Cell cycle Flashcards
Chromosome structure
Made of DNA and protein - histone
DNA- double helix, running length of chromosome- sections along length: genes
Chromosomes only visible when chromatin condenses prior to cell division after DNA replication
Two copies - sister chromatids, lie parallel along length, joined at Centromere
Chromatid
One of the two identical copies of a chromosome joined at the central mere prior to cell division
chromosome
Long thin structure of DNA and protein, in the nucleus, carrying genes
Centromere
specialised region of a chromosome which two chromatids join and to which microtubules of spindle attach at cell vision
Haploid
Having one complete set of chromosomes
homologous
Chromosomes in homologous pairs are identical in size and shape and they carry the same gene- loci.
One chromosome of each pair comes from each parent
Same pairs of sex chromosomes eg. X,Y are different sizes on and not homologous pairs
diploid
Having two complete sets of chromosomes
ploidy level
Number of complete sets of chromosomes in an Organism
polyploid
Organisms with more than two complete sets of chromosomes
Mitosis
Cell division in which two daughter cells have the number of chromosomes and are genetically identical with each other and the parent cell
4 stages
Cell cycle
Sequence of events that take place between the cell division and the next
interphase
Period of synthesis and growth
Longest phase of the Southside core with much metabolic activity
Made up of G1, G2, S phase, mitosis and cytokinesis
G1
Organelles are replicated, if the cell possesses restriction points it must divide
If it doesn’t, it can differentiate and become locked in G1
Stem cells are temporarily out of cycle and are in G0
G2
Organelles needed for division are replicated
Energy reserves are built up as ATP is needed for division
stages of mitosis
Prophase
metaphase
Anaphase
Telophase
Prophase 1
mi
- chromosomes condense, coil and gets shorter and thicker.
become visible as long thin threads
become distinguishable as pairs of chromatids
Prophase 2
mi
Centrioles present in animal cells separate and moves to opposite ends (poles) of cell
organises a partner as they move. by the time they reached the poles they are in pairs again
prophase 3
mi
Protein microtubules form, radiating from each centriole making the spindle. Spindle Fibre extend from pole to pole to the centromere of each chromosome
Prophase 4
mitosis
towards the end of prophase, nuclear envelope disintegrates and the nucleolus disappears
Pair of chromatids can clearly be seen lying free in cytoplasm
Metaphase
Each chromosome is a pair of chromatids joined at the centromere
Centromere attaches to the Spindle fibres so that chromosomes are aligned at the equator
Anaphase
rapid stage
Rapid stage
Spindle fibres shorten and centromere separate, pulling the now seperated chromatids to the poles, centromere first
Telophase
Chromatids reach poles of cells - chromosomes
Chromosomes uncoil and lengthen
Spindle fibres breakdown
Nuclear envelope reforms, nucleolus reappears
cytokinesis
Division of nucleus by mitosis is followed by cytokinesis which is a division of cytoplasm to make two cells
cytokinesis in animal cells
Occurs by construction of the parent cell around the equator from the outside inwards
cleavage furrow
cytokinesis in plant cells
droplets of cell wall material, a cell plate, form across the equator of the parent cell from the centre outwards and they extend and join to form the new cell wall
Difference between mitosis in animal and plant cells
Shape, centrioles, cytokinesis, spindle, occurrence
shape:
A- cell becomes rounded before mitosis
P- No shape change
Centrioles:
A- present
P- Absent from higher plant cells
Cytokinesis:
A- cleavage Furrow develops from outside inwards
P- Cell plate develops from centre outwards
Spindle:
A- Degenerates at telophase
P- Remains throughout new cell wall formation
Occurrence:
A- In mammals, epithelia, born marrow, hair folicles, nail beds for cell replacement. Other sites for tissue repair
P- meristems
significance of mitosis- chromosome number
Mitosis produces two cells that have the same number of chromosomes as the parents cell and as each other
Daughter cell is exact replica of parental cell
Mitosis produces genetically identical cells- giving genetic stability
significance of mitosis- growth
producing new cells - and grows, repairs tissues and replaces dead cells
Significance of mitosis- asexual reproduction
asexual reproduction produces complete offspring genetically identical to parent
controlled genes
length of cell cycle
Controlled by genes - ensuring mitosis occurs appropriately
allowed timely replacement of cells and repaired tissues in adults and correct development in embryos
Meiosis
Two stage cell division in sexually reproducing organisms that produce four genetically distinct haploid gametes each with half the number of parent cell
number of chromosomes in meiosis
diploid to haploid
In meiosis, diploid number has halved into haploids.
Haploids gametes fuse art fertilisation, zygote formed has two complete sets of chromosomes- one from each gamete
Restoring diploid condition
Without halving, number would double every generation
if genes are damaged
Sell me fail to divide or divide too much at the wrong time
Radiation, some chemicals and viruses can mutate DNA and DNA sequencing can identify specific gene mutations that affect this time of cell cycle
tumour suppressor genes
Gene controls the cell cycle by acting as a brake preventing cell cycle from repeating continually
Called tumour suppressor genes as they prevent rapid replication, which could lead the tumours
Formation of a tumour
If genes are mutated - break is damaged and cell may go immediately from one round of mitosis to the next and cells replicate too fast
In solid tissue, tumour forms
In bone marrow, immature blood cells accumulate that they spill out into general circulation as blood cancers
proto-oncogenes
genes that have the potential to cause cancer If they become mutated or sellers infected with a virus
oncogenes
Genes that once altered and able to cause cancer
cancer
uncontrolled mitosis
2 divisions of meiosis
Meiosis 1
Meiosis 2
Each division goes through the same sequence of steps as meiosis
Between two divisions there is no more DNA replication. Only happens once before meiosis 1.
Meiosis 1 summary
Homologous pairs separate. Daughter cell has half the initial number of chromosomes, but each chromosome comprises two chromatids
meiosis 2 summary
Chromated separate. Store to sell has the half initial number of chromosomes, each with only one chromatid
Prophase 1
of meiosis
Parental and maternal chromosomes come together in homologous pairs. Pairing called synapsis, each homologous chromosome pair is a bivalent
Chromosones coil app, condensing, shorter and thicker. Visible as two chromatids
Centrioles separate and move to the poles of the cells
Centrioles organise the polymerisation of microtubules, which radiates out of them, spindle forms
how does prophase 1 differ from prophase in mitosis
Homogeneous chromosomes associates in their pairs- bivalent
Chromatids wrap around each other and partially repel but remain joined at Chiasmata
prophase 1- at chiasma
A segment of DNA from one chromatid may be exchanged with equivalent part from a chromated of homologous chromosome
Swapping is called crossing over and is a source of genetic variation - mixes jeans from two parents in one chromosome
genetic recombanation- prophase 1
Produces new combinations of alleles
Single crossover occurring during meiosis 1 results in four haploid gametes having different compositions
Crossing over can happen at several places along chromatid therefore huge numbers of genetic combinations
end of prophase 1
meiosis
Nuclear envelope disintegrated and nucleolus has disappeared
metaphase 1
Pair of homologous chromosomes arrange themselves at equator of Spindle
Lie at equator randomly, with either one facing either Pole
Independent assortment
Either of a pair of homologous chromosomes faces to either Poel at Metaphase one of meiosis, independently of the chromosomes of other homologous pairs
Either of a pair of chromatids faces to either pull at metaphase two independently of the chromatids of other chromosomes
Anaphase 1
chromo in each biv
Chromosomes in each by bivalent separate
Spindle fibres shorten
Each pair is pulled to one pole and the other to the opposite pole
Each poem receives only one of each homologous pair of chromosomes and because of random arrangement at the metaphase 1, there is a random mixture of maternal and parental chromosomes
Telophase 1
in some
In some species, the nuclear envelope reforms around the haploid group of chromosomes and the chromosomes decondense and are no longer visible.
In many species, the chromosomes stay in their condensed form
Cytokinesis 1
Division of cytoplasm occurs, making two haploid cells
Prophase 2
centrioles seperate
organise
central separate and organised a new spindle at right angles to the old spindle
metaphase 2
b cen
Chromosomes line up on the equator with each chromosome attached to a spindle fibre by its centromere
Independent assortment happens because chromatids of chromosomes can face either pole
Anaphase 2/
meiosis
Spindle Fibre shorten and centromere separate, chromatids to opposite poles
Telophase 2
At the poles, the chromatids lengthen and can no longer be distinguished in the microscope
Spindle disintegrates and the nuclear envelope and nucleoli reform
Cytokinesis takes place, producing four haploid daughter cells
significance of meiosis
Keeps chromosome number constant from one gen to the next
gen
Genetic variation in the gummy the zygotes that they produce.
Two ways genetic variation occurs
- Crossing over during prophase 1
- independent assortment at:
Metaphase 1, so that daughter cells contain diff combos of maternal and parental chromosomes
Metaphase 2, so daughter cells have diff combis of chromatids
In order for species to survive in constantly changing environments and to colonise new ones
comparison of meiosis 1 and meiosis 2
1‘
prophase, metaphase, anaphase
Meiosis 1:
Prophase- follows DNA replication and crosses over
Metaphase- homologous pairs aligned either side of equator and independent assortment of homologous chromosomes
Anaphase- chromosomes separate, 2 daughter cells, haploid
comparison of meiosis 1 and meiosis 2
2’
Meiosis 2:
Prophase- doesn’t follow DNA replication and doesn’t cross over
Metaphase- chromosomes aligned at equator and chromatids are independently assorted
Prophase- separation of chromatids, 4 daughter cells, haploid
comparison of mitosis and meiosis
Mitosis
Mitosis:
One number of divisions
Two daughter cells
Same chromosome number in daughter cells as parent cell
Diploid daughter cells
Absent chiasmata
No genetic crossing over
No independent assortment
Genetic composition is genetically identical with parent cell and each other
Comparison of mitosis and meiosis
Meiosis
Meiosis:
Two number of divisions
Four daughter cells
Chromosome number in daughter cells is half the number of parents
Haploid
Present chiasmata
Independent assortment in metaphase 1 &2
Genetic crossing over in prophase 1
Genetically different genetic composition
s phase
DNA is synthesised
Amounts of DNA doubles and after DNA replicated it now consists of two identical strands joined at a centromere. Each strand is a chromatid
