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.

Cell Cycle Figure 17.1

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

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

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

Transcription of a Gene into mRNA Figure 17.6

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

Genetic Code of mRNA Figure 17.7

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

Three Steps of Translation Figure 17.8

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

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)

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

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

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

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

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

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