Lecture Exam 3 Study Guide Flashcards
Catabolism and Anabolism
- Catabolism is the set of metabolic pathways that breaks down molecules into smaller units, releasing energy. Cellular respiration, which breaks down glucose in the presence of oxygen, is a catabolic pathway.
- Anabolism refers to metabolic pathways that construct molecules from smaller units, requiring energy. An example of anabolism is the synthesis of protein from amino acids.
Thermodynamics
Thermodynamics is the study of energy transformations.
The First Law of Thermodynamics
The first law of thermodynamics, also known as the principle of conservation of energy, states that the energy of the universe is constant. Energy cannot be created or destroyed, but it can be transferred or transformed.
The Second Law of Thermodynamics
The second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe. Entropy is a measure of disorder or randomness.
Entropy
- Entropy is the measure of disorder or randomness in a system. The second law of thermodynamics implies that entropy increases in the universe over time.
- Living cells inherently convert organized forms of energy into heat, a less ordered form of energy. Organisms replace ordered forms of matter and energy with less ordered forms.
- While organisms can create ordered structures from less ordered materials, the overall entropy of the universe still increases.
Open and Closed Systems
- A closed system is isolated from its surroundings, preventing the transfer of energy and matter. A thermos is an example of a closed system.
- An open system allows the transfer of energy and matter between the system and its surroundings. Organisms are open systems.
Equilibrium
Equilibrium is a state of maximum stability in a system. Free energy, a measure of a system’s instability, decreases as the system moves towards equilibrium. A process is spontaneous and can perform work only when moving toward equilibrium.
Exergonic and Endergonic Reactions
- An exergonic reaction releases free energy and proceeds spontaneously. Cellular respiration is an example of an exergonic reaction.
- An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous. Photosynthesis is an example of an endergonic reaction.
- Enzymes are catalysts that speed up metabolic reactions by lowering the activation energy (Ea) barrier. They do not change the free energy change (ΔG) of the reaction.
Redox Reactions
- Redox reactions, or oxidation-reduction reactions, involve the transfer of electrons between reactants.
- Oxidation is the loss of electrons, often associated with gaining oxygen or losing hydrogen.
- Reduction is the gain of electrons, often associated with losing oxygen or gaining hydrogen.
- The reducing agent is the electron donor, while the oxidizing agent is the electron acceptor.
Cellular Respiration Location
- Glycolysis occurs in the cytoplasm of the cell.
- The citric acid cycle takes place in the mitochondrial matrix.
- Oxidative phosphorylation, including the electron transport chain and chemiosmosis, occurs in the inner mitochondrial membrane.
Role of Oxygen in Cellular Respiration
Oxygen is the final electron acceptor in the electron transport chain during aerobic respiration. Oxygen’s role is crucial because it allows for the complete oxidation of glucose, maximizing ATP production. Without oxygen, only glycolysis can occur, and fermentation or anaerobic respiration must be used to regenerate NAD+ for continued ATP production.
Most ATP Production
Oxidative phosphorylation generates the most ATP, accounting for about 34 ATP molecules per glucose molecule.
ATP Production in Each Stage
- Glycolysis: 2 ATP molecules (net) are produced by substrate-level phosphorylation.
- Citric acid cycle: 2 ATP molecules are produced by substrate-level phosphorylation.
- Oxidative phosphorylation: Approximately 34 ATP molecules are produced by chemiosmosis.
Fermentation
- Fermentation is a metabolic process that occurs in the absence of oxygen. It involves glycolysis followed by reactions that regenerate NAD+, allowing glycolysis to continue.
- Fermentation produces only 2 ATP molecules per glucose molecule.
- Two common types of fermentation are alcohol fermentation and lactic acid fermentation.
Autotrophs
Autotrophs are organisms that can produce their own food from inorganic sources, such as carbon dioxide and water. They are the producers of the biosphere. Most plants are photoautotrophs, using sunlight to make organic molecules.
Heterotrophs
Heterotrophs are organisms that obtain their food by consuming other organisms. They are the consumers of the biosphere. Heterotrophs rely on autotrophs for food and oxygen.
Tracking Molecules in Cellular Respiration and Photosynthesis
You should be able to track the production of ATP, NADH, and FADH2, as well as the consumption and production of CO2 and H2O, in diagrams of glycolysis, the citric acid cycle, and oxidative phosphorylation.
Endergonic and Exergonic Reactions
Endergonic reactions require energy input, meaning ATP is consumed. Exergonic reactions release energy, meaning ATP is generated.
Kinase
A kinase is an enzyme that adds phosphate groups to molecules.
H+ Pumping and ATP Synthase Location in Mitochondria
- H+ ions are pumped from the mitochondrial matrix to the intermembrane space by the electron transport chain.
- ATP synthase is located in the inner mitochondrial membrane, allowing H+ ions to flow back into the matrix and drive ATP synthesis.
H+ Pumping and ATP Synthase Location in Chloroplasts
- H+ ions are pumped from the stroma into the thylakoid space by the electron transport chain.
- ATP synthase is located in the thylakoid membrane, allowing H+ ions to flow back into the stroma and drive ATP synthesis.
Light Reaction and Calvin Cycle Location
Light reactions occur in the thylakoid membranes of chloroplasts. The Calvin cycle takes place in the stroma of chloroplasts.
Light Reaction
Split H2O, releasing O2. Reduce NADP+ to NADPH. Generate ATP from ADP by photophosphorylation.
Calvin Cycle Products
Uses ATP and NADPH from light reactions to convert CO2 into the sugar glyceraldehyde-3-phosphate (G3P). Regenerates its starting material, ribulose bisphosphate (RuBP).
Pigment Reflection and Absorption
- Pigments are substances that absorb visible light. Different pigments absorb different wavelengths of light. Wavelengths that are not absorbed are reflected or transmitted, giving the pigment its color.
- Chlorophyll appears green because it reflects and transmits green light.
Function of Light Reaction
Capture light energy and convert it into the chemical energy of ATP and NADPH.
Function of Calvin Cycle
Uses ATP and NADPH from the light reactions to fix carbon dioxide into sugar.
Theodore Engelmann Experiment
In 1883, Theodor Engelmann conducted an experiment to demonstrate the action spectrum of photosynthesis. He used a prism to disperse light onto a filamentous alga and observed the growth of aerobic bacteria, which clustered in areas illuminated by red and blue light, indicating higher oxygen production due to more efficient photosynthesis.
C3 plants
C3 plants fix carbon dioxide directly into a three-carbon compound (3-phosphoglycerate) using the enzyme rubisco. They are susceptible to photorespiration, especially in hot and dry conditions, which reduces their photosynthetic efficiency.
C4 plants
C4 plants minimize photorespiration by using the enzyme PEP carboxylase to fix carbon dioxide into a four-carbon compound in mesophyll cells. This compound is then transported to bundle-sheath cells, where it releases carbon dioxide for use in the Calvin cycle, creating a higher concentration of carbon dioxide around rubisco.
CAM plants
CAM plants open their stomata at night to fix carbon dioxide into organic acids, storing it as malate. During the day, the stomata close to conserve water, and the stored carbon dioxide is released for use in the Calvin cycle.
Photorespiration
- Photorespiration is a process that occurs when the enzyme rubisco adds oxygen instead of carbon dioxide to RuBP in the Calvin cycle.
- This process consumes oxygen and organic fuel, releases carbon dioxide, and does not produce ATP or sugar, making it energetically wasteful.
- Photorespiration is more likely to occur in hot and dry conditions when stomata close, limiting carbon dioxide intake and increasing oxygen concentration.
