How Cells Work Chapter 4

Beer, Enzymes and Your Liver Alcohol is toxic Cells in liver break down alcohol to nontoxic compounds Breakdown is accelerated by enzymes Heavy drinking damages liver and other organs

Impacts, Issues Video Alcohol, Enzymes, and Your Liver

Energy Laws Energy: the capacity to do work Total amount of energy in the universe is constant Energy flows from higher to lower energy forms

ENERGY LOST With each conversion, there is a one-way flow of a bit of energy back to the environment. ENERGY GAINED Sunlight energy reaches environments on Earth. Producers secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work. ENERGY LOST Energy continually flows from the sun. Fig. 4-1, p.59

ATP 3 phosphate groups nucleotide base (adenine) sugar (ribose) Main energy carrier in cells Can give up phosphate group to another molecule Phosphorylation energizes molecules to react

The Cell’s Energy Currency ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP Energy Input (from nutrients like glucose) ADP + P i ATP Energy Output (to allow muscle contraction)

reactions that release energy reactions that require energy cellular work (e.g., synthesis, breakdown, or rearrangement of substances; contraction of muscle cells; active transport across a cell membrane) ATP ADP + P i ATP Fig. 4-2, p.59 base sugar three phosphate groups

Structure of ATP The Role of ATP

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

glucose (product) energy in starting substances O 2 6 Fig. 4-3a, p.60 Energy in Glucose Photosynthesis

energy out products glucose + 6O 2 (starting substances) Fig. 4-3b, p Energy in Glucose This energy helps make ATP 

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 Are proteins

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

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

Enzymes and temperature Effect of Temperature

Concentration Gradient Different numbers of molecules or ions in different regions Substances tend to move down gradient - from higher to lower concentration

oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules glucose and other large, polar, water- soluble molecules; ions (e.g.,H +, Na +, K +, Ca ++, Cl – ) Selective Permeability

Cell Membranes Show Selective Permeability Selective permeability

Fig. 4-12, p.65 dye water Diffusion Net movement of molecules or ions down a concentration gradient

Diffusion Diffusion of dye in water

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

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

Which Way Will Water Move? Water diffuses across cell membranes

Osmosis Diffusion of water molecules across a selectively permeable membrane, down the water concentration gradient Higher solute concentration = lower water concentration

water moleculesprotein molecules semipermeable membrane between two compartments Fig. 4-15, p.68 Osmosis

Solute concentration and osmosis

Membrane Traffic Exocytosis –Vesicle fuses with membrane, releasing substance into intracellular fluid

Membrane Traffic Endocytosis –Membrane forms vesicle, bringing substance into cell

Endocytosis (vesicles in) Exocytosis (vesicles out) Fig. 4-20, p.71

Phagocytosis

Fig. 4-18, p.70 a b exocytosis (out from cytoplasm) endocytosis (into cytoplasm)