Cell Structure, Bioenergetics, and Cellular Respiration: Key Concepts and Processes

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 membrane-bound nucleus and organelles. Their genetic material is found in a nucleoid region. Examples include Bacteria and Archaea.

• Eukaryotic cells have a true nucleus enclosed by a nuclear membrane and possess various membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Examples include plants, animals, fungi, and protists.

Example: Escherichia coli is a prokaryote; Homo sapiens cells are eukaryotic.

Structure and Function of Organelles

Organelles are specialized structures within eukaryotic cells that perform distinct functions necessary for cellular life.

• Nucleus: Stores genetic information and controls cellular 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.

Organelle Function and Cellular Activity

• Each organelle contributes to the overall function and survival of the cell.

• For example, mitochondria provide energy for cellular processes, while the nucleus regulates gene expression.

Endosymbiosis Theory

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

• Evidence includes the presence of their own DNA, double membranes, and similarities to certain bacteria.

Chapter 8: Bioenergetics and Enzyme Function

Potential vs. Kinetic Energy in Chemical Reactions

Energy exists in two main forms: potential (stored) and kinetic (motion). In chemical reactions, potential energy is stored in chemical bonds, while kinetic energy is the energy of moving particles.

• Example: Glucose contains potential energy in its bonds, which is released as kinetic energy during cellular respiration.

Endergonic vs. Exergonic Reactions and Gibbs Free Energy

Reactions are classified based on energy changes:

• Endergonic reactions require energy input (ΔG > 0).

• Exergonic reactions release energy (ΔG < 0).

Gibbs Free Energy Equation:

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

• Where $\Delta G$ is the change in free energy, $\Delta H$ is the change in enthalpy, $T$ is temperature in Kelvin, and $\Delta S$ is the change in entropy.

Enzyme Catalysis and Activation Energy

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

• They do not change the overall ΔG of the reaction.

• Enzymes are specific to their substrates.

Factors Affecting Enzyme Function

• Temperature: Each enzyme has an optimal temperature range.

• pH: Enzymes function best at specific pH levels.

• Substrate concentration: Higher concentrations can increase reaction rate up to a saturation point.

Chapter 9: Cellular Respiration

Stages of Cellular Respiration

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

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate.

• Pyruvate oxidation and Citric Acid Cycle (Krebs Cycle): Occur in the mitochondria; further oxidize pyruvate and generate electron carriers.

• Electron Transport Chain (ETC) and Oxidative Phosphorylation: Use electrons from carriers to produce ATP.

Inputs and Outputs of Each Stage

• Glycolysis: Input: Glucose; Output: 2 Pyruvate, 2 ATP, 2 NADH

• Citric Acid Cycle: Input: Acetyl-CoA; Output: CO2, NADH, FADH2, ATP

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

Glycolysis Regulation

• Regulated by feedback inhibition, especially at the enzyme phosphofructokinase.

Citric Acid Cycle Key Role

• Completes the oxidation of glucose derivatives and provides electron carriers for the ETC.

Electron Transport Chain and Oxidative Phosphorylation

• Electrons are transferred through protein complexes, creating a proton gradient used to synthesize ATP.

• Oxidative phosphorylation is the process of ATP formation using the energy from the ETC.

Aerobic vs. Anaerobic Respiration

• Aerobic respiration uses oxygen as the final electron acceptor; produces more ATP.

• Anaerobic respiration uses other molecules as electron acceptors; less efficient.

Fermentation

• Occurs when oxygen is absent; regenerates NAD+ for glycolysis.

• Produces lactic acid (animals) or ethanol (yeast).

Chapter 10: Photosynthesis

Inputs and Outputs of Photosynthesis

Photosynthesis converts light energy into chemical energy in plants, algae, and some bacteria.

• Inputs: CO2, H2O, light energy

• Outputs: Glucose, O2

Pigments and Light Absorption

• Chlorophyll is the main pigment; absorbs light most efficiently in the blue and red wavelengths.

• Accessory pigments expand the range of light absorption.

Z-Scheme and Electron Transport

• The Z-scheme describes the flow of electrons from water to NADP+ via photosystems II and I, generating ATP and NADPH.

Light-Dependent Reactions and Calvin Cycle

• Light-dependent reactions: Occur in the thylakoid membranes; produce ATP and NADPH.

• Calvin cycle: Occurs in the stroma; uses ATP and NADPH to fix CO2 into sugars.

Phases of the Calvin Cycle

• Fixation: CO2 is attached to RuBP by the enzyme Rubisco.

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

• Regeneration: RuBP is regenerated for the cycle to continue.

Photorespiration and Adaptations

• Photorespiration occurs when Rubisco fixes O2 instead of CO2, reducing photosynthetic efficiency.

• C4 and CAM plants have adaptations to minimize photorespiration by spatially or temporally separating carbon fixation from the Calvin cycle.

Process	Location	Main Inputs	Main Outputs
Glycolysis	Cytoplasm	Glucose	Pyruvate, ATP, NADH
Citric Acid Cycle	Mitochondrial matrix	Acetyl-CoA	CO2, NADH, FADH2, ATP
Electron Transport Chain	Inner mitochondrial membrane	NADH, FADH2, O2	ATP, H2O
Light-dependent reactions	Thylakoid membrane	Light, H2O	ATP, NADPH, O2
Calvin Cycle	Stroma	CO2, ATP, NADPH	Glucose (G3P)