Cellular Reproduction Chapter 9

The larger the cell, the more difficult it is Limits of Cell Growth: The larger the cell, the more difficult it is for materials to enter and leave it. Rates of Cell Growth: E. coli can double its volume in = 30 minutes. In one day, a single cell would grow into a 14 kg mass of bacteria. In 3 days = mass of the earth

Controls on Cell Growth: cells of the heart and nervous system rarely grow. Cells of the skin and digestive tract grow and divide rapidly throughout Life; old, worn out, and damaged cells. Cells will grow until they come into contact with each other. Uncontrolled Cell Growth: Cancer cells grow out of control until they have used up all of their nutrients

Chromosomes: Made up of chromatin (DNA and protein) Total length of DNA is = 10,000 x length of the chromosome. In 1973, Don and Ada Olins and Christopher Woodcock discovered the chromosome’s DNA was coiled around special proteins called histones. DNA and histone molecules form beadlike structures called nucleosomes. Nucleosomes form a thick fiber, shortened by a system of loops and coils.

Chromosome Structure Composed of 2 sister chromatids and a centromere.

Binary Fission of a Prokaryote

The Cell Cycle Is the period from the beginning of one mitosis to the beginning of the next Consists of interphase and M phase

Prophase Metaphase Anaphase Telophase Interphase

Controls On The Cell Cycle

Interphase

Interphase Is a period of intense activity Proteins are made DNA copied ATP is made and utilized Nucleus is synthesizing mRNA to direct cellular activities

Interphase Consists of G1, S, and G2 Cells do not move through the cycle at the same rate G1 consists of cell growth and development; increase in supply of proteins, and synthesis of some organelles S stands for synthesis: DNA replication occurs here G2 synthesis of more organelles and the cell prepares for mitosis (shortest of the phases)

Mitosis Division of the nucleus Occurs in somatic or body cells Can last from a few minutes to several days

Mitosis Diagram

Prophase (longest phase) Chromosomes become visible as they shorten and thicken Disintegration of the nucleolus and the nuclear envelope Centrioles move apart Formation of the mitotic spindle fibers Takes up about 50-60% of mitosis

Metaphase (shortest phase) Centrioles have reached the opposite poles Chromosomes line up along the equator or middle of the cell Centromere of each chromosome is attached to a spindle fiber

Anaphase (3rd phase) Centromeres split Spindle fibers draw chromatids to poles of cells Chromatids are now individual chromosomes

Telophase Chromosomes have reached opposite poles Chromosomes uncoil and become less distinct Nuclear membrane begins to reform around chromosomes Spindle begins to break apart Nucleolus reappears Cells begin to divide by formation of cell plate in plant cells and cleavage furrow in animal cells Formation of two new daughter cells

Telophase (final phase)

Cytokinesis Division of the cytoplasm Occurs at the end of telophase Results in two identical daughter cells

Review of Mitotic Stages

Meiosis The process of gamete formation in which the chromosome number is reduced to half the normal number Requires two nuclear divisions called Meiosis I and Meiosis II

Meiosis I Interphase-the cell replicates its chromosomes Prophase I-each pair of homologous chromosomes comes together to form a four-part structure called tetrad Crossing Over-homologous chromosomes exchange genetic material Metaphase I-homologous chromosomes line up in tetrads independently of each other Anaphase I-centromeres do not split, this ensures that each new cell will receive only one chromosome from each homologous pair Telophase I-each new cell has one half of the genetic information

Crossing over Pairing of homologous chromosomes Chiasma formation Breakage and joining Recombinant

Crossing Over Animated www.contexo.info/.../images/mimovchanged2.gif

Metaphase I Anaphase I Telophase I Prophase II Prophase I

Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Result of Meiosis 4 Haploid cells Gametes

Meiosis begins by replicating the chromosomes

Centromeres Do Not Split at Meiosis I

Centromeres Split at Meiosis II

Oogenesis Process by which egg cells are made Results in four haploid gametes One functional ovum capable of fertilization Three polar bodies disintegrate

Spermatogenesis Process by which sperm cells are produced Results in four functional sperm cells

MITOSIS Somatic cells MEIOSIS Cells in sexual cycle 1 cell division: 2 daughter cells 2n 2n MEIOSIS Cells in sexual cycle 2 cell divisions: 4 product of meiosis n n 2n n n n=chromosome number

Final result Mitosis : two genetically identical diploid cells from one diploid parent cell Diploid organism: two sets of chromosomes (one from each parent); 2n   Mitosis Conservative process: Daughter cells genotypes identical to parental genotypes

Four genetically different haploid cells; from one diploid parent cell Meiosis : Four genetically different haploid cells; from one diploid parent cell Haploid organism: one set of chromosomes; n Meiosis Promotes variation among the product of meiosis (crossing over)

Mitosis vs Meiosis Alike Both have the stages PMAT Both go through Cytokinesis Both divide and make daughter cells Both are a form of reproduction Both take place inside the cell Chromosomes duplicate and DNA replication occurs in each process Different Mitosis produces two identical daughter cell, meiosis produces four genetically different cells Crossing over and tetrad formation (synapsis) occur in prophase I of Meiosis The centromeres split in Anaphase II Mitosis has one division, Meiosis has two Mitosis occurs in somatic or body cells Meiosis occurs in reproductive organs; producing gametes Mitosis is asexual reproduction Meiosis ensures sexual reproduction