Chapter 6 Metabolism

You will need to read on the aging process in your textbook Metabolism: refers to the cell’s capacity to acquire energy and use it to build, store, break apart, and eliminate substance in controlled ways

Potential energy: is the capacity to make things happen, to do work – Measured in kilocalories – Also called chemical energy Kinetic Energy: is the energy of motion – Heat energy Heat: transfer of energy from ATP also resulted in the release of another form of energy Energy

Energy from the sun or from organic substances becomes coupled to thousands of energy-requiring processes in cells Cells use the energy to perform chemical, mechanical, and electrochemical work. What can cells do with energy?

First law of thermodynamics: states that the total amount of energy in the universe is constant; it can’t be created nor destroyed, it can only change forms – Energy can not be produced by the cell- it can only be borrowed from someplace else – High quality energy is usable – Low quality (such as heat) is released into the universe How much energy is available?

Second law of thermodynamics: states that the spontaneous direction of energy flow is from high to low quality forms – Each conversion produces energy (usually heat) that is unavailable for work – Entropy: the measure of disorder One way flow energy

Energy changes in living cells tend to proceed spontaneously in the direction that results in a decrease in usable energy Endergonic (“energy in”) reactions require input resulting in products with more energy than reactants – Example: Photosynthesis Cells and Energy Hills

Exergonic (“energy out”) reactions release energy such that the products have less energy than the reactants had – Example: Cellular Respiration Continue…

ATP is composed of adenine, ribose, and three phosphates – Energy input links phosphate to ADP to produce ATP (phosphorlyation  phosphate transfer) – ATP can in turn donate a phosphate group to another molecule, which then becomes primed and energized for specific reactions ATP couples energy inputs with outputs

ATP is like currency in an economy – Earning ATP is an exergonic reaction and spending (using) ATP is a endergonic reaction – ADP can be recycled to ATP very rapidly in the ATP/ADP cycle Continue…

Electrons are transferred in nearly every reaction that harnesses energy for use in the formation of ATP (Oxidation-Reduction Reaction) In plant cells sunlight energy drives electrons from water molecules to initiate the reactions that will eventually produce carbohydrates In aerobic respiration, the degradation of glucose release energy that can be transferred to ATP – This actually makes more ATP Electrons transfer drive ATP formation

Reactants: are substances that enter a reaction Products: what is produced from a reaction Intermediates: are compounds that are formed between the reactant and product. Energy Carriers: are mainly ATP- usually activate enzymes and other factors Participants in Metabolic Reactions

Cofactors: are small molecules and metal ions that help enzymes by carrying atoms or electrons (EXAMPLE: NAD+) Transport Proteins: are membrane bound proteins that participate in adjusting concentration gradients that will influence the direction of metabolic reactions Continue…

Metabolic Pathways form series of reactions that regulate the concentration of substanceds within cells by enzyme-mediated linear and circular sequences Biosynthetic pathways, small molecules are assembled into large molecules without the need for energy – Example: Simple sugars assembled into larger complex carbohydrates What are Metabolic Pathways?

Degradative pathways: large molecules such as carbohydrates,lipids, and proteins, are broken down to form products fo lower energy. – Released energy can be used for cellular work Continue…

Chemical reactions can proceed from reactants to products, which if they are allowed to accumulate, will be convert back to reactants The direction of concentrations and the collision of molecules Are Reactions Reversible?

When reaction approaches chemical equilibrium, the forward and reverse raction proceed at equal rates – No net change in concentration – Every reaction has it own ratio of products to reactants at equilibrium Continue..

The law of conservation of mass states that the total mass of all substances entering a reaction equals the total mass of all products. – This is why we must “BALANCE” a chemical equation by having equal number of atoms of each element on both sides of the arrow. C0 2 + H 2 0  C 6 H 12 O 6 + O 2 Balance the equation No vanishing atoms at the end of the run

Energy is released from storage molecules (such as glucose) in controlled steps via a series of intermediate molecules – Electrons released during bond breaking are transferred stepwise through the components of electron transport systems located on various cells membranes – Oxidized: Electrons are donated – Reduced: Electrons are gained Electron Transfer Chains in the Main Metabolic Pathways

Coenzymes: are large organic molecules such as NAD+, FAD, and NADP+ that transfer protons and electrons from one substrate to another. Electrons are similar to staircases where the electrons flow down the steps from the top (most energy available) to the bottom (least amount of energy) The energy is harnessed to move H+ ions which turns establish pH and electric gradient Continue…

Enzymes helps organisms exist through speeding up chemical reactions Without enzymes could not process food, build new cells, get rid of old cells, keep your brain working, and to contract muscles Enzymes increases the rate of reaction by lowering the activation energy (the amount of energy needed to get a reaction going) Enzymes

1- speed up a chemical reaction 2- can be reused 3- at least some of them, can recognize both reactants and products in order to catalyze a reaction in both directions 4- very selective about substrates Enzymes have four features:

Active Site: pockets or crevices where substrates are bound and specific reaction are catalyzed – Increases the rate of reaction by creating a microenvironment that is energetically more favorable for the reaction How do enzymes lower energy hills?

Activation Energy brings the reactive chemical groups into alignment so that chemical bonds can be broken, created, and rearranged. The substrate is brought to its transition state– point where the reaction takes place Transition at the Top of the Hill

Binding energy: energy released from all of the weak interactions Which helps bring about transition state by four mechanisms: – 1. helping substrate get together – 2. orienting substrate in position to favor a reaction – 3. shutting out water – 4. inducing changes in enzyme shape (induced-fit model) How Enzyme Work?

Cofactors are nonprotein groups that bind to many enzymes and make them more reactive Inorganic metal ions such as Fe++ also serve as cofactors when assisting membrane cytochrome proteins in their electron transfer in chloroplast and mitochondria About those cofactors

A large molecule affords structural stability Extensive folding of polypeptide chains puts amino acids and functional groups in location and orientations that favor interactions with water and substrate Why are enzymes so big?

Some controls regulate the number of enzyme molecules available by speeding up/slowing down their synthesis Sometimes enzymes bind to other sites than their active site How Enzymes Activity Controlled?

Allosteric enzymes (in addition to active site) regulatory sites where control substances can bind to alter enzyme activity; I fthis control substance is the end product in the enzyme’s metabolic pathway, the feedback inhibition occurs (shutdown) Continue…

Enzymes operate best within defined temperature ranges – High temperature decreases reaction rate by disrupting the bond that maintain 3-D shape (denaturation occurs) – Most enzymes function best at the pH range of 6 to 8 Exception: stomach enzyme: Pepsin – Higher or lower pH can disrupt the shape and function Do Temperature and pH affect Enzymes?

Fireflies use enzymes (luciferase) to produce light by bioluminescence Researchers transferred genes for bioluminescence into strains of Salmonella so that the course of infection could be tracked by visualization Light Up the Night