AP bio midterm 2

Solutions and Transport Mechanisms

  • Types of Solutions:

    • Hypotonic Solution: Less solute, more free water; water moves into cells.

    • Hypertonic Solution: More solute, leading to water moving out and cellular dehydration (e.g., using salt water for gargling).

    • Isotonic Solution: Equal solute concentration, no net movement of water.

  • Types of Transport:

    • Passive Transport: No energy (ATP) needed; includes osmosis and diffusion.

      • Osmosis: Movement of water across a semipermeable membrane.

    • Active Transport: Requires energy (ATP) to move substances against the concentration gradient (low to high).

      • Analogous to pushing a ball up a hill.

  • Facilitated Transport: A subset of passive transport using protein channels (e.g., aquaporins).

Enzymes and Chemical Reactions

  • Key Processes:

    • Dehydration Synthesis: Building larger molecules with the removal of water.

    • Hydrolysis: Breaking down molecules with the addition of water.

  • Reaction Mechanisms:

    • Endergonic Reactions: Require energy, not spontaneous.

    • Exergonic Reactions: Release energy, spontaneous (e.g., hydrolysis of ATP).

Mitochondria and Cellular Respiration

  • Glycolysis Overview:

    • Breakdown of glucose into pyruvic acid, produces a net gain of 2 ATP.

    • If oxygen is absent, results in lactic acid formation in animals or alcohol in yeast (fermentation).

  • Krebs Cycle and Electron Transport Chain (ETC):

    • Pyruvic acid enters mitochondria, where it undergoes oxidation, generating NADH and FADH2.

    • Final Electron Acceptor: Oxygen in aerobic respiration.

    • Creation of proton gradient in ETC crucial for ATP synthase to produce ATP (oxidative phosphorylation).

Photosynthesis Overview

  • Light Reactions:

    • Occur in thylakoid membranes; utilize light energy to create a proton gradient via electron transport chain.

    • NADP+ is the final electron acceptor, becoming NADPH.

  • Calvin Cycle:

    • Uses ATP and NADPH to convert CO2 into glucose.

    • Involves carbon fixation and production of glyceraldehyde-3-phosphate (G3P).

Cell Communication

  • Ligands: Molecules that bind to receptors to initiate cell signaling pathways. Examples include epinephrine (a protein ligand).

  • G Protein-Coupled Receptor Pathway:

    • Ligand binds, activating a G protein, which then activates adenylyl cyclase to produce cyclic AMP (secondary messenger).

Important Concepts for the Exam

  • Surface Area to Volume Ratio: Affects exchange rates in cells; larger ratios are more efficient for diffusion.

  • Mutation Effects on Proteins: Changes in nucleotide sequences affect amino acid sequences and protein structure/function.

  • Graphs and Data Interpretation Skills: Focus on correct labeling of axes, understanding error bars, and calculation for bar graphs.

  • Enzyme Function and Kinetics: Understand factors affecting enzyme activity, including temperature, pH, and substrate concentration.

    • Free Response Questions (FRQs) include topics on active transport and mitochondria analysis.

Unit 3: Key Concepts

ATP and Energy Reactions

  • ATP Hydrolysis: It is highly exergonic, releasing energy to drive cellular processes.

  • Coupled Reactions: Endergonic reactions do not occur spontaneously and always need an input of energy ( +G), with ATP often providing that energy.

Enzymes and Substrates

  • Active Site Specificity: Enzymes are specific due to the shape and charge of their active sites.

    • Shape: The configuration of the active site is complementary to the substrate, enabling effective binding.

    • Charge: The active site has opposite charges to attract substrates, facilitating the reaction process.

  • Denaturation: Changes in temperature or pH can alter the amino acid sequence, leading to changes in shape and charge, resulting in potential loss of enzyme function.

Cofactors and Enzyme Regulation

  • Cofactors: Non-protein molecules that assist enzymes in catalyzing reactions, often required for the proper functioning of the enzyme.

  • Allosteric Regulation: Enzyme activity can be affected by the binding of effectors, with pH and temperature influencing their activity.

Glycolysis and Cellular Respiration

  • Glycolysis: Occurs in the cytosol, breaking down glucose to produce pyruvate, yielding a net gain of 2 ATP.

  • Anaerobic Respiration (Fermentation): Can lead to the formation of lactic acid in animals or alcohol in yeast, allowing ATP production without oxygen.

  • Aerobic Cellular Respiration: Takes place in the mitochondria and includes:

    • Matrix: Site of Krebs Cycle, yielding ATP through substrate-level phosphorylation.

    • NADH & FADH2: Electron carriers move to the inner mitochondrial membrane to participate in the electron transport chain (ETC).

    • ETC: Establishes a proton gradient; electrons flow through the chain to power proton movement. Oxygen serves as the final electron acceptor.

    • Chemiosmosis and ATP Synthase: ATP is produced during oxidative phosphorylation; the end products are 36 ATP molecules and water.

Photosynthesis Overview

  • Location: Occurs in chloroplasts, involving two main stages:

    • Light Reactions:

      • Occur in thylakoid membranes where chlorophyll absorbs light energy and drives the ETC, creating a proton gradient. The final electron acceptor is NADP+, forming NADPH. ATP is also produced here.

    • Light Independent Reactions (Calvin Cycle): Occur in the stroma, involving carbon fixation, reduction, and regeneration of RuBP. End products are organic compounds and CO2 from the Calvin Cycle.

Proton Gradient Creation in ETC

  • The proton gradient in both chloroplasts and mitochondria is created by the active transport of protons out of the mitochondrial matrix or thylakoid lumen, facilitated by the energy released from electron transport through the chain.

Unit 4: Key Concepts

Cell Communication

  • Plasmodesmata: Channels between plant cells that allow for intercellular communication and transport of materials.

  • Cell Signaling Pathways:

    • Reception: The initial detection of a signal molecule by its receptor.

    • Transduction: The process of converting the signal into a functional response within the cell.

    • Response: The final outcome of the signaling cascade, leading to cellular changes.

  • Reception Differences: Lipid ligands typically pass through the membrane and bind intracellularly, while protein ligands bind to receptors on the cell surface.

  • Function of cAMP: Acts as a secondary messenger in G-protein-coupled receptor pathways, amplifying the signal transduced to elicit a response.

  • Feedback Mechanisms: Regulatory mechanisms that determine whether signaling continues or is suppressed based on the output.

  • Phases of Mitosis: Understand the stages of mitosis including prophase, metaphase, anaphase, and telophase, focusing on the events that occur in each stage and their significance in cell division.

Phases of Mitosis

  1. Prophase:

    • Chromatin condenses into distinct chromosomes, each consisting of two sister chromatids joined at the centromere.

    • The nucleolus disappears and the nuclear envelope breaks down.

    • The mitotic spindle forms, with spindle fibers extending from the centrosomes to the centromeres of chromosomes.

  2. Metaphase:

    • Chromosomes align along the metaphase plate in the center of the cell, ensuring that each sister chromatid faces opposite poles of the spindle.

    • Spindle fibers attach to the centromeres of the chromosomes, anchoring them in place.

  3. Anaphase:

    • The sister chromatids are pulled apart at the centromere and move toward opposite poles of the cell.

    • The cell elongates as the spindle fibers shorten, separating and guiding the chromatids to the poles.

  4. Telophase:

    • Chromatids reach the poles and begin to de-condense back into chromatin.

    • The nuclear envelope reforms around each set of chromosomes, resulting in two distinct nuclei.

    • The nucleolus reappears in each nucleus.

  5. Cytokinesis (not a phase of mitosis, but often occurs concurrently):

    • The cytoplasm divides, resulting in two separate daughter cells, each with a nucleus and complete set of chromosomes.

    • In animal cells, this occurs through the formation of a cleavage furrow that pinches the cell in two; in plant cells, a cell plate forms between the two new nuclei to divide the cell.

Significance of Mitosis:

  • Mitosis is crucial for growth, tissue repair, and asexual reproduction, allowing for the production of genetically identical cells from a single parent cell.