BIOL1040 Lecture Notes - Lecture 16: G1 Phase, Sister Chromatids, Cell Division

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MITOSIS
LEARNING GOALS
Purpose of cell division
DNA organisation chromatin
Types of chromosomes
Cell division M phase, G1 phase, S phase, G2 Phase, Interphase (G1-G2 Phase)
Mitosis Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Cytokinesis
CELL DIVISION
Cell division is essential for growth and reproduction
Unicellular organisms (both prokaryotic and eukaryotic) cell division is reproduction
Multicellular organisms cell division allows them to grow from a single cell fertilised egg.
Also repairs and renewal of cells, e.g. bone marrow making new blood cells
Most cell division results in genetically identical daughter cells
More cell division to occur there has to be a rearrangement of the cell to ensure daughter cells
are the same
DNA ORGANISATION
DNA is organised in millions or billions of base pairs
Each human cell has about 2 m of DNA
This DNA must be copied before division
DNA is packaged into chromosomes which are non- condensed (apart from when division
occurs)
Prokaryotes have one cirular hroosoe • Huas hae  pairs
Referred to as chromatin when DNA bound with protein
CHROMATIN
In a Resting Nucleus where no division is occurring no chromosomes are present.
Heterochromatin densely stained inactive chromatin
Euchromatin less densely stained active chromatin
Chromatin has a regular structure.
It has a eads o a strig appearae, hih are alled Nuleosoes.
The Nucleosome is the fundamental packing unit of the Chromatin / DNA & Histone.
The Protein Histone locks the structure together.
DNA TO CHROMOSOME
Duplicated chromosomes are made up of sister chromatids
These are joined all along their length but more closely at the centromere
Repetitive DNA
sequences along binding by proteins gives a waist
Chromatid arms
3 FORMS OF A CHROMOSOME
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CHROMOSOME NUMBER IN A SPECIES
All members of a species have the same number of chromosomes in their Somatic Cells (Body
Cells).
There are two of each type of Chromosomes in the cells. Each pair has the:
o Same length
o Centromere location
o Hereditary instructions dealing with the same traits
These are referred to as Homologous Pairs or Homologous Chromosomes.
EXAMPLES OF CHROMOSOME NUMBERS
CHROMOSOME
HOMOLOGUS
PAIRS
Mosquito
6
3
Garden Pea
14
7
Frog
26
13
Earthworm
36
18
Human
46
23
Gorilla and Chimpanzee
48
24
Adder's tongue fern
1000+
500+
CHROMOSOME NUMBERS
When a species grows it is the process of Mitosis that assures that the number of
Chromosomes are maintained through division after division.
The full compliment of chromosomes is the Diploid (2N) number of Chromosomes of which
there are two of each type in somatic cells.
o Ploidy refers to the number of Chromosome Sets.
o 23 Homologous pairs in Humans
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o Haploid (1N) is 1 set which we will look at in
Meiosis! Gametes have these but WHY???
CHROMOSOME NUMBER MITOSIS
MITOSIS
Miotosis is the division of a cell into two daughter cells containing the same number of
chromosomes as the parent
Meiosis daughter cells have half the chromosomes (eggs, sperm)
After division of DNA there is division of the cytoplasm - cytokinesis
Cell Division is different in Prokaryons and Eukaryons.
CELL DIVISION IS PROKARYOTES
Prokaryotes have a single, circular DNA molecule attached to plasma membrane.
DNA is circular allowing it to fit inside the cell since it is up to 500 x longer than the cell.
Chromosome attached to membrane.
Chromosomes replicates (origin of replication) and both are attached to the cell membrane.
Cell growth occurs to approximately double its size.
Eventually plasma membrane pinches inward forming two new cells.
Referred to as Binary Cell Division or Binary Fission.
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Document Summary

Learning goals: purpose of cell division, dna organisation chromatin, types of chromosomes, cell division m phase, g1 phase, s phase, g2 phase, interphase (g1-g2 phase, mitosis prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis. It has a (cid:862)(cid:271)eads o(cid:374) a stri(cid:374)g(cid:863) appeara(cid:374)(cid:272)e, (cid:449)hi(cid:272)h are (cid:272)alled nu(cid:272)leoso(cid:373)es. Dna to chromosome: duplicated chromosomes are made up of sister chromatids, these are joined all along their length but more closely at the centromere, repetitive dna, chromatid arms sequences along binding by proteins gives a waist. Chromosome number in a species: all members of a species have the same number of chromosomes in their somatic cells (body. Cells): there are two of each type of chromosomes in the cells. Each pair has the: same length, centromere location, hereditary instructions dealing with the same traits, these are referred to as homologous pairs or homologous chromosomes. Chromosome numbers: when a species grows it is the process of mitosis that assures that the number of.

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