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The Cell Cycle

The Cell Cycle

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The Cell Cycle

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  1. The Cell Cycle

  2. The Cell Theory: All organisms consist of cells and arise from preexisting cells • Mitosis is the process by which new cells are generated. • Meiosis is the process by which gametes are generated for sexual reproduction.

  3. Cell and Chromosome Structure • Prokaryotic cells have no nucleus • DNA is organized into one circular chromosome Ribosomes Flagella Cytoplasm Chromosome Chromosome Cell membrane Cell wall

  4. Cell and Chromosome Structure • In eukaryotic cells, the genetic material is found within a membrane-bound nucleus • DNA is organized into multiple linear shaped chromosomes Chromosome Nucleus Nuclear membrane Cell membrane Cytoplasm

  5. DNA is packaged into chromosomes

  6. Eukaryotic chromosomes may be in their unreplicated or unreplicated state Sister chromatids DNA replication Centromere One chromosome (Unreplicated state)= One-double stranded DNA molecule One chromosome (Replicated state)= Two double stranded DNA molecules

  7. Chromosomes in cells • All individuals of a particular species have a characteristic number of chromosomes • Fruit flies have 8 chromosomes in their nuclei • Humans have 46 chromosomes in their nuclei • Chromosomes of most species come in pairs One pair of homologous chromosomes- Replicated state One pair of homologous chromosomes- Unreplicated state

  8. Homologous chromosomes • Each member of a pair of homologous chromosomes: • Same size • Same shape, centromere location • Same genetic loci = physical location of a gene on a chromosome Gene for eye color Gene for eye color One pair of homologous chromosomes

  9. Homologous chromosomes • But: • Each member of the pair (each “homolog”) may carry different versions of the gene • Different versions of the same gene = alleles • Eye color gene: • Brown allele • Blue allele Brown eye allele Blue eye allele

  10. A cell with 2 pairs of homologous chromosomes Eye color gene: B= brown eye allele b= blue eye allele Height gene: T= tall allele t= short allele b b B b DNA replication T B B t t T T t

  11. Ploidy: chromosomes don’t always come in pairs • Haploid = a cell with only one of each kind of chromosome • Diploid = a cell with two of each kind of chromosome • Triploid = a cell with three of each kind of chromosome 2n = 4 3n = 6 1n = 2 Number of each type of chromosome How many different kinds of chromosome Total number of chromosomes

  12. A cell that is 2n = 4 Unreplicatedchromosomes Chromosome Number of chromosomes: 4

  13. A cell that is 2n = 4 Replicated chromosomes Chromosome Sisterchromatids Centromere Number of chromosomes: 4

  14. Humans are diploid 23 pairs of chromosomes: 2n = 46

  15. Overview of Mitosis: Parent cell Replicated chromosomescondense at the start of mitosis Mitosis Sister chromatids separate and two daughter cells are formed. Parent cell and daughter cell contain thesame complement of chromosomes.

  16. The cell cycle represents all phases in the life of a cell • Interphase: • DNA replication (S phase) must precede mitosis so that all daughter cells receive the same complement of chromosomes as the parent cell. • The Gap phases separate mitosis from S phase. This is the time when molecular signals mediate the switch in cellular activity. • Mitosis: division of nucleus • Cytokinesis: division of cytoplasm

  17. The cell cycle:

  18. Functions of Mitosis • Mitosis produces genetically identical cells • Purpose • Asexual Reproduction • Growth and Development • Tissue repair

  19. Asexual Reproduction in Amoeba

  20. Growth and development 1-celled zygote (2n) mitosis Sand dollar embryo Multi-cellular adult (2n)

  21. Tissue renewal Dividing bone marrow cells give rise to new blood cells