Transcript Lecture 3
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 3.1 3-4 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 3.2 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 & identity markers Fig 3.2 3-6 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 3.2 3-7 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 3.3 3-8 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 3. vesicle forming 2. membrane pouching inward 4.vesicle inside cell Fig 3.4 3-10 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 3.5 3-12 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 3.8 3-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organelles Are cytoplasmic structures that perform specialized functions for cells Fig 3.1 3-16 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 3.10 3-19 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 3.11 3-20 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 Rough ER 3-21 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 3.13 3-22 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 3.15 3-23 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 3.15 3-24 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 3.16 3-29 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 3.17 3-31 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 3.18 3-34 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 3.19 3-36 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 3.20 3-37 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 3.21 3-39 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 3.22 3-40 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 Fig3.23 3-41 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 3.24 3-42 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 3.26 3-47 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: G1 - cell performs normal physiological roles S - DNA is replicated in preparation for division G2 - chromatin condenses prior to division Fig 3.27 3-50 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 3.28 3-54 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 3.29 3-57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued Fig 3.29 3-58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitosis (M phase) continued Fig 3.29 3-59 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 centrioles Fig 3.30 3-60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Role of Centrosome continued Centrosome is duplicated in G1 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 3.33 3-67