Lecture 1 Outline (Ch. 5) I. Membrane Structure II. Permeability III. Transport Across Membranes A. Passive B. Facilitated C. Active D. Bulk

Membrane structure 1915, knew membrane made of lipids and proteins • Reasoned that membrane = bilayer Where to place proteins? Lipid layer 1 Proteins Lipid layer 2

Membrane structure

Membrane structure • freeze fracture • proteins intact, one layer or other • two layers look different

Membrane structure Experiment to determine membrane fluidity: • marked membrane proteins mixed in hybrid cell

Membrane structure Membrane fluidity • phospholipid f.a. “tails”: saturation affects fluidity • cholesterol buffers temperature changes

Membrane structure “fluid mosaic model” – 1970s • fluid – phospholipids move around • mosaic – proteins embedded in membrane

Membrane structure • cell membrane – amphipathic - hydrophilic & hydrophobic hydrophilic hydrophobic hydrophilic • membrane proteins inserted, also amphipathic

Membrane Proteins Membrane proteins: Integral: inserted in membrane - transmembrane – span membrane Peripheral: next to membrane - inside or outside

Membrane structure • Two transmembrane proteins: different structure Bacteriorhodopsin: proton pump Bacterial pore protein

Membrane Proteins

Movement of molecules Simple Diffusion: most basic force to move molecules • Disperse until concentration equal in all areas

Movement of molecules Cell membranes only allow some molecules across w/out help: • Small, non-polar molecules OK ex. steroids, O2, CO2 • No charged, polar, or large molecules ex. sugars, ions, water*

Transport Across Membranes Types of transport: Passive transport - Simple diffusion - Facilitated diffusion - Osmosis B. Active transport C. Bulk transport • Energy Required? • Directionality?

Passive Transport - Simple Diffusion • NO ENERGY required - non-polar molecules (steroids, O2, CO2) • DOWN concentration gradient • molecules equally distribute across available area by type

Passive Transport – Facilitated Diffusion • NO ENERGY required • DOWN concentration gradient • molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein.

Passive Transport - Osmosis • osmosis – movement of water across cell membrane • water crosses cell membranes via special channels called aquaporins • moves into/out of cell until solute concentration is balanced

Passive Transport - Osmosis In each situation below, does water have net movement, and which direction: fewer solutes in solution, than in cell equal solutes in solution as in cell more solutes in solution, than in cell

Passive Transport - Osmosis • tonicity – # solutes in solution in relation to cell animal cell plant cell - hypotonic – fewer solutes in solution - isotonic – equal solutes in solution - hypertonic – more solutes in solution

Passive Transport - Osmosis Paramecium example • regulate water balance • pond water hypotonic • water into contractile vacuole – water expelled

Passive Transport - Osmosis Scenario: in movie theater, watching a long movie. You are: drinking water What happens to your blood? You are: eating popcorn What happens to your blood?

Active Transport • Ex. Na-K ion pump • ENERGY IS required - Na+ ions: inside to out • UP/AGAINST concentration gradient - K+ ions: outside to in • transport proteins a. ion pumps (uniporters) • antiporter: two molecules move opposite directions (UP gradient) b. symporter/antiporter c. coupled transport

Active Transport - uniporter • Ex. proton (H+) pump • ATP used pump H+ ions out • uniporter: ONE molecule UP gradient • against concentration and charge gradients *gradients – used by cell for energy potential

Active Transport – coupled transport • coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions) • Ex. Active glucose transporter • Na+ diffusion used for glucose active transport • Na+ moving DOWN concentration gradient • Glucose moving UP concentration gradient

Bulk Transport • ENERGY IS required • Several or large molecules • Molecules moved IN - endocytosis • phagocytosis – “food” in • pinocytosis – water in

Bulk Transport • receptor-mediated endocytosis – proteins bind molecules, vesicles inside • Molecules moved OUT - exocytosis

Self-Check Type of transport Energy required? Movement direction? Examples: Simple diffusion no Down conc. gradient O2, CO2, non-polar molecules Osmosis Facilitated diffusion Active transport Bulk transport

Lecture 1 Outline (Ch. 6) I. Energy and Metabolism II. Thermodynamics A. 1st Law – conservation of energy B. 2nd Law - entropy Free Energy Chemical Reactions V. Cellular Energy - ATP VI. Enzymes A. Function B. Regulation

The capacity to cause change Energy What is Energy? The capacity to cause change Where does energy on earth come from originally? 40 million billion calories per second!

Metabolism Metabolism –chemical conversions in an organism Types of Energy: - Kinetic Energy = energy of movement - thermal - Potential = stored energy - chemical

Thermodynamics Thermodynamics – study of energy transformation in a system Potential energy can be converted to kinetic energy (& vice versa) Potential Energy Kinetic Energy

Thermodynamics Laws of Thermodynamics: Explain the characteristics of energy 1st Law: Energy is conserved Energy is not created or destroyed Energy can be converted (Chemical  Heat) 2nd Law: During conversions, amount of useful energy decreases No process is 100% efficient Entropy (measure of disorder) is increased Energy is converted from more useful to less useful forms

Metabolism Metabolic reactions: Chemical reactions in organism Two Types of Metabolic Reactions: Catabolic = breaks down molecules Anabolic = builds up molecules

Chemical Reactions Chemical Reactions: Like home offices – tend toward disorder

Chemical Reactions Chemical Reactions: Endergonic – energy required to complete reaction Exergonic – energy given off Exergonic Endergonic

+ + Chemical Reactions Chemical Reaction: Process that makes and breaks chemical bonds + Reactants + Products Two Types of Chemical Reactions: 1) Exergonic = releases energy 2) Endergonic = requires energy

Chemical Reactions 1. Exergonic reactions: “Energy out” Reactants have more energy than products Reaction releases energy 2. Endergonic reactions: “Energy in” Products have more energy than reactants Requires influx of energy

Chemical Reactions Glucose  CO2 + H20 CO2 + H20  Glucose release free energy intake free energy spontaneous non-spontaneous • Exergonic reaction • Endergonic reaction

Chemical Reactions Activation Energy: Energy required to “jumpstart” a chemical reaction Must overcome repulsion of molecules due to negative charged electrons Nucleus Repel Nucleus Repel Activation Energy

Chemical Reactions Exergonic Reaction: “Downhill” reactions Exergonic Reaction: Reactants have more energy than products But will sugar spontaneously burst into flames? Activation energy: Make sugar and O2 molecules collide sugar + O2 water + CO2

Cellular Energy - ATP • ATP = adenosine triphosphate • ribose, adenine, 3 phosphates • last (terminal) phosphate - removable

Cellular Energy - ATP • ATP hydrolyzed to ADP • stores 7.3 calories per mole ATP + H2O ADP + Pi • Energy released, coupled to another chemical reaction

Cellular Energy - ATP • ATP regenerated • need 7.3 kcal/mol to build ATP • cells power building ATP by coupling to exergonic reactions - cellular respiration

Enzymes Energy of activation (EA) • reactants – absorb energy called: EA • Reach EA, reaction proceeds (limiting step) Exergonic – energy given off • EA from ambient heat usually insufficient • This is GOOD!

Enzymes Enzymes • lower EA • only for specific rxns • cell chooses which reactions go forward! enzymes: -do not make endergonic exergonic -do speed up rxn would occur anyway

Enzymes • enzyme – specific to substrate • active site – part of enzyme -substrate • binding tightens fit – induced fit • form enzyme-substrate complex • catalytic part of enzyme: converts reactant(s) to product(s)

Enzymes

Enzymes • Enzymes lowers EA by: -template orientation -stress bonds • substrate(s) enter -microenvironment • enzyme reused • products formed • What factors might affect enzyme activity?

Enzymes • inhibitors: • Drug – blocks HIV enzyme at the active site

Enzymes Feedback Inhibition: Like your furnace: Detector cold room Furnace turns on Room is warm warm room

Lecture 1 Summary 1. Membrane composition and function (Ch. 5) Phospholipids and cholesterol Integral and peripheral proteins 2. How molecules cross membranes (Ch. 5) Passive Transport Active Transport Bulk Transport 3. Energy (Ch. 6) Types, conversion 4. Metabolic/chemical reactions (Ch. 6) Catabolic/Endergonic Anabolic/Exergonic 5. ATP (Ch. 6) 6. Enzymes (Ch. 6) Purpose Function Regulation