General Biology Exam Review: Cell Structure, Metabolism, and Energy

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

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

• Prokaryotic cells lack a nucleus and membrane-bound organelles. Their genetic material is found in the nucleoid region.

• Eukaryotic cells possess a nucleus and various membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

• Structures present in plant cells (a type of eukaryotic cell) include the cell wall, chloroplasts, and central vacuole.

Example: The cell wall is present in plant cells but not in animal cells.

Identifying Cell Organelles

Cell organelles have distinct shapes and functions. Diagrams often label organelles such as:

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplast: Site of photosynthesis in plant cells.

• Vacuole: Storage of water and other substances.

Example: In a labeled diagram, the nucleus is typically centrally located, mitochondria are oval-shaped, and chloroplasts are green and disc-shaped.

Cellular Respiration and Metabolism

Overview of Cellular Respiration

Cellular respiration is the process by which cells convert glucose and oxygen into ATP, the energy currency of the cell.

• Occurs in three main stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), and Electron Transport Chain.

• Produces ATP, NADH, and FADH2 as energy carriers.

• Final electron acceptor in aerobic respiration is oxygen.

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Glycolysis and Krebs Cycle

Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate, producing ATP and NADH. The Krebs Cycle occurs in the mitochondria and generates more NADH and FADH2.

• Glycolysis: Converts glucose to pyruvate, net gain of 2 ATP and 2 NADH per glucose.

• Krebs Cycle: Each turn produces 3 NADH, 1 FADH2, and 1 ATP (or GTP).

Example: Pyruvate is converted to Acetyl-CoA before entering the Krebs Cycle.

Electron Transport Chain (ETC) and ATP Synthesis

The ETC is located in the inner mitochondrial membrane and is responsible for the majority of ATP production via oxidative phosphorylation.

• Electrons from NADH and FADH2 are transferred through protein complexes, creating a proton gradient.

• ATP synthase uses the proton gradient to synthesize ATP from ADP and inorganic phosphate.

• Oxygen acts as the final electron acceptor, forming water.

Equation:

$\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

Energy Yield of Cellular Respiration

The total ATP yield from one molecule of glucose during aerobic respiration is typically 30-32 ATP.

• Glycolysis: 2 ATP

• Krebs Cycle: 2 ATP

• ETC: ~26-28 ATP

Example: NADH and FADH2 produced in earlier steps donate electrons to the ETC, resulting in ATP synthesis.

Enzymes and Reaction Energetics

Enzyme Function and Activation Energy

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

• Activation energy (Ea): The energy required to initiate a chemical reaction.

• Enzymes do not change the overall free energy change ($\Delta G$) of a reaction.

• Enzyme activity can be affected by temperature, pH, and substrate concentration.

Equation:

$\Delta G = \text{G}_{\text{products}} - \text{G}_{\text{reactants}}$

Reaction Progress and Energy Diagrams

Energy diagrams illustrate the changes in free energy during a reaction, showing the activation energy and the effect of enzymes.

• Enzymes lower the peak of the activation energy barrier.

• The difference between reactants and products is the free energy change ($\Delta G$).

Example: In a diagram, the catalyzed reaction has a lower activation energy than the uncatalyzed reaction.

Photosynthesis and Energy Conversion

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

• Occurs in the chloroplasts of plant cells.

• Consists of light-dependent reactions and the Calvin Cycle (light-independent reactions).

• Produces oxygen as a byproduct.

Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Light Absorption and Pigments

Photosynthetic pigments such as chlorophyll absorb light at specific wavelengths, driving the light-dependent reactions.

• Chlorophyll a and chlorophyll b absorb light most efficiently in the blue and red regions of the spectrum.

• Action spectra show the rate of photosynthesis at different wavelengths.

Example: The rate of photosynthesis is highest at wavelengths where chlorophyll absorbs most strongly.

ATP Production and Energy Transfer

ATP Synthase and Chemiosmosis

ATP synthase is an enzyme complex that synthesizes ATP using the energy from a proton gradient across a membrane.

• Protons flow through ATP synthase, driving the phosphorylation of ADP to ATP.

• This process is called chemiosmosis.

Equation:

$\text{ADP} + \text{P}_i \xrightarrow{\text{ATP synthase}} \text{ATP}$

Tables

Comparison of Cellular Respiration Stages

Stage	Location	Main Products
Glycolysis	Cytoplasm	2 ATP, 2 NADH, 2 Pyruvate
Krebs Cycle	Mitochondrial Matrix	2 ATP, 6 NADH, 2 FADH2
Electron Transport Chain	Inner Mitochondrial Membrane	~26-28 ATP, H2O

Photosynthetic Pigments and Absorption

Pigment	Absorption Peaks (nm)	Role
Chlorophyll a	~430, ~662	Main pigment in photosynthesis
Chlorophyll b	~453, ~642	Accessory pigment
Carotenoids	~400-500	Protects against photooxidative damage

Additional info: Some explanations and table entries were inferred to provide complete academic context for exam preparation.