Cell Membrane
Draw and label a phospholipid bilayer. Include the lipid, protein, and carb components.
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A cell needs to perform a reaction with a free-energy change of +8 kJ/mol. ATP hydrolysis has a free-energy change of −12 kJ/mol. Calculate the overall free-energy change when the reactions are coupled and explain whether the combined process is energetically favorable.
Overall free energy is -4 kJ/mol, so the reaction is exergonic and spontaneous.
Explain how the electron transport chain establishes a proton gradient across the inner mitochondrial membrane and how ATP synthase uses this gradient to produce ATP. Include the role of oxygen as the final electron acceptor.
NADH and FADH₂ deliver high-energy electrons to the mitochondrial electron transport chain to pump protons from the mitochondrial matrix into the intermembrane space. Protons then flow back into the matrix through ATP synthase, allowing it to produce ATP from ADP and inorganic phosphate.
Using the overall photosynthesis reaction, identify which molecule is oxidized and which is reduced. Explain which atoms lose electrons, which atoms gain electrons, and how these electron transfers affect the energy stored in the products.
Water is oxidized: It loses electrons, and oxygen gas is released.
Carbon dioxide is reduced: Its carbon atoms gain electrons overall as carbon dioxide is converted into carbohydrate.
The products have greater potential energy than reactants because it is endergonic reaction.
Compare simple diffusion, osmosis, facilitated diffusion, active transport. For each process, explain how substances move, whether energy is required, and provide one biological example.
Simple diffusion: movement through membrane, gas
Osmosis: movement through membrane, water
Facilitated diffusion: movement of molecules through integral protein
Active diffusion: movement of molecules through integral protein, use ATP
Explain how phosphorylation can change a molecule's free energy and reactivity. Include the role of the phosphate group's negative charges and explain why phosphorylation does not automatically make every reaction exergonic.
The negative charges on the phosphate group can molecule more reactive, allowing it to undergo a chemical reaction. Phosphorylation can make reactions exergonic, but only when the entire reaction's free energy becomes negative.
Explain how fermentation allows cells to continue producing ATP from glucose when oxygen is unavailable.
Fermentation allows glycolysis to continue when oxygen is unavailable by regenerating NAD⁺ from NADH.
What occurs in the three major stages of photosynthesis?
1. PSII makes ATP using light energy
2. PSI makes NADPH using light energy
3. Makes sugar using ATP + NADPH + CO2
Explain why charged ions and polar molecules do not cross the hydrophobic interior of the plasma membrane efficiently without transport proteins. Compare the properties of sodium ions and oxygen molecules in your explanation.
They cannot properly interact with the nonpolar tails of the phospholipids, which prevents them from being able to cross the bilayer. Sodium ions are positively charged and get repelled from the membrane while oxygen is a nonpolar gas and can pass through by simple diffusion.
Explain why the region of an enzyme where a substrate binds is called the active site. Describe how the enzyme's shape and chemical properties allow it to interact with its substrate.
Its three-dimensional shape and chemical properties allow it to interact with particular substrates through forces such as hydrogen bonding, ionic interactions, and hydrophobic interactions. The active site is called active because it is the location where catalysis occurs.
A toxin inhibits the enzyme responsible for converting pyruvate into acetyl-CoA.
Glycolysis may continue producing a small amount of ATP, especially if NAD⁺ can be regenerated through fermentation. Overall ATP production decreases.
What do PSI and PSII have in common?
Both have chlorophyll embedded throughout machine, inside chloroplast, utilize high energy electrons.
Rank oxygen, carbon dioxide, water, glucose, and sodium ions from fastest to slowest in crossing a pure phospholipid bilayer without transport proteins. Explain how molecular size, polarity, and electrical charge affect your ranking.
A reasonable ranking from fastest to slowest is:
Oxygen
Carbon dioxide
Water
Glucose
Sodium ions
An enzyme has its highest reaction rate at pH 7 and 37∘C, but its activity decreases sharply at pH 3 and 70∘C. Interpret these results and explain how pH and temperature affect the enzyme's structure, active site, and catalytic activity. What do the results suggest about the enzyme's typical cellular environment?
pH alters chemical interactions, while excessive temperature can destabilize the protein's structure, or denature the protein.
A chemical makes the inner mitochondrial membrane permeable to protons, allowing them to return to the mitochondrial matrix without passing through ATP synthase. Predict the effects on the proton gradient, ATP production, and oxygen consumption.
Proton gradient decreases, ATP synthase loses driving force, and oxygen consumption remains stable.
Explain to an 8-year-old how the carbon dioxide in the air contributes to the mass of a growing redwood tree. Describe where the tree gets most of the atoms used to build its organic molecules and how photosynthesis turns those atoms into plant material.
A redwood tree gets most of the carbon it uses to build its trunk, branches, and leaves from carbon dioxide in the air.
Explain how tail length, saturation, and cholesterol affects membrane permeability and fluidity.
The longer the tail, the less permeable and less fluid. The higher the saturation, the less permeable and less fluid. The greater the number of cholesterol, the less permeable and less fluid.
Create an energy diagram for an endergonic reaction and label the graph. How would this graph change if the reaction is coupled with an exergonic reaction? How would this graph change if the reaction has a catalyst?
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Cyanide inhibits the final stage of the electron transport chain, preventing electrons from being transferred to oxygen. Predict the effects.
Oxygen consumption decreases sharply, NADH levels increase, the proton gradient decreases over time, and oxidative phosphorylation decreases.
Describe the energy transformations in PSII.
Light energy transforms to chemical energy at PSII, then transfers chemical energy to ETC, then to mechanical energy in ETC, then to electrical energy in ATP synthase, then mechanical energy in ATP synthase to chemical energy.