energy in mitochondria and chloroplasts

Metabolism

the sum of all chemical reactions occurring in a cell or organism that obtain, transform, and use energy and matter

Beta Oxidation (β-Oxidation)

cyclic metabolic pathway that breaks down fatty acids into acetyl-CoA, NADH, and FADH2 for ATP production

Purpose of Beta Oxidation

to convert stored fat into usable energy by generating acetyl-CoA and reduced electron carriers

Location of Beta Oxidation

primarily in the mitochondrial matrix of eukaryotic cells

Fatty Acid Activation

ATP-dependent process that attaches coenzyme A to a fatty acid, forming fatty acyl-CoA before oxidation can occur

Acyl-CoA Synthase (Thiokinase)

enzyme that activates fatty acids by linking them to coenzyme A using ATP

Fatty Acyl-CoA

activated fatty acid attached to coenzyme A that serves as the substrate for β-oxidation

Carnitine Shuttle

transport system that moves fatty acyl groups across the inner mitochondrial membrane because fatty acyl-CoA cannot cross directly

Role of Carnitine

binds fatty acids and transports them into the mitochondrial matrix for oxidation

One Round of Beta Oxidation

removes a two-carbon acetyl-CoA unit from a fatty acid while producing one NADH and one FADH2

Products of Beta Oxidation

acetyl-CoA, NADH, and FADH2, which all contribute to ATP production

Importance of Acetyl-CoA from Fatty Acids

enters the citric acid cycle to generate additional ATP, NADH, and FADH2

Importance of NADH and FADH2 from Fatty Acid Oxidation

donate electrons to the electron transport chain to drive oxidative phosphorylation and ATP synthesis

Fatty Acids as an Energy Source

major long-term energy storage molecules that yield more ATP per molecule than carbohydrates

Anaerobic Respiration

bacterial process that generates ATP using electron acceptors other than oxygen

Photoautotroph

organism that uses light energy and carbon dioxide to produce organic molecules through photosynthesis

Major Photoautotrophs

approximately 50% land plants, 30% aquatic protists, and 20% prokaryotes

Chloroplast

double-membrane organelle where photosynthesis occurs in plants and algae

Granum

stack of thylakoid membranes within a chloroplast where light reactions occur

Photosynthesis

process that converts solar energy into chemical energy stored in carbohydrates using carbon dioxide and water

Importance of Photosynthesis

provides nearly all organic molecules and energy that support life on Earth

Overall Photosynthesis Equation

carbon dioxide and water are converted into carbohydrates and oxygen using light energy

Photosynthesis as a Redox Reaction

water is oxidized and carbon dioxide is reduced during photosynthesis

Photosynthesis as an Endergonic Process

requires a large input of energy from sunlight to synthesize carbohydrates

Light-Dependent Reactions

photosynthetic reactions in thylakoid membranes that produce ATP, NADPH, and oxygen

Light-Independent Reactions (Calvin Cycle)

reactions in the stroma that use ATP and NADPH to convert carbon dioxide into sugars

Thylakoid

membrane-bound compartment within chloroplasts where light reactions occur

Stroma

fluid-filled region surrounding thylakoids where the Calvin cycle takes place

ATP in Photosynthesis

provides energy for carbon fixation and sugar synthesis during the Calvin cycle

NADPH in Photosynthesis

provides reducing power and high-energy electrons for carbon fixation

Photon

discrete packet of light energy that can excite electrons in pigments

Pigment

molecule that absorbs specific wavelengths of light energy

Chlorophyll a

primary photosynthetic pigment that directly participates in light reactions

Chlorophyll b

accessory pigment that broadens the range of light absorption and transfers energy to chlorophyll a

Carotenoids

accessory pigments that absorb blue-green light, transfer energy to chlorophyll, and protect against oxidative damage

Why Plants Appear Green

chlorophyll reflects and transmits green wavelengths while absorbing mainly red and blue light

Excited Electron

electron raised to a higher energy level after absorbing light energy

Antenna Complex

group of pigments that captures light and funnels excitation energy toward the reaction center

Reaction Center

specialized chlorophyll molecule where excited electrons are transferred to an electron acceptor

Photosystem II (PSII)

protein-pigment complex that absorbs light, splits water, releases oxygen, and begins electron transport

Pheophytin

primary electron acceptor in Photosystem II that accepts excited electrons from chlorophyll

Plastoquinone (PQ)

mobile electron carrier that transfers electrons and protons within the thylakoid membrane

Cytochrome Complex

electron transport protein complex that pumps protons into the thylakoid lumen using electron energy

Photolysis of Water

light-driven splitting of water that produces electrons, protons, and oxygen gas

Source of Oxygen in Photosynthesis

oxygen released during photosynthesis comes from water molecules, not carbon dioxide

Proton Pumping in Photosynthesis

movement of protons from the stroma into the thylakoid lumen to create a proton gradient

Thylakoid Lumen

interior space of thylakoids where protons accumulate during light reactions

Proton Motive Force (PMF)

electrochemical gradient of protons across the thylakoid membrane that stores energy

Chemiosmosis in Chloroplasts

use of proton flow through ATP synthase to drive ATP production

ATP Synthase in Chloroplasts

molecular motor that uses the proton gradient to synthesize ATP in the stroma

Photosystem I (PSI)

photosystem that re-energizes electrons and transfers them to NADP+ to form NADPH

Ferredoxin

iron-sulfur protein that carries electrons from Photosystem I to NADP reductase

NADP+ Reductase

enzyme that reduces NADP+ to NADPH using electrons from Photosystem I

NADPH

high-energy electron carrier produced during light reactions and used in the Calvin cycle

Noncyclic Photophosphorylation

linear electron flow from water through Photosystem II and Photosystem I to NADP+, producing ATP, NADPH, and oxygen

Why Two Photosystems Are Needed

one photosystem does not provide enough energy to move electrons from water to NADP+, so two energy boosts are required

Linear Electron Transport

movement of electrons from water to NADP+ through Photosystem II, the ETC, and Photosystem I

Light Reactions Summary

light energy drives water oxidation, proton pumping, ATP synthesis, and NADPH production

Calvin Cycle

C3 pathway in the chloroplast stroma that fixes carbon dioxide into carbohydrate molecules

Purpose of the Calvin Cycle

to convert inorganic carbon dioxide into organic molecules using ATP and NADPH

Carbon Fixation

incorporation of atmospheric CO2 into an organic molecule

Rubisco

enzyme that catalyzes carbon fixation by attaching CO2 to RuBP; considered the most abundant protein on Earth

RuBP (Ribulose-1,5-Bisphosphate)

five-carbon sugar that accepts carbon dioxide during carbon fixation

3-Phosphoglycerate (3-PGA)

first stable product formed after carbon fixation in the Calvin cycle

G3P (Glyceraldehyde-3-Phosphate)

three-carbon sugar produced by the Calvin cycle that can be used to synthesize glucose and other organic molecules

Phase 1 of Calvin Cycle: Carbon Fixation

Rubisco attaches CO2 to RuBP, producing 3-PGA

Phase 2 of Calvin Cycle: Reduction

ATP and NADPH convert 3-PGA into G3P

Phase 3 of Calvin Cycle: Regeneration

ATP is used to regenerate RuBP so the cycle can continue

Calvin Cycle Stoichiometry

three turns fix three CO2 molecules and produce one net G3P molecule

Products of Light Reactions

ATP, NADPH, and oxygen

Products of Calvin Cycle

G3P and ultimately glucose and other organic molecules

Photorespiration

process in which Rubisco binds oxygen instead of carbon dioxide, reducing photosynthetic efficiency

Causes of Photorespiration

high oxygen levels, low carbon dioxide levels, and warm temperatures

Effect of Photorespiration

consumes energy and releases carbon dioxide, reducing sugar production

Why Photorespiration Occurs

Rubisco cannot always distinguish between oxygen and carbon dioxide

Stomata Closure and Photorespiration

hot, dry conditions cause stomata to close, increasing oxygen and decreasing carbon dioxide inside leaves

C3 Plants

plants that fix carbon dioxide directly through the Calvin cycle using Rubisco

C4 Plants

plants that reduce photorespiration by initially fixing carbon dioxide into four-carbon compounds before the Calvin cycle

CAM Plants

plants that open stomata at night and store carbon dioxide to reduce water loss and photorespiration

Endosymbiotic Theory of Chloroplast Origin

theory proposing that chloroplasts evolved from photosynthetic bacteria engulfed by ancestral eukaryotic cells

Mitochondrial Heat Production

generation of heat through proton leakage rather than ATP production, especially in brown fat

Thermogenin (Uncoupling Protein 1)

protein that allows protons to bypass ATP synthase, releasing energy as heat

Brown Adipose Tissue

specialized tissue rich in mitochondria that performs non-shivering thermogenesis

Additional Mitochondrial Functions

calcium storage, apoptosis regulation, heme synthesis, ammonia detoxification, and heat production

Relationship Between Photosynthesis and Respiration

photosynthesis stores solar energy in organic molecules, while cellular respiration releases that stored energy to make ATP