage Happens before going into the mitosis
Spindle assembly checkpoint
It is in the mitosis stage, just before it finishes.
it is also called the metaphase and it ensures that all the chromosomes are attached to spindle fibres. If it isn’t mitosis can’t happen.
Cell- cycle regulation and cancer
The passing of a cell cycle checkpoint is done by kinase, which is an enzyme that catalyses the addition of a phosphate group to a protein (called phosphorylation). When kinases binds to a variety of checkpoint proteins called cyclins. It creates a “Cyclin- Dependent kinase complex”. By having them, it ensures that a cell progresses through phases at the correct times.
Define cancer
caused by uncontrolled division of cells
Define tumour
an abnormal mass of cells.
They are caused by the damage or spontaneous mutation of genes.
Define benign
If the tumour stops growing and don’t travel.
Define malignant
If the tumour can move and continues to grow.
CDK can also be used as…
A target for chemical inhibitors to treat cancer. It would reduce CKDs, and reduce cell division, hence cancer cell formation.
what is mitosis
When a cell divides to create 2 daughter cells that are identical to the parental cell. Generally good for growth, replacement, repair or asexual reproduction.
Before and after of replication of chromosomes.
Before: there’s a single chromatid per chromosomes.
After: 2 chromatids per chromosomes.
4 stages of mitosis
Prophase
Metaphase
Anaphase
Telophase.
Prophase
Nuclear membrane disintegrates and breaks down.
The chromatin fibres condense into individual chromosomes as they begin to coil.
The nucleolus disappears.
Centrioles will move to the poles.
The centrioles form protein microtubules.
Metaphase
In this stage, the chromosomes move to the equator and the middle, creating a mitotic spindle.
The spindle fibres attach to the chromosomes at the centromere.
Anaphase
In this stage, the chromosomes are actually pulled apart to the opposite ends. This is because the centromere actually divides as well. Motor proteins can help sometimes too.
Note for anaphase
This process needs a lot of ATP, so mitochondria gathers around the spindle fibre.
Telophase
The chromatids reach the ends of the poles and are now called chromosomes.
The nuclear membrane forms again.
Chromosomes begin to uncoil.
Nucleolus is also formed again
Cytokinesis
It begins during the telophase.
The cleavage furrow pinches the cell together. An indentation of the plasma membrane, as it folds inwards by the cytoskeleton, until it is close enough to fuse together.
Plant cells and cytoskeleton
They have cell walls that can’t allow a cleavage furrow to be formed. Instead vesicles from the Golgi form along the equator and they fuse to create a “cell plate”, dividing into 2 cells.
Explain meiosis
The nucleus divides twice to produce 4 daughter cells (called gametes (sex cells)).
How many chromosomes does a haploid gamete have
- it only has 1 set of chromosome.
What is meiosis often called
A reduction division
Explain homologous chromosomes
You have 46 chromosomes in your cells, of which, you get 23 from your mum, and another 23 from your dad. Each 23 chromosomes is called a set of chromosomes. This means that chromosome 1 from your mum and chromosome 1 from your dad will not be the same, however it will code for the same type of genes. They will have different or maybe the same allele, depending on what characteristic it codes for and if your parents have that same characteristic.
What do homologous chromosomes have in common
same length
same size
centromeres in the same position
same genes in the same position
stages in meiosis
meiosis 1: first division
Each cell contains only 1 full set of genes rather than 2 (haploid)
meiosis 2: second division
The chromosomes in each daughter cell are separated, forming 2 more cells, resulting in 4 haploid cells in total.
Interphase in meiosis 1
The chromosomes replicate, they create 2 sister chromatids that are joined together by a centromere
Prophase in meiosis 1
Nuclear envelope disintegrates
Chromosomes condense and they coil
Nucleolus disappears
The homologous chromosomes join together, to create a bivalent (a homologous chromosome pair).
As the chromosomes move, they often get tangled together, which creates crossing over. When this happens, the alleles that get crossed over can swap. This causes genetic variation.
Metaphase in meiosis 1
The chromosomes line up along the metaphase plate.
The orientation of each bivalent is completely independent. The father chromosomes can face the north or the south pole, but it results in genetic variation. This is due to the independent assortment of homologous chromosomes.
Anaphase in meiosis 1
The centrioles pull the chromosomes to either side of the pole. The chromatids stay together, but split at the chiasmata (which is the allele that has been swapped, also the breaking point).
When this exchange of genes happens, it creates a recombinant chromatid. Again, resulting in genetic variation.
