Chapter 5 The working cell

Energy and your cells Thermodynamics First law Second law Most energy on earth arises from the sun Cycled via producers, consumers and decomposers

Energy Exergonic Endergonic Releases energy Endergonic Intakes energy (required energy) These reactions are coupled in “energy coupling” where exergonic reactions drive endergonic reactions

Cellular energy Forms Energy of cells is ATP Kinetic Potential Energy lies in covalent bonds between P groups

ATP Drives reactions via phosphorylation Accepts E released by reactions and delivers to reactions that require E

ATP P groups are negatively charged and crowded together E stored in bonds between P Released P goes to another molecule Transfer of P = phosphorylation Repulsion creates unstable bonds Broken via hydrolysis reaction

As bonds break, E released ATP As bonds break, E released As bonds form, E stored

Begin a chemical reaction Activation Energy- E to begin a reaction Energy of activation (EA) Enzymes can lower EA EA barrier Reactants Products 1 2 Enzyme

Enzymes Molecules that catalyze reactions Substrate specific Generally proteins Not consumed by the reaction Substrate specific Active sites where substrate binds

Enzymes help begin chemical reactions Enzymes that lower EA are catalysts Decrease the EA needed to begin a reaction Reactants EA without enzyme EA with enzyme Net change in energy Products Energy Progress of the reaction

Active sites fit only specific substrates Specificity Specific enzymes catalyze specific reactions Shape determines which chemical reaction an enzyme catalyzes Substrate Specific reactant an enzyme acts upon Active site Region of enzyme where substrate fits Active sites fit only specific substrates

How Enzymes Catalyze Reactions 1 Enzyme available with empty active site Substrate (sucrose) Active site Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose 4 Products are released Fructose H2O 3 Substrate is converted to products Figure 5.6

Factors Influence Enzymes Temperature, pH, salinity Affect shape of the enzyme Optimal temperature Cofactors Non-protein “helper” Inorganic Ex: zinc, iron, copper Coenzyme Organic Ex: vitamin

Inhibitors Interfere with an Enzyme’s Activity Competitive inhibitor Noncompetitive inhibitor Feedback inhibition Substrate Enzyme Active site Normal binding of substrate Enzyme inhibition Noncompetitive inhibitor Competitive inhibitor

Inhibitors Interfere with an Enzyme’s Activity

Phospholipid bilayer Selectively permeable Imbedded proteins Fluid mosaic of phospholipids and proteins Water Hydrophilic heads Hydrophobic tails

Membrane Proteins Structural Cell-cell recognition Junction forming Receptors Enzymes Signal transduction Transport

Functions of membrane proteins ATP Messenger molecule Receptor Activated molecule Enzymes Receptors for messages Transport of substances

The membrane is a fluid mosaic of phospholipids and proteins Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm Figure 5.12

Mechanisms to cross Diffuse directly across plasma membrane Restricted by size, polarity Transport proteins Act as “channels” to assist molecules in crossing the membrane Specific

In and Out of Cells Diffusion Passive transport Concentration gradient Equilibrium Membrane Molecules of dye

Crossing the membrane Diffusion Speed of diffusion depends on Movement of molecule down a concentration gradient Speed of diffusion depends on Size of molecule Temperature Strength of gradient Charge Pressure

Plasma membrane (lipid bilayer) Lipids Plasma membrane (lipid bilayer) Lipids, such as these yellow molecules, can dissolve in the lipid bilayer. Notice how they move down their concentration gradient -- from where they are more concentrated to where they are less concentrated. This is an example of diffusion. Diffusion is a form of passive transport -- it does not require energy from the cell.

In and Out of Cells Facilitated diffusion Small nonpolar molecules diffuse easily across the membrane Larger or polar molecules do not easily diffuse Transport proteins provide passage across membranes Solute molecule Transport protein

Mechanisms to cross Facilitated diffusion Solute diffusion driven by concentration gradient Aided by transport protein

Fructose Plasma membrane Transport protein Most molecules can’t cross the lipid bilayer. Here, the sugar fructose moves into intestinal cells by facilitated diffusion, moving down its concentration gradient through a transport protein. Facilitated diffusion doesn’t require energy from the cell, so it’s also a form of passive transport. Transport protein

In and Out of Cells Osmosis Diffusion of water across a membrane Water travels from a solution of lower solute concentration to one of higher solute concentration Solute molecule H2O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water

Crossing the membrane Osmosis Turgor- pressure a volume of fluid exerts against a barrier Osmotic pressure- amount of turgor to stop water from diffusing

Plasma membrane Transport protein Water molecules Water crosses the plasma membrane by facilitated diffusion or by diffusing across the lipid bilayer directly. The diffusion of water across a membrane is called osmosis. Transport protein Water molecules

Balance Tonicity Isotonic Hypotonic Hypertonic Relative concentration of solutes in two fluids separated by a selectively permeable membrane Isotonic Concentration of solutes are the same Hypotonic Fluid with lower concentration of solutes Hypertonic Fluid with higher concentration of solutes

Balance Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions Plant cell H2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell Cells will always have a certain amount of solutes. With there is more in solution (outside of the cell) water flows out to “dilute” outside concentration. Figure 5.17

Balance

In and Out of Cells Active transport Requires input of energy (ATP) Transport proteins move solutes against their concentration gradient P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding 1 Phosphorylation 2 Transport 3 Protein reversion 4

Mechanisms to cross Active transport Transporting molecules against their gradient Required input of energy

Mechanisms to cross Cotransporters Active transport Move 2 substances at the same time

In and Out of Cells Exocytosis and endocytosis transport large molecules Exocytosis Export material from cell Endocytosis Take into cell Fluid outside cell Cytoplasm Protein Vesicle Figure 5.19A

Types of Endocytosis Phagosytosis Pinocytosis Cellular “eating” Pinocytosis Cellular “drinking” Receptor-mediated endocytosis Specific molecules

Videos Enzymes http://videos.howstuffworks.com/discovery/28733-assignment-discovery-enzyme-catalysts-video.htm Cell membrane/transport http://www.youtube.com/watch?v=JShwXBWGMyY Endo/exocytosis http://www.youtube.com/watch?v=K7yku3sa4Y8&feature=related Receptor-mediated endocytosis http://www.youtube.com/watch?v=PifagmJRLZ0&feature=related Active transport http://www.youtube.com/watch?v=STzOiRqzzL4&feature=related Passive transport http://www.youtube.com/watch?v=s0p1ztrbXPY&feature=related