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Anatomy Test 2

Chapter 3

Membrane Proteins • Allow communication with environment • ½ mass of plasma membrane • Most specialized membrane functions • Some float freely • Some tethered to intracellular structures • Two types: – Integral proteins; peripheral proteins
Membrane Lipids • 75% phospholipids (lipid bilayer) – Phosphate heads: polar and hydrophilic – Fatty acid tails: nonpolar and hydrophobic 5% glycolipids • – Lipids with polar sugar groups on outer membrane surface • 20% cholesterol – Increases membrane stability
Plasma Membrane • Lipid bilayer and proteins in constantly changing fluid mosaic • Plays dynamic role in cellular activity • Separates intracellular fluid (ICF) from extracellular fluid (ECF) – Interstitial fluid (IF) = ECF that surrounds cells
Generalized Cell • All cells have some common structures and functions • Human cells have three basic parts: – Plasma membrane—flexible outer boundary © 2013 Pearson Education, Inc. – Cytoplasm—intracellular fluid containing organelles – Nucleus—control center
Cell Diversity • Over 200 different types of human cells • Types differ in size, shape, subcellular components, and functions
Cell Theory • Organismal functions depend on individual and collective cell functions • Biochemical activities of cells dictated by © 2013 Pearson Education, Inc. their shapes or forms, and specific subcellular structures • Continuity of life has cellular basis
Cell structural and functional unit of life
Membrane Proteins • Integral proteins – Firmly inserted into membrane (most are transmembrane) – Have hydrophobic and hydrophilic regions • Can interact with lipid tails and water Membrane Proteins © 2013 Pearson Education, Inc. – Function as transport proteins (cha
Membrane Proteins • Peripheral proteins – Loosely attached to integral proteins – Include filaments on intracellular surface for membrane support Function as enzymes; motor proteins for Membrane Proteins © 2013 Pearson Education, Inc. – shape change during cell divi
Six Functions of Membrane Proteins 1. Transport 2. Receptors for signal transduction 3. Attachment to cytoskeleton and extracellular matrix 4. Enzymatic activity 5. Intercellular joining 6. Cell-cell recognition
Lipid Rafts • ~20% of outer membrane surface • Contain phospholipids, sphingolipids, and cholesterol • More stable; less fluid than rest of © 2013 Pearson Education, Inc. membrane – May function as stable platforms for cellsignaling molecules, membrane invagin
The Glycocalyx • "Sugar covering" at cell surface – Lipids and proteins with attached carbohydrates (sugar groups) • Every cell type has different pattern of sugars © 2013 Pearson Education, Inc. – Specific biological markers for cell to cell recognition – Allow
Cell Junctions • Some cells "free" – e.g., blood cells, sperm cells • Some bound into communities – Three ways cells are bound: © 2013 Pearson Education, Inc. • Tight junctions • Desmosomes • Gap junctions
Cell Junctions: Tight Junctions • Adjacent integral proteins fuse
Cell Junctions: Desmosomes • "Rivets" or "spot-welds" that anchor cells together at plaques (thickenings on plasma membrane) – Linker proteins between cells connect plaques Keratin filaments extend through cytosol to © 2013 Pearson Education, Inc. – opposite plaque giving sta
Cell Junctions: Gap Junctions • Transmembrane proteins form pores (connexons) that allow small molecules to pass from cell to cell – For spread of ions, simple sugars, and other small molecules between cardiac or smooth © 2013 Pearson Education, Inc. muscle cells
Plasma Membrane • Cells surrounded by interstitial fluid (IF) – Contains thousands of substances, e.g., amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products • Plasma membrane allows cell to © 2013 Pearson Education, Inc. – Obtain from IF exac
Membrane Transport • Plasma membranes selectively permeable – Some molecules pass through easily; some do not • Two ways substances cross membrane © 2013 Pearson Education, Inc. – Passive processes – Active processes
Types of Membrane Transport • Passive processes – No cellular energy (ATP) required – Substance moves down its concentration gradient Active processes © 2013 Pearson Education, Inc. • – Energy (ATP) required – Occurs only in living cell membranes
Passive Processes • Two types of passive transport – Diffusion • Simple diffusion • Carrier- and channel-mediated facilitated diffusion • Osmosis © 2013 Pearson Education, Inc. – Filtration • Usually across capillary walls
Passive Processes: Diffusion • Collisions cause molecules to move down or with their concentration gradient – Difference in concentration between two areas • Speed influenced by molecule size and © 2013 Pearson Education, Inc. temperature
Passive Processes • Molecule will passively diffuse through membrane if – It is lipid soluble, or – Small enough to pass through membrane channels or Passive Processes © 2013 Pearson Education, Inc. channels, – Assisted by carrier molecule
Passive Processes: Simple Diffusion • Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer – E.g., oxygen, carbon dioxide, fat-soluble vitamins
Passive Processes: Facilitated Diffusion • Certain lipophobic molecules (e.g., glucose, amino acids, and ions) transported passively by – Binding to protein carriers Moving through water filled channels
Carrier-Mediated Facilitated Diffusion • Transmembrane integral proteins are carriers • Transport specific polar molecules (e.g., sugars and amino acids) too large for channels © 2013 Pearson Education, Inc. • Binding of substrate causes shape change in carrier then passage across membr
Channel-Mediated Facilitated Diffusion • Aqueous channels formed by transmembrane proteins • Selectively transport ions or water • Two types: © 2013 Pearson Education, Inc. – Leakage channels • Always open – Gated channels • Controlled by chemical or electrical signals
Passive Processes: Osmosis • Movement of solvent (e.g., water) across selectively permeable membrane • Water diffuses through plasma membranes Th h li id bil © 2013 Pearson Education, Inc. – Through lipid bilayer – Through specific water channels called aquaporins (AQPs) •
Passive Processes: Osmosis • Water concentration varies with number of solute particles because solute particles displace water molecules • Osmolarity - Measure of total concentration of solute particles © 2013 Pearson Education, Inc. p • Water moves by osmosis until hydrost
Passive Processes: Osmosis • When solutions of different osmolarity are separated by membrane permeable to all molecules, both solutes and water cross membrane until equilibrium reached When solutions of different osmolarity are © 2013 Pearson Education, Inc. • separated by m
Importance of Osmosis • Osmosis causes cells to swell and shrink • Change in cell volume disrupts cell function, especially in neurons
Tonicity • Tonicity: Ability of solution to alter cell's water volume – Isotonic: Solution with same non-penetrating solute concentration as cytosol Hypertonic: Solution with higher non- © 2013 Pearson Education, Inc. – nonpenetrating solute concentration t
Membrane Transport: Active Processes • Two types of active processes – Active transport – Vesicular transport • Both require ATP to move solutes across a li i l b b © 2013 Pearson Education, Inc. living plasma membrane because – Solute too large for channels – Solute not lipid solubl
Active Transport • Requires carrier proteins (solute pumps) – Bind specifically and reversibly with substance • Moves solutes against concentration gradient © 2013 Pearson Education, Inc. – Requires energy
Active Transport: Two Types • Primary active transport – Required energy directly from ATP hydrolysis • Secondary active transport – Required energy indirectly from ionic di t t d b i ti t t © 2013 Pearson Education, Inc. gradients created by primary active transport
9/29/2013 10 Primary Active Transport • Energy from hydrolysis of ATP causes shape change in transport protein that "pumps" solutes (ions) across membrane • E.g., calcium, hydrogen, Na+-K+ pumps
Primary Active Transport • Sodium-potassium pump – Most well-studied – Carrier (pump) called Na+-K+ ATPase – Located in all plasma membranes I l di i d d ti © 2013 Pearson Education, Inc. – Involved in primary and secondary active transport of nutrients and ions
Sodium-Potassium Pump • Na+ and K+ channels allow slow leakage down concentration gradients • Na+-K+ pump works as antiporter – Pumps against Na+ and K+ gradients to maintain high intracellular K+ concentration © 2013 Pearson Education, Inc. and high extracellular Na+ co
Cytoplasm • Located between plasma membrane and nucleus – Composed of • Cytosol – Water with solutes (protein, salts, sugars, etc.) © 2013 Pearson Education, Inc. p , , g , ) • Organelles – Metabolic machinery of cell; each with specialized function; eithe
Cytoplasmic Organelles • Membranous – Mitochondria – Peroxisomes – Lysosomes E d l i ti l © 2013 Pearson Education, Inc. • Membranes allow crucial compartmentalization – Endoplasmic reticulum – Golgi apparatus • Nonmembranous – Cytoskeleton – Centrioles – Ribosomes
Mitochondria • Double-membrane structure with inner shelflike cristae • Provide most of cell's ATP via aerobic cellular respiration R i © 2013 Pearson Education, Inc. – Requires oxygen • Contain their own DNA, RNA, ribosomes • Similar to bacteria; capable of c
Ribosomes • Granules containing protein and rRNA • Site of protein synthesis • Free ribosomes synthesize soluble proteins that function in cytosol or other © 2013 Pearson Education, Inc. organelles • Membrane-bound ribosomes (forming rough ER) synthesize pro
Endoplasmic Reticulum (ER) • Interconnected tubes and parallel membranes enclosing cisterns • Continuous with outer nuclear membrane • Two varieties: © 2013 Pearson Education, Inc. – Rough ER – Smooth ER
Rough ER • External surface studded with ribosomes • Manufactures all secreted proteins • Synthesizes membrane integral proteins and phospholipids © 2013 Pearson Education, Inc. • Assembled proteins move to ER interior, enclosed in vesicle, go to Golgi appar
Smooth ER • Network of tubules continuous with rough ER • Its enzymes (integral proteins) function in – Lipid metabolism; cholesterol and steroidbased hormone synthesis; making lipids of © 2013 Pearson Education, Inc. y gp lipoproteins – Absorption, synthes
Golgi Apparatus • Stacked and flattened membranous sacs • Modifies, concentrates, and packages proteins and lipids from rough ER • Transport vessels from ER fuse with © 2013 Pearson Education, Inc. convex cis face; proteins modified, tagged for delivery, sorted, pa
Golgi Apparatus • Three types of vesicles bud from concave trans face – Secretory vesicles (granules) • To trans face; release export proteins by exocytosis © 2013 Pearson Education, Inc. y – Vesicles of lipids and transmembrane proteins for plasma membrane or or
Peroxisomes • Membranous sacs containing powerful oxidases and catalases • Detoxify harmful or toxic substances • Catalysis and synthesis of fatty acids © 2013 Pearson Education, Inc. • Neutralize dangerous free radicals (highly reactive chemicals with unpaired
Lysosomes • Spherical membranous bags containing digestive enzymes (acid hydrolases) – "Safe" sites for intracellular digestion • Digest ingested bacteria, viruses, and toxins • Degrade nonfunctional organelles © 2013 Pearson Education, Inc. eg ade o u c o a
Endomembrane System • Overall function – Produce, degrade, store, and export biological molecules – Degrade potentially harmful substances Includes ER Golgi apparatus secretory © 2013 Pearson Education, Inc. • ER, apparatus, vesicles, lysosomes, nuclear and plasma mem
Cytoskeleton • Elaborate series of rods throughout cytosol; proteins link rods to other cell structures – Three types • Microfilaments © 2013 Pearson Education, Inc. • Intermediate filaments • Microtubules
Microfilaments • Thinnest of cytoskeletal elements • Dynamic strands of protein actin • Each cell has a unique arrangement of strands © 2013 Pearson Education, Inc. • Dense web attached to cytoplasmic side of plasma membrane is called terminal web – Gives strengt
Intermediate Filaments • Tough, insoluble, ropelike protein fibers • Composed of tetramer fibrils • Resist pulling forces on cell; attach to desmosomes © 2013 Pearson Education, Inc. • E.g., neurofilaments in nerve cells; keratin filaments in epithelial cells
Microtubules • Largest of cytoskeletal elements; dynamic hollow tubes; most radiate from centrosome • Composed of protein subunits called tubulins © 2013 Pearson Education, Inc. • Determine overall shape of cell and distribution of organelles • Mitochondria, l
Motor Proteins • Protein complexes that function in motility (e.g., movement of organelles and contraction) • Powered by ATP
Centrosome and Centrioles • "Cell center" near nucleus • Generates microtubules; organizes mitotic spindle • Contains paired centrioles © 2013 Pearson Education, Inc. – Barrel-shaped organelles formed by microtubules • Centrioles form basis of cilia and flagella
Cellular Extensions • Cilia and flagella – Whiplike, motile extensions on surfaces of certain cells – Contain microtubules and motor molecules Cilia move substances across cell surfaces Cellular Extensions – – Longer flagella propel whole cells (tail of sperm)
Cilia and Flagella • Centrioles forming base called basal bodies • Cilia movements alternate between power stroke and recovery stroke
Cellular Extensions • Microvilli – Minute, fingerlike extensions of plasma membrane – Increase surface area for absorption Core of actin filaments for stiffening
Nucleus • Double-membrane barrier; encloses nucleoplasm • Outer layer continuous with rough ER and bears ribosomes • Inner lining ( nuclear lamina) maintains shape ofg ) p nucleus; scaffold to organize DNA • Pores allow substances to pass; nuclear pore com
Nucleoli • Dark-staining spherical bodies within nucleus • Involved in rRNA synthesis and ribosome subunit assembly © 2013 Pearson Education, Inc. • Associated with nucleolar organizer regions – Contains DNA coding for rRNA • Usually one or two per cell
Chromatin • Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%) • Arranged in fundamental units called nucleosomes © 2013 Pearson Education, Inc. • Histones pack long DNA molecules; involved in gene regulation • Condense into barlike bodie
Cytosolic Protein Degradation • Autophagy – Cytoplasmic bits and nonfunctional organelles put into autophagosomes; degraded by lysosomes • Ubiquitins © 2013 Pearson Education, Inc. – Tag damaged or unneeded soluble proteins in cytosol – Digested by soluble enzymes or proteasom
Extracellular Materials • Body fluids—interstitial fluid, blood plasma, and cerebrospinal fluid • Cellular secretions—intestinal and gastric fluids, saliva, mucus, and serous fluids © 2013 Pearson Education, Inc. • Extracellular matrix—most abundant extracellular material
Developmental Aspects of Cells • All cells of body contain same DNA but cells not identical • Chemical signals in embryo channel cells into specific developmental pathways by turning some genes on and others off © 2013 Pearson Education, Inc. • Development of specific and distinc
Apoptosis and Modified Rates of Cell Division • During development more cells than needed produced (e.g., in nervous system) • Eliminated later by programmed cell death (apoptosis) © 2013 Pearson Education, Inc. – Mitochondrial membranes leak chemicals that activate caspases
Apoptosis and Modified Rates of Cell Division • Organs well formed and functional before birth • Cell division in adults to replace short-lived cells and repair wounds © 2013 Pearson Education, Inc. • Hyperplasia increases cell numbers when needed • Atrophy (decreased size) results from loss
Theories of Cell Aging • Wear and tear theory—Little chemical insults and free radicals have cumulative effects • Mitochondrial theory of aging—free radicals in mitochondria diminish energy production • Immune system disorders—autoimmune y responses; progressive weakening
Theories of Cell Aging • Most widely accepted theory – Genetic theory—cessation of mitosis and cell aging programmed into genes • Telomeres (strings of nucleotides protecting ends of chromosomes) may determine number of times a cell can divide • Telomerase lengthens telom
Created by: sarahflagg



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