Chapter 9: Cellular Respiration & Fermentation

How and what do catabolic pathways produce?

Energy by oxidizing organic fuels

How and what does glycolysis harvest?

Chemical energy by oxidizing glucose to pyruvate

After pyruvate is oxidized, what does the citric acid cycle do?

Completes the energy-yielding oxidation of organic molecules

During oxidative phosphorylation, what does chemiosmosis do?

Chemiosmosis couples electrons transport to ATP synthesis

What do fermentation and anaerobic respiration enable cells to do?

Produce ATP without oxygen use

Fermentation

Partial degradation of sugars or other organic fuel that occurs without the use of oxygen

Aerobic Respiration

Most efficient catabolic pathway

Oxygen is consumed as a reactant along with the organic fuel

Anaerobic Respiration

Doesn't require oxygen

Cellular Respiration

Technically, talks about both anaerobic and aerobic respiration but now usually just refers to aerobic respiration

What is another name for redox reactions?

Oxidation-reduction reactions

What causes redox reactions?

Transfer of electrons from one reactant to another and helps decompose glucose in catabolic pathways

Oxidation

Loss of electrons from one substance

Reduction

Addition of electrons from one substance

Adding negatively charged electrons to substance reduces amount of positive charge (thus reduction)

Reducing Agent

Electron donor in reaction

Denoted Substance Xe-

Oxidizing Agent

Electron acceptor in reaction

Denoted Substance Y

Oxygen is one of the strongest because of electronegativity

Fuel

organic compounds that can participate in exergonic reactions, also FOOD

What can cells achieve through the activities of enzymes?

Cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy

What does aerobic respiration push out?

Carbon dioxide and water

What is the general equation for cellular respiration?

Organic Compounds + Oxygen → Carbon Dioxide + Water + Energy

What is the specific equation for cellular respiration using glucose?

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP + heat)

What is the main source of carbohydrates as fuel?

Starch

Is the breakdown of glucose exergonic or endergonic?

Exergonic

What happens during a C-H bond?

Electrons are shared fairly equally and stay at a high energy level

What happens during a C-O bond?

Contain less usable energy than electrons in a C-H bond as oxygen pulls the electrons much closer to itself, electrons become more stable, stable = lower potential energy

What is the comparison of types of bonds at the beginning vs. the end of respiration?

At beginning of respiration, lots of C-H bonds in glucose, by end lots of C-O bonds and H-O bonds which have much less energy

How is lost energy converted to ATP?

Pumping protons across the inner mitochondrial membrane, creating a proton gradient, using ATP synthase to make ATP

What are fuels with multiple C-H bonds oxidized to?

Products with multiple C-O bonds

Why is oxygen important in respiration?

Pulls electrons to a much lower energy state, a large amount of energy is released during their transfer

What are the stages of cellular respiration?

Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, Electron Transport Chain, Chemiosmosis (last 2 make up oxidative phosphorylation

What does the relocation of electrons release and what is this used for?

Energy stored in organic molecules, and this energy ultimately is used to synthesize ATP

What is an example of a redox reaction?

Formation of table salt

Sodium gets oxidized and loses electron, becomes Na+

Chlorine gets reduced and gains electron, become Cl-

Do redox reactions involve complete transfer of electrons?

Don't always involve complete transfer of electrons from one substance to another, some change the degree of electron sharing in covalent bonds

What type of bonds are present in methane?

Covalent bonds between carbon and hydrogen

How are the electrons shared in methane's covalent bonds?

Electrons are equally shared

What happens to the carbon atom in methane during combustion?

The carbon atom partially loses electrons

What do oxygen molecules interact with in methane combustion?

Hydrogen atoms in methane

What is formed when hydrogen in methane is oxidized?

Water

Why does hydrogen get oxidized during methane combustion?

Because oxygen is electronegative

What does a redox reaction that moves electrons closer to an electronegative atom release?

Chemical energy that can be put to work

What happens to glucose and oxygen in respiration?

Glucose becomes oxidized and oxygen reduced

When does an electron lose potential energy?

Along the way and energy is released

What do the carbohydrates and fats have a lot of and in what form?

Carbohydrates/fats have lots of electrons with hydrogens, mostly in the form of lots of C-H bonds

What does the barrier of activation energy hold back?

Flood of electrons to lower energy state

What would happen without the barrier of activation energy?

Food like glucose would almost instantly combine with oxygen

What happens when glucose is ignited in air?

It burns, releasing 686 kcal of heat per mole of glucose.

Why doesn't body temperature initiate glucose oxidation?

Body temperature is not high enough to overcome the activation energy barrier.

How do cells oxidize glucose at body temperature?

Enzymes lower the activation energy barrier, allowing step-by-step oxidation.

How are hydrogen atoms transferred?

Aren't directly transferred to oxygen but instead are passed first to electron carrier, a coenzyme called nicotinamide adenine dinucleotide, a derivative of the vitamin niacin

What can the coenzyme (nicotinamide adenine dinucleotide) cycle between?

Oxidized form (NAD+) / reduced form NADH

As an electron acceptor, how does NAD+ function?

Oxidizing agent during respiration

Dehydrogenases

enzymes that remove a pair of hydrogen atoms (2 electrons/protons) from substrate (oxidization) to help NAD+ trap electrons

What do dehydrogenases deliver?

2 electrons + 1 proton to NAD+ to become NADH while 1 proton released as hydrogen ion to surrounding solution

What has its charge neutralized when NAD+ is reduced to NADH?

Nicotinamide portion of NAD+

What is the most versatile electron acceptor in cellular respiration?

NAD+

How much potential energy do electrons lose when they are transferred from glucose to NAD+?

Very little

What does each NADH molecule formed during respiration represent?

Stored energy that can be tapped to make ATP when electrons complete fall down energy gradient from NADH to oxygen

Where do electrons extracted from glucose and stored as potential energy in NADH finally reach?

Oxygen

Where is the hydrogen that reacts with oxygen in redox reactions derived from?

Organic molecules rather than hydrogen

Where do glycolysis and subsequent cellular respiration processes occur in prokaryotes?

In the cytosol

What initial structural change happens to glucose during glycolysis?

It is split from a six-carbon sugar into two three-carbon sugars

What happens to the two three-carbon sugars after they are formed in glycolysis?

They are oxidized and rearranged to form two molecules of pyruvate

How much carbon from the original glucose molecule is released as carbon dioxide during glycolysis?

None; all carbon is accounted for in the two pyruvate molecules

Where does most of the chemical energy from glucose remain at the end of glycolysis?

Stockpiled within the two molecules of pyruvate

What is the chemical relationship between pyruvate and pyruvic acid?

Pyruvate is the ionized form of pyruvic acid

Does glycolysis require the presence of oxygen to occur?

No, it occurs whether or not oxygen is present

If oxygen is present, how is the energy stored in pyruvate and NADH extracted?

By pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation

In eukaryotes, where must pyruvate go to be oxidized to acetyl CoA?

It must enter the mitochondrion

How does pyruvate enter the mitochondrion in eukaryotic cells?

Through a transport protein

Which multienzyme complex processes pyruvate into acetyl CoA inside the mitochondrion?

Pyruvate dehydrogenase

What waste product is released and diffuses out of the cell during pyruvate oxidation?

Carbon dioxide (CO₂)

What is the destination of acetyl CoA after it is formed from pyruvate?

It enters the citric acid cycle

What occurs during the Energy Investment Phase of glycolysis?

The cell spends ATP to phosphorylate fuel molecules

What occurs during the Energy Payoff Phase of glycolysis?

ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH

How is ATP produced during the energy payoff phase of glycolysis?

Through substrate-level phosphorylation

What is substrate-level phosphorylation?

Direct transfer of a phosphate group from an organic substrate to ADP by an enzyme

In substrate-level phosphorylation, what does the term 'substrate' refer to?

An organic molecule generated as an intermediate during glucose catabolism

What is the net energy yield of glycolysis per molecule of glucose?

2 ATP and 2 NADH

What is the overall biological function of glycolysis?

Partially breaks down glucose into two molecules of pyruvate

What is the overall biological function of pyruvate oxidation?

Converts pyruvate to acetyl-CoA, releasing carbon dioxide

What is the overall biological function of the citric acid cycle?

Completes the oxidation of glucose to CO₂ while producing NADH and FADH₂

What is the overall biological function of oxidative phosphorylation?

Uses electrons from NADH and FADH₂ to generate the majority of ATP via ATP synthase

During the redox reaction in step 6 of glycolysis, which molecule acts as the oxidizing agent?

NAD+

During the redox reaction in step 6 of glycolysis, which molecule acts as the reducing agent?

Glyceraldehyde 3-phosphate (G3P)

What are the two major phases of glycolysis?

The Energy Investment Phase and the Energy Payoff Phase

What happens to the electrons released during the oxidation of glucose in glycolysis?

They are transferred to NAD+, reducing it to NADH

What enzyme complex catalyzes the conversion of pyruvate to acetyl CoA?

Pyruvate dehydrogenase complex

What form of phosphorylation does not use an electron transport chain to make ATP?

Substrate-level phosphorylation

Where is the majority of ATP generated during aerobic cellular respiration?

During oxidative phosphorylation via ATP synthase

How does pyruvate enter the mitochondrion?

Via active transport

What is pyruvate first converted to before entering the mitochondria?

Acetyl coA

What is the first part of pyruvate to be fully oxidized and released as CO₂?

The carboxyl group (-COO⁻)

What happens to the remaining two-carbon fragment after pyruvate's carboxyl group is removed?

It is oxidized, transferring electrons to NAD+ to form NADH

From what vitamin is Coenzyme A (CoA) derived?

B vitamin