Chapter 14: Energy Generation in Mitochondria and Chloroplasts

Vocabulary practice cards covering mitochondrial and chloroplast structure, the endosymbiotic theory, cellular respiration, and photosynthesis as discussed in Chapter 14.

Chemiosmosis

The process of coupling an $H^+$ gradient to generate energy.

Stage 1 of oxidative phosphorylation

Energy released by electron transport is used to pump protons across the membrane.

Stage 2 of oxidative phosphorylation

Energy stored in the proton gradient is harnessed by ATP synthase to make ATP.

ATP synthase

A large, multi-subunit protein in the inner mitochondrial membrane that generates ATP from the proton gradient.

Endosymbiotic Theory

The theory that mitochondria and chloroplasts originated as prokaryotic organisms that were engulfed by a host cell.

Mitochondrial genome

In humans, it contains $16,569$ base pairs that code for $37$ genes.

Mitochondrial gene distribution

Includes codes for $13$ polypeptides, $22$ tRNAs, and small and large rRNA subunits.

Mitochondrial division

Mitochondria can divide like a bacterium, supporting the Endosymbiotic Theory.

Mitochondrial Matrix

Contains a highly concentrated mixture of hundreds of enzymes, including those for the oxidation of pyruvate and fatty acids and the citric acid cycle.

Inner mitochondrial membrane

Folded into cristae; contains proteins for oxidative phosphorylation, the electron-transport chain, and ATP synthase.

Cristae

The numerous folds of the inner mitochondrial membrane.

Outer mitochondrial membrane

Contains large, channel-forming proteins called porins; is permeable to molecules of $5000$ daltons or less.

Porins

Channel-forming proteins in the outer mitochondrial membrane.

Intermembrane space

Contains enzymes that use ATP passing out of the matrix to phosphorylate other nucleotides and proteins released during apoptosis.

Oxidative phosphorylation

The production of most of the ATP used by eukaryotic cells in mitochondria.

Regeneration of $NAD^+$

Required for glycolysis; occurs under aerobic conditions when $NADH$ donates electrons to the respiratory chain.

Biosynthesis precursors

Intermediates from the citric acid cycle used for the synthesis of amino acids, nucleotides, and fatty acids.

Iron-sulfur clusters

Metal-containing components that play a central role in electron transport during oxidative phosphorylation.

Mitochondrial cell signaling

Mitochondria buffer the concentration of $Ca^{2+}$ ions, which are involved in processes like muscle contraction.

Reactive oxygen species (ROS)

Molecules that can damage macromolecules but are also involved in cell signaling.

Regulation of apoptosis

Molecules released from mitochondria trigger a proteolytic cascade leading to cell death.

Oxidation

The loss of an electron during a chemical reaction.

Reduction

The gain of an electron during a chemical reaction.

Glucose redox role

During cellular respiration, glucose loses electrons and is oxidized.

Oxygen ($O_2$) redox role

In cellular respiration, $O_2$ gains electrons and is reduced.

Hydrogen atom transfers

Electron transfers can move entire hydrogen atoms because protons are readily accepted from or donated to water.

Glycolysis location

Occurs in the cytoplasm.

Citric Acid Cycle location

Occurs in the mitochondrial matrix.

Respiratory chain location

Located in the inner mitochondrial membrane, with protons pumped into the intermembrane space.

NADH

A high-energy electron carrier that carries two high-energy electrons from sugar oxidation to the electron transport chain.

$$FADH_2$$

A high-energy electron carrier used in the respiratory chain.

Hydride ion ($H^-$)

A form of $NADH$ donation involving two electrons and one proton.

Terminal electron acceptor

In the mitochondrial electron transport chain, this role is played by $O_2$.

Ubiquinone

Also known as Coenzyme Q ($CoQ$); a mobile electron carrier that moves electrons between complexes.

Cytochrome c ($Cyt ext{ } c$)

A mobile electron carrier in the mitochondrial electron transport chain.

NADH dehydrogenase

The electron transport complex that binds electrons least tightly and accepts them from $NADH$.

Cytochrome c reductase

One of the complexes in the respiratory chain that extracts energy from electrons to pump protons.

Cytochrome c oxidase

The final complex in the respiratory chain that transfers electrons to $O_2$.

Low redox potential

A state with low affinity for electrons and a high $G$ value.

High redox potential

A state with high affinity for electrons and a low $G$ value.

$O_2$ affinity

Oxygen has the highest affinity for electrons in the mitochondrial respiratory chain.

Heme group

Contains iron and can serve as an electron acceptor, such as in cytochrome c.

Porphyrin ring

The structural component of the heme group of cytochrome c.

Subunit I (Cytochrome c oxidase)

Contains the heme-oxygen-binding site where $O_2$ is reduced to $H_2O$.

Subunit II (Cytochrome c oxidase)

Contains copper ($Cu$) atoms that participate in electron transfer.

Proton motive force

The sum of the forces generated by the electrical and concentration gradients of protons.

Electrical gradient

A component of the proton motive force created by the charge difference across the membrane.

ATPase function

If the proton gradient is weak, ATP synthase can run in reverse to pump protons while consuming ATP.

Mechanical motion

Produced by the movement of protons through the ATP synthase to drive ATP synthesis.

Chloroplast specialized membranes

Include the outer membrane, inner membrane, and the unique thylakoid membrane.

Thylakoid

A membrane-bound compartment unique to chloroplasts.

Stroma

The space in chloroplasts where carbon assimilation and light-independent reactions take place.

Thylakoid space

The space inside the thylakoid where protons are pumped during light reactions.

Light reactions

Light-induced energy generation that occurs in the thylakoid membrane, producing ATP and $NADPH$.

Light-independent reactions

Processes like carbon assimilation from carbon dioxide that occur in the stroma.

Calvin Cycle

The series of light-independent reactions that fix $CO_2$.

Rubisco

The enzyme that fixes $CO_2$ in the Calvin cycle.

Photosystem II

Generates ATP and splits $H_2O$ to provide electrons; light energy moves electrons to a higher energy state.

Photosystem I

Generates $NADPH$; requires light to re-energize electrons that lost energy after leaving Photosystem II.

Water-splitting enzyme

Associated with Photosystem II; splits $2H_2O$ to release $O_2$ and $4H^+$.

Chlorophyll

Molecules that harvest light energy and focus it into a reaction center.

Reaction center

The part of the photosystem where high-energy electrons are transferred to a mobile carrier.

Antenna complexes

Light-harvesting complexes that transfer energy from one chlorophyll molecule to another until it reaches the special pair.

Special pair

A specific pair of chlorophyll molecules in the reaction center that creates a charge separation upon excitation.

Linear electron transport chain

The pathway in thylakoid membranes where electrons pass from Photosystem II to Photosystem I.

Plastoquinone

A mobile electron carrier in the thylakoid membrane electron transport chain.

Cytochrome $b_6-f$ complex

A protein complex in the chloroplast electron transport chain that pumps protons into the thylakoid space.

Plastocyanin ($pc$)

A mobile electron carrier that transfers electrons from the cytochrome $b_6-f$ complex to Photosystem I.

Ferredoxin ($Fd$)

An electron carrier in chloroplasts that receives electrons from Photosystem I.

Ferredoxin-$NADP^+$ reductase ($FNR$)

The enzyme that reduces $NADP^+$ to $NADPH$ in the stroma.

Magnesium ($Mg$)

The central atom in the porphyrin-like ring of a chlorophyll molecule.

Chlorophyll hydrophobic tail

The region of the chlorophyll molecule that anchors it in the thylakoid membrane.

Carbon assimilation

The process of converting carbon dioxide into organic molecules.

Initial electron source (Photosynthesis)

Low-energy electrons taken from $H_2O$.

Final electron acceptor (Photosynthesis)

The molecule $NADP^+$ which becomes $NADPH$.

Proton pumping direction (Chloroplast)

Protons are pumped from the stroma into the thylakoid space.

Proton pumping direction (Mitochondrion)

Protons are pumped from the matrix into the intermembrane space.

ATP synthesis direction (Chloroplast)

ATP is generated in the stroma.

ATP synthesis direction (Mitochondrion)

ATP is generated in the matrix.

Porin molecular limit

Proteins in the outer mitochondrial membrane allow passage of molecules up to $5000$ daltons.

Mitochondrial ribosomal subunits

Small and large rRNA subunits coded by the mitochondrial genome.

Human mitochondrial genes

There are exactly $37$ genes in the human mitochondrial genome.

Heme-oxygen-binding site location

Located in Subunit I of Cytochrome c oxidase.

Copper atoms in respiration

Two copper centers in Subunit II of Cytochrome c oxidase.

Charge-separated state

The state created in the special pair of the reaction center when a high-energy electron is transferred to a mobile carrier.

Goal of photosynthetic light reactions

To produce energy (ATP) and $NADPH$ for light-independent reactions.

Electronic affinity of Cytochrome c oxidase

It binds electrons more tightly than ubiquinone or NADH dehydrogenase.

Electron transport Complexes

Found in the plasma membranes of modern bacteria as well as mitochondrial inner membranes.

Source of energy for electrons in PSI

Light energy is used to boost electrons to a higher energy state after they lose energy leaving PSII.

Chloroplast electron-transport location

The proteins are located specifically in the thylakoid membrane.

Pyruvate oxidation location

Takes place within the mitochondrial matrix.

Fatty acid oxidation location

Takes place within the mitochondrial matrix.

Concentration of Matrix proteins

Highly concentrated mixture containing hundreds of enzymes.

$O_2$ role in ETC

Acts as the terminal electron acceptor in the respiratory chain.

$H^+$ pumping energy (ETC)

Derived from the energy extracted from electrons as they move through protein complexes.

Electrical gradient direction

Works in the same direction as the concentration gradient to contribute to the proton motive force.

Stage 2 power source

ATP synthesis is powered by the movement of $H^+$ ions through ATP synthase.

Photosystem II splitting reaction

2H_2O ightarrow 4H^+ + O_2 + 4e^-.

Photosynthesis electron carriers

Include plastoquinone ($PQ$), cytochrome $b_6-f$ complex, and plastocyanin ($PC$).

Carbon assimilation source

Carbon dioxide ($CO_2$).