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Dr Pramote Chumnanpuen 01424111 Bio- Cell Cycle and Cell division

Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet. Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Modified from David Knuffke.

Ivlote Pramote

on 25 September 2017

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Transcript of Dr Pramote Chumnanpuen 01424111 Bio- Cell Cycle and Cell division

Cell Division
Big Questions:
Make Sure You Can:
Why Divide?
The Cell Cycle
The "continuity of life"
In order to survive, the individual must replace damaged cells.
In order to grow, cell production must be greater than cell death.
In order to survive, the species must replace individuals.
Cell division accomplishes these purposes.
A dividing amoeba
A dividing bone marrow cell
A dividing sea urchin embryo
The phases of a cell's life
G1- growth
S- DNA replication
G2- preparation for division
M - Mitosis

G0- Non-dividing state (most cells in you)
Very tightly controlled (why?)
Tightly coiled pieces of DNA that condense prior to division
Prokaryotes only have one, circular chromosome.

Eukaryotes have many, linear chromosomes
Most eukaryotic cells have 2 copies of every chromosome.

They form in attached, identical pairs.

Chromatid: 1 member of the pair
Centromere: region where they are joined
S phase
Make sure you understand the chromosome, chromatid relationship

It can be confusing...
Haploid vs. Diploid
1 copy of every chromosome (n)
2 copies of every chromosome (2n)
Human cells have 23 pairs of chromosomes

How many chromatids are present during:
Chromosomes Condense
Nuclear envelope breaks down
mitotic spindle begins to form
Animal cells: centrioles divide.
Chromosomes begin to migrate to cell equator.
2 complete spindles at cell poles.
Chromosomes are at metaphase plate.
Spindle attaches to "kinetochore" of chromosomes at centromere
Chromatids split apart at centromere.
Migration of chromatids to cell poles mediated by the kinetochore.
Chromosomes decondense
Nuclear envelope reforms
Cytokinesis: cell membrane divides
Replication of DNA
Preparation for division

Most of a cells life cycle
Newt, Whitefish, Onion
Differences between plant-like and animal-like cells (Why?)
A "contractile ring" of microfillaments pinches the cell in 2
Vessicles from both cells deposit a new cell wall partition ("cell plate") in the middle of the cell.
Organelle apportionment is essentially random.
Mitosis at a Glance
The Evolution of Mitosis
There are more similarities between eukaryotic and prokaryotic cell division than might be apparent at first glance.

Proteins involved in binary fission
& eukaryotic cell division have a
large degree of homology.
Some unicellular eukaryotes demonstrate "intermediate" modes of division.
Binary fission in bacteria
(aka "rolling circle replication")
Let's play "spot the phases"
"Non-Reductive" Eukaryotic Cell Division
Describe the roles that mitosis plays in eukaryotic organisms.

Explain how mitosis produces two genetically identical cells

Explain how interphase prepares a cell for mitosis.

Explain why many cells never divide.

Explain the function of each stage of mitosis

Compare the events of mitosis in plant-like and animal-like cells
Why do cells need to divide?

How does cell division provide for continuity of life processes in an individual and in a species?
"Binary Fission"
The splitting of the cell into two.
Watch it Happen!
(Meiotic cell division)
In humans and most animals, cells formed by meiotic division become gametes (sperms or eggs)
In plants, meiotic cell division results in the formation of meiospores that grow into haploid gametophytes
The basic result of meiosis is the same; haploid cells with increased genetic variation.
Chromosome and centriole replication occur in the S stage of interphase, Prior to the start of meiosis.
Meiosis - II
Cell Phases
The replicated members of each chromesome pair join together in a side-by-side pairing called

Begins with the separation of the members of each chromosome pair.
The centromeres do not separate
Each chromosome still consists of two sister chromatids joint at their centromeres.
Members of each chromosome pair migrate to opposite poles of the spindle in the replicated state.
Synapsed chromosomes lining up at the equatorial plane.
An exchange of chromosome segments (Crossover) frequently occurs between members of the
genetic variability
Bivalents show in the forms of X, 0, 8, + or helix
Forming a
nuclear membrane
around each set of chromosome.
chromosomes untwist
nucleolus reappears
Separate the parent cell into two daughter cells.
The nucleus of each daughter cell contains only one member of each chromosome pair in a replicated state.
Each daughter cell is haploid (n)
The centrioles replicates but chromosomes do not replicate again
The chromosomes lining up at the equator of the spindle
Each chromosome consists of two sister chromatids joined together at the centromere, kinetochore is attached to a spindle fiber.
Loss of the nuclear membrane and nucleolus.
Spindle formation attach to kinotochore of each chromosome.
The appearance of rod-shaped chromosome.
Begins with the separation of the centromeres
The sister chromatids now called daughter chromosomes, move toward opposite poles of the spinddle
Cytokinesis divides the cell to form four haploid (n) daughter cells.
To form the new nuclei.
Both cells formed by meiosis I divide again in meiosis II.
Try to identify the cell phase on each figure....
Mitosis Vs Meiosis
Occurs in both haploid (n) and diploid (2n) cells.
Completed when one cell divides to form two cells.
Duplicated chromosomes do not align themselves in homologous pairs during division.
The two daughter cells contain (a) the same genetic composition as the parent cell and (b) the same chromosome number as the parent cell.
Occurs in diploid (2n) cells, but not in haploid (n) cells.
Requires two successive cell divisions to produce four cells form the single parent cell.
Duplicated chromosomes arrange themselves in homologous pairs during the first cell division.
The four daughter cells contain (a) different genetic compositions and (b) one-half the chromosome number of the parent cell.

Cell Cycle Cell Division
Dr. Pramote Chumnanpuen
Department of Zoology
Faculty of Science
Kasetsart University
contact me ...Room 207
email ; pramote.c@ku.ac.th
The duration of G1 is very variable, in human cells is taken about 11 hours.
Synthesize new protein, nucleotides
Near the end of G1, a proportion of body cells pass a critical point, called the restriction point -->
The cells become committed and will complete their cycles and divide to form new cells
Any cell which does not pass the restriction point is unable to divide.
In most organisms, differentiated tissue cells lose the ability to divide and remain locked in G1 (or G0)
The durations of S is far less variable. (in human cells about 8 hours)
Two important events occur during the S stage
First, all the cell’s DNA undergoes replication by the semi-conservative process. -->
Each chromosome consists of two identical molecules of DNA.
Second, duplication of centrioles.
The cell mobilizes its resources for cell division
The chromosomes begin the long process of condensation, coiling ever more tightly.
4 hours
Karyokinesis (Dividing of nucleus)
4 stages
1 hour

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