Cell cycle and Cell division ACh Bio 103 Cell cycle and Cell division ACh

Overview: The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter The continuity of life is based on the reproduction of cells, or cell division © 2011 Pearson Education, Inc.

6.1 Overview of cell division Functions of cell division In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for Development from a fertilized cell Growth Repair Production of gametes Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division Growth: You started out as a single cell after mom’s egg met dad’s sperm, but today you have about 10 trillion cells in your body. All of those cells were produced from that first cell and its descendents by mitosis. When you watch plants grow taller or baby animals grow into adults, you’re seeing mitosis at work. Repair: It’s a fact of life that cells wear out and need to be replaced. For instance, you constantly shed skin cells from your surface. If your body couldn’t replace these cells, you’d run out of skin. And if an organism gets injured, its body uses mitosis to produce the cells necessary to repair the injury. Production of gametes: During sexual reproduction, gametes (cells, specifically eggs and sperm, containing half the genetic information of their parent cells) get together to make new individuals. When the genetic information of the gametes joins together, the new individual has the correct total amount of DNA. © 2011 Pearson Education, Inc.

(b) Growth and development Figure 12.2 100 m (a) Reproduction 200 m (b) Growth and development Figure 12.2 The functions of cell division. 20 m (c) Tissue renewal

6.1 Overview of Cell Division Concept: Most cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information, DNA The exception is meiosis, a special type of division that does not produce identical genetic information - can produce sperm and egg cells © 2011 Pearson Education, Inc.

6.2 Cell division in Prokaryote Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission Single chromosome makes a copy of itself The plasma membrane pinches inward, dividing the cell into two

Chromosome replication begins. Two copies of origin Figure 12.12-1 Cell wall Plasma membrane E. coli cell Bacterial chromosome 1 Chromosome replication begins. Two copies of origin Figure 12.12 Bacterial cell division by binary fission.

Chromosome replication begins. Two copies of origin Figure 12.12-2 Cell wall Plasma membrane E. coli cell Bacterial chromosome 1 Chromosome replication begins. Two copies of origin 2 Replication continues. Figure 12.12 Bacterial cell division by binary fission.

Chromosome replication begins. Two copies of origin Figure 12.12-3 Origin of replication Cell wall Plasma membrane E. coli cell Bacterial chromosome 1 Chromosome replication begins. Two copies of origin 2 Replication continues. 3 Replication finishes. Figure 12.12 Bacterial cell division by binary fission.

Chromosome replication begins. Two copies of origin Figure 12.12-4 Origin of replication Cell wall Plasma membrane E. coli cell Bacterial chromosome 1 Chromosome replication begins. Two copies of origin 2 Replication continues. 3 Replication finishes. Figure 12.12 Bacterial cell division by binary fission. https://www.youtube.com/watch?v=j8_xoM8Wwgs 4 Two daughter cells result.

6.3 Cell division in eukaryotes Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) In eukaryotes, DNA is complexed with proteins called histones to form chromatin Chromatin in a cell are packaged into chromosomes https://www.youtube.com/watch?v=9kQpYdCnU14 © 2011 Pearson Education, Inc.

6.3 Cell division in eukaryotes Cellular Organization of the Genetic Material Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Number of chromosomes in a human (male) © 2011 Pearson Education, Inc.

Karyotype A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male

6.3 Cell division in eukaryotes Cellular Organization of the Genetic Material Somatic cells (non reproductive cells) have two sets of chromosomes Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells

6.3 Cell division in eukaryotes Cellular Organization of the Genetic Material In preparation for cell division, DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell division The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached © 2011 Pearson Education, Inc.

The process of cell division 6.3 Cell division in eukaryotes The process of cell division During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei Once separate, the chromatids are called chromosomes © 2011 Pearson Education, Inc.

Chromosomal DNA molecules Figure 12.5-1 Chromosomal DNA molecules Chromosomes 1 Centromere Chromosome arm Figure 12.5 Chromosome duplication and distribution during cell division.

Chromosomal DNA molecules Figure 12.5-2 Chromosomal DNA molecules Chromosomes 1 Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation 2 Sister chromatids Figure 12.5 Chromosome duplication and distribution during cell division.

Chromosomal DNA molecules Figure 12.5-3 Chromosomal DNA molecules Chromosomes 1 Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation 2 Sister chromatids Figure 12.5 Chromosome duplication and distribution during cell division. Separation of sister chromatids into two chromosomes 3

Phases of the Cell Cycle Eukaryotic cell division consists of Interphase, cell growth and copying of chromosomes in preparation for cell division Mitosis, the division of the genetic material in the nucleus Cytokinesis, the division of the cytoplasm Gametes are produced by a variation of cell division called meiosis Meiosis yields non identical daughter cells that have only one set of chromosomes, half as many as the parent cell © 2011 Pearson Education, Inc.

Phases of the Cell Cycle G1 - primary growth phase, cell grows larger S – synthesis; DNA replicated G2 - secondary growth phase, DNA is checked by enzymes for mistakes and repaired M - mitosis C - cytokinesis Interphase ~ 90% of the time.

Mitosis is conventionally divided into four phases Prophase Metaphase Anaphase Telophase Cytokinesis overlaps the latter stages of mitosis For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files. © 2011 Pearson Education, Inc.

Prophase Chromatin condenses (coils) into chromosomes. Sister chromatids joined by centromere. Nuclear membrane dissolves. Centrioles divide and move to opposite poles forming spindle between them. Prophase Prophase occupies over half of mitosis. The nuclear membrane breaks down. A structure known as the centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell. The chromosomes condense into compact structures. Each replicated chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held together by a structure known as the centromere.

Metaphase… Sister chromatids line up on metaphase plate. Centromeres lock on to spindle fibre Metaphase The chromosomes align themselves along the metaphase plate of the spindle apparatus.

Anaphase Centromeres divide. Spindle fibers contract pulling sister chromatids apart to poles Anaphase The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by spindle fibres. The separated sister chromatids are now referred to as daughter chromosomes.

Telophase New nuclear membranes form around new nuclei Telophase The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse, and the spindle fibres disappear.

Chromosome, consisting of two sister chromatids Figure 12.7 10 m G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Fragments of nuclear envelope Nonkinetochore microtubules Aster Metaphase plate Cleavage furrow Nucleolus forming Centromere Figure 12.7 Exploring: Mitosis in an Animal Cell Plasma membrane Nucleolus Nuclear envelope Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule Nuclear envelope forming Spindle Centrosome at one spindle pole Daughter chromosomes

Cytokinesis In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow © 2011 Pearson Education, Inc.

Cell now returns to interphase The chromosomes uncoil back into chromatin The whole cell cycle starts over again

Figure 12.UN06 Figure 12.UN06 Appendix A: answer to Test Your Understanding, question 10

Name the Mitotic Stages: Interphase Prophase Telophase Metaphase Anaphase

Mitosis Animation

Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase Prophase

Uncontrolled Mitosis Cancer cells If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells

Meiosis Another type of cell division that halves the number of chromosomes Meiosis yields non identical daughter cells that have only one set of chromosomes, half as many as the parent cell Produces gametes (eggs & sperm) Occurs in the testes in males Occurs in the ovaries in females

Meiosis Figure 13.7 Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes 1 2 Homologous separate Haploid cells with replicated chromosomes Sister chromatids Haploid cells with unreplicated chromosomes Meiosis I Meiosis II Meiosis reduces the number of chromosome sets from diploid to haploid Meiosis takes place in two sets of divisions Meiosis I reduces the number of chromosomes from diploid to haploid Meiosis II produces four haploid daughter cells

Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment

Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Fertilization then restores the original number of chromosomes from mom from dad child too much! meiosis reduces genetic content The right number!

A Comparison Of Mitosis And Meiosis Prophase Duplicated chromosome (two sister chromatids) Chromosome replication Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Prophase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at the metaphase plate Tetrads Metaphase I Anaphase I Telophase I Haploid n = 3 MEIOSIS II Daughter cells of meiosis I Homologues separate during anaphase I; sister chromatids remain together Daughter cells of meiosis II n Sister chromatids separate during anaphase II Anaphase Telophase Sister chromatids separate during anaphase 2n Daughter cells of mitosis 2n = 6

Difference between mitosis and meiosis Number of divisions 1 2 Number of daughter cells 4 Genetically Identical Yes No Number of chromosomes Same as parent Half of parent Where in the body Somatic cells Gametes When Throughout life At sexual maturity Role Growth and repair Sexual reproduction

MUTATIONS Changes in DNA that affect genetic information

A mutation is a change in the sequence of nucleotides in DNA Mistakes Happen: The Consequences of Mutation A mutation is a change in the sequence of nucleotides in DNA Mutations in DNA lead to changes in RNA, which can lead to changes in proteins. When proteins change, the functions of cells and the traits of organisms can also change.

Gene Mutations Point Mutations – changes in one or a few nucleotides Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT Insertion THE FAT CAT XLW ATE THE RAT Deletion THE FAT ATE THE RAT

Gene Mutations Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function. Insertion THE FAT CAT ATE THE RAT THE FAT HCA TAT ETH ERA T Deletion TEF ATC ATA TET GER AT H H

Significance of Mutations Most are neutral Eye color Birth marks Some are harmful Sickle Cell Anemia Down Syndrome Some are beneficial Sickle Cell Anemia to Malaria Immunity to HIV

What Causes Mutations? Parent to child Environmental damage There are two ways in which DNA can become mutated: Mutations can be inherited. Parent to child Mutations can be acquired. Environmental damage Mistakes when DNA is copied

Chromosome Mutations Down Syndrome Chromosome 21 does not separate correctly. They have 47 chromosomes in stead of 46. Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

Sex Chromosome Abnormalities Klinefelter’s Syndrome XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement

Sex Chromosome Abnormalities XYY Syndrome Normal male traits Often tall and thin Associated with antisocial and behavioral problems

Sex Chromosome Mutations Turner’s Syndrome X Female sex organs don't mature at adolescence sterility short stature

Sex Chromosome Mutations XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility

Now find out how some of them were mutated?