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©2000 Timothy G. Standish Isaiah 61:1-3 1The Spirit of the Lord GOD is upon me; because the LORD hath anointed me to preach good tidings unto the meek;

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Presentation on theme: "©2000 Timothy G. Standish Isaiah 61:1-3 1The Spirit of the Lord GOD is upon me; because the LORD hath anointed me to preach good tidings unto the meek;"— Presentation transcript:

1 ©2000 Timothy G. Standish Isaiah 61:1-3 1The 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; 2To proclaim the acceptable year of the LORD, and the day of vengeance of our God; to comfort all that mourn; 3To 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.

2 ©2000 Timothy G. Standish Mitosis and Meiosis Timothy G. Standish, Ph. D.

3 ©2000 Timothy G. Standish 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

4 ©2000 Timothy G. Standish Egg 1n Haploid nucleus Fertilization Results In A Diploid Zygote Sperm 1n Haploid nucleus

5 ©2000 Timothy G. Standish Sperm 1n Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus

6 ©2000 Timothy G. Standish Sperm 1n Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus

7 ©2000 Timothy G. Standish Sperm 1n Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus

8 ©2000 Timothy G. Standish From Zygote to Embryo Zygote 2n Zygote 2n

9 ©2000 Timothy G. Standish Cleavage From Zygote to Embryo

10 ©2000 Timothy G. Standish Cleavage From Zygote to Embryo

11 ©2000 Timothy G. Standish Cleavage From Zygote to Embryo

12 ©2000 Timothy G. Standish Cleavage From Zygote to Embryo

13 ©2000 Timothy G. Standish Morula From Zygote to Embryo

14 ©2000 Timothy G. Standish 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) 2 cm Surface 24 cm 2 / volume 8 cm 3 = 3 1 cm Surface 6 cm 2 / volume 1cm 3 = 6

15 ©2000 Timothy G. Standish 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

16 ©2000 Timothy G. Standish G1 M M G2 S S The Cell Lifecycle 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 Gap 2 - Final preparation for division Mitosis - Cell division

17 ©2000 Timothy G. Standish 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

18 ©2000 Timothy G. Standish Stages 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 G1 M M G2 S S Interphase

19 ©2000 Timothy G. Standish 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

20 ©2000 Timothy G. Standish Stages 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

21 ©2000 Timothy G. Standish A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins Histone octomer B DNA Helix 2 nm

22 ©2000 Timothy G. Standish A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins B DNA Helix Histone octomer 2 nm

23 ©2000 Timothy G. Standish A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins Histone octomer Nucleosome 11 nm B DNA Helix 2 nm

24 ©2000 Timothy G. Standish Packaging DNA A T T A G C C G G C T A A T

25 ©2000 Timothy G. Standish Packaging DNA A T T A G C C G G C T A A T

26 ©2000 Timothy G. Standish Packaging DNA A T T A G C C G G C T A A T Protein scaffold 11 nm “Beads on a string” 30 nm Tight helical fiber Looped Domains 200 nm

27 ©2000 Timothy G. Standish Packaging DNA G C A T Protein scaffold Metaphase Chromosome 700 nm 11 nm 30 nm 200 nm 2 nm Looped Domains Nucleosomes B DNA Helix Tight helical fiber

28 ©2000 Timothy G. Standish Replication Chromosomes, Chromatids and Centromeres Centromere Chromosome arm Identical chromatid Chromatid Anaphase A packaged chromosome Two identical chromosomes

29 ©2000 Timothy G. Standish Chromosome Morphology Chromosome arm Centromere SubmetacentricAcrocentricTelocentricMetacentric q arm p arm petite Chromosomes can be distinguished on the basis of size and the relative location of centromeres.

30 ©2000 Timothy G. Standish 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: 1 G1S - Monitors cell size and checks for DNA damage 2 G2M - Ensures physiological conditions are right for division, including completion of DNA replication and any necessary repair 3 M - Checks for successful formation of the mitotic spindle and attachment to the kinetochores

31 ©2000 Timothy G. Standish p53

32 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)

33 ©2000 Timothy G. Standish 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)

34 ©2000 Timothy G. Standish 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

35 ©2000 Timothy G. Standish 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

36 ©2000 Timothy G. Standish 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

37 ©2000 Timothy G. Standish 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

38 ©2000 Timothy G. Standish Interphase Mother cell Stages Of Meiosis: Meiosis I Meiosis II Prophase I: Tetrad formation/ crossing over Prophase I: Tetrad formation/ crossing over Metaphase I Telophase I Prophase I: Condensing Chromosomes Prophase I: Condensing Chromosomes Anaphase I

39 Telophase I Stages Of Meiosis: Meiosis II Metaphase II Anaphase 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 II

40 ©2000 Timothy G. Standish Prophase I: Tetrad formation/ crossing over Prophase I: Tetrad formation/ crossing over Crossing Over Anaphase I Telophase II Metaphase I Telophase I Because of crossing over, every gamete receives a unique set of genetic information.

41 ©2000 Timothy G. Standish


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