Cell Cycle Interphase between cell divisions G 1
Cell Cycle § Interphase: between cell divisions § G 1: primary growth phase § S: synthesis of DNA for next cell division § G 2: final growth phase § Mitotic phase: cell division Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. § Mitosis: DNA distributes, nucleus divides Figure 17. 1
a DNA in uncondensed form Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
DNA double helix (2 -nm diameter) multiple levels of DNA packing Histones “Beads on a string” Nucleosome (10 -nm diameter) Tight helical fiber (30 -nm diameter) Supercoil (200 -nm diameter) Metaphase chromosome Figure 11. 6 Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. • DNA packing tends to block gene expression 700 nm
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.
INTERPHASE PROPHASE Centrosomes (with centriole pairs) Early mitotic spindle Centrosome Chromatin Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Figure 8. 6 Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Fragments of nuclear envelope Centrosome Kinetochore Spindle microtubules
METAPHASE ANAPHASE Cleavage furrow Metaphase plate Spindle TELOPHASE AND CYTOKINESIS Daughter chromosomes Figure 8. 6 (continued) Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Nuclear envelope forming Nucleolus forming
Cytokinesis: cell separates into two identical cells Cleavage furrow Figure 8. 7 A Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Contracting ring of microfilaments Daughter cells
THE PATH OF PROTEIN SYNTHESIS DNA 1 How does DNA control processes in cell? 1. Transcription m. RNA nucleus ribosome 2. Translation amino acids m. RNA 2 protein cytoplasm Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
Transcription of a Gene into m. RNA 1. DNA for a gene unwinds; RNA polymerase copies bases 2. Primary transcript made; introns edited out of m. RNA Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 17. 6
Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Figure 10. 7 Amino acid Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
Genetic Code of m. RNA Translates nucleic acids to amino acids Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 17. 7
Protein Synthesis: Translation Components: messenger RNA, transfer RNA, ribosomes (ribosomal RNA and proteins) Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 17. 8
b a Red object = ribosome Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. What molecules are present in this photo?
§ Human karyotype How is gene expression controlled? Figure 8. 19 x 2 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.
Activators bind to enhancer regions of DNA and to other transcription factors These interactions Enhancers turn on and off the transcription of eukaryotic Transcription genes factors DNA Promoter Gene Activator proteins Other proteins RNA polymerase Bending of DNA Figure 11. 8 Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Transcription
Eukaryotic RNA may be spliced in more than one way § After transcription, alternative splicing may generate two or more types of m. RNA from the same transcript Exons DNA RNA transcript RNA splicing or m. RNA Figure 11. 9 Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
In female mammals, one X chromosome is inactive in each cell EARLY EMBRYO TWO CELL POPULATIONS IN ADULT Active X Allele for orange fur X chromosomes Orange fur Inactive X Cell division and X chromosome inactivation Inactive X Active X Black fur Allele for black fur Figure 11. 7 Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
Chromosome DNA unpacking Other changes to DNA GENE TRANSCRIPTION GENE Exon RNA transcript Intron Addition of cap and tail Splicing Tail Cap m. RNA in nucleus NUCLEUS Flow through nuclear envelope m. RNA in cytoplasm CYTOPLASM Breakdown of m. RNA Translation Brokendown m. RNA Polypeptide Cleavage/modification/ activation ACTIVE PROTEIN Breakdown of protein Brokendown protein Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings. Figure 11. 11
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.
Copyright © 2006 Pearson Education, Inc. publishing as Benjamin Cummings.
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