mitosis and meiosis
DESCRIPTION
Cell divisionTRANSCRIPT
©2000 Timothy G. Standish
Isaiah 61:1-31 The Spirit of the Lord GOD is upon me; because the LORD hath anointed
me to preach good tidings unto the meek; he hath sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound;
2 To proclaim the acceptable year of the LORD, and the day of vengeance of our God; to comfort all that mourn;
3 To appoint unto them that mourn in Zion, to give unto them beauty for ashes, the oil of joy for mourning, the garment of praise for the spirit of heaviness; that they might be called trees of righteousness, the planting of the LORD, that he might be glorified.
©2000 Timothy G. Standish
MitosisMitosisand Meiosisand Meiosis
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
Mitosis: In The Beginning OneMitosis: In The Beginning One Most of the organisms we see started out as one cell Humans start out as a single cell, the zygote, formed by
uniting a sperm and egg The zygote divides to make approximately one trillion
cells During the process of dividing, cells become
specialized to function in the various tissues and organs of the body
Mitosis is the process of cell division in eukaryotic cells
©2000 Timothy G. Standish
Egg1n
Haploidnucleus
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Sperm1nHaploid
nucleus
©2000 Timothy G. Standish
Sperm1n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
Sperm1n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
Sperm1n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
From Zygote to EmbryoFrom Zygote to Embryo
Zygote2n
Zygote
2n
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Morula
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Why Cells Must DivideWhy Cells Must Divide In multi-celled organisms (like humans) cells
specialize for specific functions thus the original cells must divide to produce different kinds of cells
Cells can only take in nutrients and excrete waste products over the surface of the membrane that surrounds them. The surface to volume ratio decreases with the square of the volume (unless special accommodations are made)
2 cmSurface 24 cm2/volume 8 cm3 = 3
1 cm
Surface 6 cm2/volume 1cm3= 6
©2000 Timothy G. Standish
The Cell LifecycleThe Cell Lifecycle The cell lifecycle is well defined and can be
divided into four stages:– Gap 1 (G1) - The growth phase in which most cells
are found most of the time– Synthesis (S) - During which new DNA is synthesized– Gap 2 (G2) - The period during which no
transcription or translation occurs and final preparations for division are made
– Mitosis - Cell division
©2000 Timothy G. Standish
G1G1
MM
G2G2
SS
The Cell Life CycleThe Cell Life CycleGap 1 - Doubling of cell size. Regular cellular activities. transcription and translation etc.
Synthesis of DNA - Regular cell activities cease and a copy of all nuclear DNA is made
Gap 2 - Final preparation for division
Mitosis - Cell division
©2000 Timothy G. Standish
Stages Of MitosisStages Of MitosisDuring mitosis an exact copy of the
genetic material in the “mother” cell must be distributed to each “daughter” cell
Each stage of mitosis is designed to achieve equal and exact distribution of the genetic material which has been copied during the S phase of the cell cycle
©2000 Timothy G. Standish
Stages Of InterphaseStages Of Interphase Interphase - The in between stage - Originally
interphase was thought to be a resting stage. Now we know that this is the stage most cells spend their time in as they do the things cells do including, if they are preparing to divide, growing and replicating their DNA
G1G1
MM
G2G2
SS
Interphase
©2000 Timothy G. Standish
Stages Of MitosisStages Of Mitosis Prophase - The beginning phase - DNA which was
unraveled and spread all over the nucleus is condensed and packaged
Metaphase - Middle stage - Condensed chromosomes line up along the equator of the cell
Anaphase - One copy of each chromosome moves to each pole of the cell
Telophase - End stage - New nuclear membranes are formed around the chromosomes and cytokinesis (cytoplasm division) occurs resulting in two daughter cells
©2000 Timothy G. Standish
Stages Of MitosisStages Of Mitosis
Interphase
Anaphase
Telophase
Metaphase Mitotic spindle
Prophase
Nucleus with un-condensed chromosomes Equator
of the cell
Condensed chromosomes
Disappearing nuclear membrane
Poles of the cell
Mother cell
Two daughter
cells
Metaphase plate
©2000 Timothy G. Standish
A TT AG CC
G
G C
TA
T
AG
C
C G
G C
T A
A T
Packaging DNAPackaging DNA
Histone proteins
Histoneoctomer
B DNA Helix 2 nm
©2000 Timothy G. Standish
A TT AG CC
G
G C
TA
T
AG
C
C G
G C
T A
A T
Packaging DNAPackaging DNA
Histone proteins
B DNA Helix
Histoneoctomer
2 nm
©2000 Timothy G. Standish
A TT AG CC
G
G C
TA
T
AG
C
C G
G C
T A
A T
Packaging DNAPackaging DNA
Histone proteins
Histoneoctomer
Nucleosome
11 nm
B DNA Helix 2 nm
©2000 Timothy G. Standish
Packaging DNAPackaging DNA
A TT AC G
C G
G C
T A
A T
©2000 Timothy G. Standish
Packaging DNAPackaging DNA
A TT AC G
C G
G C
T A
A T
©2000 Timothy G. Standish
Packaging DNAPackaging DNA
A TT AC G
C G
G C
T A
A T
Protein scaffold
11 nm“Beads on a string”
30 nm
Tight helical fiber
Looped Domains200 nm
©2000 Timothy G. Standish
Packaging DNAPackaging DNA
G
C
A
T
Protein scaffold
Metaphase Chromosome
700 nm
11 nm
30 nm200 nm
2 nm
Looped Domains
Nucleosomes
B DNA Helix
Tight helical fiber
©2000 Timothy G. Standish
Replication
Chromosomes, Chromatids Chromosomes, Chromatids and Centromeresand Centromeres
Centromere
Chromosome arm
Chromosome arm
Identicalchromatid
Chromatid
Anaphase
A packaged chromosome
Two identical chromosomes
©2000 Timothy G. Standish
Chromosome MorphologyChromosome Morphology
Chromosome arm
Chromosome arm
Centromere
Submetacentric Acrocentric TelocentricMetacentric
q arm
p armpetite
Chromosomes can be distinguished on the basis of size and the relative location of centromeres.
©2000 Timothy G. Standish
Controlling The Cell CycleControlling The Cell Cycle CDC Mutants - Cell Division Cycle mutants helped elucidate
genetic control points of the cell cycle Three major checkpoints controlled by Cyclin dependant kinase
(Cdk) proteins which add phosphates to cyclin proteins changing their activity:
1 G1S - Monitors cell size and checks for DNA damage2 G2M - Ensures physiological conditions are right for division
including completion of DNA replication and any necessary repair3 M - Checks for successful formation of the mitotic spindle and
attachment to the kinetochores
©2000 Timothy G. Standish
p53p53
©2000 Timothy G. Standish
Meiosis: In The Beginning TwoMeiosis: In The Beginning Two Humans and many other complex multi-celled
organisms incorporate genetic recombination in their reproduction
Reproduction in which there is a re-mixing of the genetic material is called sexual reproduction
Two cells, a sperm and an egg, unite to form a zygote, the single cell from which the organism develops
Meiosis is the process of producing sperm and eggs (gametes)
©2000 Timothy G. Standish
Gametes Are HaploidGametes Are Haploid Gametes must have half the genetic material of a normal cell If the genetic material in the gametes was not halved, when they
combined the zygote would have more genetic material than the parents
Meiosis is specialized cell division resulting in cells with half the genetic material of the parents
Gametes have exactly one set of chromosomes, this state is called haploid (1n)
Regular cells have two sets of chromosomes, this state is called diploid (2n)
©2000 Timothy G. Standish
Stages Of MeiosisStages Of Meiosis Meiosis resembles mitosis except that it is
actually two divisions not one These divisions are called Meiosis I and Meiosis
II Meiosis I results in haploid cells with
chromosomes made up of two chromotids Meiosis II is essentially mitosis on haploid cells Stages of meiosis resemble mitosis with two
critical differences: the first in prophase I and the second in Metaphase I
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IStages Of Meiosis - Meiosis I Prophase I - The beginning phase -
– DNA which was unraveled and spread all over the nucleus is condensed and packaged
– Homologous chromosomes (each made of two identical chromatids) come together and form tetrads (4 chromatids)
– Crossing over, in which chromatids within tetrads exchange genetic material, occurs
Metaphase I - Middle stage - Tetrads line up along the equator of the cell
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IStages Of Meiosis - Meiosis I Anaphase I - One copy of each
chromosome still composed of two chromatids moves to each pole of the cell
Telophase I - End stage - New nuclear membranes are formed around the chromosomes and cytokinesis (cytoplasm division) occurs resulting in two haploid daughter cells
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IIStages Of Meiosis - Meiosis II Prophase II - Cells do not typically go into
interphase between meiosis I and II, thus chromosomes are already condensed
Metaphase II - Chromosomes line up at the equator of the two haploid cells produced in meiosis I
Anaphase II - Chromosomes made up of two chromatids split to make chromosomes with one chromatid which migrate to the poles of the cells
Telophase II - Cytokinesis and reformation of the nuclear membrane in haploid cells each with one set of chromosomes made of one chromatid
©2000 Timothy G. Standish
InterphaseInterphase
Mother cell Stages Of Meiosis: Stages Of Meiosis: Meiosis IMeiosis I
Meiosis IIMeiosis II
Prophase I:Tetrad formation/
crossing over
Prophase I:Tetrad formation/
crossing overMetaphase I Metaphase I
Telophase ITelophase I
Prophase I:Condensing
Chromosomes
Prophase I:Condensing
Chromosomes
Anaphase I Anaphase I
Telophase ITelophase I
Stages Of Meiosis: Stages Of Meiosis: Meiosis IIMeiosis II
Metaphase II Metaphase II
Anaphase II Anaphase II
Telophase II Telophase II
The products of mitosis are 2 diploid cells with identical chromosomes.
The products of meiosis are 4 haploid cells each with a unique set of chromosomes.
Prophase IIProphase II
©2000 Timothy G. Standish
Prophase I:Tetrad formation/
crossing over
Prophase I:Tetrad formation/
crossing over
Crossing OverCrossing Over
Anaphase I Anaphase I
Telophase II Telophase II
Metaphase I Metaphase I
Telophase ITelophase IBecause of crossing over, every gamete receives a unique set of genetic information.
©2000 Timothy G. Standish