Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Honors Biology - Chapter 5 The Working Cell

2 5.2 Energy Transformations in a Cell Cell metabolism - uses or makes energy a) exergonic reaction - make energy: - release energy stored in molecules - oxidation (catabolic) ex. cell respiration b) endergonic reaction - use energy: - use energy (ATP) to do cell work - reduction, (anabolic) ex. move, synthesize Coupled reactions - energy released in exergonic reactions is used to power endergonic

3 5.5 ATP - energy molecule in a cell ATP - adenosine triphosphate -adenine, ribose (adenosine) + three phosphates -bonds between phosphates are easily broken -  phosphate transfers energy

4 ATP - ADP ATP ADP + P triphosphate diphosphate phosphate group P is free energy - powers cellular work Phosphorylate - add a phosphate group to a molecule - transfers energy to new molecule

5 ATP is renewable energy ATP breakdown products (ADP + P) remain in cell are used again to regenerate more ATP when needed Energy from exergonic reactions Energy for endergonic reactions ATP made in cell respiration ATP used for cellular work Very fast!! 10 million ATP/second in a cell; needs help of enzymes

6 5.4 How ATP powers cellular work Biosynthesis - P  reactant - Reactants bond - Product forms - P released Mechanical Motion P onto motor protein  protein changes shape Pulls on muscle fibers  muscle contracts P released Membrane Transport P  membrane protein Protein changes shape Protein pushes solute through membrane P released

7 5.10: Membranes organize chemical activities in a cell a) keep structural order b) compartments have specific enzymes Plasma membrane - boundary between cell and its environment

Fluid Mosaic Model Describes structure of cell membranes “mosaic” – sea of lipids with scattered proteins “fluid” – molecules float and move around within the layer

5.11 Phospholipids make cell membranes Phospholipid = lipid molecule with phosphate on one end glycerol + two fatty acids + phosphate group phosphate group = polar end (hydrophilic “head”) Fatty acids = nonpolar end (hydrophobic “tails”)

Phospholipids form a double layer in water Nonpolar tails are on the inside (away from water) Unsaturated – keep membrane flexible Polar heads are on the outside ( touch water)

Features of the Cell Membrane Semipermeable = some substances can pass through - some cannot - depends on: molecule size, charge, polar or nonpolar, needs of cell, signals from environment Cholesterol – scattered among the phospholipids - in animal cells - keep membrane flexible in changing temperatures Carbohydrates – glucose chains on outside of cell - Identification “tags” - Receptor sites for messenger molecules

12 Fluid-Mosaic Model ProteinMicrofilaments

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Membrane Proteins have many functions Transport EnzymeReceptor Allows a specific Catalyzes a Site for molecule to reaction inside messenger pass through the cell or molecule to the membrane in membrane attach

Transport Proteins 15 Channels, pores, and carriers move particles across the membrane Specific May use energy

Signal Transduction Message from outside cell is relayed to a specific molecule inside cell Chemical signal binds to receptor protein - message sent inside cell - causes response in cell Ex. hormones, neurotransmitters 16

17 Example: insulin receptors - cause a different membrane protein to allow glucose into cell

More Membrane Proteins Identification: Junctions: cells Structure: attach “SELF”; cell belongs join to form to cytoskeleton or in this organism tissues, extracellular matrix Ex. immunity communicate

How do membranes keep homeostasis? Cell membranes are selectively permeable The lipid layer blocks most substances Some molecules can cross the membrane –By passive or active transport Some are too big to cross at all

PASSIVE TRANSPORT USES NO CELL ENERGY Diffusion: Molecules move randomly – spread out until evenly distributed

DIFFUSION Diffusion: movement of particles from an area of high concentration to an area of lower concentration Adjacent areas with different concentrations = concentration gradient Particles move in all directions (random) NET movement is from high concentration to low “Down the concentration gradient”

Diffusion Particles spread out until evenly distributed  equilibrium (homogeneous) Still move randomly, but  NO further change in concentration

Cell Membranes allow some particles to cross Particles can diffuse across the lipid bilayer if they are: Small Nonpolar (lipid-soluble) Examples: CO 2, O 2, fatty acids

24 Two or more solutes – each moves down its own gradient Ex. Gas exchange in lungs

25 Transport proteins- specific for one substance Down the gradient - no cell energy needed Particles can cross by facilitated diffusion if they are: Small POLAR (water soluble) or CHARGED Examples: H 2 O, glucose, amino acids, ions Others need help to get through - Facilitated Diffusion.

5.15: Facilitated Diffusion 26 Channel (pore) Carrier

5.16: OSMOSIS Diffusion of water across a membrane Important process in cell homeostasis Water crosses the cell membrane easily - Small enough to pass between lipid molecules -Also pass through special proteins, aquaporins

28 Water diffuses easily across membranes; many solutes don’t

29 Osmotic Pressure – tendency of water to move across a membrane Which way does water go? From side with more water (less solutes) to side with less water (more solutes) Type of solutes doesn’t matter, only total concentration Water will diffuse down its gradient

Osmotic equilibrium 30 when concentrations are equal or when force of gravity equals osmotic pressure

Why osmosis matters Water crosses membrane easily, faster than many solutes Will try to reach equilibrium If NET water moves into or out of cell  disrupts homeostasis Water balance is needed for homeostatis

TONICITY = osmotic pressure in cells ISOTONIC Equal concentrations of solutes inside and outside cell –Equal concentrations of water –Water goes in and out of cell at equal ra tes

Isotonic pressure in cells No NET movement of water into or out of cell Normal water pressure in animal cells Wilted (“flaccid”) water pressure in plant cells

When solute concentration is different on two sides of a membrane lower solute concentration = hypotonic Higher solute concentration = hypertonic Solutes will move down their gradient IF THEY CAN CROSS THE MEMBRANE

Water concentration is OPPOSITE of solutes Low solutes  HIGH WATER concentration High solutes  LOW WATER concentration Water WILL diffuse down its gradient and crosses the cell membrane easily Goes TO whichever side has more solutes

Cells in hypotonic solutions Cytoplasm swells - animal cells: swell, may burst (“lyse”) - plant cells: high osmotic pressure “turgor” - won’t burst - cell wall - “Turgid” – stiff and firm, upright stem Solutes are lower outside cell, water is higher Water enters cell by osmosis

Cells in hypertonic solutions Solutes are higher outside cell, water is lower Water leaves cell by osmosis Cytoplasm shrinks - “plasmolysis” - animal cells: shrivel - plant cells: low turgor pressure - cytoplasm pulls away from cell wall - but cell wall does not shrink

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Osmosis in Animal Cells Animal cells like ISOTONIC conditions best

Osmosis in Plant Cells Plant cells like HYPOTONIC conditions be st

41 Red blood cells -in isotonic in hypotonic in hypertonic Plant cells in hypotonic solution Plant cells in hypertonic solution

Contractile Vacuoles Fresh-water protists (like Paramecia or Amoeba) must constantly remove water that comes into the cell by osmosis

Active transport uses cell energy Protein pumps move particles against the gradient - from LOW concentration to HIGH Cells can maintain a concentration that is NOT at equilibrium

Why would cells use active transport? 1) To concentrate substances: Examples: kidneys : wastes in urine - intestine : nutrients in blood 2) To maintain an ion concentration - sodium-potassium pump: nerve impulses

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46 Sodium-potassium pump Proton pump – in photosynthesis and cell respiration

Bulk Transport – uses energy For particles too big to pass through membrane Endocytosis = brings material into cell - fold cell membrane around it  form a vacuole a. Phagocytosis = “cell eating” - large particles or whole cells - examples: amoeba white blood cells pseudopods

Pinocytosis – “cell drinking” Example: small intestine absorbs some water this way Small folds of membrane take in liquids

49 Endocytosis – substance pulled INTO CELL

: Exocytosis – substance goes OUT OF cell - enclosed in membrane vesicle - vesicle fuses with plasma membrane - releases contents outside cell

Exocytosis For secretory cells ex. Hormones from endocrine glands, pancreas: insulin  bloodstream; digestive juices from pancreas, intestine  food cavity 51

52 Receptor-mediated endocytosis Receptors on plasma membrane - for a specific molecule Membrane encloses molecule  forms a vesicle “coated pit” on membrane

LDL Cholesterol cholesterol: essential for normal cell functioning and for making other lipids a) carried in the blood by low-density lipoproteins (LDL) b) LDL has a surface protein that fits a receptor on cell membranes - cells remove it from the blood by receptor-mediated endocytosis 53

: Hypercholesterolemia If receptors are faulty or missing, cholesterol remains in the blood  collects inside blood vessels (high risk for heart disease) and in pockets under the skin Cholesterol in pockets under skin cholesterol inside blood vessel