Isaiah 61:1-3 1 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.

Mitosis and Meiosis Timothy G. Standish, Ph. D.

Mitosis: 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

Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Sperm 1n Haploid nucleus

Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Sperm 1n Haploid nucleus

Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus Sperm 1n

Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus Sperm 1n

From Zygote to Embryo Zygote 2n Zygote 2n

From Zygote to Embryo Cleavage

From Zygote to Embryo Cleavage

From Zygote to Embryo Cleavage

From Zygote to Embryo Cleavage

From Zygote to Embryo Morula

Why Cells Must Divide In multicelled 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) 1 cm Surface 6 cm2/ volume 1cm3= 6 2 cm Surface 24 cm2/ volume 8 cm3 = 3

The 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

The Cell Lifecycle G1 S G2 M Gap 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 G1 S G2 Gap 2 - Final preparation for division M Mitosis - Cell division

Stages Of Mitosis During 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

Stages Of Interphase 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 Interphase G1 M G2 S

Stages 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

Stages Of Mitosis Mother cell Nucleus with un-condensed chromosomes Interphase Nucleus with un-condensed chromosomes Prophase Condensed chromosomes Equator of the cell Metaphase Metaphase plate Disappearing nuclear membrane Poles of the cell Anaphase Two daughter cells Mitotic spindle Telophase

Packaging DNA T G A Histone C octomer Histone proteins 2 nm T A G C C G TA T A G C C G G C T A A T Packaging DNA Histone proteins Histone octomer 2 nm B DNA Helix

Packaging DNA T G A Histone C G C octomer Histone proteins 2 nm TA G C T A C G A T A T 2 nm C G B DNA Helix G C T A

Packaging DNA T G A 11 nm Histone C G C octomer Histone proteins TA G C T A C G Nucleosome A T A T 2 nm C G B DNA Helix G C T A

Packaging DNA A T T A G C C G C G G C T A A T

Packaging DNA A T T A G C C G C G G C T A A T

Packaging DNA “Beads on a string” 11 nm 30 nm Looped Domains 200 nm A T T A G C C G C G G C T A A T 30 nm Looped Domains 200 nm Tight helical fiber Protein scaffold

Packaging DNA 11 nm 30 nm 200 nm 2 nm 700 nm Metaphase Chromosome Looped Domains Nucleosomes B DNA Helix Tight helical fiber 700 nm G C A T Metaphase Chromosome Protein scaffold

Chromosomes, Chromatids and Centromeres A packaged chromosome Chromatid Identical chromatid Replication Anaphase Chromosome arm Two identical chromosomes Centromere Chromosome arm

Chromosome Morphology Chromosomes can be distinguished on the basis of size and the relative location of centromeres. Metacentric Submetacentric Acrocentric Telocentric Chromosome arm Centromere p arm petite q arm

Controlling 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: G1S - Monitors cell size and checks for DNA damage G2M - Ensures physiological conditions are right for division, including completion of DNA replication and any necessary repair M - Checks for successful formation of the mitotic spindle and attachment to the kinetochores

p53

Meiosis: 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)

Gametes Are Haploid Gametes must have half the genetic material of a normal cell If the genetic material in the gametes were 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)

Stages 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

Stages 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

Stages 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

Stages 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

Stages Of Meiosis: Meiosis I Interphase Mother cell Prophase I: Condensing Chromosomes Prophase I: Tetrad formation/ crossing over Metaphase I Anaphase I Telophase I Meiosis II

Stages Of Meiosis: Meiosis II The products of meiosis are 4 haploid cells each with a unique set of chromosomes. Telophase I Prophase II Metaphase II The products of mitosis are 2 diploid cells with identical chromosomes. Anaphase II Telophase II

Crossing Over Prophase I: Metaphase I Anaphase I Telophase I Tetrad formation/ crossing over Metaphase I Anaphase I Telophase I Because of crossing over, every gamete receives a unique set of genetic information. Telophase II

The End