1. CHAPTER 17 CELL REPRODUCTION & DIFFERENTIATION
PowerPoint® Lecture Slide Presentation by Robert J. Sullivan, Marist College
Human Biology
Concepts and Current Issues
Second Edition
MICHAEL D. JOHNSON
CHAPTER 17 CELL REPRODUCTION & DIFFERENTIATION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

2. Cell Cycle
Figure 17.1

3. Cell Cycle: Creates New Cells
Interphase: between cell divisions
G1: primary growth phase
S: synthesis of DNA for next cell division
G2: final growth phase
Mitotic phase: cell division
Mitosis: DNA distributes, nucleus divides
Cytokinesis: cell divides

4. DNA Replication Process: DNA strands uncoil and “unzip”
DNA nucleotides are positioned and linked by DNA polymerase
Old and new sides are “zipped” together
Centromere holds duplicate strands together

5. DNA Mutations and Mechanisms of Repair
Mutations: most frequent during DNA replication
Causes: chemical and physical forces
Effects: none (neutral), nudge in evolution (beneficial), cell death or cancer (harmful)
Mechanisms of Repair: DNA repair enzyme

6. Transcription of a Gene into mRNA
Figure 17.6

7. Protein Synthesis: Transcription
Process:
DNA for a gene unwinds
RNA polymerase assists in copying base sequence in RNA nucleotides
Primary transcript made, includes introns and exons
Introns edited out
Messenger RNA strand produced

8. Genetic Code of mRNA
Figure 17.7

9. Genetic Code Codon: sequence of three RNA bases, code for amino acids
Duplicate codons: all but one amino acid (methionine) have more than one codon
DNA grammar
Start: AUG (methionine), begin all genes
Stop: UAA, UAG, UGA, one ends each gene

10. Three Steps of Translation
Figure 17.8

11. Protein Synthesis: Translation
Components: messenger RNA, transfer RNA, ribosomes of ribosomal RNA and proteins
Process:
Initiation: initiator tRNA finds start codon, binds ribosome and mRNA
Elongation: tRNA brings specific amino acids to developing protein chain
Termination: stop codon terminates developing chain, protein is released from ribosome

12. Cell Reproduction: Mitosis and Cytokinesis
Phases:
Prophase: mitotic spindle formed, centrioles migrate to cell poles, chromosomes condense, nuclear membrane dissolves, metabolic activity decreases
Metaphase: duplicate choromosomes form single line at the equator between cetriole poles
Anaphase: duplicate choromosomes separate, are pulled toward poles by microtubules, centromeres broken
Telophase: reverse of prophase, duplication of centrioles
Cytokinesis: cell separates into two identical cells (diploid)

13. Cell Reproduction: Meiosis
Process: two cell divisions, reducing chromosome number by half
Meiosis I
Metaphase: pairs of chromosomes line up, double line
Crossing over between homologous pairs possible
Anaphase: pairs of chromosomes separated

14. Cell Reproduction: Meiosis (cont.)
Meiosis II
Same process as mitosis
Anaphase: duplicated chromosomes (chromatids) separate
Telophase: nuclei made with half the chromosome number (haploid)

15. Sex Differences in Meiosis
Males: four sperm produced from each meiotic division, all viable
Female: one egg and one polar body produced from each meiotic division, only the egg viable

16. Regulation of Cell Reproduction
Selective gene expression: only those genes needed are expressed
Repressor proteins: prevent gene expression
Activator proteins: needed to activate genes
Regulatory genes: code for repressor and activator proteins
Structural genes: code for an enzyme or structural protein

17. Regulation of Cell Reproduction (cont.)
Environmental factors: can modify cell cycle at three natural stopping points
G1: if cells do not divide in adults, cycle stops
Before mitosis
Arrest mitosis at metaphase

18. Environmental Factors Influencing Cell Differentiation
Differentiation in early development
After 8-cell stage, cells exposed to different environments inside versus outside the ball
Cloning: can occur at 8-cell stage
Differentiation in later development
Two factors:
Developmental history of earlier cells
Local environment