Chapter 14: Energy Generation In Mitochondria and chloroplasts

How is a mitochondria able to divide?

Through fission similarly to a bacterium

What is unique about the mitochondria and chloroplast?

They are double-membrane organelles that have

• their own unqiue genomes

• Machinery that allows them to replicates their own DNA to produce RNA and proteins

• Both have their own special set of ribosomes

Where is the mitochondria usually located?

Near locations with high ATP utilization

• such as the cardiac muscle cell where ATP hydrolysis provides energy for muscle contraction

What does oxidative phosphorylation in the mitochondria provide?

It provides most of the ATP used by eukaryotic cells

What does the mitochondria usually form?

They usually form elongated, tubular networks that extend throughout the cytoplasm

What are the four compartments that separates the mitochondria?

• The mitochondrial matrix

• the inner membrane

• the outer membrane

• The inter-membrane space

With each compartment having their own set of unique proteins that enables them to perform distinct functions

How does NADH dontate its high-energy electron?

It donates its high-energy electron by removing its hydride ion and converting it into a proton and two high-energy electrons

What are Ubiquinone and cytochrome C molecules?

They are mobile carriers that help pass on electrons from one complex to the next when reduced

What is ATP synthase?

A molecular machine that converts the energy from protons moving down their electrochemical gradient into ATP

• Additionally, can be driven in 2 directions: ATP synthesis and ATP hydrolysis

What does ATP synthase consist of?

It consists of a stationary head called F1 ATPase and a rotary ring called F0

What occurs if the electrochemical proton gradient falls below a certain level?

The ∆G energy for proton transport wont be large enough to drive ATP production, resulting in ATP synthase instead hydrolyzing ATP to rebuild the proton gradient to drive ATP production again

How are pyruvates and phosphates importated into the inner membrane of the mitochondria

They are imported as protons move down their electrochemical gradient

What does the mitochondrial matrix contain?

It contains a highly concentrated mixture of enzymes, including those required for oxidizing pyruvates and fatty acids for the CAC

What does the inner membrane of the mitochondria contain?

It contains proteins that are responsible for carrying out oxidative phosphorylation, and is where the ETC and ATP synthase reside

• Additionally, it can divide into 2 distinct sub compartments that differs in protein composition and function

What does the outer membrane of the mitochondria contain?

It contains channel forming proteins, aka porins

What does the mitochondrial inter-membrane space contain?

It contains several enzymes that use the ATP leaving the matrix to phosphorylate other nucleotides

Oxidative phosphorylation (part 1)

NADH donates its high-energy electron to the electron transport chain located in the inner membrane

Oxidative phosphorylation (part 2)

The donated electron from NADH is then passed along ETC through 3 respiratory enzyme complexes

Oxidative phosphorylation (part 3)

As the electron gets passed down, protons derived from water are pumped across the membrane from matrix into the intermembrane space by each enzyme complex

Oxidative phosphorylation (Part 4)

As the protons are being pumped into the intermembrane space, an electrochemical proton gradient is generated across the inner membrane

Oxidative phosphorylation (Part 5)

The electron eventually reaches an oxygen at the end of the ETC and generates a water molecule

Oxidative phosphorylation (Part 6)

The electrochemical proton gradient generated then causes ATP synthases rotor ring to begin spinning rapidly, allowing protons in the intermembrane to move down their gradient through the ATP synthase, resulting in ATP being generated from ADP and phosphate

Whats the role redox potential plays in oxidative phosphorylation?

Measures electron affinity and increases along the ETC, allowing for each respiratory enzyme complex to pump out protons as they transfer electrons

what occurs when a proton in the matrix binds to a protein with high H+ affinity?

Energy from electron transport causes it to have a low H+ affinity, releasing the proton into the intermembrane space as a result

What does the addition of an uncoupling agent thats a H+ carrier result in?

It results in the permeability of the inner mitochondrial membrane to increase, allowing for protons to be leaked back into the matrix

What happens to the sugar and metabolites produced from photosynthesis in plants?

They get exported into the cytosol of the plant cell and enters the citric acid cycle in the mitochondria, eventually producing ATP

What are thylakoid membranes?

They are compartments found in the chloroplast where photosynthesis takes place

What are the 2 stages of photosynthesis?

• Light dependent stage

  • Takes place in the thylakoid membrane and produces ATP and NADPH at the end, along with electrons extracted from water

• Light-independent stage

  • Begins in the chloroplast stroma and continues in the cytosol

How does chlorophyll absorb light?

Chlorophyll contains a porphyrin ring with a network of electrons that allows them to absorb light, with the hydrophobic tails of the ring holding them down to thylakoid membrane

What happens in Photosystem II when light is absorbed?

When light is absorbed by chlorophyll molecules in the antenna complex, a high-energy electron is passed from molecule to molecule until it reaches the chlorophyll special pair in the PSII reaction center, exciting the pair as a result

What happens after the chlorophyll special pair become excited?

1. The high-energy electrons are transferred to plastoquinone (PQ)

2. A water splitting enzyme then hydrolyzes 2 H2O molecules and extracts 4 electrons, replacing electrons lost by the special pair and producing 4 H+ and an O2, which is released

What happens at the cytochrome b6f complex?

After the electrons have been transferred to plastoquinone

1. Plastoquinone transfers the electrons to the cytochrome complex, which uses the energy to pump protons from the stroma into the thylakoid space, resulting in an proton gradient being produced

2. The electrons are then passed to plastocyanin, which carriers them to the PSI reaction center

What occurs in PSI after the electrons arrive from plastocyanin?

1. Light energy is captured by PSI and causes the electrons to be re-excited

2. The electrons are then transferred to ferredoxin and carried to ferredoxin-NADP+ reductase (FNR), producing NADPH as a result

3. At the same time, the proton gradient generated powers the ATP synthase embedded in the thylakoid membrane, generating an ATP molecule

What happens in Carbon fixation phase?

A covalent bond forms between a CO2 and a rubisco, generating an intermediate that then reacts with water and forms a 3-phosphoglycerate (3PG) molecule

What happens in the Sugar formation phase?

After 3PG has been made:

• ATP and NADPH produced from the light-dependent stage converts 3PG into G3P, with some exiting the cycle to produce glucose

What happens in the Regeneration of RuBP phase?

G3P is used to regenerate RuBP for the cycle to continue, with some G3Ps being transported out of the chloroplast stroma

What are the 3 mobile electron carriers involved in Photosynthesis?

• Plastoquinone

• Plastocyanin

• Ferredoxin

Where does the calvin cycle?

in the chloroplast stroma