Lecture 13 (Eukaryotic cell division - mitosis) Flashcards
What areas of human endeavour does genetics impact?
Medicine Law Agriculture Sociology Philosophy Ecology Agriculture
How do acellular life store genetic information?
Viruses generally store their genetic information as double-stranded or single-stranded, DNA or RNA
How do prokaryotic organisms store genetic information?
Bacteria generally store their genetic information ass circular, single copy, naked (not surrounded by a vast amount of proteins like eukaryotes) double-stranded DNA
How do eukaryotic organisms store genetic information?
Protists, animals, plants and fungi generally store their genetic information as linear, greater than or equal to one single copy, histone-bound DNA; sexual cycle
How much DNA does a human have?
Each 3000 base pairs is approximately 1 micron. Humans have 3x10^9 base pairs therefore each human cell contains about 2 metres of DNA. Humans have approximately 21000 genes.
Karyotype
An ordered, visual representation of chromosomes in a cell.
Karyotype process
You start off by getting cells t a very particular stage in cell division (metaphse)
Take blood sample
Treat cells with mitogen
Then colchicine
Then stain
Human chromosomes
1-22 are called autosomes
X and Y are sex chromosomes
Autosome
An autosome is any chromosome that is not a sex chromosome
Homologous pairs
Chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the mother; the other is inherited from the father.
Locus
Particular location where the gene is found
Gene
a sequence of nucleotides in DNA or RNA that encodes the synthesis of a gene product, either RNA or protein
A gene is a section of DNA that codes for a protein
Allele
Alternative form of a gene
Difference forms of a gene at that locus
Homozygote
2 alleles are the same at that particular locus
Heterozygote
2 alleles are different at that particular locus
Multicellular organisms depend on cell division for …
Development from a fertilised cell (growth and development)
Growth to adult (10^14 - we get here because the original cell divided and the cell division of those products formed occurs etc. etc.)
Repair
How does a eukaryotic cell divide its DNA equally?
Basically, all you cells (except a few that have mutations) have the same DNA sequence (same geners, same chromosomes). This occurs because of a specific way that chromosomes are organised during cell division so that every cell gets a copy of every chromosome. Makes sure cell division gives you products that are essentially genetically identical to the cells that they have come from…this is what mitosis does
Stages of the cell cycle
G1, Synthesis phase, G2 and then mitosis
Chromosome
A cellular structure consisting of one DNA molecule and associated protein molecules.
Interphase
Interphase is the phase of the cell cycle in which a typical cell spends most of its life. During interphase, the cell copies its DNA in preparation for mitosis.
G1 phase
A cell grows during this phase
Cellular growth and production of proteins and other materials
Synthesis phase (S phase)
A cell continues to grow as it copies its chromosomes
Cell replicates its DNA during S phase
The newly replicated chromosomes which are dispersed in the nucleus in the form of thread like strands of chromatin, slowly begin to coil and condense into a compact form which we can see under a light microscope. The condensed replicated chromosomes each consist of two replicates called chromatids joined together by a constricted area known as the centromere. At this constricted region, each of the two chromatids of a replicated chromosome has a kinetochore, a special structure of proteins and DNA
G2 phase
A cell keeps on growing as it completes preparations for cell division
Duplicated chromosome
Two sister chromatids, which later seperate during mitosis
During the S phase of interphase, duplication occurs. Before this you have one copy of each chromosome and then this chromosome duplicates (to form two sister chromatids connected at the centromere) and in anaphase essentially that connection gets spilt apart with one of these chromatids in each cell.
Mitosis
Cell division that produces two genetically identical daughter cells // the division of one nucleus into two genetically identical nuclei
Consists of 5 phases - prophase, prometaphase, metaphase, anaphase, telophase
Five phases of mitosis
prophase, prometaphase, metaphase, anaphase, telophase
Prophase
Every chromosome has doubled into a pair of sister chromatids, so there are two sister chromatids that are genetically identical to one another
The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope
Spindle (made up of microtubules) begins to form
This is the first stage of mitosis
Prometaphase
Nuclear envelope fragments
Chromosomes have become even more condensed
A kinetochore, a specialised protein structure, has now formed at the centromere of each chromatid (therefore there are two per chromosome)
Some of the microtubules attach to the kinetochores, becoming “kinetochore microtubules” which jerk the chromosomes back and forth
Non-kinetochore microtubules interact with those from the opposite pole of the spindle, lengthening the cell
Metaphase
Pairs of sister chromatids line up along the central part of the cell which is known as the metaphase plate (halfway between the two centrosomes)
Chromosomes/pairs of sister chromatids line up in an organised way due to the connection via the kinetochore to the kinetochore microtubule, so the kinetochore microtubules act in such a way that all the chromosomes are lined up on the metaphase plate
Spindles consist of both kinetochore microtubules and the non-kinetochore microtubules and the non-kinetochore microtubules as well as the centrosomes at opposite side of the cell
The chromosomes’ centromeres now lie at the metaphase plate
For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles
Anaphase
Mitosis works because in anaphase, the parts of sister chromatids get ripped apart, one going to one side and the other chromatid going to the opposite side. Remember that each sister chromatid is a copy of the other one so you are effectively sending one lot of genetic information one way and another lot in the opposite direction. This works because the kinetochore microtubules getting shorter which pulls the sister chromatids apart right at the centromere. The non kinetochore microtubules get longer and push the two ends of the cell apart
By the end of anaphase, the two ends of the cell have equivalent and complete collections of chromosomes
Telophase and cytokinesis
telophase - Furrow starts to form, nucleolus forming, nuclear envelope forming, chromosomes become less condensed, mitosis is now complete
Cytokinesis - this is how the cytoplasm divides, eventually the two cells will seperate and there will be a cell membrane surrounding them (and if you are talking about plant cells then there could be a cell wall that forms as well). Cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two
Each daughter cell of mitosis has…
One copy of every chromosome (sister chromatids seperate during anaphase)
Sister chromatids in mitosis each have…
1 double-stranded copy of their DNA molecule
During mitotic anaphase what happens to non-kinetochore and kinetochore microtubules …
Non-kinetochore microtubules lengthen and kinetochore microtubules shorten
Kinetochore microtubule
Spindle microtubules that attach to the kinetochores. The kinetochore microtubules attach to chromosomes and move them towards poles.
A pair of sister chromatids are connected by the centromere and the centromere connects to the kinetochore which connects to the kinetochore microtubule.
Non-kinetochore microtuble
Spindle microtubules that do not attach to kinetochores. Nonkinetochore microtubules are responsible for elongating the cell during anaphase.
Kinetochore
a complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach.
Centrosome
an organelle that is the main place where cell microtubules are organized
Centromere
The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore.
Mitosis rate in skin versus muscle and neurons
In humans, our skin cells have a high turnover rate due to wear and tear and go through mitosis very frequently whereas other cells such as adult neurons and muscle cells rarely divide
Chromatin
Chromatin is a mass of genetic material composed of DNA and proteins that condense to form chromosomes during eukaryotic cell division. Chromatin is located in the nucleus of our cells.
Replicated chromosome
A replicated chromosome is considered to be one chromosome consisting of two chromatids.
Chromatid in anaphase
Remember that during anaphase each chromatid becomes a single chromosome
