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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Outline  Plasma Membrane  Cytoplasm and 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 the basic unit of structure and function in body  Is a highly organized molecular factory  Has 3 main components: plasma membrane, cytoplasm and organelles 3-4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma Membrane  Surrounds and gives cell form; is selectively permeable  Formed by a double layer of phospholipids  Which restricts passage of polar compounds 3-5

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 and identity markers 3-6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma Membrane continued  Carbohydrates in form of glycoproteins and glycolipids are part of outer surface  Impart negative charge to surface  Can serve as cell surface markers (antigens) 3-7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport  Is way cells move large molecules and particles across plasma membrane  Some cells use phagocytosis to take in particulate matter  E.g. white blood cells and macrophages 3-8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport continued  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 continued  Receptor-mediated endocytosis uses receptors to take in specific compounds  Including some viruses 3-10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bulk Transport continued  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 line respiratory and reproductive tracts  Cilia contain microtubules 3-12

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

Cytoplasm and Its Organelles 3-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm and 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 and Cytoskeleton continued  Cytoskeleton is a latticework of microfilaments and microtubules filling cytoplasm  Gives cell its shape and structure  Forms tracks upon which things are transported around cell 3-16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organelles  Are cytoplasmic structures that perform specialized functions for cells 3-17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lysosomes  Are vesicle-like organelles containing digestive enzymes and matter being digested (Fig 3.9)  Involved in recycling cell components  Involved in programmed cell death 3-18

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 3-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondria  Are energy-producing organelles  Believed to have originated from symbiotic bacteria 3-20

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 3-21

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 and inactivation 3-22

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, and leave other side  Lysosomes and secretory vesicles are formed in Golgi 3-23

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 3-24

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus  Nuclear pore complexes fuse inner and outer membranes together  Small molecules can diffuse through pore  Proteins, RNA must be actively transported 3-25

Gene Expression 3-26

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 3-27

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 3-28

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 3-29

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genome and Proteome  Genome refers to all genes in an individual or in a species  Proteome refers to all proteins produced by a genome 3-30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatin  Is made of DNA and its associated proteins (=histones)  Histones are positively charged and form spools around which negatively charged DNA strands wrap  Each spool and its DNA is called a nucleosome 3-31

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 3-32

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatin continued 3-33

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 3-34

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 and unzips strands  Nearby are promoter regions, which regulate levels of transcription  Transcription factors must bind to promoter to initiate transcription 3-35

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Only one strand of DNA contains the gene and 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 3-36

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Transcription produces four 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 3-37

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 and ends of exons spliced together to produce final mRNA 3-38

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  Human genome has <25,000 genes  Yet produces >100,000 different proteins  1 gene codes for an average of 3 different proteins  Accomplished by alternative splicing of exons  This allows a given gene to produce several different mRNAs 3-39

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RNA Synthesis continued  A newly discovered type of RNA is involved in regulating gene expression  These perform RNA interference (RNAi) or silencing  Interfere with or silence expression of some genes  siRNA (short interfering RNA) and miRNA (micro RNA) molecules pair in varying degrees with different mRNAs  Thereby interfering with expression of those mRNAs  1 miRNA may interfere with up to 200 different mRNAs 3-40

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis  Occurs one 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 3-41

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 3-42

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued 3-43

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued  Translation of codons is achieved by tRNA and enzymes  tRNA contains 3 loops, one of which contains an anticodon  Which is complementary to a specific mRNA codon  Each tRNA carries the amino acid specified by its anticodon 3-44

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis continued  In a ribosome, anticodons on tRNA bind to mRNA codons  Amino acids on adjacent tRNAs are brought together and linked enzymatically by peptide bonds  This forms a polypeptide; at a stop codon it detaches from ribosome 3-45

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Functions of ER  Proteins to be secreted are made in ribosomes of rough ER  Contain a leader sequence of 30+ hydrophobic amino acids that directs such proteins to enter cisternae of ER  Where leader sequence is removed; protein is modified 3-46

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Functions of Golgi  Secretory proteins leave ER in vesicles and go to Golgi  In the Golgi complex carbohydrates are added to make glycoproteins  Vesicles leave Golgi for lysosomes or exocytosis 3-47

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Degradation  The activity of many enzymes and regulatory proteins is controlled by rapidly degrading them  By proteases in lysosomes  And by cytoplasmic proteasomes  Proteins are directed to proteasomes by ubiquitin tags 3-48

DNA Replication 3-49

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Replication  When cells divide, DNA replicates itself and identical copies go to 2 daughter cells 3-50

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 and makes new complementary copy of old strand  Using A-T, C-G pairing rules  Thus each copy is composed of 1 new strand and 1 old strand (called semiconservative replication)  Original DNA sequence is preserved 3-51

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Replication continued 3-52

Cell Cycle 3-53

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 3-54

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 3-55

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 3-56

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  Tumor suppressor gene p53 encodes a transcription factor  It halts cell division when DNA is damaged  Then either promotes repair of the DNA; or apoptosis (cell death)  Mutations in p53 are found in 50% of all cancers 3-57

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  Involves activation of cytoplasmic caspases, which lead to cell death 3-58

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 and duplicated  Consist of 2 duplicate strands called chromatids  Which are connected by a centromere 3-59

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued  Consists of 4 stages: prophase, metaphase, anaphase, telophase 3-60

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 3-61

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued 3-62

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued 3-63

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued 3-64

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 3-65

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 3-66

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 3-67

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Telomeres continued  Germinal and cancer cells can divide indefinitely and do not age  Have the enzyme telomerase which replaces telomere nucleotides not duplicated by DNA polymerase during divisions 3-68

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis  Is type of cell division occurring in ovaries and testes to produce gametes (ova and sperm)  Has 2 divisional sequences - DNA is replicated once and divided twice 3-69

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 3-70

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 3-71

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis continued 3-72

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis continued  Genetic recombination occurs in prophase I  Parts of one homologous chromosome are exchanged with its partner homolog (= crossing- over)  Provides tremendous genetic diversity 3-73

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Epigenetic Inheritance  Occurs when gene silencing is passed on to daughter cells  Gene silencing is enacted by DNA methylation or post-translational modification of histones  Can contribute to diseases such as cancer, fragile X syndrome, and lupus 3-74