T2.3 - Cell cycle Flashcards
List the three main stages in the cell cycle
Interphase, mitosis and cytokinesis.
What are the products of cell division?
Two diploid daughter cells genetically identical to each other and the parent cell
Name the three stages of interphase
G1, S-phase, G2
What happens during G1?
● Production of organelles
● Protein synthesis
● Cell increases in size - increase volume of cytoplasm
● Normal metabolic processes occur e.g. respiration
What happens during the S-phase?
Semi-conservative replication of DNA
What happens during G2?
● Production of organelles
● Protein synthesis
● Cell increases in size - increase volume of cytoplasm
● Normal metabolic processes occur e.g. respiration
● Enzymes check the copying of DNA has been done properly.
State what is meant by the term mitosis
Nuclear divisoin
State what is meant by the term cytokinesis
Division of the cytoplasm
During which phase of the cell cycle does the amount of DNA double?
S-phase
What are sister chromatids?
Duplicated chromosomes attached by a centromere
Name the part of a chromosome that links sister chromatids
Centromere
What organelle produces spindle fibres?
Centrioles
Name the protein mass containing centrioles in animal cells
Centrosome
Name the part of a chromosome made of DNA and histone proteins
Chromatin
Why is DNA coiled around histone proteins?
Chromosomes need to be stored compactly to fit within the nuclei
How many chromosomes are in a human body cell?
46
23 pairs
Name the four stages of mitosis in order
Prophase, Metaphase, Anaphase, Telophase
Which stage of mitosis is the longest?
Prophase
Which stage of mitosis is the shortest?
Anaphase
Describe the events of prophase
● Chromosomes condense (shorten and thicken) and become visible due to DNA coiling.
● Centrioles move to opposite poles tand form spindle fibres.
● Nuclear envelope breaks down and is no longer visible.
● Nucleolus disappears.
Why do chromosomes condense during mitosis?
During mitosis chromosomes need to be short and compact enough that they can be separated and moved to each end of the nucleaus
Describe the events of metaphase
Chromosomes line up at the equator of the cell,
and attach to the spindle fibres by their centromeres.
Describe the events of anaphase
● Centromeres split into two
● The replicated sister chromatids are separated
● Spindle microtubules shorten and contract causing them to pull the sister chromatids to opposite poles
Describe the events of telophase
● Chromatids reach the poles and are now called chromosomes again
● They uncoil and lengthen to form chromatin again, losing the ability to be seen clearly
● Spindle fibres disintegrate
● Nuclear envelope re-forms around the chromosomes at each pole
Outline what happens to chromosomes during mitosis
● Condense and become visible during prophase
● Attach to spindle fibres at the equator via their centromere during metaphase
● Centromeres split and sister chromatids separated and moved to opposite poles during anaphase.
● Uncoil and lengthen forming chromatin again during telophase
Describe describe cytokinesis in animals
● Microtubule fimalments form a concentric ring around the centre of the cell.
● The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre.
● When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed
Describe cytokinesis in plants
● Carbohydrate-rich form in a row at the centre of the cell (equator).
● The vesicles fuse together and an early begins to form within the middle of the cell.
● The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
Compare cell division in animals and plant cells
● Most animal cells are capable of mitosis and cytokinesis, whereas only meristem cells are capable of mitosis and cytokinesis in plants.
● Animal cells contain centrioles that produce spindle, but plant cells do not so spindle is formed in the cytoplasm.
● In animals, cytokinesis starts from the outside where a contractile ring of microfilaments causes constriction at cell centre forming a cleavage furrow, whereas in plant cells sytokinesis
What is the mitotix index?
The ratio between the number of cells undergoing mitosis and the total number of cells observed in the sample.
How do you calculate mitotic index?
No. of cells in mitosis / Total no. of cells
What does high mitotic index indicate?
High mitotic index can indicate cancer as cancer cells divide more rapidly, so spend more time undergoing mitosis.
Name the three checkpoints during the cell cycle
G1 checkpoint, G2 checkpoint, spindle assembly checkpoint
What happens during the G1 checkpoint?
Checks for:
Cell size
Nutrients
Growth factors
DNA damage
What happens during the G2 checkpoint?
Checks for:
Cell size
DNA replication
DNA damage
What happens during the spindle assembly checkpoint?
Checks for chromosome attachment to spindle fibres in metaphase
What are permanent cells?
Cells that leave the cycle and stop dividing. (G1 to G0)
They carry out all their normal functions, differentiate into specialised cells that need to last a lifetime
Name the proteins that control the progression of the cell cycle
Cyclins
Name the enzymes involved in controlling the progression of the cell cycle
Cyclin-dependent kinases (CDKs)
Explain how the cell cycle is controlled
● Cyclins bind to enzymes called cyclin-dependent kinases (CDKs).
● The cyclin-CDK complex will bind to a target protein and modify it via phosphorylation (attachment of phosphate)
● The phosphorylated target proteins become active and carry out specific tasks e.g. spindle formation, chromatid alignment, centrosome duplication.
● After the event has occurred, the cyclin is degraded and the CDK is rendered inactive again.
Why do cyclin concentrations need to be tightly regulated?
Different cyclins specifically bind to, and activate, different classes of cyclin dependent kinases.
Cyclin concentrations will peak when their target protein is required for function and remain at lower concentrations at all other times to ensure the cell cycle progresses in the proper sequence
Explain how a tumour forms
● Proto-oncogenes code for proteins that stimulate the cell cycle and promote cell growth and proliferation.
● Tumour suppressor genes code for proteins that inhibit cell cycle progression and promote apoptosis (cell death).
● If a mutation occur in proto-oncogenes or tumour supressor genes it can result in uncontrolled cell division.
State the role of mitosis in living organisms
Growth, repair of tissues, asexual reproduction
State how bacteria divide
Binary fission
What is the use of mitosis to regenerate a whole organism from a fragment of the original called?
Fragmentation
Name the process involving mitosis in the production of asexual spores that can grow into new individuals
Sporulation
State what is meant by the term clone
Genetically identical offspring produced as a result of natural or artificial asexual reproduction
The process by which a plant forms a structure by mitosis that develops into a fully differentiated, genetically identical new plant
Vegetative propagation
Name the process by which an unfertilised egg cell develops into a new individual
Parthenogenesis
What is the use of mitosis to regrow a body part that has been lost called?
Regeneration
What is the production by mitosis of an outgrowth from the parent organism that develops into a small independent organism called?
Budding
State what is meant by the term growth
A permanent increase in the number of cells, or in the mass or size of an organism.
Which process increases cell number, cell mass, and cell size?
● Cell number is increased by mitosis.
● Cell size is increased by cell elongation (plants only)
● Cell mass is increased by assimilation of nutrients
State what is meant by the term assimilation
The digestion and absorption of food or nutrients by the body or any biological system
State what is meant by the term dry mass
The mass of the body of an organism with all the water removed from it
State an advantage and disadvantage of using dry mass to measure the growth of an organism
Advantage: Dry mass is more accurate as it does not include water content.
Disadvantage: Organisms are dead.
How could you use dry mass to investigate the effect of an abiotic factor, e.g. temperature, light intensity, water availability, on the growth of an organism?
● Grow large samples
● Grow genetically identical organisms under similar conditions
● Take random samples at intervals
● Dry samples to a constant dry mass.
Explain what type of organisms you could investigate using their dry mass
Plants, fungi, bacteria.
It is not easy or ethical to maintain large colonies of identical vertebrates and then kill and dry them, so scientists use less reliable indicators such as height and wet mass to measure
growth when working with animals
What is a growth curve?
A graphical representation of the growth that takes place throughout the life of an organism
State what is meant by the term continuous growth
A permanent increase in the number of cells, or in the mass or size of an organism, which continues throughout life - even when
it stops at maturity.
State what is meant by the term discontinuous growth
A permanent increase in the number of cells, or in the mass or size of an organism, but which occurs in a series of steps, e.g. insects grow in a series of moults
Describe the difference between continuous and discontinuous growth
Continuous continues throughout life - even when it stops at maturity, whereas discontinuous occurs in a series of steps.
Name the region of mitosis and growth in a plant shoot or root
Meristem
State what is meant by the term scenescence
The onset of old age; when mitosis occurs less frequently and the cells dying outnumber the new cells being formed.
Where does meiosis occur?
Sex organs (ovaries and testes / anthers)
What type of cells does meiosis produce?
Gametes (sperm and ova / pollen and ovules)
State the products of meiosis
Four genetically different haploid daughter cells, which differentiate into gametes
Explain the importance of meiosis in the production of gametes
● Reduction division produces daughter cells with haploid nucleus so that the diploid number of chromosomes is restored during fertilisation.
● Increases genetic variation via crossing over and independent assortment of alleles.
State what is meant by the term homologous chromosome
Homologous chromosomes are a pair of chromosomes that are the same size and contain the same genes at the same loci, but not always the same alleles.
What is a karyogram?
A diagram or photograph of the chromosomes present in a nucleus (of a eukaryotic cell) arranged in homologous pairs of decreasing length.
Which stage of meiosis is reduction division?
Meiosis I
Describe what happens to chromosomes during Prophase I
● Chromosomes condense and become visible.
● Homologous chromosomes associate together and form a bivalent via synapsis
● Crossing over of non-sister chromatids forming recombinant chromatids.
Name the point at which non-sister chromatids cross over.
Chiasma
Describe what happens to chromosomes during Metaphase I
● Bivalents line up on the equator, attached to the spindle at the centromere.
● Bivalents orient randomly– either maternal or paternal chromosome can face either pole.
Describe what happens to chromosomes during Anaphase I
Homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles
Describe what happens to chromosomes during Telophase I
Chromosomes reach the poles and they uncoil and lengthen to form chromatin again, losing the ability to be seen clearly.
Describe the events of Prophase II
● Chromosomes condense (shorten and thicken) and become visible due to DNA coiling.
● Centrioles move to opposite poles form spindle fibres.
● Nuclear envelope breaks down and is no longer visible.
● Nucleolus disappears.
Describe the events of Metaphase II
● Chromosomes line up at the equator of the two daughter cells, and attach to the spindle fibres by their centromeres.
● Chromosomes orientate randomly – the recombinant or non-recombinant chromatid can face either pole.
Describe the events of Anaphase II
● Centromeres split into two
● The sister chromatids are separated
● Spindle microtubules shorten and contract causing them to pull the sister chromatids to opposite poles
Describe the events of Telophase II
● Chromatids reach the poles and are now called chromosomes again
● They uncoil and lengthen to form chromatin again, losing the ability to be seen clearly
● Spindle fibres disintegrate
● Nuclear envelope re-forms around the chromosomes at each pole
Name of a chromatid or cell that has a different combination of alleles as a result of crossing over
Recombinant
State the meaning of the term diploid
A cell with a nucleus containing two full sets of chromosomes
State the meaning of the term haploid
a cell with a nucleus containing one complete set of chromosomes
Compare mitosis and meiosis
Products:
● Mitosis produces two daughter cells, whereas meisosi produces four.
● Mitosis produces genetically identical daughter cells, but meiosis produces genetically different daughter cells.
● Mitosis produces diploid daughter cells, where meiosis produces haploid daughter cells.
Events:
● Mitosis has one division, whereas meiosis there is two.
● Recombination of alleles occurs in meisosis but not in mitosis.
● Sister chromatids are separated during anaphase in mitosis, whereas sister chromatids move to same pole during anaphase I in meiosis and are spearated during anaphase II.
Explain Mendel’s Law of Independent Assortment
The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.
The alleles of unlinked genes become independently assorted into the gametes due to random orientation of the chromosomes in
metaphase I, and random orientation of chromatids in metaphase
Explain how meiosis increases genetic variation
● Crossing over swaps sections of non-sister chromatids in prophase I giving rise to new combinations of alleles in gametes.
● Independent assortment of chromosomes gives rise to different combinations of maternal and paternal chromosomes in gametes due to random orientation of homologous pairs in metaphase I and of chromatids in metaphase II.
State what is meant by chromosome mutation
Changes to segments of a chromosome, resulting in large scale changes in the DNA of an organism.
State what is meant by translocation
Segments of two chromosomes are exchanged.
Explain the result of non-disjunction
Non-disjunction is the failure of chromosomes to separate during meiosis, resulting in aneuploidy; one too few or one too many
chromosomes:
● Failure of homologous chromosomes to separate in anaphase I results in affected daughter cells.
● Failure of sister chromatids to separate in anaphase ll results in only two daughter cells being affected.
State what is meant by the term aneuploidy
When a cell contains too few or too many chromosomes
State the term used to describe the absence of one member of a pair of chromosomes
Monosomy
Describe an example of monosomy in humans
Turner’s syndrome occurs in females with a missing X chromosomes (XO).
They are infertile and do not mature without sex hormone treatment.
State the term used to describe the presence of at least one more chromosome relative to normal
Polysomy
Describe an example of polysomy in humans
Down’s syndrome occurs when there is non-disjunction of chromosome 21 in an egg or sperm resulting in two copies of the
chromosome being present. After fertilisation with a normal gamete the resulting zygote will contain three copies of chromosome 21 - trisomy 21
