Chapter 10 - Krebs Cycle

What type of electron acceptor does cellular respiration use?

an external electron acceptor

What is the terminal electron acceptor in aerobic respiration?

Oxygen

In anaerobic respiration, other terminal electrons acceptors, such as ____, ______, and ______ ____ are used, especially _____, and _____

Sulfur

Protons

Ferric ions

Bacteria

Archaea

Most aerobic ATP production in eukaryotic cellstakes place in the

Mitochondrion

In bacteria, the plasma membrane and cytoplasm are analogous to the

mitochondrial inner membrane and matrix

Aerobic respiration has the potential of generating up to _____ ATP molecules per glucose

38

Oxygen provides a means of continuous reoxidation of _____ and other reduced coenzymes

NADH

What is the first stage of respiration?

The glycolytic pathway

What happens in the second stage of respiration?

Pyruvate is oxidized to generate acetyl CoA (acetyl coenzyme A)

What occurs in the third stage of respiration?

Acetyl CoA enters the citric acid cycle, where it is completely oxidized to CO2

What is the fourth stage of respiration?

Electron transport, the transfer of electrons from reduced coenzymes to oxygen coupled to active transport of protons across a membrane

What is the fifth stage of respiration?

The electrochemical proton gradient formed in step 4 is used to drive ATP synthesis (oxidative phosphorylation)

The mitochondrion are only in ____________ cells

eukaryotic

What is the site for all the reactions associated with the citric acid cycle, electron transport, and oxidative phosphorylation?

Mitochondrion

Mitochondrion are found in virtually all _______ cells of eukaryotes

aerobic

Mitochondria are frequently clustered in regions of cells with the greatest need for

ATP

The outer membrane contains _____ that allow passage of molecular less than 5000

porins

The intermembrane space between the inner and outer membrane is

continuous with cytosol

What is the function of the inner membrane of the mitochondrion?

It is impermeable to most solutes, partitioning the mitochondrion into two separate compartments.

What are the two compartments created by the inner membrane of the mitochondrion?

The intermembrane space and the mitochondrial matrix.

The inner membrane of most mitochondria has many infoldings called

cristae

Increase surface area of the inner membrane and provide more space for

electron transport to occur

The interior of the mitochondrion is filled with

semifluid matrix

The matrix contains many enzymes involved in mitochondrial function as well as

DNA molecules and ribosomes

specific functions and pathways have been localized within mitochondria by

fractionation studies

Where are most enzymes involved in pyruvate oxidation found?

Matrix

Where are most enzymes involved in the citric acid cycle found?

Matrix

Where are most enzymes involved in the catabolism of fatty acids found?

Matrix

Where are most enzymes involved in the catabolism of amino acids found?

Matrix

Most electron transport intermediates are

integral inner membrane components

What happens to pyruvate in the presence of oxygen?

Pyruvate is oxidized fully to carbon dioxide.

What is the energy released from the oxidation of pyruvate used for?

To drive ATP synthesis.

Citrate is an important intermediate in

citric acid cycle

The citric acid cycle metabolizes ___________ produced from ___________ _______________

Acetyl CoA

Pyruvate decarboxylation

Acetyl CoA transfers its acetate group to a four-carbon acceptor called

oxaloacetate

What does oxaloacetate do?

it continues in the cycle and goes back to turn acetyl-coa into citrate

After its formation, citrate undergoes

two successive decarboxylations

Each round of the citric acid cycle involves

the entry of two carbons

the release of two carbon dioxides

the regeneration of oxaloacetate

each round of citric acid cycle, electrons are accepted by

coenzymes

The glycolytic oathway ends with

pyruvate

______ Can enter the intermembrane space of the mitochondrion

Pyruvate

At the inner mitochondrial membrane, a specific symporter transports ________ into the matrix, along with a ______

Matrix

Proton

Pyruvate is converted to Acetyl CoA by what enzyme

Pyruvate dehydrogenase complex (PDH)

The conversion is a decarboxylation because

one carbon is liberated as CO2

In each round, two carbon atoms enter as ______ and leave as _______

acetate

carbon dioxide

In CAC-1, the two-carbon acetate group is transferred from ________ to _______ to form _________

Acetyl CoA

Oxaloacetate (4C)

Citrate (6C)

Citrate is converted to ____________ in the second step

isocitrate

the enzyme ________ catalyzes the reaction of citrate converting to isocitrate

aconitase

Isocitrate has a hydroxyl group that is easily

oxidized or dehydrogenated

Four steps in the citric acid cycle are oxidations, those four are:

CAC-3

CAC-4

CAC-6

CAC-8

CAC-3 and CAC-4 are ______________ steps, releasing one CO2 ine each step

decarboxylation

Isocitrate is oxidized by ____________ _____________________ to ____________________, with NAD+ as the electron acceptor

isocitrate dehydrogenase

oxalosuccinate

Oxalosuccinate immediately undergoes decarboxylation to form

a-ketoglutarate (5C)

a-ketoglutarate is oxidized to succinyl CoA, by

a ketoglutarate dehydrogenase (CAC-4)

Succinyl CoA has been _________ it has a _____-________ _____________ ________

generated

high-energy thioester bond

The energy from hydrolysis of the high energy thioester bond is used to generate

One GTP (CAC-5)

Succinate is oxidized to ___________ by ____________ _______________

Fumarate

succinate dehydrogenase(CAC-6)

The succinate oxidation to fumarate trandfers electrons to _____ a ______-_________ ____________

FAD

Lower-energy coenzyme

Fumarate is hydrated to produce ________ by __________ ___________

malate (CAC-7)

Fumarate hydratase

In reaction CAC-8, catalyzed by ________ _____________, the malate is converted to ______________ as electrons are accepted by NAD+ to produce NADH

Malate dehydrogenase

oxaloacetate

Like all metabolic pathways, the citric acid cycle must be

carefully regulated to meet cellular needs

Most of the control of the cycle involves ___________ _____________ of four key enzymes by specific acceptor molecules

allosteric regulation

Effector molecules may be

activators of inhibitors

The PDH or Pyruvate dehydrogenase complex is reversibly inactivated by _______________ and activated by _____________

phosphorylation

dephosphorylation

PDH is inhibited by ___, which is abundant where energy is plentiful

ATP

PDH and isocitrate dehydrogenase are activated by ___ and ___, which are more abundant when energy is needed

AMP and ADP

Overall availability of acetyl CoA is determined mainly by

the activity of the PDH complex

PDH is allosterically inhibited by ___, ____ and _______ ___ and _____ ___/___ _______

ATP, NADH, and acetyl CoA and high ATP/ADP ratio (enzyme: PDH kinase)

PDH is activated by ___, ____, and _____ ____ and ____ ___/___ ______

AMP, NAD+, and free CoA and low ATP/ADP ratio (enzyme: PDH phosphatase)

Chemotrophic energy metabolism through the citric acid cycle accounts the synthesis of ______ ___ per glucose

ATP

in the citric acid cycle, chemotrophic energy metabolism through the citric acid cycle makes four ATP from

Two ATP from glycolysis and two ATP from the citric acid cycle

Coenzyme reoxidation by transfer of electrons to oxygen is called

electron transport

Electron transport and ATP generation are not

independent processes; they are functionally linked to each other

Although many electron carriers are part of theETS, most are organized into

multiprotein complexes

CoQ accepts both _____ and _______ when it is reduced

protons and electrons

CoQ releases both _____ and _______ when it is oxidized

protons and electrons

Complex I transfers electrons from NADH to CoQ and is called

the NADH-coenzyme Q oxidation complex (or NADH dehydrogenase)

Complex II transfers to CoQ the electrons derivedfrom succinate (CAC-6) and is called

the succinate-coenzyme Q oxidoreductase complex, or succinate dehydrogenase

Complex III is called

the coenzyme Q-cytochromeoxidoreductase complex (and cytochrome b/c1complex)