cell division Flashcards
What is the order of the cell cycle
M phase
metaphase checkpoint
~ G0
G phase 1
G1 checkpoint
s phase
G phase 2
G2 checkpoint
What happens at metaphase checkpoint
cell checks that all the spindle fibres Are attached to the centromeres of the Chromosome And if not metaphase is stopped
What is G0
When a cell moves out of the cell cycle permanently or temporarily either because it has differentiated or has been damaged and can’t be used anymore
What causes a cell to become damaged and go to G0
neighbouring cells communicate that conditions aren’t suitable for dividing e.g. lack of nutrients which inhibits growth/ A cell can only divide a certain number of times because Telomeres (the end of chromosomes) shorten each time and so cell division eventually has to stop
What happens in the growth phases
The cell grows new organelles and proteins needed for cell division
What happens at G1 checkpoint
Controls the progression of cell cycle into s phase Only if conditions are right and dna is all correct
- The cell checks that the chemicals needed for replication are present
- It checks for cell size and nutrients
- if there is any damage to the DNA, Issues are fixed or cell is destroyed
What happens at Sphase
Dna replication occurs ready to divide
What happens at G2 checkpoint
The cell checks whether all the DNA has been replicated without any damage
What happens throughout interphase
The cell Performs normal functions
it grows and prepares for division
DNA unravels and replicates to form two strand chromosomes to double genetic content
ATP is increased to provide energy for cell division
What is the sequence of structure of chromosomes in mitosis
After interphase - 46 2-strand chromosomes
In anaphase - Split into 92 sister chromatids
After mitosis - 46 1-strand chromosomes
What happens at prophase in mitosis
- Chromosomes condense
- centrioles start moving to the opposite end of the cells forming a network of protein fibres called spindle
- the nuclear envelope breaks down
What happens at metaphase in mitosis
- The chromosomes line up along the equator
- spindle fibres attached to their centromere
- metaphase checkpoint occurs
what happens at Anaphase in mitosis
- centromere split separating sister chromatids
- spindle fibres contract, pulling chromatids to the opposite side of the cell
what happens at telophase In mitosis
- chromatids reached the opposite poles of the cell they uncoil and become long and thin again and are now called 1-strand chromosomes
- Nuclear envelope forms around the 2 sets of chromosomes
what happens in cytokinesis in mitosis
Cytoplasm divides and there are now 2 identical diploid daughter cells
How is a zygote formed and developed into a new organism
A sperm cell gamete and an egg cell gamete join together at fertilisation and form a Zygote
What is a gamete
A cell with a haploid number of chromosomes
What are homologous chromosomes
A pair of chromosomes in diploid cells, one from the mum and one from the dad
they code for the same gene but may be different versions of that gene called alleles
what is meiosis
A cell division that happens in the reproductive organs to produce gametes starting off as diploids to form 4 haploid cells that are all genetically unique
What is the sequence of the structure of chromosomes in meiosis
After interphase - 46 2-strand chromosomes
In anaphase 1 - pull into 2 sets of 23 2-strand
After Meiosis 1 - 23 2-strand chromosomes
In anaphase 2 - chromatids , centromere Split
After Meiosis 2 - 23 1-strand chromosomes
What is crossing over
The paired up homologous chromosomes twist around each other at the chiasmata (point of breakage) and bits of the chromatids swap over so they contain the same genes but different combination of alleles causing genetic variation in offspring
What is Independent assortment
Each homologous pair of chromosomes is made up of one chromosome from mum and one from dad. when the pair lines up in the centre and pairs are separated It is a random orientation, and it is random which chromosome from who ends up with the daughter cell so this means they have different combinations of maternal and paternal chromosomes causing genetic variation in potential offspring
when are there additional steps of Homologous chromosomes pairing up and crossing over
in meiosis 1 prophase
When does independent/ random assortment occur
independent assortment - meiosis 1 metaphase
random assortment - meiosis 2 metaphase
how are the anaphases different in mitosis and meiosis 2 vs meiosis 1
In meiosis 1, Homologous pairs are pulled apart but chromatids stay attached at the centromere
What is the difference in telophase of mitosis and meiosis
m - 46 1-strand chromosomes are produced
m1 - 23 2-strand chromosomes
m2 - 23 1-strand chromosomes
Explain the difference between mitosis and cytokinesis
mitosis is the process of dividing the genome into two nuclei
cytokinesis is the physical division of the cell and its cytoplasm
Explain the importance of G2 checkpoint with reference to structure and function of proteins if damage to the DNA has occurred
The cell checks whether all the DNA has been replicated without any damage
If there is a change in a sequence of bases, it could cause a mutation
Which would lead to a change in amino acid sequence
and would determine a different protein shape Which is reliant on the territory structure which is dependent on the primary structure which would be different which the proteins function relies on so it may no longer work and has to be destroyed
Suggested disadvantage of indefinite cell division
Mutations occur during DNA replication,
Accumulating many mutations
which increases the chance of harmful mutations
What are telomeres
- Telomere are repetitive sequences of DNA at the end of chromosomes
- they protect the genes at the end and stop the ends of chromosomes fusing
- DNA is not replicated all the way to the end each time so bits of the telomere are lost and telomeres shorten
- this limits the number of times a cell can divide called hayflick limit
XxX are enzymes that result in elongation of telomeres and are not present in differentiated cells, what could it cause if they are
Indefinite cell division leading to many mutations leading to formation of tumour which could cause cancer
for a cell to divide successfully What two things must it do in interphase
Replicate its DNA and grow
Which phase does DNA replication take place
S phase
Which phase does cell division take place
M phase
Which division in meiosis is called the reduction division
Division 1
what does G1 and G2 mean and what is the importance of these stages
Gap 1 and gap 2, cell checks if everything is correct before proceeding, Could avoid a mutation causing cancer
How does cancer occur even with the checkpoints
These checkpoints have failed which means the cell containing faulty DNA is able to replicate in an uncontrollable division
How is cancer treated
medicines are aimed at killing cells that are rapidly dividing, they inhibit the synthesis growth signals for that type of cell
This is called chemotherapy
How would the cancer cell look Different to a normal cell
Small cytoplasm, multiple nuclei
why are chromosomes more likely seen as a double structure (2-strand chromosomes) containing two chromatids
They are more visible under the microscope as they have replicated and bunched together during mitosis/meiosis Rather than free in the chromatin
describe the differences between cytokinesis in animal and plant cells
In animal cells cleavage furrow forms around the middle of the cell furrow pulls inwards and fuses
In plant cells furrows cant form due to cell wall so Vesicles made of the Cell membrane assemble across the centre and Fuse together
why are plant root tips a good source of cell to examine for mitosis
The root tips called meristems are stem cells that have not yet differentiated so are constantly dividing, plant cells are easy to obtain and prepare for microscopy
Why is a reduction division necessary in the production of gametes
A reduction division means halving the number of chromosomes,
gametes are the sex cells and two sex cells (1 from each parent) must combine to produce a diploid Offspring
therefore gametes must only contain haploid member of chromosomes
What is the importance of the creation of different allele combinations in populations
It is important for genetic variation
in the process of natural selection
giving unique characteristics to individuals
might be an advantage in a changing environment
otherwise one disease could wipe out a whole Population
they would all be vulnerable to external factor
there would be no opportunity for adaptation
What type of cells undergo mitosis
mostly Only stem cells
