General Biology: Cell Structure, Metabolism, and Photosynthesis Study Guide

Chapter 7: Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

Cells are the basic units of life and can be classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles. Their genetic material is located in the nucleoid region. Examples include Bacteria and Archaea.

• Eukaryotic cells: Possess a true nucleus and various membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Examples include Animal, Plant, Fungi, and Protist cells.

• Key differences: Size, complexity, and compartmentalization.

Structure and Function of Organelles

Organelles perform specialized functions that contribute to cellular activity and survival.

• Nucleus: Stores genetic material and coordinates cell activities.

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breaking down macromolecules.

Organelle Function and Cellular Activity

Each organelle contributes to the overall function and efficiency of the cell.

• Energy production: Mitochondria and chloroplasts generate ATP for cellular processes.

• Protein synthesis: Ribosomes, ER, and Golgi apparatus work together to produce and process proteins.

• Waste removal: Lysosomes degrade and recycle cellular waste.

Endosymbiosis Theory

The endosymbiosis theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, circular DNA, and similarities to prokaryotic ribosomes.

• Significance: Explains the evolutionary relationship between prokaryotes and eukaryotic organelles.

Chapter 8: Energy and Enzymes

Potential vs. Kinetic Energy in Chemical Reactions

Energy exists in different forms and is essential for driving chemical reactions in cells.

• Potential energy: Stored energy due to position or structure (e.g., chemical bonds).

• Kinetic energy: Energy of motion (e.g., movement of molecules).

• Application: Chemical reactions convert potential energy in bonds to kinetic energy as heat or work.

Endergonic vs. Exergonic Reactions and Gibbs Free Energy

Reactions are classified based on energy changes, which can be quantified using Gibbs free energy ($\Delta G$).

• Endergonic reactions: Require energy input; $\Delta G > 0$.

• Exergonic reactions: Release energy; $\Delta G < 0$.

• Gibbs free energy equation:

$\Delta G = \Delta H - T\Delta S$

• Where: $\Delta H$ = change in enthalpy, $T$ = temperature (Kelvin), $\Delta S$ = change in entropy.

Enzyme Catalysis and Activation Energy

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

• Activation energy ($E_a$): The minimum energy required to initiate a reaction.

• Enzyme function: Stabilizes the transition state, reducing $E_a$ and increasing reaction rate.

Factors Affecting Enzyme Function

Enzyme activity is influenced by environmental conditions.

• pH: Each enzyme has an optimal pH range.

• Temperature: Higher temperatures increase activity up to a point, but extreme heat can denature enzymes.

• Other factors: Substrate concentration, inhibitors, and cofactors.

Chapter 9: Cellular Respiration

Stages of Cellular Respiration

Cellular respiration is a multi-step process that converts glucose into ATP.

• Four stages:

  1. Glycolysis

  2. Pyruvate oxidation

  3. Citric acid cycle (Krebs cycle)

  4. Electron transport chain (ETC) and oxidative phosphorylation

Inputs and Outputs of Each Stage

Each stage has specific reactants and products.

• Glycolysis: Input: Glucose; Output: Pyruvate, ATP, NADH

• Pyruvate oxidation: Input: Pyruvate; Output: Acetyl-CoA, NADH, CO2

• Citric acid cycle: Input: Acetyl-CoA; Output: CO2, ATP, NADH, FADH2

• ETC and oxidative phosphorylation: Input: NADH, FADH2, O2; Output: ATP, H2O

Glycolysis: Phases and Regulation

Glycolysis consists of two phases and is tightly regulated.

• Energy investment phase: Consumes ATP to phosphorylate glucose.

• Energy payoff phase: Produces ATP and NADH.

• Regulation: Key enzymes (e.g., phosphofructokinase) control the rate of glycolysis.

Citric Acid Cycle

The citric acid cycle completes the oxidation of glucose derivatives, generating electron carriers for the ETC.

• Key role: Produces NADH and FADH2 for ATP synthesis.

Electron Transport Chain (ETC) and Oxidative Phosphorylation

The ETC uses electron carriers to create a proton gradient, driving ATP synthesis.

• Relationship: Electrons from NADH and FADH2 pass through protein complexes, pumping protons across the inner mitochondrial membrane.

• Oxidative phosphorylation: ATP synthase uses the proton gradient to generate ATP.

Aerobic vs. Anaerobic Respiration and Fermentation

Cells can generate energy with or without oxygen.

• Aerobic respiration: Requires oxygen; produces more ATP.

• Anaerobic respiration: Does not require oxygen; less efficient.

• Fermentation: Occurs when oxygen is absent; regenerates NAD+ and produces lactate or ethanol.

Chapter 10: Photosynthesis

Inputs and Outputs of Photosynthesis

Photosynthesis converts light energy into chemical energy in plants, occurring in two major stages within the chloroplast.

• Inputs: CO2, H2O, light energy

• Outputs: Glucose, O2

• Stages: Light-dependent reactions (thylakoid membrane) and Calvin cycle (stroma)

Light Absorption and Pigments

Pigments such as chlorophyll absorb light energy, which is used to drive photosynthesis.

• Chlorophyll: Absorbs blue and red light; reflects green light.

• Absorption spectrum: Range of wavelengths absorbed by pigments.

Z-Scheme and Electron Transport in Photosynthesis

The Z-scheme describes the flow of electrons during the light-dependent reactions.

• ATP generation: Via a proton gradient across the thylakoid membrane.

• NADPH generation: Via electron transport from water to NADP+.

Connecting Light-Dependent and Calvin Cycle Reactions

ATP and NADPH produced in the light-dependent reactions are used in the Calvin cycle to fix carbon.

• Inputs to Calvin cycle: ATP, NADPH, CO2

• Outputs: Glucose, ADP, NADP+

Calvin Cycle: Phases and Enzyme Function

The Calvin cycle consists of three phases and is catalyzed by the enzyme RuBisCO.

• Phases:

  1. Fixation: CO2 is attached to RuBP by RuBisCO.

  2. Reduction: ATP and NADPH are used to convert 3-PGA to G3P.

  3. Regeneration: RuBP is regenerated for the next cycle.

• RuBisCO: The key enzyme for carbon fixation.

C4 and CAM Plant Adaptations

C4 and CAM plants have evolved mechanisms to minimize photorespiration by separating carbon fixation from the Calvin cycle.

• C4 plants: Spatial separation; CO2 is fixed in mesophyll cells and Calvin cycle occurs in bundle sheath cells.

• CAM plants: Temporal separation; CO2 is fixed at night and Calvin cycle occurs during the day.

Table: Comparison of C3, C4, and CAM Photosynthesis

Type	CO2 Fixation	Photorespiration	Adaptation
C3	Direct (Calvin cycle)	High	None
C4	Spatial separation	Low	Hot, dry climates
CAM	Temporal separation	Low	Arid environments

Example: Corn is a C4 plant; cactus is a CAM plant.