How Cells Work Chapter 5

Energy Laws Energy is the capacity to do work The total amount of energy in the universe is constant (1 st law) Energy is flowing from high-energy forms to forms lower in energy. This is called ENTROPY

ENERGY Energy is the capacity to do work Energy exists in multiple forms –Light –Heat –Electricity –Chemical bond energy –Etc. These various types of energy can be placed into two groups –Kinetic energy –Potential energy

KINETIC ENERGY “Energy of motion” Anything that moves possesses kinetic energy –e.g., Heat, light, balls on a pool table, flowing water, flowing electrons, etc.

POTENTIAL ENERGY “Energy of location or structure” “Stored energy” Resting objects may still possess energy –e.g., A rock at the top of a hill, chemical bond energy

Adenosine triphosphate - ATP Main energy carrier in cells Can give up phosphate group to another molecule Phosphorylation primes a molecule to react “Currency” our cells use

We take in large energy sources glucose, starch, lipids, etc. We break these down, take the energy that was stored in bonds, and store the energy as ATP Adenosine triphosphate - ATP Not the only way we store energy

ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP ATP  ADP releases energy ADP  ATP requires energy

The Cell’s Energy Currency ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP Regeneration of ATP happens quickly 10 million/sec/cell in active muscle

ATP The “high energy bond” is not so high in, energy, but very unstable.

Energy Changes Endergonic reactions require energy –Synthesis of glucose from carbon dioxide and water during photosynthesis Exergonic reactions release energy –Breakdown of glucose to carbon dioxide and water by aerobic respiration Energy + 6H 2 O + 6CO 2  C 6 H 12 O 6 + 6O 2 C 6 H 12 O 6 + 6O 2  Energy + 6H 2 O + 6CO 2

Reactions

Electron Transfers Extracting energy in small pieces/less waste Oxidation: loss of an electron Reduction: gain of an electron Electron transfer chains are vital to the formation of ATP during photosynthesis and aerobic respiration

Vs. If the reaction slowed, we can extract energy in more places All energy lost at once

Participants in Metabolic Pathways Reactants – starting substances (also called substrate) Intermediates – substances formed during the reaction Products – what remains at the end of the reaction C 6 H 12 O 6 + 6O 2  Energy + 6H 2 O + 6CO 2

Participants in Metabolic Pathways Energy carriers – provide energy to activate enzymes Enzymes – speed reactions Cofactors – assist enzymes with reactions Transport proteins – help substances across cell membranes

Metabolic Pathways Biosynthetic (anabolic) pathways –Require energy inputs –Assemble large molecules from subunits –Photosynthesis Degradative (catabolic) pathways –Release energy –Breakdown large molecules to subunits –Aerobic respiration

Enzymes Catalyze (speed up) reactions Recognize and bind specific substrates Act repeatedly – emerge unchanged Most are proteins

Activation Energy Minimum amount of energy required to get a reaction started For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller

What are some reasons why it is a good thing that enzymes lower the activation energy? Why is it a good thing that enzymes usually only bind to one type of substrate (reactant)?

How do enzymes lower activation energy? Tough question, but they put the reactants in an environment more favorable for a reaction. increases concentration of substrate reorients excludes water

ENZYME EXAMPLE

Factors Influencing Enzyme Activity Coenzymes and cofactors Competitive and noncompetitive inhibitors Allosteric regulators Temperature pH Salt concentration

Coenzymes and cofactors Cofactor – inorganic helpers that bind to the active site or substrate that speed reactions Coenzyme – organic helpers that bind to the active site or substrate that speed reactions Many enzymes require non-protein helpers for catalytic activity e.g., DNAse requires Mg 2+ as a cofactor –Removal of Mg 2+ inactivates the enzyme

Competitive and noncomp. Inhibitor Binds to active site and clogs Binds somewhere else and changes shape Bio-warfare, toxins Allosteric site

Allosteric or noncompetitive control Activator or inhibitor binds to an enzyme NOT in the active site, like non-competitive inhib. Binding changes enzyme shape Change hides or exposes active site Your body does this on purpose Feedback inhibition –Product of pathway binds to and inhibits enzyme in the pathway

Allosteric Control inhibition activation Figure 4.8

Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site

pH shifts and salts also denature proteins

Concentration Gradient Means the number of molecules or ions in one region is different than the number in another region In the absence of other forces, a substance moves from a region where it is more concentrated to one where it is less concentrated: “down” gradient TRANSPORT

Diffusion The net movement of like molecules or ions down a concentration gradient Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient) e.g. perfume open in a room

Factors Affecting Diffusion Rate Steepness of concentration gradient –Steeper gradient, faster diffusion Molecular size –Smaller molecules, faster diffusion Temperature –Higher temperature, faster diffusion Electrical or pressure gradients

Span the lipid bilayer Interior is able to open to both sides Change shape when they interact with solute, only let one type through Move water-soluble substances across a membrane Transport Proteins

Passive and Active Transport Doesn’t require energy inputs Solutes diffuse through a channel inside the protein’s interior, or through cell membrane Net movement is down concentration gradient Passive TransportActive Transport Requires ATP Protein is an ATPase pump Pumps solute against its concentration gradient

Active Transport of Na and K

Osmosis Diffusion of water across a selectively permeable membrane Hypotonic – solution with a lower concentration of solute Hypertonic – solution with a higher concentration of solute Water always moves from a hypotonic solution to a hypertonic solution

Osmosis

Hydrostatic Pressure Pressure that a fluid exerts against structure enclosing it Increases with increased solute concentration Influences the osmotic movement of water Think of a water balloon

Membrane Traffic Endocytosis –Membrane sinks inward around a substance bringing it into the cell in a vesicle Exocytosis –Vesicle carrying substance fuses with membrane releasing it into the intracellular fluid

Types of Endocytosis Pinocytosis – “drinking” fluids Phagocytosis – “eating” particles Receptor-mediated endocytosis - specific

Pinocytosis Phagocytosis Receptor mediated