Cellular Energetics, Metabolism, and Photosynthesis: Study Guide

Study Guide - Smart Notes

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Cellular Energetics and Metabolism

Potential Energy and Kinetic Energy

Energy exists in two main forms: potential and kinetic. Understanding these forms is essential for studying biological processes.

Potential Energy: Stored energy due to position or structure (e.g., chemical bonds in glucose).
Kinetic Energy: Energy of motion (e.g., movement of molecules, muscle contraction).
Example: ATP hydrolysis releases potential energy, which is converted to kinetic energy for cellular work.

Exergonic and Endergonic Reactions

Chemical reactions in cells are classified by their energy changes.

Exergonic Reactions: Release energy; products have less free energy than reactants. Spontaneous.
Endergonic Reactions: Require energy input; products have more free energy than reactants. Non-spontaneous.
Equation:
Example: Cellular respiration is exergonic; photosynthesis is endergonic.

Use of Heat in Cell Function

Heat is a byproduct of metabolic reactions and helps maintain body temperature in homeothermic organisms.
Excess heat can denature proteins and disrupt cell function.

Enzyme Function

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

Active Site: Region where substrate binds and reaction occurs.
Specificity: Each enzyme acts on specific substrates.
Example: Sucrase catalyzes the hydrolysis of sucrose.

Non-Competitive Inhibitor

Binds to an enzyme at a site other than the active site (allosteric site).
Changes enzyme shape, reducing its activity.

Feedback Inhibition

End product of a metabolic pathway inhibits an earlier step, preventing overproduction.
Example: Isoleucine inhibits threonine deaminase in amino acid synthesis.

Metabolic Pathways

Series of enzyme-catalyzed reactions transforming a starting molecule to a product.
Can be catabolic (breakdown, e.g., glycolysis) or anabolic (synthesis, e.g., Calvin cycle).

Oxidation-Reduction (Redox) Reactions

Oxidation: Loss of electrons.
Reduction: Gain of electrons.
Essential for energy transfer in cellular respiration and photosynthesis.

Scaffolding Proteins

Organize groups of interacting signaling proteins, increasing efficiency of signal transduction.

Formation of NADH

NAD+ is reduced to NADH during glycolysis and the Krebs cycle, capturing high-energy electrons.
Equation:

Glycolysis Location

Occurs in the cytoplasm of both prokaryotic and eukaryotic cells.

ATP Made During Glycolysis

Net gain of 2 ATP molecules per glucose via substrate-level phosphorylation.

Role of Oxygen in Cellular Respiration

Acts as the final electron acceptor in the electron transport chain, forming water.

Final Electron Acceptor of the Electron Transport Chain

Molecular oxygen (O2).

End Products of Glycolysis

2 Pyruvate, 2 ATP (net), 2 NADH, and 2 H2O per glucose molecule.

Fermentation and Cellular Respiration

Fermentation: Anaerobic process; regenerates NAD+ by reducing pyruvate.
Cellular Respiration: Aerobic; complete oxidation of glucose to CO2 and H2O.

Movement of H+ During the Electron Transport Chain

H+ ions are pumped from the mitochondrial matrix to the intermembrane space, creating a proton gradient.

Number of ATP Produced from Breakdown of Glucose in Krebs Cycle

2 ATP per glucose via substrate-level phosphorylation in the Krebs cycle.
Most ATP is produced later via oxidative phosphorylation.

Membrane Receptors That Attach Phosphates to Specific Amino Acids

Receptor tyrosine kinases (RTKs) phosphorylate tyrosine residues on target proteins.

Synthesis of ATP

Occurs via substrate-level phosphorylation (glycolysis, Krebs cycle) and oxidative phosphorylation (electron transport chain and chemiosmosis).

Proteins of the Electron Transport Chain Location

Embedded in the inner mitochondrial membrane.

Types of Membrane Receptors

G protein-coupled receptors (GPCRs)
Receptor tyrosine kinases (RTKs)
Ion channel receptors

Second Messenger

Small molecules (e.g., cAMP, Ca2+) that relay signals from receptors to target molecules inside the cell.

Role of pH Gradient in Cellular Respiration

Proton (H+) gradient across the inner mitochondrial membrane drives ATP synthesis via ATP synthase.

ATP Synthase Location

Inner mitochondrial membrane (cellular respiration)
Thylakoid membrane (photosynthesis)

Substrate-Level Phosphorylation

Direct transfer of a phosphate group to ADP from a phosphorylated intermediate.
Occurs in glycolysis and the Krebs cycle.

Photosynthesis

Calvin Cycle Location

Stroma of the chloroplast.

Phosphatase and Protein Kinase

Protein Kinase: Enzyme that adds phosphate groups to proteins (phosphorylation).
Phosphatase: Enzyme that removes phosphate groups from proteins (dephosphorylation).

Chlorophylls Location

Embedded in the thylakoid membranes of chloroplasts.

Role of Visible Light in Photosynthesis

Provides energy to excite electrons in chlorophyll, initiating the light reactions.

Absorption Spectrum and Action Spectrum

Absorption Spectrum: Wavelengths of light absorbed by pigments.
Action Spectrum: Wavelengths of light most effective for photosynthesis (measured by O2 production or CO2 consumption).

Other Pigments Absorbing Light

Carotenoids, xanthophylls, and phycobilins absorb light and transfer energy to chlorophyll.

Most Effective Wavelength in Driving Photosynthesis

Red (around 680 nm) and blue (around 450 nm) wavelengths are most effective.

Importance of Hydrogen Ion [H+] Gradient in Photosynthesis

Drives ATP synthesis as H+ flows through ATP synthase from the thylakoid lumen to the stroma.

ATP Synthase Complexes Location

Thylakoid membrane of chloroplasts.

Electron Transport Chain Location in Plant Cells

Thylakoid membrane (photosynthesis)
Inner mitochondrial membrane (cellular respiration)

End Products of Light Reaction in Photosynthesis

ATP, NADPH, and O2

Primary Function of the Calvin Cycle

Fixes atmospheric CO2 into organic molecules (G3P), which can be used to synthesize glucose and other carbohydrates.

CAM Plants

Open stomata at night to minimize water loss; fix CO2 into organic acids, which are used during the day for photosynthesis.
Example: Succulents like Crassulaceae.

C4 Plants

Fix CO2 into four-carbon compounds in mesophyll cells; release CO2 in bundle-sheath cells for the Calvin cycle, reducing photorespiration.
Example: Corn (Zea mays), sugarcane.

Fermentation Pathways

Alcoholic Fermentation

Pyruvate is converted to ethanol and CO2; regenerates NAD+.
Equation:
Example: Yeast fermentation in brewing and baking.

Lactic Acid Fermentation

Pyruvate is reduced to lactic acid; regenerates NAD+.
Equation:
Example: Muscle cells during intense exercise, some bacteria (yogurt production).

Osmosis and Tonicity

Isotonic, Hypertonic, Hypotonic Solutions

Isotonic: Solute concentration equal inside and outside the cell; no net water movement.
Hypertonic: Higher solute concentration outside; cell loses water and shrinks.
Hypotonic: Lower solute concentration outside; cell gains water and may burst.

Autotrophs and Heterotrophs

Autotrophs: Organisms that produce their own food from inorganic sources (e.g., plants via photosynthesis).
Heterotrophs: Obtain energy by consuming organic molecules produced by other organisms (e.g., animals, fungi).

Summary Table: Key Processes and Locations

Process	Main Location	Key Products
Glycolysis	Cytoplasm	2 Pyruvate, 2 ATP, 2 NADH
Krebs Cycle	Mitochondrial Matrix	CO2, NADH, FADH2, 2 ATP
Electron Transport Chain	Inner Mitochondrial Membrane	ATP, H2O
Light Reactions	Thylakoid Membrane	ATP, NADPH, O2
Calvin Cycle	Chloroplast Stroma	G3P (sugar)
Alcoholic Fermentation	Cytoplasm	Ethanol, CO2, ATP
Lactic Acid Fermentation	Cytoplasm	Lactate, ATP

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard introductory biology textbooks.