exam_2_study_guide_

Chapter 7: Prokaryotic and Eukaryotic Cells

Prokaryotic Cells

• Structure: Lack a nucleus, single cellular structure made of DNA and proteins.

• Organelles: Rarely contains membrane-bound organelles.

• Genetics: Contains genes (DNA segments coding for proteins) and plasmids (small circular DNA).

• Cellular Components:

  • Cytoplasm: All components inside the cell.

  • Ribosomes: Protein manufacturing centers, translating RNA into proteins.

  • Cytoskeleton: Made of protein filaments, maintains cell structure.

  • Cell Membrane/Cell Wall: Protects and supports the cell.

Eukaryotic Cells

• Structure: Contains a nucleus and is generally larger than prokaryotic cells.

• Organelles: Compartmentalized cytoplasm with various organelles enhancing efficiency.

• Key Components:

  • Nucleus Envelope: Double membrane structure with four lipid layers.

  • Nucleolus: Ribosomal RNA synthesis and ribosome assembly.

  • Ribosomes: Free and bound forms for cytosolic and secreted proteins respectively.

  • Rough ER: Involved in protein synthesis.

  • Smooth ER: Involved in synthesis of macronutrients.

  • Lysosomes: Contains enzymes to break down macromolecules; optimized at pH 5.

  • Vacuoles: Storage centers in plants and fungi.

  • Peroxisomes: Involved in detoxification and oxidation/reduction reactions.

  • Mitochondria: ATP production, contains its own DNA and ribosomes.

  • Chloroplasts: Site of photosynthesis, also has its own DNA and ribosomes.

  • Cytoskeleton: Composed of three filaments (microtubules, microfilaments, intermediate filaments).

Comparison: Prokaryotic vs. Eukaryotic Cells

• Size: Eukaryotic cells are larger and contain a nucleus.

• Cytoplasm: Organized into membrane-bound organelles in eukaryotic cells.

• Efficiency: Multiple organelles increase the efficiency of chemical reactions.

Comparison: Plant Cells vs. Animal Cells

• Plant Cells: Contain cellulose cell walls, chloroplasts, and large vacuoles.

• Animal Cells: Contain centrioles and lysosomes; lack cell walls and chloroplasts.

Protein Import and Export

Import into the Nucleus

• Regulated by nuclear pore complex (NPC).

• Proteins have a nuclear localization sequence (NLS) at the C-terminus.

Export from the Cell

• Synthesized in ribosomes, enter Rough ER, packaged into vesicles, sorted in Golgi, and secreted via plasma membrane.

Targeting to the ER

• ER signal sequence synthesized at N-terminus, binds to signal recognition particle (SRP) that directs it to receptors on the ER.

Sorting in the Golgi Apparatus

• Proteins have destination tags, transported by vesicle budding and membrane fusion.

Cell Junctions (Chapter 11)

• Tight Junctions: Water-tight seals between cells.

• Desmosomes: Strong adhesions anchoring the cytoskeleton for structural support.

• Gap Junctions: Protein channels allowing communication between adjacent cells, facilitating ion and small molecule passage.

• Plasmodesmata: Gaps in plant cell walls for communication without proteins.

Cell-Cell Signaling

Steps in Signal Transduction

1. Signal Reception: Binding of a signal molecule changes a receptor's activity.

2. Signal Transduction: Uses second messengers (e.g., cAMP) for intracellular signal transmission.

3. Signal Response: Triggers cellular actions like growth or metabolism changes.

4. Signal Deactivation: Rapid responses to deactivate signals; methods vary by type.

Types of Molecules in Cell Signaling

Lipid-Soluble Molecules

• Diffuse through the cell membrane, bind to cytosolic receptors, and affect transcription in the nucleus.

Lipid-Insoluble Molecules

• Bind to transmembrane receptors resulting in a signaling pathway without crossing the membrane.

Chemical Reactions and Energetics (Chapter 8)

Reaction Favorability

• Negative delta H: Products have less potential energy than reactants.

• Positive delta H: Products possess more potential energy.

Spontaneity of Reactions

• A reaction is spontaneous if delta H is negative and delta S is positive.

Factors Influencing Reaction Rates

• Affecting factors: Temperature and concentration.

Oxidation and Reduction

Definitions

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Oxidizing Agent: Substance that causes oxidation, typically oxygen unless a stronger agent (like fluorine) is present.

Enzyme-Catalyzed Reactions

1. Initiation: Substrates bind to enzyme.

2. Lowering Activation Energy: Enzymes stabilize transition states to lower energy barriers.

3. Release: Products released, enzyme returns to original form.

Cellular Respiration Inputs and Outputs (Chapter 9)

• Glycolysis: Inputs - glucose, outputs - 2 ATP, 2 NADH.

• Pyruvate Oxidation: Connects glycolysis to citric acid cycle.

• Citric Acid Cycle: Outputs include ATP, NADH, FADH2.

• Oxidative Phosphorylation: Major ATP production occurring in mitochondria.

• Fermentation: ATP production in absence of oxygen, regenerates NAD+.

Photosynthesis Inputs and Outputs

• Light Reactions: Inputs - water and light; Outputs - oxygen, ATP, NADPH.

• Calvin Cycle: Utilizes ATP and NADPH from light reactions to synthesize glucose.

Comparison of Photosystems

• Photosystem II: Occurs first; oxidizes water.

• Photosystem I: Received electrons from ETC to reduce NADP+ into NADPH.

Electron Flow in Photosynthesis

• Noncyclic Flow: Involves both photosystems, producing ATP and NADPH.

• Cyclic Flow: Generates additional ATP when NADPH production is not sufficient.

Rubisco and Photorespiration

• Rubisco converts CO2 into sugars; also erroneously binds O2, leading to inefficiency in plants.

C3, C4, and CAM Plants

• C3 Plants: Normal Calvin cycle.

• C4 Plants: CO2 fixed into 4C compounds, improving efficiency.

• CAM Plants: Fix CO2 at night and perform the Calvin cycle during the day.