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The Cell • Common cell structures • Protein Trafficking basics • Cytoskeleton • Extracellular Matrix Reading Ch 6: The Cell Ch 7: Membranes / Transport Homework Diffusion & Osmosis Membrane Transport / Permeability Ch 8 Prequiz Membrane proteins & Transport Ch 9 Prequiz •Pores/channels, Carriers, Pumps Cell Respiration prequiz •Endocytosis & Exocytosis Passive vs Active Extra Credit Science Seminar cytoskeleton • Fiber network throughout the cytoplasm • Organizes cell’s structures and activities, anchoring many organelles – support the cell and maintain its shape – interacts with motor proteins to produce motility – May regulate biochemical activities • composed: – Microtubules – Microfilaments – Intermediate filaments Microtubules • The thickest – ~25 nm in diameter & ~200 nm to 25 microns long • Functions: – Shaping the cell – Guiding movement of organelles – Separating chromosomes during cell division Cilia and Flagella • Microtubules control the beating of cilia and flagella, locomotor appendages of some cells • Cilia and flagella differ in their beating patterns Microfilaments (Actin Filaments) • Thinnest - solid rods ~7 nm in diameter, • built as a twisted double chain of actin subunits • structural role - to bear tension, resisting pulling forces within the cell • Microfilaments that function in cellular motility contain the protein myosin in addition to actin Intermediate Filaments • range in diameter from 8–12 nanometers • support cell shape and fix organelles in place • more permanent cytoskeleton fixtures than the other two classes The Extracellular Matrix (ECM) of Animal Cells • Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) • made of glycoproteins such as collagen (fibrous), proteoglycans, and fibronectin • ECM proteins bind to receptor proteins in the plasma membrane called integrins Cells are not just floating around Fig. 6-30a Collagen Cells are not just floating around Proteoglycan complex EXTRACELLULAR FLUID Fibronectin Integrins Plasma membrane Microfilaments CYTOPLASM The plasma membrane is a collage spotted with many different proteins (mosaic) in the fluid matrix of the lipid bilayer ~45% protein 45% phospholipid 10% other • Proteins determine most of the membrane’s specific functions Phospholipid bilayer Fig. 7-3 Hydrophobic regions of protein Hydrophilic regions of protein Membrane Proteins Characteristics • Peripheral – bound (loosely) to surface • Integral = transmembrane proteins (tightly bound) hydrophobic regions - stretches of nonpolar amino acids, often coiled into alpha helices Often span multiple times N-terminus C-terminus Helix EXTRACELLULAR SIDE CYTOPLASMIC SIDE Fig. 7-8 Which of the following is likely to be in the transmembrane region of bacteriorhodopsin? a)Tryptophan b)Serine c) Aspartic acid d)Lysine Membrane Transport • Plasma membranes are selectively permeable • Some molecules easily pass through the membrane; others do not aka penetrating Mixtures • Most matter exists as mixtures – Two or more components physically intermixed • Three types of mixtures – Solutions – Colloids – Suspensions Solutions • Homogeneous mixtures • Usually transparent, e.g., atmospheric air or seawater – Solvent • Present in greatest amount, usually a liquid (usually H2O, but also oil, alcohol and others) – Solute(s) (small molecules, ie-ions, glucose, aa’s proteins) • Present in smaller amounts • In H2O solvent solutions, excess solutes usually crystalize Solution Colloids and Suspensions • Colloids (emulsions) proteins & lipids – Heterogeneous translucent mixtures, e.g., cytosol – Large solute particles that do not settle out – Undergo sol-gel transformations • Suspensions: cells – Heterogeneous mixtures, e.g., blood – Large visible solutes tend to settle out Colloid Solutions Suspension Solutions Colloids Suspensions Concentration of Solutions • Expressed as – Percent, or parts per 100 parts – Milligrams per deciliter (mg/dl) – Molarity, or moles per liter (M) • 1 mole = the atomic weight of an element or molecular weight (sum of atomic weights) of a compound in grams • 1 mole of any substance contains 6.02 1023 molecules (Avogadro’s number) Concentration •Percent (by volume), or parts per 100 parts 1gram/100ml = 1% or g/ml x 100% •Molarity, or moles per liter (M) A mole = molecular weight (sum of atomic weights) in grams 1 Mole = 6.02 x 1023 molecules Atomic weight of Na is 22.99 1 mole of Na = 22.99g 1 M (molar) solution of Na = 1mole/Liter or = 22.99g/Liter What is the % conc of 5g NaCl in 50ml of water? a) 1% b) 5% c) 10% d) 50% Concentration •Molarity, or moles per liter (M) A mole = molecular weight (sum of atomic weights) in grams 1 Mole = 6.02 x 1023 molecules Atomic weight of Na is 22.99 1 mole of Na = 22.99g 1 M (molar) solution of Na = 1mole/Liter or = 22.99g/Liter Solutes Diffusion: If solutes permeable (penetrating): Solutes: High Low No net H2O movement (Because of hydrostatic pressure) H2O Initial Movement Osmotic Pressure = Attraction (snapshot) Osmolarity H2O: Low High (solutes) (based on all solute particles) Tonicity LONG TERM / NET 2. Tonicity (overall / NET H2O movement) If solutes Impermeable (non-penetrating): H2O: Low High (solutes) (based on non-penetrating particles only) “Random” Movement Brownian collisions 30 Process of diffusion Solutes follow their concentration gradient = High Low Diffusion Rate of diffusion increases as a function of conc. larger gradient = faster rate of diffusion 2000 mM 10 mM Faster 100 mM 50 mM Slower Note: NET? describes overall movement not all movement Really molecules move back and forth, but overall high low Also: NET can be final long-term movement overall Diffusion of 1 solute does not affect diffusion of another Diffusion: between 2 compartments Dependent on: 1. Concentration gradient 2. Permeability Membrane permeable to sugar (penetrating) Permeable membrane. What is the NET movement of Na+? 15mM Na+ a)Inward b)Outward 150mM Na+ c) No Net movement d)Not enough info What is the NET movement of Na+? Trick! 15mM Na+ a)Inward b)Outward 150mM Na+ c) No Net movement d)Not enough info Osmosis = solvent (water) movement Importance: as water enters or leaves a cell Changes in cell water disrupts cell function by altering – Volume – concentrations Crenation Water movement also base on solutes Each particle needs water to surround it Na Attracts water Doesn’t necessarily take up space H2O drawn to solutes 1. Solutes: High Low 2. H2O: Low High (solutes) Each particle needs water to surround it Solutes act like sponges and soak up /attract water Water Movement Permeable to solute Inside 4 6 7 solutes 8 12HH 2O’s 2O’s Concentration 7/8 solutes 1/2 Outside 4 2 1 solutes 8 4 H2O’s Concentration 1/2 1/8 solutes Osmotic Pressure vs Tonicity Terms to describe what happens to water Osmotic Pressure = force (attraction) = initial movement Tonicity predicts Long-term (seconds) movement of water Osmotic pressure: Initially there are more solutes inside Permeable to solute Solutes are attracting water Osmotic pressure is inward After time Permeable to solute Concentrations have changed, and osmotic pressure changes, so osmotic pressure is an instant in time Calculating Osmotic Pressure = Osmolarity Each particle needs water to surround it So each individual particle contributes to osmotic pressure Expressed as OSMOLARITY = Total # of solute particles 100 mM Na+ = 100 mOsmoles (mOsm) 100 mM Na+ & 100mM K+ = 200 mOsm NaCl Na+ Cl- Calculating Osmotic Pressure = Osmolarity Consider Disassociation of ionic compounds Solid NaCl Na+ Cl- 100 mM NaCl = 100 mM Na+ & 100mM Cl= 200 mOsm aqueous Hyper-osmotic = Higher [solute] stronger pressure Hypo-osmotic = lower [solute] weaker pressure Iso-osmotic = equal [solute] equal pressure Hyper-osmotic Hypo-osmotic Solutes Diffusion: If solutes permeable (penetrating): Solutes: High Low H2O Osmotic Pressure / Osmolarity = Attraction = Initial H2O: Low High (all solutes) Hypo-osmotic Hyper-osmotic Calculating Osmolarity ALL SOLUTE PARTICLES 1 HypOosmotic 2 permeable - Na+ ClImpermeable - K+ Solution 1 Solution 2 100 mM K+ 50 mM NaCl 50 mM K+ 100 mM NaCl 200 mOsm HypERosmotic 250 mOsm Osmotic pressure: There is a pressure for water to move OUT Diffusion: Na & Cl follow gradient move IN This is only temporarily / initially (While this difference lasts) Eventually Na & Cl will even out What is the osmolarity inside? 15mM Na+ a) 0 mOsmols 150mM Na+ b)15 mOsmols c) 150 mOsmols d)165 mOsmols Which solution is hypo-osmotic? 15mM Na+ 150mM Na+ a)Inward b)Outward c) No osmotic pressure What is the osmotic pressure? 15mM Na+ 150mM Na+ a)Inward b)Outward c) No osmotic pressure Long term Water Movement / Tonicity Permeable to solute Inside 4 6 7 solutes 8 12HH 2O’s 2O’s Concentration 7/8 solutes 1/2 Outside 4 2 1 solutes 8 4 H2O’s Concentration 1/2 1/8 solutes Tonicity / Long-Term Movement? If water moved then solution should change volume What prevents movement? Hydrostatic Pressure There is usually a force that resists changes in volume Initial Long-term Note: gravity Permeable membrane Blood vessel pressure no Long term (NET) water movement What happens if membrane is impermeable / non-penetrating? What determines permeability later… Impermeable (non-penetrating) membrane Initial Long-term Impermeable membrane Because solutes are impermeable, the only way to equilibrate the concentration is for water to move Osmosis Impermeable to solute Lysis Permeability affects long-term water movement Tonicity is determined ONLY by impermeable solutes Initial Permeable to solutes • Solutes diffuse • Osmotic pressure right • Long-Term – no H2O movement Impermeable to solutes • Solutes don’t diffuse • Osmotic pressure right • Long-Term – H2O right Long-term Permeable membrane Impermeable membrane Tonicity • Tonicity: potential water movement = measure of non-penetrating solutes • Isotonic: A solution with the same solute concentration • Hypertonic: A solution having greater solute concentration • Hypotonic: A solution having lesser solute concentration Commonly in reference to a solution’s ability to cause a cell to shrink or swell (net water movement) Calculating Tonicity Only NON-Penetrating (impermeable) particles 1 2 permeable - Na+ ClImpermeable - K+ Solution 1 Solution 2 100 mM K+ 50 mM NaCl 50 mM K+ 100 mM NaCl 100 mM 50 mM HypER tonic HypOtonic Long-term Movement of water is INWARD Solutes Diffusion: If solutes permeable (penetrating): Solutes: High Low H2O Osmolarity / Osmotic Pressure = [solute] = Attraction = Initial H2O: Low High (all solutes) Hypo-osmotic Hyper-osmotic Tonicity =LONG TERM = [Impermeable solute] H2O: Low High (IMPERMEABLE solutes ONLY) hypotonic hypertonic Semi-Permeable Impermeable to Na+, Permeable to H2O What is the long-term movement of H2O? 15mM Na+ a)Inward b)Outward 150mM Na+ c) No movement d)Not enough info Impermeable to Na+, Permeable to K+ Which is hypertonic? 15mM Na+ 150 mM K+ 150mM Na+ 15mM K+ a)Inside b)Outside c)Neither Impermeable to Na+, Permeable to K+ Long-term Water movement? 15mM Na+ 150 mM K+ a)Inward b)Outward 150mM Na+ 15mM K+ c) No movement d)Not enough info Calculating Osmolarity ALL SOLUTE PARTICLES 1 HypOosmotic 2 permeable - Na+ ClImpermeable - K+ Solution 1 Solution 2 100 mM K+ 50 mM NaCl 50 mM K+ 100 mM NaCl 200 mOsm HypERosmotic 250 mOsm Osmotic pressure: There is a pressure for water to move OUT Diffusion: Na & Cl follow gradient move IN This is only temporarily / initially (While this difference lasts) Eventually Na & Cl will even out What you will need to be able to do Predicting movement Permeable: Na+ & HCO3Impermeable to Glucose NaHCO3 moves: 200 mM Glu 50 mM NaHCO3 a)Inward b)Outward 100 mM Glu 100 mM NaHCO3 c)Neither d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose Glu moves: 200 mM Glu 50 mM NaHCO3 a)Inward b)Outward 100 mM Glu 100 mM NaHCO3 c)Neither d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose Osmolarity inside is: 200 mM Glu 50 mM NaHCO3 a)50 mOsm b)200 mOsm 100 mM Glu 100 mM NaHCO3 c)250 mOsm d)300 mOsm Permeable: Na+ & HCO3Impermeable to Glucose The Hyperosmotic solution is: 200 mM Glu 50 mM NaHCO3 a)Inside b)Outside 100 mM Glu 100 mM NaHCO3 c)Neither Iso-osmotic d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose Osmotic pressure is: 200 mM Glu 50 mM NaHCO3 100 mM Glu 100 mM NaHCO3 a)H2O in b)H2O out c)Neither d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose Hypertonic solution is: 200 mM Glu 50 mM NaHCO3 100 mM Glu 100 mM NaHCO3 a)Inside b)Outside c)Neither d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose NET H2O movement is: 200 mM Glu 50 mM NaHCO3 a)Inward b)Outward 100 mM Glu 100 mM NaHCO3 c)Neither d)Not enough info Permeable: Na+ & HCO3Impermeable to Glucose What will happen to the cell? 200 mM Glu 50 mM NaHCO3 a)Lysis b)Crenation 100 mM Glu 100 mM NaHCO3 c)No change d)Not enough info Estimate tonicity Before: Given permeability & 2 solution concentrations Determine movement Now: given 1 solution concentration and movement Determine concentration of 2nd solution Impermeable to Na+ permeable to Ethanol The osmotic pressure is: 300 mOsm a)Inward b)Outward c)Neither 300 mOsm d)Not enough info RBCs have a tonicity equivalent to 0.9% NaCl or 0.3 M Na+ (impermeable particle concentration) Cell crenates when placed in an unknown mystery solution, The unknown solution is: a)0% NaCl 0.9% NaCl or 300 mM Na+ b)0.9 % NaCl c)10 % NaCl d) 300 mM NaCl Unknown solution e)0.3 M NaCl A cell of unknown solute concentration (potato) Cell loses weight when put in 500 mM Na+. The cytosol could possibly be: a)0 mM NaCl equivalent Unknown b)500 mM NaCl equivalent c)1000 mM NaCl equivalent 500 mM NaCl d)1 M NaCl equivalent Determine permeability Given 2 concentrations and movement Determine permeability RBCs - 0.3 M Na+ - impermeable Cell placed in 300 mM urea Outside solution is 300 mM Na+ a)Hyper-osmotic b)Hypo-osmotic c)Iso-osmotic 300 mM urea RBCs - 0.3 M Na+ - impermeable Cell placed in 300 mM urea Cell explodes Water moved: 300 mM Na+ a)In b)Out c)Neither 300 mM urea d)unknown RBCs - 0.3 M Na+ - impermeable Cell placed in 300 mM urea Cell explodes Outside solution must be: 300 mM Na+ a)Hypertonic b)Hypotonic c)Isotonic 300 mM urea d)unknown RBCs - 0.3 M Na+ - impermeable Cell placed in 300 mM urea Cell explodes Urea is: 300 mM Na+ a)Impermeable b)Permeable c)unknown 300 mM urea What Determines Permeability? Based on Plasma Membrane • Separates intracellular fluid (ICF) from extracellular fluid (ECF) – Interstitial fluid (IF) = ECF that surrounds cells Compartmentalization Passive Processes: Simple Diffusion Passive = no energy Lipidsoluble solutes Lipids Water molecules CO2 & O2 Simple diffusion: directly through the membrane What? Simple Based on lipid bilayer – lipids, H2O, O2, CO2 Direction? diffusion Based on Concentration Gradient Passive Processes: Osmosis • Movement of solvent (water) across a selectively permeable membrane • Water diffuses through plasma membranes: – Through the lipid bilayer – Through water channels called aquaporins (AQPs) Facilitated and/or simple Passive Processes: Facilitated Diffusion • Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins, both of which: – Exhibit specificity (selectivity) – Are saturable; rate is determined by number of carriers or channels – Can be regulated in terms of activity and quantity Specificity Only K fits Confromational change of a K+-carrier Facilitated Diffusion Using Channel Proteins • Aqueous channels formed by transmembrane proteins selectively transport ions or water • Two types: – Leakage channels • Always open – Gated channels • Controlled by chemical or electrical signals Open channels are free flowing Facilitated Diffusion Facilitated = uses membrane protein diffusion Conc Gradient Channel – Free Diffusion Ex: Na+-channel (leakage) Or Acetylcholine-gated Na+-channel Facilitated Diffusion - Channels mostly ions selected on basis of size and charge 500 mM Na+ 10 mM Cl- Na+ Na+/Cl- Channel 50 mM Na+ 100 mM ClFree flow - Na doesn’t affect Cl but depends on conc. gradient Cl- Gated Channels Receptor closed ligand open Receptor – anything that can bind another molecule Can refer to protein as a whole or only a specific region of the protein Ligand – something that binds to a receptor Usually a small molecule (ie- not a protein) Facilitated Diffusion: Carrier Proteins • transport specific polar molecules (e.g., sugars and amino acids) • Binding causes shape change in carrier Carrier – set ratios Ex: Na+-carrier Na+/Glucose-symport 3Na+/2K+-antiport X # of molecules each time Symport or antiports Glucose Symport – carrier that transports substrates in the same direction Antiport – carrier that transports substrates in opposite directions Can be sequential or simultaneous Facilitated Diffusion - Carriers 500 mM Na+ 10 mM Cl- Na+ Na+/Cl- antiport 50 mM Na+ 100 mM Cl- Fixed Ratio: For every Na In one Cl out & vice versa For every Na Out one Cl In Depends on conc. gradient Cl- Facilitated Diffusion - Carriers 500 mM Na+ 10 mM ClNa+/Cl- symport Na+ Cl- No movement Or impaired Na wants In Cl wants out 50 mM Na+ 100 mM ClFixed Ratio: For every Na In one Cl In & vice versa For every Na Out one Cl Out Depends on conc. gradient A cell has Mg2+-channels. Which of the following is NOT permeable? a)Estrogen b)CO2 c) Ca2+ d)Mg2+ A cell has Ach-gated Ca2+-channels. Which of the following is permeable in the presence of ACh a)Na+ Ca2+ b)Clc) Ca2+ d)Mg2+ e) None of the above A cell has Ach-gated Ca2+-channels. Which of the following is permeable in the absence of ACh a)Na+ Ca2+ b)Clc) Ca2+ d)Mg2+ e) None of the above A cell has Ach-gated Na+-channels. 150mM Na+ outside, 10 mM Inside What happens in the presence of ACh? 150 Na+ Na+ a)Na+ influx b)Na+ outflux 10 Na+ c)No movement A cell has Ach-gated Na+/K+-channels. 150mM Na+ outside, 10 mM Inside 20mM K+ outside, 80mM Inside What happens in the presence of ACh? 150 Na+ 20mM K+ Na+ /K+ a)Na+ influx, K+ influx b)Na+ outflux, K+ influx c) Na+ influx, K+ outflux 10 Na+ 80mM K+ d)Na+ outflux, K+ outflux e)None of the above A cell has Ach-gated Na+/K+-channels. 150mM Na+ outside, 10 mM Inside 80mM K+ outside, 20mM Inside What happens in the presence of ACh? 150 Na+ 80mM K+ Na+ /K+ a)Na+ influx, K+ influx b)Na+ outflux, K+ influx c) Na+ influx, K+ outflux 10 Na+ 20mM K+ d)Na+ outflux, K+ outflux e)None of the above A cell has Na+/K+-symports. 150mM Na+ outside, 10 mM Inside 80mM K+ outside, 20mM Inside What happens in the ABSENCE of ACh? 150 Na+ 80mM K+ a)Na+ influx, K+ influx Na+/K+ symport b)Na+ outflux, K+ influx c) Na+ influx, K+ outflux 10 Na+ 20mM K+ d)Na+ outflux, K+ outflux e)None of the above A cell has Na+/K+-antiports. 150mM Na+ outside, 10 mM Inside 80mM K+ outside, 20mM Inside 150 Na+ 80mM K+ a)Na+ influx, K+ influx Na+/K+ antiport b)Na+ outflux, K+ influx c) Na+ influx, K+ outflux 10 Na+ 20mM K+ d)Na+ outflux, K+ outflux e)None of the above Active Transport- Primary PUMP – Like Carrier but uses ATP Independent of conc. gradient Active Transport- Primary Na+-K+ pump = ATPase = enzyme Uses ATP to drive Ion movement Antiport Transported substances move in the opposite direction Adenosine Triphosphate (ATP) source of usuable energy = “molecular currency” The cell’s rechargable battery Adenine RNA nucleotide with two additional phosphate groups Active Transport- Primary 500 mM Na+ 10 mM Cl- 50 mM Na+ 100 mM Cl- Na pump that pumps Na out Na+ Na pump that pumps Na In Independent of conc. gradient Na+ A cell has 3Na+/2K+-pump. 150mM Na+ outside, 10 mM Inside 80mM K+ outside, 20mM Inside a)Na+ influx, K+ influx b)Na+ outflux, K+ influx c)Na+ influx, K+ outflux d)Na+ outflux, K+ outflux e)not enough info A cell has 3Na+/2K+-pump. Given time, the concentration of Na and K will be: a)Na+ high outside, K+ High Outside b)Na+ high out, K+ High In c)Na+ high In, K+ High out d)Na+ high In, K+ High In Membrane Potential Typical conc’s – Electrochemical gradient Secondary active transport use of an exchange pump (such as the Na+/K+-pump) indirectly to drive the transport of other solutes Extracellular fluid Glucose Na+-K+ pump Na+-glucose symport transporter loading glucose from ECF Na+-glucose symport transporter releasing glucose into the cytoplasm Symport Transported substances move in the same direction Endocytosis – enables large particles and macromolecules to enter the cell Receptor mediated Endocytosis – specific macromolecules Pinocytosis – nonspecific small Phagocytosis – whole cells / solid particles PHAGOCYTOSIS • In phagocytosis a cell engulfs a particle • fuses with a lysosome to digest the particle 1 Extracellular fluid Plasma membrane Cytoplasm Transport vesicle Uncoated endocytic vesicle Lysosome (a) (b) Figure 3.12 PINOCYTOSIS • In pinocytosis, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles RECEPTOR-MEDIATED ENDOCYTOSIS • In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formation • A ligand is any molecule that binds specifically to a receptor site of another molecule Exocytosis – moves substance from the cell interior to the extracellular space