* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download PowerPoint
Survey
Document related concepts
Chemical biology wikipedia , lookup
Biochemistry wikipedia , lookup
Cell culture wikipedia , lookup
Neuronal lineage marker wikipedia , lookup
Artificial cell wikipedia , lookup
State switching wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Introduction to genetics wikipedia , lookup
Signal transduction wikipedia , lookup
Developmental biology wikipedia , lookup
Symbiogenesis wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Cell (biology) wikipedia , lookup
Transcript
Chapter 3: The Cellular Level of Organization 1 Cellular Organization • Cell = smallest living unit • Performs all life functions 2 Figure 3–1 Two Categories of Cells • Sex cells (germ cells): – reproductive cells – male sperm – female oocytes (eggs) • Somatic cells (soma = body): – all body cells except sex cells 3 Cellular Organization • Different cells have different shapes • Unique morphology is related to function • All cells surrounded by plasma membrane: – Separates cells from the environment • Plasma membrane “holds in” the cytoplasm • Cytoplasm consists of cytosol (fluid) and organelles (structures) • Body cells surrounded by interstitial fluid – Interstitial fluid = fluid outside the membrane 4 Organelle Functions Table 3–1 (1 of 2) 5 Organelle Functions Table 3–1 (2 of 2) 6 The structures and functions of the cell membrane. 7 1. The Plasma (Cell) Membrane - Mostly phospholipid bilayer - Interface between cell and environment 8 Figure 3–2 Functions of Plasma (Cell) Membrane • Physical barrier: – Maintain homeostasis: • Separates intracellular fluid from extracellular fluid, different conditions in each • Regulates exchange with environment: – ions and nutrients enter – waste and cellular products released • Monitors the environment: – extracellular fluid composition – Cell communication and signaling • Structural support: – anchors cells and tissues 9 Plasma Membrane: Components • • • • Phospholipid bilayer Cholesterol: resist osmotic lysis Carbohydrates Proteins 10 Plasma Membrane: Components 1. Phospholipid Bilayer: – hydrophilic heads—toward watery environment, both sides – hydrophobic fatty-acid tails—inside membrane – barrier to ions and water soluble compounds 2. Cholesterol: resist osmotic lysis 11 Plasma Membrane: Components 3. Carbohydrates: • Membrane Carbohydrates including: – Proteoglycans, glycoproteins, and glycolipids • extend outside cell membrane • form sticky carb layer or “sugar coat” called the glycocalyx 12 Functions of Membrane Carbohydrates • Lubrication and protection • Anchoring and locomotion • Specificity in binding – Acts as receptors • Recognition – Self recognition – immune response 13 Plasma Membrane: Components 4. Protein: – ½ mass of membrane – Integral proteins: span width of membrane • within the membrane – Peripheral proteins: • Adhere to inner or outer surface of the membrane 14 6 Functions of Membrane Proteins 1. Anchoring proteins (stabilizers): – attach to inside or outside structures 2. Recognition proteins (identifiers): – Self identification by immune system – Label cells normal or abnormal 3. Enzymes: – catalyze reactions in cytosol in extra cellular fluid 4. Receptor proteins: – bind and respond to ligands (ions, hormones) or signaling, or import/export 5. Carrier proteins: – transport specific solutes through membrane 6. Channels: – 15 regulate water flow and solutes through membrane Which component of the cell membrane is primarily responsible for the membrane’s ability to form a physical barrier between the cell’s internal and external environments? A. B. C. D. phospholipid bilayer glycocalyx peripheral proteins proteoglycans 16 Which type of integral protein allows water and small ions to pass through the cell membrane? A. B. C. D. receptor proteins carrier proteins channel proteins recognition proteins 17 How things get in and out of cells. 18 Overcoming the Cell Barrier • The cell membrane is a barrier, but: – nutrients must get in – products and wastes must get out • Permeability determines what moves in and out of a cell: • A membrane that: – lets nothing in or out is impermeable – lets anything pass is freely permeable – restricts movement is selectively permeable 19 Selective Permeability • Cell membrane is selectively permeable: – allows some materials to move freely – restricts other materials • Restricts materials based on: – – – – size electrical charge molecular shape lipid solubility 20 Transport • Transport through a cell membrane can be: – active (requiring energy and ATP) – passive (no energy required) • 3 Categories of Transport – Diffusion (passive) – Carrier-mediated transport (passive or active) – Vesicular transport (active) 21 Solutions • All molecules are constantly in motion • Molecules in solution move randomly • Random motion causes mixing 22 Concentration Gradient • Concentration is the amount of solute (glucose) in a solvent (e.g. H20) • Concentration gradient: – more solute in 1 part of a solvent than another • Function = Diffusion – – – – molecules mix randomly solute spreads through solvent eliminates concentration gradient Solutes move down a concentration gradient • From high concentration to low concentration 23 Factors Affecting Diffusion Rates • Distance the particle has to move • Molecule size: – smaller is faster • Temperature: – more heat, faster motion • Gradient size: – the difference between high and low concentration • Electrical forces: – opposites attract, like charges repel 24 Diffusion and the Cell Membrane • Diffusion can be simple or channel-mediated 25 Figure 3–15 Simple Diffusion • Materials which diffuse through cell membrane: – lipid-soluble compounds (alcohols, fatty acids, and steroids) – dissolved gases (oxygen and carbon dioxide) 26 Channel-Mediated Diffusion • Materials which pass through transmembrane proteins (channels): – are water soluble compounds – are ions • Passage depends on: – size – charge – interaction with the channel 27 Osmosis • Osmosis is the diffusion of water across the cell membrane 28 Figure 3–16 How Osmosis Works • More solute molecules, lower concentration of water molecules • Membrane must be freely permeable to water, selectively permeable to solutes • Osmosis Water Movement – Water molecules diffuse across membrane toward solution with more solutes – Volume increases on the side with more solutes • Osmotic Pressure – Is the force of a concentration gradient of water – Equals the force (hydrostatic pressure) needed to 29 block osmosis Osmotic Pressure 30 Isotonic • A solution that does not cause osmotic flow of water in or out of a cell – iso = same, tonos = tension • The osmotic effect of a solute on a cell: – 2 fluids may have equal osmolarity 31 Figure 3–17a Cells and Hypotonic Solutions • hypo = below • Has less solutes – Loses water through osmosis • A cell in a hypotonic solution: – gains water – ruptures (hemolysis of red blood cells) Lysis 32 Figure 3–17b Cells and Hypertonic Solutions • hyper = above • Has more solutes – Gains water by osmosis • A cell in a hypertonic solution: – loses water – shrinks (crenation of red blood cells) Crenation 33 Figure 3–17c KEY CONCEPT • Concentration gradients tend to even out • In the absence of membrane, diffusion eliminates concentration gradients • When different solute concentrations exist on either side of a selectively permeable membrane, osmosis moves water through the membrane to equalize the concentration gradients 34 How would a decrease in the concentration of oxygen in the lungs affect the diffusion of oxygen into the blood? A. decrease in molecule size results in decreased diffusion B. decrease in distance results in increased diffusion C. increase in electrical forces results in increased diffusion D. decrease in gradient size results in decreased speed of diffusion 35 Some pediatricians recommend the use of a 10% salt solution to relieve congestion for infants with stuffy noses. What effect would such a solution have on the cells lining the nasal cavity, and why? A. Cells will lose water because this is a hypertonic solution. B. Cells will lose water because this is a hypotonic solution. C. Cells will gain water because this is a hypertonic solution. D. Cells will gain water because this is a hypotonic solution. 36 Carrier-Mediated Transport • Carrier-mediated transport of ions and organic substrates: – facilitated diffusion (No energy needed) – active transport (Energy is needed) 37 Characteristics of Carrier-Mediated Transport • Specificity: – 1 transport protein, 1 set of substrates • Saturation limits: – rate depends on transport proteins, not substrate (same as enzymatic reactions) • Regulation: – cofactors such as hormones 38 Carrier-Mediated Transport • Cotransport – 2 substances move in the same direction at the same time • Countertransport – 1 substance moves in while another moves out 39 Facilitated Diffusion • Passive, Carrier mediated • Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids): – molecule binds to receptor site on carrier protein – protein changes shape, molecules pass through – receptor site is specific to certain molecules 40 Figure 3–18 Active Transport • Active transport proteins: – move substrates against concentration gradient – require energy, such as ATP – ion pumps move ions (Na+, K+, Ca+, Mg2+) – exchange pump countertransports 2 ions at the same time 41 Active Transport, Carrier Mediated • E.g. Sodium-Potassium Exchange Pump – 3 Na+ out – 2 K+ in – 1 ATP Moves 3 Na+ EXTRACELLULAR FLUID 3 Na+ • 40% cell ATP Sodium— potassium exchange pump 2 K+ ATP ADP 42 CYTOPLASM Secondary Active Transport • Na+ concentration gradient drives glucose transport • ATP energy pumps Na+ back out Cotransport Countertransport 43 Figure 3–20 Transport Vesicles • Also called bulk transport • Vesicles: – endocytosis (endo = into) – active transport using ATP: • receptor-mediated • pinocytosis • phagocytosis – exocytosis (exo = out of) 44 Receptor-Mediated Endocytosis 45 Figure 3–21 Receptor-Mediated Endocytosis • Receptors (glycoproteins) bind target molecules (ligands) • Coated vesicle (endosome) carries ligands and receptors into the cell 46 Pinocytosis • Pinocytosis (cell drinking) • Endosomes “drink” extracellular fluid and enclose it in membranous vesicles at the cell surface – Similar to the steps in receptor-mediated endocytosis, except that ligand binding is not the trigger 47 Figure 3–22a Phagocytosis • Phagocytosis (cell eating) – pseudopodia (psuedo = false, podia = feet) – engulf large objects in phagosomes 48 Figure 3–22b Exocytosis • Is the reverse of endocytosis 49 Figure 3–7b Summary The 7 methods of transport 50 Table 3–3 Transmembrane potential 51 Electrical Charge • Selective permeability of membrane allows different concentrations of molecules in/outside cells • Cell membrane – Inside cell: slightly negative • due to the abundance of proteins – Outside cell: slightly positive • due to cations in extracellular fluids • Phospholipids hold charges apart creating a transmembrane potential – Unequal charge across the cell membrane • Resting potential ranges from – 10 mV to —100 mV, depending on cell type 52 During digestion in the stomach, the concentration of hydrogen ions (H+) rises to many times that in cells of the stomach. Which transport process could be responsible? A. B. C. D. facilitated diffusion osmosis active transport endocytosis 53 During digestion in the stomach, the concentration of hydrogen ions (H+) rises to many times that in cells of the stomach. Which transport process could be responsible? A. B. C. D. facilitated diffusion osmosis active transport endocytosis 54 If the cell membrane were freely permeable to sodium ions (Na+), how would the transmembrane potential be affected? A. it would move closer to zero B. it would become more positive C. it would become more negative D. it would become unstable 55 When they encounter bacteria, certain types of white blood cells engulf the bacteria and bring them into the cell. What is this process called? A. B. C. D. pseudocytosis exocytosis pinocytosis phagocytosis 56 Increase Surface Area: Microvilli • Surface area of membrane can be increased by microvilli – For absorption or secretion • Microvilli: ‘fingers’ of cell membrane containing a web of microfilaments and cytoplasm, anchored to cytoskeleton 57 2. Cytoplasm • Material enclosed by plasma membrane • Occupies space between plasma membrane and nuclear membrane • Components: – cytosol (fluid): • High K+, low Na+ • Colloid Solution: proteins and enzymes • Nutrient Reserves: carbohydrates, lipids, and amino acids – Inclusions: • Type and number varies with cell • E.g. glycogen, melanin, steroids, etc. – organelles: • • • • Carry out cellular functions Each has separate function Some have membranes Some free in cytosol 58 Cell organelles and their functions 59 Types of Organelles • Nonmembranous organelles: – no membrane – direct contact with cytosol • Membranous organelles: – covered with plasma membrane – isolated from cytosol 60 Nonmembranous Organelles • 6 types of nonmembranous organelles: – – – – – – cytoskeleton Microvilli centrioles cilia ribosomes proteasomes 61 3. The Cytoskeleton • Structural proteins for shape and strength (Internal Framework) • 4 types of filaments – – – – Microfilaments Intermediate filaments Thick filaments Microtubules 62 Figure 3–3a A. Microfilaments • • • • Thin filaments (<6nm diameter) Composed of the protein actin Usually at periphery of the cell Functions: – provide additional strength by attaching the membrane to the cytoplasm – Attach integral proteins to cytoskeleton – Pairs with thick filaments of myosin for muscle movement 63 Intermediate Filaments & Thick Filaments B. Intermediate Filaments: – 7-11 nm diameter • Mid-sized between microfilaments and thick filaments – Durable, type varies with cell (collagen, elastin, keratin) – Functions: • strengthen cell and maintain shape • stabilize position of organelles • stabilize the cell relative to other cells C. Thick Filaments – – – – 15 nm diameter Composed of myosin Muscle cells only Function • Interact with actin to produce movement 64 D. Microtubules • • • • Large (25nm diameter), hollow tubes Composed of tubulin protein Originate from centrosome Functions: – Foundation of the cytoskeleton – Allows the cell to change shape and assists in mobility – Involved in transport • Molecular motors travel along microtubule “tracks” • move vesicles within cell – Makes up the spindle apparatus for nuclear division (mitosis) – The structural part of some organelles • Centrioles, cilia, flagella 65 4. Centrioles in the Centrosome Centrioles :form spindle apparatus during cell division Centrosome: cytoplasm surrounding centriole near the nucleus – Consists of matrix and paired centrioles – Functions as microtubule organizing center – Responsible for assembling spindle apparatus during mitosis 66 Figure 3–4a 5. Cilia and Flagella • Hair like projections • Contain a microtubule core with cytoplasm covered in plasma membrane • Anchored in the cytosol by basal bodies • Cilia: Short, numerous – Function: sweep substances over cell surface • Flagella: Long, singular – Function: propel cell through environment 67 Figure 3–4b,c 6. Ribosomes • Site of protein synthesis (polypeptide formation) • Two subunits composed of rRNA & protein: – free ribosomes in cytoplasm: • Manufacture proteins for use in cytoplasm – fixed ribosomes attached to Endoplasmic reticulum: • Manufacture proteins for export or use in membrane 68 Cells lining the small intestine have numerous fingerlike projections on their free surface. What are these structures, and what is their function? A. microvilli; move substances across cell surface B. microvilli; increase cell’s surface area and absorptive ability C. cilia; increase cell’s surface area and absorptive ability D. cilia; move substances across cell surface 69 Membranous Organelles • 5 types of membranous organelles: – – – – – endoplasmic reticulum (ER) Golgi apparatus lysosomes peroxisomes mitochondria 70 7. Endoplasmic Reticulum (ER) Location: - Attached to the Nuclear Envelope 71 Figure 3–5a Endoplasmic Reticulum (ER) • endo = within, plasm = cytoplasm, reticulum = network • Cisternae are storage chambers within membranes • Function: – – – – Synthesis of proteins, carbohydrates, and lipids Storage of synthesized molecules and materials Transport of materials within the ER Detoxification of drugs or toxins 72 Smooth Endoplasmic Reticulum (SER) • No ribosomes attached • Tubular Membrane • Functions: – – – – – Lipid metabolism (synthesis, breakdown, transport) Synthesis of steroid hormones (reproductive system) Detoxification of drugs Breakdown of glycogen (storage in muscles) to glucose Store ions (e.g. Ca2+) 73 Rough Endoplasmic Reticulum (RER) • Surface covered with ribosomes: • Ribosomes synthesize proteins and feed them into RER cisternae to be modified – E.g. +carbs = glycoprotein • Modified proteins are put into transport vesicles to go to Golgi • These proteins for exocytosis or use in membrane 74 Golgi Apparatus • Stack of cisternae with associated transport vesicles • Near nucleus but not attached • Function: – Modify, concentrate, and sort export proteins 75 Figure 3–6a Golgi Apparatus • Transport vesicles from RER dock on cis (forming) face of golgi and release contents into golgi • Proteins (and glycoproteins) are modified – Phosphate, carbs, or lipids attached • Proteins transit between cisternae via vesicles from cis face (forming) to trans face (maturing) 76 Vesicles of the Golgi Apparatus • At trans face, proteins are packaged into: – Secretory vesicles: • modify and package products for exocytosis – Membrane renewal vesicles: • Carry products to membrane – Lysosomes: • Membrane bound sacs of digestive enzymes 77 Exocytosis • Ejects secretory products and wastes 78 Figure 3–7b 9. Lysosomes • Powerful enzyme-containing vesicles: – lyso = dissolve, soma = body • Digestion centers for large molecules or structures • Endosomes or phagosomes containing endocytosed things, and organelles targeted for destruction are fused with lysosome and broken down • Some solutes diffuse into cytoplasm for use, remaining debris are exocytosed 79 Figure 3–8 Lysosome Structures and Function • Primary lysosome: – formed by Golgi and inactive enzymes • Secondary lysosome: – lysosome fused with damaged organelle – digestive enzymes activated – toxic chemicals isolated • Functions: – Clean up inside cells: • • • • break down large molecules Attack bacteria recycle damaged organelles ejects wastes by exocytosis 80 Autolysis • Self-destruction of damaged cells: – – – – – auto = self, lysis = break lysosome membranes break down digestive enzymes released cell decomposes cellular materials recycle 81 Tay Sach’s Disease • Caused by lysosomes that fail to break down glycolipids in nerve cells • Accumulation of glycolipids disrupts nerve function • Progressive mental retardation • Death by age 18 months 82 10. Peroxisomes • Are enzyme-containing vesicles: – break down fatty acids – Membrane sacs containing oxidases and catalases to neutralize free radicals that are formed during catabolism of organic molecules • produce hydrogen peroxide (H2O2) – Peroxisomes not made by golgi • appear to self replicate 83 11. Proteasomes • Cylindrical structure composed of protein digesting enzymes (proteases) • Disassemble damaged proteins for recycling – E.g. degrade proteins tagged with ubiquitin to recycle amino acids 84 KEY CONCEPT • Cells: basic structural and functional units of life – respond to their environment – maintain homeostasis at the cellular level – modify structure and function over time 85 12. Mitochondrion Structure • Sausage-shaped with double membrane – Outer membrane: Smooth – Inner membrane: folded into cristae – Center: matrix 86 Figure 3–9a Mitochondrial Function: Power House of the Cell • Aerobic respiration occurs on surface of cristae – takes chemical energy from food (glucose) – With the use of oxygen, Glucose is catabolized creating CO2 waste to convert ADP into ATP • Mitochondria supply most of cell’s energy • Have their own DNA (maternal) • Can replicate independent of the cell glucose + oxygen + ADP carbon dioxide + water + ATP 87 Figure 3–9b KEY CONCEPT • Mitochondria provide cells with energy for life: – require oxygen and organic substrates – generate carbon dioxide and ATP 88 Certain cells in the ovaries and testes contain large amounts of smooth endoplasmic reticulum (SER). Why? A. to produce large amounts of proteins B. to digest materials quickly C. to store large amounts of hormones D. to produce large amounts of steroid hormones 89 What does the presence of many mitochondria imply about a cell’s energy requirements? A. a high demand for energy B. a low demand for energy C. fluctuating energy needs requiring flexibility D. number of mitochondria provides no implication of energy needs 90 How the nucleus controls the cell 91 13. The Nucleus • Is the cell’s control center • Contains DNA: genetic material • Most cells have one, exceptions: – Skeletal muscle (many), RBCs (none) 92 Figure 3–10a Structure of the Nucleus • Nucleus: – largest organelle • Nuclear envelope: – double membrane around the nucleus, connected to ER • Nuclear pores with regulator proteins: – Control exchange of materials between cytoplasm and nucleus 93 Within the Nucleus • Nucleoplasm: – fluid containing ions, proteins (enzymes), DNA, RNA, and nucleoli • Nucleoli: Dark areas – site of rRNA synthesis and packaging into ribosomal subunits • In non-dividing cells DNA is loose – Called chromatin 94 Organization of DNA • DNA in chromatin is organized into Nucleosomes: – DNA coiled around histones • During Nuclear Division, Chromatin is tightly coiled into visible chromosomes (23 pairs in humans) • Chromosomes: – tightly coiled DNA (cells dividing) 95 Figure 3–11 The Genetic Code 96 DNA and Genes • DNA: contains genes – instructions for every protein in the body • Gene: functional units of heredity – DNA instructions for a product: RNA or protein • Humans have 30-75 thousand potential genes (only 1.5% of total DNA) – Remainder is involved with control of genes or appear to be junk (25%) – Noncoding parts of DNA (non-genes) is highly variable from one person to the next – Variability allows for identification of an individual 97 by DNA fingerprinting Gene Activation • In order for a gene to be expressed (used to make a product) it must be unwound from the histone proteins so it can be read • Disassembly of the nucleosomes and unwinding of the DNA is called gene activation 98 Genetic Code • The chemical language of DNA instructions: – Read off a gene in order to assemble a protein – sequence of bases (A, T, C, G) – triplet code: • 3 bases of DNA = 1 amino acid (codon) – A gene = all the codons for all the amino acids in one protein in the correct order 99 Gene Structure and Expression • Structure Promoter Start Codon Open Reading Frame Terminator Stop Codon • Expression (original) (copy) (product) DNA RNA Protein 100 Transcription Translation KEY CONCEPT • The nucleus contains chromosomes • Chromosomes contain DNA • DNA stores genetic instructions for proteins • Proteins determine cell structure and function 101 How DNA instructions become proteins 102 Protein Synthesis • Transcription: – copies instructions from DNA to mRNA (in nucleus) • Translation: – ribosome reads code from mRNA (in cytoplasm) – assembles amino acids into polypeptide chain • Processing: – by RER and Golgi apparatus produces protein 103 mRNA Transcription • A DNA gene is transcribed to mRNA in 3 steps: – gene activation – DNA to mRNA – RNA processing 104 mRNA Transcription DNA STEP Gene G C A T A T T A G C A T G C T A A T C G G C G C C G T A C G G C A T T A T A Template strand STEP G C A RNA polymerase A T Promoter Coding strand Triplet 1 G G G A G 2 C G C C C G C C T A 3 T T C C A 4 Codon 4 (stop codon) • T G A Codon 1 G G G Triplet 4 2 Codon 3 C C C Codon 2 T 1 mRNA strand U T A G Triplet 3 A G C Triplet 2 Codon 1 A A A C G G T STEP T T RNA nucleotide KEY A Adenine G Guanine C Cytosine U Uracil (RNA) T Thymine 105 Step 1: Gene Activation • Uncoils DNA, removes histones • Start (promoter) and stop codes on DNA mark location of gene: – coding strand is code for protein – template strand used by RNA polymerase molecule 106 Step 2: DNA to mRNA • Enzyme RNA polymerase transcribes DNA: – binds to promoter (start) sequence – reads DNA code for gene – binds nucleotides to form messenger RNA (mRNA) – mRNA duplicates DNA coding strand, uracil replaces thymine 107 Step 3: RNA Processing • At stop signal, mRNA detaches from DNA molecule: – – – – code is edited (RNA processing) unnecessary codes (introns) removed good codes (exons) spliced together triplet of 3 nucleotides (codon) represents one amino acid 108 Codons 109 Table 3–2 Key Concept • The timing of gene activation (transcription) for any gene is controlled by signals from outside the nucleus, either from within the cell or in response to external cues – E.g. Hormones 110 Translation • Making a protein using the mRNA blueprint • Occurs in the cytoplasm on free ribosomes or on fixed ribosomes on the RER • mRNA moves: – from the nucleus – through a nuclear pore 111 Figure 3–13 Translation STEP STEP NUCLEUS mRNA The mRNA strand binds to the small ribosomal subunit and is joined at the start codon by the first tRNA, which carries the amino acid methionine. Binding occurs between complementary base pairs of the codon and anticodon. 1 KEY A Adenine Small ribosomal subunit •tRNA delivers amino acids to mRNA 2 1 tRNA Anticodon tRNA binding sites G Guanine C Amino acid The small and large ribosomal subunits interlock around the mRNA strand. U A C Cytosine U Uracil Start codon mRNA strand Large ribosomal subunit 112 Translation STEP STEP A second tRNA arrives at the adjacent binding site of the ribosome. The anticodon of the second tRNA binds to the next mRNA codon. 1 STEP The first amino acid is detached from its tRNA and is joined to the second amino acid by a peptide bond. The ribosome moves one codon farther along the mRNA strand; the first tRNA detaches as another tRNA arrives. Peptide bond 2 1 The chain elongates until the stop codon is reached; the components then separate. Small ribosomal subunit 3 2 1 Stop codon U A C A U G Completed polypeptide 2 3 G G C C C G A G C C G A G C U Large ribosomal subunit A 113 Genetic Code 114 Examples using the Genetic Code: Coding Strand DNA: ATgCAgTTTACgCAgAAgATCAgTTAg Template strand DNA: complement A-T, C-G TACgTCAAATgCgTCTTCTAgTCAATC Transcription to form mRNA: complementary base pairing to template, U replaces T AUgCAgUUUACgCAgAAgAUCAgUUAg Translation to form protein: read codons from genetic code e.g. AUg = Met/Start (start codon) Aug/CAg/UUU/ACg/CAg/AAg/AUC/AgU/UAg Met-Gln-Phe-Thr-Glu-Lys-Ile-Ser UAg = stop codon (no tRNA, no amino acid) 115 Mutations • Most non-infectious disease, conditions, and disorders are due to mutations in the DNA that change the amino acids in the protein – E.g. sickle cell anemia • Point mutation in DNA: A T • Changes on codon: GAG GTG • Changes one amino acid: – Glutamic acid (-charge) valine (neutral) • This alters the 3D shape of the whole hemoglobin protein: globular fibrous • Which changes the shape of the red blood cell: – Disc crescent • Which prevents the RBC from carrying oxygen, and 116 causes it to block capillaries Mutations • Point mutations = change in 1 base of DNA can be a silent mutation if the amino acids is not changed – common at the 3rd base in a codon • Insertion mutation = addition of a base which changes the reading frame;whole protein after the mutation is wrong • Deletion Mutation = removal of a base, alter reading frame, protein wrong. 117 KEY CONCEPT • Genes: – are functional units of DNA – contain instructions for 1 or more proteins • Protein synthesis requires: – several enzymes – ribosomes – 3 types of RNA • Mutation is a change in the nucleotide sequence of a gene: – can change gene function • Causes: – exposure to chemicals – exposure to radiation – mistakes during DNA replication 118 How does the nucleus control the activities of a cell? A. B. C. D. through nuclear pores through the nuclear matrix through DNA through RNA 119 What process would be affected by the lack of the enzyme RNA polymerase? A. nothing would be affected; DNA polymerase would take over B. cell’s ability to duplicate DNA C. cell’s ability to translate DNA D. cell’s ability to transcribe RNA 120 How cells reproduce 121 Cell Life Cycle • Life span of cell depends on type of cell • All cells eventually die – Apoptosis: controlled cell death, lysosomes are defused • Some cells must divide to make cells to replace dying cells; function of stem cells • To divide, DNA must be replicated and equally distributed between the stem cell and new daughter cell 122 Figure 3–3 Interphase • Most of a cell’s life is spent in a nondividing state (interphase) – Period of time that a cell performs its normal functions • The nondividing period: – G-zero phase—specialized cell functions only • If a cell never divides • Cells preparing for dividing, will go through 3 stages – G1 phase—cell growth, organelle duplication, protein synthesis, synthesizes enough cytoplasm for 2 cells – S phase—DNA replication and histone synthesis – G2 phase—finishes protein synthesis and centriole replication 123 3 Stages of Cell Division • Body (somatic) cells divide in 3 stages: – DNA replication duplicates genetic material exactly – Mitosis divides genetic material equally – Cytokinesis divides cytoplasm and organelles into 2 daughter cells 124 DNA Replication 125 DNA Replication • DNA helicases unwind the DNA and separates the strands • DNA polymerase bind to the DNA and synthesizes complementary antiparallel strands – DNA polymerase only add to the 3’ end of the molecule • Leading strand: synthesized continuously • Lagging strand: synthesized in pieces called Okasaki fragments – Okasaki fragments are attached end to end into one strand by DNA Ligase • DNA rewinds into double helix molecules – New molecules contains one strand of the original DNA and one newly synthesized strand 126 Figure 3–24 Overview of Cell Life Cycle INTERPHASE S DNA replication, synthesis of histones G1 Normal cell functions plus cell growth, duplication of organelles, protein synthesis G2 Protein synthesis THE CELL CYCLE M Indefinite period G0 Specialized cell functions MITOSIS (See Figure 3-25) 127 Mitosis • Mitosis (nuclear division) divides duplicated DNA into 2 sets of chromosomes: – DNA coils tightly into chromatids – chromatids connect at a centromere – protein complex around centromere called the kinetochore • Followed by cytokinesis: – Separation of the cells 128 Stage 1: Prophase • Nucleoli disappear • Centriole pairs move to cell poles • Microtubules (spindle fibers) extend between centriole pairs • Nuclear envelope disappears • Spindle fibers attach to kinetochore 129 Figure 3–25 (Stage 1) Stage 2: Metaphase • Chromosomes align in a central plane (metaphase plate) 130 Figure 3–25 (Stage 2) Stage 3: Anaphase • Microtubules pull chromosomes apart • Daughter chromosomes groups near centrioles 131 Figure 3–25 (Stage 3) Stage 4: Telophase • Nuclear membranes reform • Chromosomes uncoil • Nucleoli reappear • Cell has 2 complete nuclei 132 Figure 3–25 (Stage 4, 1 of 2) Overview of Mitosis 133 KEY CONCEPT • Mitosis duplicates chromosomes in the nucleus for cell division 134 Stage 4: Cytokinesis • Division of the cytoplasm • Cleavage furrow around metaphase plate • Membrane closes, producing daughter cells 135 Figure 3–25 (Stage 4, 2 of 2) What regulates cell division 136 Mitotic Rate and Life Span • Rate of cell division: – slower mitotic rate means longer cell life – cell division requires energy (ATP) • Cell Life Span: – Muscle cells, neurons rarely divide – Exposed cells (skin and digestive tract) live only days or hours 137 Regulating Cell Life • Normally, cell division balances cell loss • Increases cell division: – internal factors (MPF) – extracellular chemical factors (growth factors) • Decreases cell division: – repressor genes (faulty repressors cause cancers) – worn out telomeres (terminal DNA segments) 138 Chemicals Controlling Cell Division 139 Table 3–4 A cell is actively manufacturing enough organelles to serve two functional cells. This cell is probably in which phase of its life cycle? A. B. C. D. S G1 G2 M 140 During DNA replication, a nucleotide is deleted from a sequence that normally codes for a polypeptide. What effect will this deletion have on the amino acid sequence of the polypeptide? A. no effect, deletion will be skipped B. no effect, deletion will be automatically repaired C. amino acid sequence will disintegrate D. the amino acid sequence would be altered 141 What would happen if spindle fibers failed to form in a cell during mitosis? A. centromeres would not appear B. nuclear membrane would not disintegrate C. chromosomes would not separate D. chromatin would not condense 142 Cancer • Cell division: controlled by internal and external factors – In adult cell growth = cell death – If growth exceeds death a tumor can form • Cancer: – illness that disrupts cellular controls – produces malignant cells 143 Cancer • Benign tumors: – grow in a connective tissue capsule and remain in one place • Malignant tumor: ignore growth control mechanisms – spread into surrounding tissues (invasion) – start new tumors (metastasis) • Cancer develops in steps: 1. abnormal cell 2. primary tumor 3. metastasis 4. secondary tumor 144 Cancer • Cancer: caused by mutation in a growth control gene (oncogene = mutated genes that cause cancer) – 1° tumor: cells grow uncontrolled – 2° tumor: cells metastasize in blood and lymph to establish new growth elsewhere • Tumors trigger growth of blood vessels to support the cells – In order for diffusion to bring nutrients and remove wastes all cells have to be within 125µm of a vessel • Eventually the tumor will crowd out normal tissues causing organ failure 145 Figure 3–26 KEY CONCEPT • Mutations disrupt normal controls over cell growth and division • Cancers often begin where stem cells are dividing rapidly • More chromosome copies mean greater chance of error 146 Cell Differentiation 147 What is cell differentiation? • Cells specialize or differentiate: – All somatic cells in the body have the same DNA but different sizes, shapes, and functions – As cells specialize to become a specific cell type many genes get turned off permanently, cells are considered differentiated – Differentiated cells only express genes related to their function – Stem cells are undifferentiated: • Embryonic stem cells can express all of their genes and become any cell type • Other stem cells can express most of their genes – All stem cells do not show many specialized functions and can differentiate into many types of tissue 148 KEY CONCEPT • All body cells, except sex cells, contain the same 46 chromosomes • Differentiation depends on which genes are active and which are inactive 149 SUMMARY • Structures and functions of human cells • Structures and functions of membranous and nonmembranous organelles • ATP, mitochondria, and the process of aerobic cellular respiration • Structures and functions of the nucleus: – control functions of nucleic acids – structures and replication of DNA – DNA and RNA in protein synthesis 150 SUMMARY • Structures and chemical activities of the cell membrane: – – – – diffusion and osmosis active transport proteins vesicles in endocytosis and exocytosis electrical properties of plasma • Stages and processes of cell division: – DNA replication – mitosis – cytokinesis • Links between cell division, energy use, and cancer 151 Homework Lecture • Study Chapter 1, 2, and 3 for Exam #1 • Complete Homework #1 Laboratory 152