BIOL1040 Lecture Notes - Lecture 16: G1 Phase, Sister Chromatids, Cell Division
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 cirular hroosoe • Huas hae 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 strig appearae, hih are alled Nuleosoes.
• 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.