The Cell Cycle and Cell Division Flashcards
What is binary fission?
Cell division in prokaryotic cells
What are the three phases of eukaryotic cell division?
Interphase, mitosis and cytokinesis.
Can chromosomes be resolved by light structures?
no
How do chromosomes appear under a light microscope?
like diffuse structures: chromatin.
What are the 5 important features of chromosomes?
- Characteristic Shape
- Homologous pairs
- Fixed number between species.
- Homologous chromosomes may not carry the same alleles
- Chromosome are copied before mitosis so they appear to have doubled.
What is the centromere
The region in between the p and the q ends of the chromosome..
Always in the same position.
Whaat is a somatic cell?
Any cell in the body that isn’t a germ cell or an undifferentiated stem cell.
What is a homologous chromosome?
A pair of chromosome in a diploid cell that has the same size and shape. They also carry the same genes in the same order, but not necessarily the same alleles.
What is a diploid organism?
one that carries two copies of each chromosome
How many chromosomes in somatic cells of humans?
46 (22 autosomes diploid + XX or XY)
What does karyotype mean?
The number and shape of chromosomes in a somatic cells of a particular organism
What does locus mean?
The position a particular gene occupies on a specific chromosome
What is an allele?
One of two or more different forms of the same gene
What is a chromatid?
The chromosome after DNA replication and before mitosis, when the chromosomes are condensed
What are the stages of interphase?
G1, S and G2
What happens during G1?
Cytoplasm is active,
New organelles are formed so cytoplasm increases in size,
Cells are biochemically activated to grow
Pre-mRNA is synthesized
Pre-mRNA becomes mature-mRNA
What happens during S phase?
Semi-conservative replication occurs
New histones are synthesized and attached to new DNA
Each chromosome becomes two chromatids, attached via the centromere
Growth continues
What happens during G2?
More cell growth, preparation for mitosis
Replicated DNA is checked for errors and corrected.
If correction of DNA is not possible, the cell cycle can be halted here.
Cell growth continues by further synthesis of proteins and organelles
Stages of mitosis
Prometaphase
metaphase
anaphase
telophase
What happens during cytokinesis?
Division of cytoplasm
Two cells formed.
What happens in prophase?
Chromosomes increasingly shorten into a super-coiled structure. - become visible as long, thin threads.
Nucleolus disappears and the nuclear membrane breaks down.
Centrioles divide and move to opposite ends of the cell, radiating a network of microtubules which form the spindles.
Spindle fibers attach to the centromeres and begin to contract to move the chromosomes apart
What happens in metaphase?
The chromosomes are aligned down a centre.
They line up on the equator of the spindle
What happens in anaphase?
The centromere of each chromosome divides
The spindle fibres attached to them shorten, resulting to two chromatids being pulled by their centromeres to opposite poles of the spindle - once separated the chromatids are referred to as chromosomes again
What happens in telophase?
The nuclear membrane reforms around both groups of chromosomes at opposite ends of the cell.
Chromosomes decondense
What happens in cytokinesis of animals
This is different in animal and plants cells. Animals:
A cleavage furrow develops in the middle of the cell
Contraction o this furrow ‘pinches’ the cytoplasm in half, as this happens the organelles become distributed between the two cells.
What happens in cytokinesis of plant cells?
Vesicles of the Golgi collect along the equator of the spindle, known as the cell plate.
These vesicles secrete a gel-like layer of calcium pectate called the middle lamella.
On to this, they secrete transverse layers of microfibers of cellulose, forming the cell wall.
More layers of cellulose are added, often at right angles, forming the secondary cell wall.
Many cell walls become impregnated with lignin.
What does meristem mean?
A group of plant cells that are able to divide by mitosis
How many daughter cells does meiosis produce?
4
How meiosis daughter cells genetically identical of different?
different.
Where does meiosis occur in humans?
Gonads - testes and ovaries
what karyotype are the daughter cells produced from meiosis?
haploid
What happens during meiosis I?
Homologous chromosomes are separated
What happens during Meiosis II?
Chromatids of each chromosome are separated
Stages of meiosis in sequence
Prophase I (Early) Prophase I (Mid) Prophase I (late) Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II
Prophase I (Early, mid and late)
E. The replicated chromosomes become condensed - shorter and thicker.
M. Homologous pairs align and centrioles duplicate
L. Chromosomes repel each other. Sites where chromosomes have broken and rejoined are now visible
Metaphase I
Nuclear membrane breaks down
Spindles form
Bivalents line up at the equator, attached via centromeres
Anaphase I
Homologous chromosomes separate
Whole chromosomes are pulled towards opposite poles of the spindle, centromere first.
Telophase I
Nucealr membrane reforms around the nuclei.
chromosome numbers have halved
Chromosomes start to decondense
Prophase II
Chromosomes condense
Centrioles duplicatte
Metaphase II
Nuclear membrane breaks down
Spindles form
Chromosomes attach to the spindles via their centromeres at the equator of the spindle
Anaphase II
Chromosomes separate at their centromeres
Telophase II
Chromosomes decondense
Nuclear membrane reforms
What does bivalent mean?
The name given to two homologous chromosomes in a diploid cell when they are seen paired together during meiosis I. As each chromosome is currently present as two chromatids, there are four chromatids in a single bivalent.
Non-sister chromatids
Chromatids on different pairs of homologous chromosomes
What is a Chiasma?
A point seen during meiosis I at which the non-sister chromatids seem locked
What does “crossing over” mean in meiosis?
The process of non-sister chromatids exchange genes following chiasma.
What is chromosome translocation?
When part of a chromosome breaks off and rejoins a different chromosome.
What is chromosome non-disjunction?
The failure of homologous chromosomes to separate properly during the first division f meiosis, resulting in daughter cells with either too few or too many chromosomes.
What does polysomy mean?
Describes a diploid organism with more than two copies of a particular chromosome
What does monosomy mean?
Describes a diploid organism with only one copy of a particular chromosome.
An example of monosomy in humans
Turners syndrome
What is Turner’s syndrome? (genetically)
When women only have one copy of the X chromosome
An example of polysomy in humans
Downs syndrome
What is downs syndrome? (genetically)
Non-disjunction of Chr 21, resulting in three copies, giving them 47 chromosomes in total.
