Chapter 15: Bioenergetics Concepts

What is metabolism?

The sum of all chemical reactions occurring in a living organism

What is a metabolic pathway?

A series of enzyme-catalyzed reactions in which the product of one reaction becomes the substrate for another

What are the two major types of metabolism?

Catabolism and anabolism

What is catabolism?

The breakdown of complex molecules into simpler molecules while releasing usable energy

What is anabolism?

The synthesis of complex molecules from simpler molecules using energy

How are catabolism and anabolism connected?

Catabolism provides energy and building blocks that support anabolic reactions

Why are metabolic pathways interconnected?

Products from one pathway can become reactants in other pathways

Why do cells break down fuels through multiple enzyme-catalyzed steps?

To capture energy in useful forms instead of releasing it all at once

What are the three broad stages of catabolism?

Macromolecule breakdown followed by formation of central metabolic units followed by complete oxidation

What happens during stage 1 of catabolism?

Large molecules are broken into smaller building blocks

What happens during stage 2 of catabolism?

Small fuel molecules are converted into central metabolic units such as acetyl-CoA

What happens during stage 3 of catabolism?

Central metabolic units are oxidized and energy is captured through electron transport and ATP production

What is the major role of ATP in metabolism?

It transfers usable chemical energy to energy-requiring cellular processes

What are the three components of ATP?

Adenine and ribose and three phosphate groups

What is adenosine made of?

Adenine and ribose

What are the three ATP phosphate groups called?

Alpha and beta and gamma

Which ATP phosphate is closest to ribose?

Alpha phosphate

Which ATP phosphate is terminal?

Gamma phosphate

What type of bond connects ribose to ATP's alpha phosphate?

Phosphoester bond

What type of bonds connect ATP's phosphate groups?

Phosphoanhydride bonds

How many phosphoanhydride bonds are in ATP?

Two

What is ATP hydrolysis?

Reaction of ATP with water to produce ADP and inorganic phosphate

What is the standard free-energy change for ATP hydrolysis?

Approximately negative 30.5 kJ/mol

Why is ATP hydrolysis energetically favorable?

The products have lower free energy and are more stable overall than ATP and water

What stabilizes the products of ATP hydrolysis?

Resonance stabilization and improved hydration and relief of electrostatic repulsion

Does breaking an ATP bond alone release energy?

No breaking a chemical bond requires energy and the overall hydrolysis releases energy because product formation is favorable

What is a coupled reaction?

A process where a favorable reaction helps drive an unfavorable reaction

How does ATP hydrolysis help drive an unfavorable reaction?

Its negative free-energy change can offset the positive free-energy change of the coupled process

Why is ATP considered an intermediate phosphoryl-group donor?

Some compounds have higher phosphoryl-transfer potential and others have lower potential

What does ATP become after transferring one terminal phosphate group?

ADP

What does ADP stand for?

Adenosine diphosphate

What does AMP stand for?

Adenosine monophosphate

Why is Mg2+ important for ATP-dependent enzymes?

It helps coordinate ATP and stabilize negative charges on phosphate groups

What is the difference between ATP and NADH?

ATP primarily transfers phosphoryl groups while NADH carries high-energy electrons

What is the main role of NAD+?

To accept electrons during oxidation reactions

What happens when NAD+ is reduced?

It accepts a hydride and becomes NADH

What is a hydride?

A hydrogen atom with two electrons and a negative charge

What is the main function of NADH?

To carry electrons from fuel oxidation toward processes that can produce ATP

What happens to NADH when it donates electrons?

It is oxidized back to NAD+

What is the role of FAD?

It accepts electrons and hydrogen equivalents during oxidation reactions

What is the reduced form of FAD?

FADH2

What is the oxidized form of FADH2?

FAD

What is NADPH mainly used for?

Providing reducing power for biosynthesis and other cellular processes

What is acetyl-CoA primarily used to transfer?

An acetyl group

What is oxidation?

Loss of electrons

What is reduction?

Gain of electrons

What is an oxidizing agent?

A substance that accepts electrons and is itself reduced

What is a reducing agent?

A substance that donates electrons and is itself oxidized

How can you recognize a more reduced carbon?

It generally has more carbon-hydrogen bonds and fewer carbon-oxygen bonds

How can you recognize a more oxidized carbon?

It generally has more bonds to oxygen and fewer bonds to hydrogen

Why do fats generally provide more energy per gram than carbohydrates?

Fat molecules contain more reduced carbon and release more energy during complete oxidation

What is the final carbon oxidation product of complete glucose breakdown?

Carbon dioxide

What is the final electron acceptor in aerobic respiration?

Oxygen

What does oxygen become after accepting electrons and protons?

Water

What happens to glucose during cellular respiration?

Glucose is oxidized while oxygen is reduced

What is energy transduction?

The conversion of energy from one form into another usable form

What is the general sequence of energy transduction in aerobic respiration?

Fuel oxidation transfers energy to reduced electron carriers then a proton gradient then ATP

What is the purpose of the electron transport chain?

To transfer electrons and use the released energy to help build a proton gradient

What is the purpose of the proton gradient?

To store potential energy that can drive ATP synthesis

What enzyme uses the proton gradient to make ATP?

ATP synthase

What is substrate-level phosphorylation?

Direct transfer of a phosphoryl group from a substrate to ADP to make ATP

What is oxidative phosphorylation?

ATP synthesis powered by the proton gradient generated through electron transport

What is the difference between substrate-level and oxidative phosphorylation?

Substrate-level phosphorylation directly transfers phosphate while oxidative phosphorylation uses a proton gradient and ATP synthase

What is the difference between aerobic and anaerobic metabolism?

Aerobic respiration uses oxygen as the final electron acceptor while anaerobic pathways operate without using oxygen as that acceptor

Why can glycolysis occur without oxygen?

None of its ten reactions directly requires molecular oxygen

Why must NAD+ be regenerated for glycolysis to continue?

NAD+ is needed to accept electrons during the oxidation of GAP

What happens to pyruvate during aerobic metabolism?

It can be converted to acetyl-CoA for further oxidation

What happens to pyruvate during anaerobic glycolysis in human muscle?

It can be reduced to lactate to regenerate NAD+

What is phosphocreatine?

A rapidly available phosphoryl-group reserve that can help regenerate ATP

What enzyme transfers phosphate between phosphocreatine and ADP?

Creatine kinase

Why is phosphocreatine useful during short intense exercise?

It rapidly replenishes ATP when energy demand suddenly increases

Why do high-energy molecules not necessarily break down quickly?

Thermodynamic favorability does not determine the rate of reaction

What is an enzyme's main effect on a reaction?

It lowers activation energy and increases the reaction rate

Does an enzyme change the overall free-energy change of a reaction?

No it changes reaction speed but not overall thermodynamic favorability

Does an enzyme change the equilibrium position of a reaction?

No it accelerates both forward and reverse reactions without changing equilibrium