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NUCLEUS • Nuclear proteins help condense DNA - Nucleosomes: DNA wrapped around histones - Chromatin Figure: 3.23 Protein Synthesis Fig. 3.24 PROTEIN SYNTHESIS DNA strand TRANSCRIPTION RNA TRANSLATION Polypeptide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Protein Synthesis: TRANSCRIPTION • DNA sequences: - Promoter - Terminator • RNA polymerase: catalyzes RNA synthesis - RNA nucleotides • snRNPs: perform mRNA splicing • Exons vs. Introns Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Protein Synthesis: TRANSCRIPTION • Pre-mRNAs are spliced to remove introns - Exons: expressed regions (encode protein) • Alternative splicing: one gene may code for more than one protein DNA (gene) Pre-mRNA E I E I E (Splicing) Mature mRNA Nucleus Cytoplasm Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Protein Synthesis THE GENETIC CODE • Codons: triplet nucleotide groups in mRNA strand - Each codon corresponds to a specific amino acid • Redundancy in the code • Start/Stop codons Protein Synthesis: TRANSLATION • mRNAProtein • Amino acids are joined together with peptide bonds - Peptide bonds are catalyzed by ribosomes Fig. 3.26 Protein Synthesis: TRANSLATION Amino acid attachment site Transfer RNA (tRNA) Anticodon Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Protein Synthesis: TRANSLATION Fig. 3.27 Protein Synthesis: TRANSLATION Fig. 3.27 Protein Synthesis: TRANSLATION Fig. 3.27 GENE EXPRESSION Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cell Division: The Cell Cycle Fig 3.28 The Cell Cycle: DNA Replication • Synthesis of daughter strands from parental strands - Each parental strand serves as a template for a daughter strand - Each daughter strand will be identical to its parental strand • Complementary base pairing Fig 3.29 The Cell Cycle: DNA Replication (S Phase) • Parental (old) strands separated DNA polymerase molecule Leading strand synthesized continuously - H-bonds are broken • Daughter (new) strands are synthesized - Complementary base pairing - DNA polymerase - Leading daughter strand: continuously synthesized - Lagging daughter strand: discontinuously synthesized • DNA ligase Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lagging strand synthesized in pieces DNA ligase joins the pieces Overall direction of replication Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle: Mitosis • Four stages - Events at each stage • Overall significance of the process Fig 3.30 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle: Mitosis Interphase Prophase Chromatin condensation Chromatids, centromeres Mitotic spindle: Microtubules attach to kinetochores Nuclear envelope Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle: Mitosis Metaphase Chromatids line up along center of mitotic spindle Anaphase Telophase Chromatids separate Chromosome movement stops Chromosomes pulled to opposite poles Nuclear envelope and nucleolus Metaphase plate Cleavage furrow Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage Furrow & Cytokinesis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Diversity • • • • Size Shape Function Mitotic index Fig. 3.33 http://bio.winona.msus.edu/berg/ANIMTNS/a01an.gif http://users.rcn.com/jkimball. BIOLOGY 240 Human Anatomy and Physiology Lecture PLASMA MEMBRANE: Fluid Mosaic Model • Lipids are a barrier to entry or exit of polar substances • ~ 50 lipid molecules for each protein molecule http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html Polar head (Phospho-) Hydrophobic tails (-lipid)
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