Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Cell Structure and Genetic Control 3-1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Outline  Plasma Membrane  Cytoplasm & Its Organelles  Gene Expression  DNA Replication  Cell Cycle 3-2

Plasma Membrane 3-3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell  Is basic unit of structure & function in body  Is highly organized molecular factory  Has 3 main components: plasma membrane, cytoplasm & organelles Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma Membrane  Surrounds & gives cell form, is selectively permeable  Formed by a double layer of phospholipids  Which restricts passage of polar compounds Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma Membrane continued  Proteins customize membranes  Provide structural support  Serve as transporters, enzymes, receptors & identity markers Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma Membrane continued  Carbohydrates in form of glycoproteins & glycolipids are part of outer surface  Impart negative charge to surface Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport  Is way cells move large molecules & particles across plasma membrane  Some cells use phagocytosis to take in particulate matter  E.g. white blood cells & macrophages Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport  Some cells use endocytosis to take in large compounds  Membrane invaginates to take in a vesicle of extracellular substance  Pinocytosis is non-specific intake 3-9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport  Receptor-mediated endocytosis uses receptors to take in specific compounds  Including some viruses 1. plasma membrane pit forming 2. membrane pouching inward 3. vesicle forming 4.vesicle inside cell Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport  Cells use exocytosis to export products into the extracellular fluid  Via secretory vesicles 3-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surface Specializations  Some epithelial cells have cilia projecting from surface  Hair-like structures that beat in unison  E.g. cilia lining respiratory & reproductive tracts Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surface Specializations  Some epithelial cells have microvilli on surface to increase surface area for absorption (Fig 3.6)  Fingerlike structures to expand surface area 3-13

Cytoplasm & Its Organelles 3-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm & Cytoskeleton  Cytoplasm is the jellylike matrix within a cell  Consists of fluidlike cytosol plus organelles 3-15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm & Cytoskeleton  Cytoskeleton is a latticework of microfilaments & microtubules filling cytoplasm  Gives cell its shape & structure  Forms tracks upon which things are transported around cell Fig 3.7 Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organelles  Are cytoplasmic structures that perform specialized functions for cells Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lysosomes  Are vesicle-like organelles containing digestive enzymes & matter being digested  Involved in recycling cell components  Involved in programmed cell death 3-17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Peroxisomes  Are vesicle-like organelles containing oxidative enzymes  Involved in detoxification in liver 3-18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondria  Are energy-producing organelles  Believed to have originated from symbiotic bacteria Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ribosomes  Are protein factories  Where cell's proteins are synthesized  Composed of 2 rRNA subunits Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endoplasmic Reticulum (ER)  A system of membranes specialized for synthesis or degradation of molecules  Rough ER contains ribosomes for protein synthesis  Smooth ER contains enzymes for steroid synthesis & inactivation Fig 3.12 Smooth ER 3-21 Rough ER

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Golgi Complex  Is a stack of flattened sacs  Vesicles enter from ER, contents are modified, & leave other side  Lysosomes & secretory vesicles are formed in Golgi Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus  Contains cell's DNA  Enclosed by a double membrane nuclear envelope  Outer membrane is continuous with ER Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus  Nuclear pore complexes fuse inner & outer membranes together  Small molecules can diffuse through pore  Proteins, RNA must be actively transported Fig

Gene Expression 3-25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gene Expression  Genes are lengths of DNA that code for synthesis of RNA  mRNA carries info for how to make a protein  Is transported out of nucleus to ribosomes where proteins are made 3-26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gene Expression continued  Takes place in 2 stages:  Transcription occurs when DNA sequence in a gene is turned into a mRNA sequence  Translation occurs when mRNA sequence is used to make a protein 3-27

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gene Expression continued  Each nucleus contains 1 or more dark areas called nucleoli (Fig 3.14)  These contain genes actively making rRNA 3-28

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genome & Proteome  Genome refers to all genes in an individual or in a species  Proteome refers to all proteins produced by a genome

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatin  Is made of DNA & its associated proteins (=histones)  Histones are positively charged & form spools around which negatively charged DNA strands wrap  Each spool & its DNA is called a nucleosome Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatin continued  Euchromatin is the part of chromosomes active in transcription  Light in color  Heterochromatin is highly condensed region where genes are permanently inactivated  Darker in color 3-30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatin continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis  One gene codes for one polypeptide chain  Each gene is several thousand nucleotide pairs long 3-32

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  For transcription RNA polymerase binds to a "start" sequence on DNA & unzips strands  Nearby are promoter regions which regulate levels of transcription  Transcription factors must bind to promoter to initiate transcription 3-33

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Only 1 strand of DNA contains the gene & is transcribed  Its bases pair with complementary RNA bases to make mRNA  G pairs with C  A pairs with U  RNA polymerase detaches when hits a "stop" sequence Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Transcription produces 4 types of RNA:  pre-mRNA - altered in nucleus to form mRNA  mRNA - contains the code for synthesis of a protein  tRNA (transfer RNA) - decodes the info contained in mRNA  rRNA - forms part of ribosomes 3-35

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Pre-mRNA is much larger than mRNA  Contains non-coding regions called introns  Coding regions are called exons  In nucleus, introns are removed & ends of exons spliced together to produce final mRNA Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis  Occurs 1 amino acid at-a-time according to sequence of base triplets in mRNA  In cytoplasm mRNA attaches to ribosomes forming a polysome where translation occurs Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued  Ribosomes read 3 mRNA bases (= a triplet) at-a-time  Each triplet is a codon which specifies an amino acid  Ribosomes translate codons into an amino acid sequence that becomes a polypeptide chain 3-38

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued  Translation of codons is achieved by tRNA & enzymes  tRNA contains 3 loops, one of which contains an anticodon  Which is complementary to a specific mRNA codon  tRNA carries the amino acid specified by its anticodon Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued  In a ribosome, anticodons of tRNA bind to mRNA codons  Amino acids on adjacent tRNAs are brought together & linked enzymatically by peptide bonds  Polypeptide forms; at end detaches from ribosome Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Functions of ER  Protein to be secreted is made in ribosomes of rough ER  Amino acids in leader sequence of newly-made proteins are attracted to ER membrane  Causing new protein to enter cisternae of ER  Where leader sequence removed, protein modified Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Functions of Golgi  Secretory proteins leave ER in vesicles & go to Golgi  In the Golgi complex carbohydrates are added to make glycoproteins  Vesicles leave Golgi for lysosomes or exocytosis 3-43

DNA Replication 3-44

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Replication  When cells divide, DNA replicates itself & identical copies go to 2 daughter cells 3-45

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Replication continued  Helicases break hydrogen bonds to produce 2 free strands of DNA  DNA polymerase binds to each strand & makes new complementary copy of old strand  Using A-T, C-G pairing rules  Thus each copy is composed of 1 new strand & 1 old strand (called semiconservative replication)  Original DNA sequence is preserved 3-46

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Replication continued Fig

Cell Cycle 3-48

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Cycle  Most cells of body are in interphase--the non-dividing stage of life cycle 3-49

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Cycle continued  Interphase is subdivided into:  G 1 - cell performs normal physiological roles  S - DNA is replicated in preparation for division  G 2 - chromatin condenses prior to division Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cyclins  Are proteins that promote different phases of cell cycle  Overactivity of genes that code for cyclins is associated with cancer 3-51

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oncogenes  Are genes whose mutations are associated with cancer  Tumor suppressor genes inhibit cancer development  E.g. gene p53 inhibits cyclin activity  Mutations in p53 are associated with cancer 3-52

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Death  Occurs in 2 ways:  Necrosis occurs when pathological changes kill a cell  Apoptosis occurs as a normal physiological response  Also called programmed cell death 3-53

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase)  Is phase of life cycle when cell divides  Chromosomes are condensed & duplicated  Consist of 2 duplicate strands called chromatids  Which are connected by a centromere Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued  Consists of 4 stages: prophase, metaphase, anaphase, telophase 3-55

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued  In prophase chromosomes become visible distinct structures  In metaphase chromosomes line up single file along equator  Positioned there by spindle fibers  In anaphase centromeres split  Spindle fibers pull each chromatid to opposite poles  In telophase cytoplasm is divided (= cytokinesis), producing 2 daughter cells 3-56

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Role of Centrosome  All animal cells have a centrosome located near nucleus in interphase  Contains 2 centrioles Fig centrioles

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Role of Centrosome continued  Centrosome is duplicated in G 1 if cell is going to divide  Replicates move to opposite poles by metaphase  Microtubules grow from centrosomes to form spindle fibers  Which attach to centromeres of chromosomes  Spindle fibers pull chromosomes to opposite poles during anaphase 3-61

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Telomeres  Are non-coding regions of DNA at ends of chromosomes  Each time a cell divides, a length of telomere is lost  Because DNA polymerase can’t copy the very end of DNA strand  When telomere is used up, cell becomes senescent  Believed to represent a molecular clock for aging  That ticks down with each division 3-62

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Telomeres continued  Germinal & cancer cells can divide indefinitely & do not age  Have enzyme telomerase which replaces nucleotides lost from telomere during divisions 3-63

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis  Is type of cell division occurring in ovaries & testes to produce gametes (ova & sperm)  Has 2 divisional sequences--DNA is replicated once & divided twice 3-64

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis continued  In 1st division homologous chromosomes pair along equator of cell rather than singly as in mitosis  1 member of homolog pair is pulled to each pole  This gives each daughter cell 23 different chromosomes, consisting of 2 chromatids 3-65

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis continued  In 2nd division each daughter divides, chromosomes split into 2 chromatids  1 goes to each new daughter cell  Each daughter contains 23 chromosomes  Rather than 46 like mother cell  Which is why meiosis is called reduction division 3-66

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis continued Fig