Biochemistry Cellular Respiration Quiz

Cellular Energetics

• Cellular energetics is the study of how cells produce and use energy.
• It is based on the laws of thermodynamics.
• It relates to the capture, storage, and conversion of energy within cells.

Course Learning Objectives (ILOs)

• Explain free energy and entropy concepts.
• Use thermodynamics to explain enzyme effectiveness in metabolic pathways.
• Detail the function of ATP in coupling energy-releasing and energy-requiring processes.
• Explain the role of oxidation-reduction reactions in generating energy.
• Define glycolysis, the Krebs cycle, electron transport chain, chemiosmosis, oxidative phosphorylation and cellular respiration.
• Identify the location and name the main pathways for ATP production under aerobic and anaerobic conditions.

Bioenergetics

• How cells produce and use energy
• Based on the laws of thermodynamics
• Relates to energy capture (respiration, photosynthesis), storage (ATP, NADH, proton gradient) and conversion (light, chemical, kinetic).

Energy Conservation and Conversion

• First Law of Thermodynamics: Energy cannot be created or destroyed, only converted from one form to another.
• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe. Energy transfer involves loss to the environment via heat.

Energy Conservation & Conversion in Biological Systems

• Living organisms undergo constant energy input to perform work (e.g., movement, growth).
• Organisms lose some energy to the environment as heat
• Some energy becomes irreversibly fixed, like in secondary plant metabolites

Energy Balance (Ecosystem & Individual)

• Energy is continually converted between forms in all individuals, and ecosystems.
• Energy is converted into various forms like heat energy, loss and storage (e.g., ATP).
• The process of energy's metabolic processes are shown in the food chain diagram

Metabolism & ATP

• Metabolism: the sum of all chemical reactions in an organism.
  • Anabolism (building up): Energy used to build complex molecules (e.g., protein synthesis from amino acids).
  • Catabolism (breaking down): Energy released via the breakdown of complex molecules (e.g., glucose breakdown in glycolysis).
• ATP acts as an energy reservoir in cells, driving cellular work (chemical, transport, movement).

Gibbs Free Energy (G)

• Gibbs free energy (G) is the portion of a system's energy that can perform work.
• ΔG = ΔH - TΔS (where ΔH is enthalpy, T is temperature, and ΔS is entropy).
  • A negative ΔG indicates a spontaneous process.

Chemical Reactions and Energy

• Exergonic reactions: Release energy (ΔG < 0).
• Endergonic reactions: Require energy input (ΔG > 0).
  • Energy released from exergonic reactions can be utilized to drive endergonic reactions.
• Enzymes accelerate chemical reactions by lowering activation energy.

Enzymes

• Enzymes, often pH-dependent, regulate metabolic pathways by lowering activation energies, and are regulated by gene expression and modification.
  • The end-product often inhibits further reaction.

ATP as Energy Currency

• ATP (adenosine triphosphate) releases energy when an inorganic phosphate (Pi) is cleaved off, yielding ADP (adenosine diphosphate).
• The stored chemical energy comes from the negative charges repelling each other.

How ATP is Formed

• Substrate-level phosphorylation: Transfer of phosphate group directly from a substrate molecule to ADP (e.g., glycolysis).
• Oxidative phosphorylation (chemiosmosis): ATP synthase utilizes the H+ gradient across a membrane.

Redox Potential & Electron Transport Chain

• Redox potential reflects the relative tendency of substances to gain or lose electrons.
• Relocating electrons from a substance with low electronegativity (e.g., a sugar) to a substance with high electronegativity (e.g., oxygen) releases energy.

NADH

• NADH (nicotinamide adenine dinucleotide) acts as an electron carrier.
• Many NADH molecules are produced during food breakdown.

Energy Harvest (Chemiosmosis)

• Energy is stored in a transmembrane proton (H+) gradient.
• This gradient is used to produce ATP.
• Movement of H+ ions across a membrane is associated with electron transport.

Energy Harvest: From Electrons to ATP

• NADH is used in redox reactions to transfer protons with electrons during the electron transport chain.
• The proton gradient powers ATP production.

Cellular Respiration

• Cellular respiration is a metabolic process to obtain energy by oxidizing nutrients and releasing waste.
• It involves pathways concerned with energy metabolism and proceeds across cellular compartments.
• It involves three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation.

Glycolysis

• Glycolysis is the breakdown of glucose into pyruvate.
• It occurs in the cytoplasm and yields two ATP.
• It produces NADH, an electron carrier.

Preparing Pyruvate for Citric Acid Cycle

• Occurs in the mitochondrion.
• It produces Acetyl CoA, releasing CO2 and generating NADH.

Citric Acid Cycle

• Also called the TCA (tricarboxylic acid) cycle, or the Krebs cycle.
• It is a cyclical set of reactions in the mitochondrion.
• It uses Acetyl CoA and produces NADH, FADH2, and ATP (or GTP).

Oxidative Phosphorylation

• Occurs in the inner mitochondrial membrane and generates a substantial number of ATP using an electron transport chain.
• Chemiosmosis occurs to establish the H+ proton gradient

Electron Transport Chain & ATP Synthase

• The electron transport chain utilizes electrons carried by NADH and FADH2 to generate an electrochemical proton (H+) gradient across a membrane.
• ATP synthase is the enzyme that produces ATP using the potential energy stored from the H+ gradient.

Fermentation

• A metabolic process to produce ATP in the absence of oxygen.
• Types include alcohol and lactic acid fermentation and yield only two ATP per glucose molecule.

Overall Cellular Respiration

• Energy balance involves oxidative phosphorylation producing substantially more ATP per glucose molecule than the overall energy gained from fermentation in the lack of oxygen.