Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Cell Cycle Figure 17.1  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

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. a DNA in uncondensed form

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 11.6 DNA double helix (2-nm diameter) Metaphase chromosome 700 nm Tight helical fiber (30-nm diameter) Nucleosome (10-nm diameter) Histones “Beads on a string” Supercoil (200-nm diameter) DNA packing tends to block gene expression multiple levels of DNA packing

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. DNA Replication DNA strands uncoil and “unzip” DNA nucleotides are positioned and linked by DNA polymerase Centromere holds duplicate strands together

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. 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 polymerase and DNA repair enzymes

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. DNA - key molecule that carries information to direct all cell functions

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. INTERPHASEPROPHASE Centrosomes (with centriole pairs) Chromatin NucleolusNuclear envelope Plasma membrane Early mitotic spindle Centrosome Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Kinetochore Spindle microtubules Figure 8.6

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. METAPHASETELOPHASE AND CYTOKINESIS Metaphase plate SpindleDaughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming ANAPHASE Figure 8.6 (continued)

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Cytokinesis: cell separates into two identical cells Cytokinesis Figure 8.7A Cleavage furrow Contracting ring of microfilaments Daughter cells

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. THE PATH OF PROTEIN SYNTHESIS 1 mRNA DNA nucleus cytoplasm 2 ribosome amino acids mRNA protein How does DNA control processes in cell? 1.Transcription 2.Translation

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Transcription of a Gene into mRNA Figure DNA for a gene unwinds; RNA polymerase copies bases 2. Primary transcript made; introns edited out of mRNA

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Genetic Code of mRNA Figure 17.7 Translates nucleic acids to amino acids

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Protein Synthesis: Translation Figure 17.8 Components: messenger RNA, transfer RNA, ribosomes (ribosomal RNA and proteins)

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. b a Red object = ribosome What molecules are present in this photo?

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.  Human karyotype Figure 8.19x2 How is gene expression controlled?

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Regulation of Gene Expression  only those genes needed are expressed  Structural genes: code for an enzyme or structural protein  Regulatory genes: code for repressor and activator proteins  Activator, repressor proteins control use of DNA

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. These interactions turn on and off the transcription of eukaryotic genes Activators bind to enhancer regions of DNA and to other transcription factors Enhancers DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Promoter Gene Figure 11.8

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Exons DNA RNA splicing or RNA transcript mRNA  After transcription, alternative splicing may generate two or more types of mRNA from the same transcript Eukaryotic RNA may be spliced in more than one way Figure 11.9

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. In female mammals, one X chromosome is inactive in each cell Figure 11.7 EARLY EMBRYO Cell division and X chromosome inactivation X chromosomes Allele for orange fur Allele for black fur TWO CELL POPULATIONS IN ADULT Active X Inactive X Orange fur Inactive X Active X Black fur

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Chromosome GENE RNA transcript mRNA in nucleus mRNA in cytoplasm Polypeptide ACTIVE PROTEIN GENE Exon Intron Tail Cap NUCLEUS Flow through nuclear envelope CYTOPLASM Breakdown of mRNA TranslationBroken- down mRNA Broken- down protein Cleavage/modification/ activation Breakdown of protein DNA unpacking Other changes to DNA TRANSCRIPTION Addition of cap and tail Splicing Figure 11.11

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Environmental Factors Influencing Cell Differentiation  Differentiation in early development  After 8-cell stage, cells are exposed to different environments inside versus outside the ball  Cloning: can occur at 8-cell stage  Differentiation in later development  Developmental history of earlier cells  Local environment

Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.