Cellular Energetics
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105 Terms
What is the purpose of enzymes?
Speed up chemical reactions by lowering activation energy.
What types of reactions can enzymes facilitate?
Anabolic (building) and catabolic (breaking down) reactions.
What are most enzymes made of?
Proteins made of amino acids.
Why is an enzyme's structure important?
Its shape determines which substrate it can bind.
What is a substrate?
The reactant an enzyme acts on.
What is the active site?
The part of an enzyme where the substrate binds.
Why can enzymes be reused?
They are not used up in reactions.
What is activation energy?
The minimum energy needed to start a reaction.
How do enzymes speed up reactions?
They lower activation energy.
What is denaturation?
A change in a protein's shape that causes it to lose function.
What can denature an enzyme?
Extreme temperature, extreme pH, and certain chemicals.
How does temperature affect enzyme activity?
Activity rises to an optimum, then drops if the enzyme denatures.
How does pH affect enzymes?
Each enzyme has an optimal pH; extreme pH can change its shape.
How does substrate concentration affect reaction rate?
Rate increases until all active sites are occupied.
How does enzyme concentration affect reaction rate?
More enzyme usually increases the rate if substrate is available.
What is an acid?
A substance with higher H+ concentration; pH below
What is a base?
A substance with lower H+ concentration; pH above 7.
What is neutral pH?
pH 7
How do you calculate rate from a graph?
Rate = change in y divided by change in x.
What is a competitive inhibitor?
An inhibitor that competes with the substrate for the active site.
What is a noncompetitive inhibitor?
An inhibitor that binds elsewhere and changes enzyme activity.
Competitive vs. noncompetitive inhibitors?
Competitive blocks the active site; noncompetitive binds elsewhere.
What is the second law of thermodynamics?
Energy transfers increase the entropy of the universe.
What is ATP?
The main energy-carrying molecule in cells.
How does ATP release energy?
Hydrolysis removes its terminal phosphate, forming ADP and phosphate.
How does ATP transfer energy to other molecules?
It transfers a phosphate group to another molecule.
What is energy coupling?
Using energy from a favorable reaction to power an unfavorable one.
What is a metabolic pathway?
A series of enzyme-controlled chemical reactions.
What were important early photosynthetic organisms?
Cyanobacteria, which released oxygen.
Why were cyanobacteria important?
They helped oxygenate Earth's atmosphere.
What is the balanced photosynthesis equation?
6CO2 + 6H2O + light → C6H12O6 + 6O2.
What is the purpose of photosynthesis?
Convert light energy into chemical energy stored in sugars.
What do pigments do?
Absorb specific wavelengths of light.
What happens in the light-dependent reactions?
Light energy makes ATP and NADPH; water splitting releases O2.
What happens in the Calvin cycle?
CO2 is used with ATP and NADPH to produce G3P, which can form sugars.
What is a chloroplast made of?
Double membrane, thylakoids, grana, and stroma.
What are thylakoids?
Membrane sacs where the light-dependent reactions occur.
What is the stroma?
Chloroplast fluid where the Calvin cycle occurs.
What is oxidation?
Loss of electrons.
What is reduction?
Gain of electrons.
Where does the oxygen released in photosynthesis come from?
Water (H2O).
Where does the carbon in glucose come from?
Carbon dioxide (CO2)
Why does a pigment appear a certain color?
It reflects or transmits that color and absorbs other wavelengths.
Why are multiple pigments useful?
They absorb different wavelengths, capturing more light energy.
What does chlorophyll do?
Absorbs light and excites electrons.
What does Photosystem II do?
Excites electrons and splits water to replace them.
What does Photosystem I do?
Re-energizes electrons to help produce NADPH.
What does NADP+ do?
Accepts electrons and H+ to become NADPH
What does NADPH do?
Carries high-energy electrons to the Calvin cycle.
What does ATP do in photosynthesis?
Provides energy for the Calvin cycle.
What does the photosynthetic electron transport chain do?
Uses electron energy to pump H+ into thylakoid spaces.
Why is a proton gradient important in photosynthesis?
H+ flows through ATP synthase to make ATP.
What does ATP synthase do?
Uses H+ flow to produce ATP.
What happens to water in the light reactions?
It splits into electrons, H+, and oxygen.
What happens to oxygen during photosynthesis?
It is released as a byproduct.
What does the Calvin cycle need?
CO2, ATP, and NADPH.
What is G3P?
A three-carbon sugar used to build glucose and other carbohydrates.
How do plants use glucose?
For respiration, starch storage, cellulose, and other molecules.
What is the balanced cellular respiration equation?
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.
What is the purpose of cellular respiration?
Break down food to produce ATP.
Which organisms perform cellular respiration?
Nearly all organisms, including plants, animals, fungi, and many microbes.
Which organisms perform fermentation?
Some animal cells, yeast, and bacteria.
What does aerobic mean?
Requires oxygen.
What does anaerobic mean?
Occurs without oxygen.
What are the main stages of cellular respiration?
Glycolysis, pyruvate oxidation, Krebs cycle, and oxidative phosphorylation.
What is the structure of a mitochondrion?
Outer membrane, folded inner membrane, intermembrane space, and matrix.
What are cristae?
Folds of the inner membrane that increase surface area for ATP production.
Where does glycolysis occur?
In the cytosol.
What happens during glycolysis?
Glucose becomes two pyruvate, producing net 2 ATP and 2 NADH.
What is glucose's role in glycolysis?
It is broken down into two pyruvate molecules.
What is ATP's role in glycolysis?
Two ATP are used to start breaking down glucose.
What does NAD+ do in glycolysis?
Accepts electrons to become NADH
What does NADH do?
Carries high-energy electrons to the electron transport chain.
What do ADP and phosphate do in glycolysis?
Combine to form ATP
What is pyruvate?
The three-carbon product of glycolysis.
Where does pyruvate oxidation occur?
In the mitochondrial matrix in eukaryotes.
What happens during pyruvate oxidation?
Pyruvate becomes acetyl-CoA, producing NADH and CO2.
What is acetyl-CoA?
A two-carbon molecule that enters the Krebs cycle
Where does the Krebs cycle occur?
In the mitochondrial matrix.
What enters the Krebs cycle?
Acetyl-CoA.
What does the Krebs cycle produce per glucose?
4 CO2, 6 NADH, 2 FADH2, and 2 ATP.
What are NADH and FADH2 used for?
Deliver electrons to the electron transport chain.
Where does oxidative phosphorylation occur?
Across the inner mitochondrial membrane.
What does the respiratory electron transport chain do?
Uses electrons to pump H+ into the intermembrane space.
What is oxygen's role in respiration?
Final electron acceptor; combines with electrons and H+ to form water.
What is the mitochondrial proton gradient?
Higher H+ concentration in the intermembrane space than in the matrix.
What does ATP synthase do in mitochondria?
Uses H+ flow into the matrix to produce ATP.
Why is the intermembrane space more acidic?
The electron transport chain pumps H+ into it.
Why is the matrix more basic during oxidative phosphorylation?
It has a lower H+ concentration.
What is photophosphorylation?
Light-driven ATP production in chloroplasts.
What is oxidative phosphorylation?
ATP production using an electron transport chain and proton gradient in respiration.
How are photophosphorylation and oxidative phosphorylation similar?
Both use an electron transport chain, H+ gradient, and ATP synthase.
How are photophosphorylation and oxidative phosphorylation different?
Photophosphorylation uses light in chloroplasts; oxidative phosphorylation uses food-derived electrons in mitochondria.
Where are electron transport chains found in prokaryotes?
In the plasma membrane.
What is uncoupling in oxidative phosphorylation?
H+ bypasses ATP synthase, lowering ATP production and releasing more heat.
What is aerobic cellular respiration?
Uses oxygen as the final electron acceptor and produces lots of ATP.
What is anaerobic cellular respiration?
Uses an electron transport chain with a final acceptor other than oxygen.
What is fermentation?
A process that regenerates NAD+ without an electron transport chain.
How does fermentation keep glycolysis going?
It regenerates NAD+, which glycolysis needs.
Aerobic respiration vs. fermentation?
Aerobic respiration uses oxygen and an ETC; fermentation does not use an ETC and yields 2 ATP per glucose.