Metabolism: Energy, Enzymes, and Regulation Chapter 9 Metabolism: Energy, Enzymes, and Regulation

An Overview of Metabolism metabolism is the total of all chemical reactions in the cell and is divided into two parts catabolism – larger molecules are broken down to smaller molecules. Energy is released. Cellular respiration anabolism – the synthesis of complex organic molecules from simpler ones. Energy is used. photosynthesis

Overview of Metabolism Figure 8.1

Energy and Work energy capacity to do work or to cause particular changes

Types of work carried out by organisms chemical work synthesis of complex molecules transport work take up of nutrients, elimination of wastes, and maintenance of ion balances mechanical work Cell motility and movement of structures within cells

ATP – quick source of energy in cells Energy carrier molecule Synthesis, movement, transport ATP ----- ADP + Phosphate + energy ADP + phosphate + energy ---- ATP

The cell’s energy cycle Figure 8.7

Oxidation-Reduction Reactions and Electron Carriers many metabolic processes involve oxidation-reduction reactions (electron transfers) electron carriers are often used to transfer electrons from an electron donor to an electron acceptor Leo says ger

Oxidation-Reduction (Redox) Reactions transfer of electrons from a donor to an acceptor can result in energy release, which can be conserved and used to form ATP Leo says ger

Oxidation reduction reactions are coupled They take place simultaneously

Enzymes protein catalysts catalyst substrates products have great specificity for the reaction catalyzed and the molecules acted on catalyst substance that increases the rate of a reaction without being permanently altered substrates reacting molecules products substances formed by reaction

Almost all the chemical reactions – enzymes Biological catalysts Speed up chemical reactions Come out of the reaction unchanged Absence enzymes – chemical reactions take place slow – cells cannot survive Specific for its substrate Substrate – substance with which the enzyme reacts.

Bring molecules together Weaken bonds in a molecule – breaks down

sucrose Glucose+ fructose sucrase Perfect fit

Structure and Classification of Enzymes some enzymes are composed solely of one or more polypeptides some enzymes are composed of one or more polypeptides and nonprotein components

Enzyme structure apoenzyme cofactor holoenzyme = apoenzyme + cofactor protein component of an enzyme cofactor nonprotein component of an enzyme prosthetic group – firmly attached – heme group – cytochrome c oxidase coenzyme – loosely attached – NAD+ holoenzyme = apoenzyme + cofactor

Coenzymes They transport Substances NAD+ transports electron and Hydrogen Figure 8.14

Enzyme inhibitors – competitive, noncompetitive Compete with the substrate for the active site. Sulfanilamide – synthetic drug – UTI Para aminobenzoic acid (PABA) ------ folic acid Enzyme Drug takes the place of PABA on the enzyme Inactivates the enzyme

Noncompetitive inhibitor binds to the allosteric site on the enzyme Allosteric site – site other than the active site Shape of the active site is changed Enzyme is inactivated Cyanide

PABA sulfanilamide

denaturation Enzymes are saturated No free enzymes to interact With the excess substrate.

Cell does not make The product that is In abundance All 20AA for making proeins Leucine-isoleucine Enzyme Product – Non competitive Inhibitor of the enzyme allosteric site Feedback inhibition Normal – regulate synthesis Product of a reaction Inhibits the enzyme that Catalyzes the reaction. Reaction does not take place