ch 10 - aerobic metabolism II (electron transport and oxidative phosphorylation)

___ is used by aerobic organisms as a terminal electron acceptor in energy generation

dioxygen

oxygen diffuses ___ across cell membranes

easily

___ is a reactive diradical and an excellent oxidizing agent, readily accepting electrons from other species

oxygen

what molecules are produced in glycolysis?

• NADH

• FADH2

what is the β-oxidation pathway?

glycolysis

what cycle/pathway generate usable energy in the electron transport pathway

• β-oxidation pathway

• the citric acid cycle

what does β-oxidation pathway consist of?

series of redox carriers that receive electrons from NADH and FADH2

At the end of the β-oxidation pathway the electrons, along with protons, are donated to ___ to form ___

oxygen; H2O

During the oxidation of NADH, there are ___ steps in which the energy loss is sufficient to account for ATP synthesis

three

what are the steps energy loss is sufficient to account for ATP synthesis (during the oxidation of NADH)?

• complexes I

• III

• IV of the ETC

what is oxidative phosphorylation?

the mechanism by which electron transport is coupled to the synthesis of ATP

according to the chemiosmotic theory, the creation of a proton gradient that accompanies electron transport is coupled to ___

ATP synthesis

the complete oxidation of a molecule of glucose results in the synthesis of ___ molecules of ATP, depending on whether the glycerol-3-phosphate shuttle or the malate–aspartate shuttle transfers electrons from cytoplasmic NADH to the mitochondrial ETC

29.5 to 31

the use of oxygen by ___ is linked to the production of ROS

aerobic organisms

why do the production of ROS form?

diradical oxygen molecule accepts electrons one at a time

what are examples of ROS?

• superoxide radical

• hydrogen peroxide

• the hydroxyl radical

• singlet oxygen

what are examples of prominent RNSs?

• nitric oxide

• nitrogen dioxide

• peroxynitrite

what is redox proteome?

a diverse group of proteins that undergo reversible redox reactions that link electron transfer reactions to metabolic processes

Proteins with ionizable cysteine thiol groups are referred to as the

cysteine proteome

what is the redox code?

a set of principles that describe the relationships between NAD(P)+/NAD(P)H, GSH/GSSG, the cysteine proteome, and other redox molecules involved in numerous cellular processes

Complexes I and II of the electron transport complex transfer electrons from NADH and succinate, respectively, to

Coenzyme Q (CoQ or ubiquinone)

The functional respiration unit within the mitochondria of plants and animals is called

electron transport chain or respirasome

___ is a small matrix protein that functions as an electron acceptor for dehydrogenases in fatty acid oxidation

Electron transfer flavoprotein (ETF)

___ catalyzes the redox reaction between UQH₂ (ubiquinol) and cytochrome c.

Complex III

Electron transport within complex I begins with the reduction of ___ by NADH

FMN (flavin mononucleotide)

what are the principal sources of electrons for the electron transport pathway?

• NADH – produced in glycolysis, the citric acid cycle (TCA cycle), and β-oxidation.

• FADH₂ – generated in the TCA cycle and during fatty acid oxidation.

• Succinate – donates electrons via Complex II.

• Glycerol-3-phosphate – in certain shuttle systems, donates electrons to FAD.

• Electron-transferring flavoprotein (ETF) – receives electrons from fatty acid oxidation

list several reasons why oxygen is widely used by living organisms in energy production.

• High electronegativity

• Large energy yield

• Availability

• Non-toxic products

• Supports aerobic respiration

list the protein complexes in the mitochondrial ETC and describe their functions

• Complex I (NADH:ubiquinone oxidoreductase)

  • Accepts electrons from NADH, transfers them to Coenzyme Q (CoQ), and pumps 4 protons (H⁺) into the intermembrane space.

• Complex II (Succinate dehydrogenase)

  • Accepts electrons from succinate (via FADH₂) and transfers them to CoQ, but does not pump protons.

• Complex III (Cytochrome bc₁ complex)

  • Transfers electrons from reduced CoQ (UQH₂) to cytochrome c. Pumps 4 protons per pair of electrons via the Q cycle.

• Complex IV (Cytochrome c oxidase)

  • Accepts electrons from cytochrome c and transfers them to O₂, forming H₂O. Pumps 2 protons per pair of electrons.

• ATP Synthase (Complex V)

  • Not part of the electron transport chain itself but uses the proton gradient created by Complexes I, III, and IV to synthesize ATP from ADP and Pi

the electron transport complex consists of a series of oxidations rather than one reaction. Why is this an important feature of energy capture?

• Efficient energy capture: Energy is released gradually and can be harnessed to pump protons across the membrane.

• Avoids waste as heat: A single-step electron transfer would release energy as heat, wasting it rather than capturing it for ATP synthesis.

• Controlled regulation: Multiple steps allow for fine regulation of energy production.

• Minimizes damage: Prevents production of excessive reactive oxygen species (ROS) that could damage cells

what metabolites accumulate when azide is added to actively respiring mitochondria?

azide (N₃⁻) inhibits Complex IV (cytochrome c oxidase) by binding to the heme iron in the active site, preventing electron transfer to oxygen

heat generation by brown adipose tissue cells is referred to as

non-shivering thermogenesis

the control of aerobic respiration by ADP is referred to as

respiratory control (or ADP control)

hydrophobic polypeptides that dissipate osmotic gradients by inserting themselves into a membrane to form a channel are called

ionophores

___ are small molecules that collapse a proton gradient by equalizing the proton gradient on both sides of a membrane

uncouplers

an electrochemical proton gradient across a membrane is referred to as the

proton motive force (PMF)

the major enzymatic defense against oxidative stress is provided by superoxide dismutase, glutathione peroxidase, peroxiredoxin, and ___

catalase

a chemical species with an unpaired electron is called

free radical

macrophages utilize an oxygen-consuming process called the ___ in which reactive oxygen species are generated to kill microorganisms or damaged cells.

respiratory burst

under conditions of ___, the antioxidant mechanisms of cells are overwhelmed

oxidative stress

which of the following molecules remains oxidized when the electron transport inhibitor antimycin A is added to a suspension of actively respiring mitochondria?

cytochrome c

which of the following ATP synthase components prevents the α,β hexamer from rotating?

b

the control of aerobic respiration by ___ is called respiratory control.

ADP

Which of the following dehydrogenases delivers electrons to directly to UQ in the electron transport pathway from the intermembrane space side of the inner mitochondrial membrane?

glycerol-3-phosphate dehydrogenase

The aspartate–malate shuttle transfers electrons from cytoplasmic NADH to the electron transport system. Which of the following molecules is not directly involved in this pathway?

citrate