cell division Flashcards by Uha Parlapalli

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

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What is the use of mitosis

Growth and repair,
production of gametes from haploid cells, asexual reproduction,
production of new stem cells

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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

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What is G0

the stage 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 replicated anymore so it doesn’t move to s phase

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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 It has reached the end of its development so cell division eventually has to stop

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What happens in the growth phases

The cell grows new organelles and proteins needed for cell division

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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

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What happens at Sphase

Dna replication occurs ready to divide

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What happens at G2 checkpoint

The cell checks whether all the DNA has been replicated without any damage

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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

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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

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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

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What happens at metaphase in mitosis

The chromosomes line up along the equator
spindle fibres attached to their centromere
metaphase checkpoint occurs

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what happens at Anaphase in mitosis

centromere split separating sister chromatids
spindle fibres contract, pulling chromatids to the opposite side of the cell

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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

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what happens in cytokinesis in mitosis

Cytoplasm divides and there are now 2 identical diploid daughter cells

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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

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What is a gamete

A cell with a haploid number of chromosomes

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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

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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

in prophase 1, condensed 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. this results in 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 - metaphase 1 random assortment - metaphase 2

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

How can you tell the cell cycle stops at G2 checkpoint and doesn't reach mitosis

Nuclear membrane is present no visible chromosomes on the microscope contains more DNA contains larger number of organelles

How can you tell a cell has not moved on from G2 checkpoint from a microscope

The cell contains a nuclear membrane and no visible chromosomes so chromosomes have not condensed and mitosis hasn’t occurred

What is the benefits of asexual reproduction

Genetically identical offspring can be produced rapidly all with favourable adaptations Resulting in a rapid increase in population requiring minimal time and energy

Why does sexual reproduction have to happen in unfavourable conditions

All offspring might die in unfavourable conditions if asexual So if sexual reproduction happens some of spring may have a chance of survival as they have useful alleles