Bio Exam 3 - Concepts

What is the first law of thermodynamics?

Energy cannot be created or destroyed; it can be transferred or converted into other forms.

What is the second law of thermodynamics?

Energy transformations increase the total entropy of the universe. Cells maintain local order by using energy and increasing entropy in their surroundings.

How can cells maintain order without violating the second law of thermodynamics?

They take in energy and release heat and waste, increasing entropy in their surroundings while maintaining local order.

On a free-energy diagram, how do the products of an exergonic reaction compare with the reactants?

The products have lower free energy than the reactants; Delta G is negative.

On a free-energy diagram, how do the products of an endergonic reaction compare with the reactants?

The products have higher free energy than the reactants; Delta G is positive.

What does the peak of a reaction-energy diagram represent?

The transition state. The rise from the reactants to the peak is the activation energy barrier.

Does a spontaneous reaction necessarily happen quickly?

No. Spontaneous describes a favorable free energy change, not reaction speed. An activation energy barrier may make the reaction slow.

What are the products of ATP hydrolysis?

ADP and inorganic phosphate (Pi). ATP + H2O -> ADP + Pi; the reaction releases free energy.

How does ATP coupling drive an energy-requiring reaction?

Enzymes link exergonic ATP hydrolysis to an endergonic process, often by transferring a phosphate. The coupled process proceeds when its total free energy change is negative.

What three types of cellular work can ATP power?

Chemical work such as building molecules; transport work such as pumping ions; mechanical work such as movement.

How does an enzyme speed up a reaction?

It lowers the activation energy barrier by stabilizing the transition state and providing a favorable reaction environment.

Does an enzyme change a reaction's Delta G or equilibrium?

No. It speeds the approach to equilibrium without changing the overall free energy change or equilibrium position.

Can an enzyme alone make an endergonic reaction energetically favorable?

No. An energy source, such as coupling to ATP hydrolysis, is needed; lowering activation energy does not change Delta G.

What is induced fit?

Substrate binding slightly changes an enzyme's shape, positioning the substrate for the reaction.

What is the basic sequence of enzyme action?

Substrate binds the active site -> enzyme-substrate complex forms -> reaction occurs -> products leave -> enzyme is available again.

Is an enzyme consumed by the reaction it catalyzes?

No. The enzyme is reusable after products are released.

Where does a competitive inhibitor bind?

At the active site, where it competes with the substrate and blocks substrate access.

How can increasing substrate concentration affect competitive inhibition?

It can reduce inhibition because substrate molecules compete more effectively for the active site.

How does a noncompetitive inhibitor affect an enzyme?

It binds at a site other than the active site and reduces enzyme activity, often by altering enzyme shape or function.

Can adding more substrate overcome pure noncompetitive inhibition?

No. The inhibitor reduces enzyme activity without competing for the active site.

How can extreme temperature or pH affect enzyme activity?

They can disrupt enzyme shape and reduce activity; severe changes can denature the enzyme.

What is the balanced equation for aerobic cellular respiration?

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy captured in ATP and released as heat.

How does the human body use ATP?

ATP powers muscle contraction, nerve signaling, active transport, molecule synthesis, growth, and repair.

What are the three main stages of cellular respiration?

Glycolysis, the citric acid cycle, and oxidative phosphorylation. Pyruvate oxidation connects glycolysis to the cycle.

What happens during glycolysis?

One six-carbon glucose is split into two three-carbon pyruvate molecules, producing net ATP and NADH.

Where does glycolysis occur?

In the cytosol, the fluid portion of the cytoplasm.

Does glycolysis directly require oxygen?

No. Glycolysis can occur without oxygen, provided NAD+ is available.

What are the main products of glycolysis per glucose?

2 pyruvate, 2 NADH, and 2 net ATP. Two water molecules are also formed.

How many ATP are invested and produced in glycolysis?

2 ATP are invested and 4 ATP are produced, for a net gain of 2 ATP per glucose.

What happens during pyruvate oxidation?

Each pyruvate loses one carbon as CO2; its remaining two-carbon acetyl group joins coenzyme A to form acetyl-CoA, and NADH is produced.

Where does pyruvate oxidation occur in eukaryotic cells?

In the mitochondrial matrix.

What are the products of pyruvate oxidation per pyruvate?

1 acetyl-CoA, 1 CO2, and 1 NADH; no ATP is made directly.

What are the products of pyruvate oxidation per glucose?

2 acetyl-CoA, 2 CO2, and 2 NADH; no ATP is made directly.

What happens during the citric acid cycle?

Acetyl groups are oxidized to CO2, electron carriers NADH and FADH2 are formed, and a small amount of ATP or GTP is produced.

Where does the citric acid cycle occur in eukaryotic cells?

In the mitochondrial matrix.

How many citric acid cycle turns occur per glucose?

Two turns, because one glucose produces two acetyl-CoA molecules.

What are the citric acid cycle products per acetyl-CoA?

2 CO2, 3 NADH, 1 FADH2, and 1 ATP equivalent, which may be made as GTP.

What are the citric acid cycle products per glucose?

4 CO2, 6 NADH, 2 FADH2, and 2 ATP equivalents.

What molecule is regenerated at the end of the citric acid cycle?

Oxaloacetate, which can accept another acetyl group and keep the cycle running.

What do NADH and FADH2 carry to the respiratory electron transport chain?

High-energy electrons harvested during the breakdown of fuel molecules.

What happens to NADH when it donates electrons to the respiratory chain?

It is oxidized to NAD+, which can be reused in earlier metabolic reactions.

Where does oxidative phosphorylation occur in eukaryotic cells?

At the inner mitochondrial membrane.

How does the respiratory electron transport chain help make ATP?

Electron transfers release energy that pumps H+ from the matrix into the intermembrane space, building a gradient that powers ATP synthase.

Where do H+ ions accumulate during mitochondrial electron transport?

In the intermembrane space.

In which direction do H+ ions flow through mitochondrial ATP synthase?

From the intermembrane space into the mitochondrial matrix, down their electrochemical gradient.

How does ATP synthase make ATP?

H+ flow drives rotation and shape changes that join ADP and inorganic phosphate (Pi) to form ATP.

What is the final electron acceptor in aerobic respiration?

Oxygen. It accepts electrons and combines with H+ to form water.

Why does a lack of oxygen stop the aerobic electron transport chain?

Without its final electron acceptor, the chain cannot keep transferring electrons or maintain normal proton pumping.

Which stage of cellular respiration produces the most ATP?

Oxidative phosphorylation, because it uses energy carried by NADH and FADH2 from earlier stages to power chemiosmosis.

What is a common modern ATP yield per glucose in eukaryotic aerobic respiration?

About 30-32 ATP total, including about 26-28 from oxidative phosphorylation. Some courses use older totals of 36-38; use your instructor's stated convention.

How much ATP is made directly before oxidative phosphorylation, per glucose?

4 ATP equivalents: 2 net ATP from glycolysis and 2 ATP equivalents from the citric acid cycle.

How many electron carriers are produced before oxidative phosphorylation, per glucose?

10 NADH and 2 FADH2. They are electron carriers, not extra ATP to add to the final ATP total.

Which stages release CO2 during glucose respiration?

Pyruvate oxidation releases 2 CO2 and the citric acid cycle releases 4 CO2 per glucose. Glycolysis releases none.

Why do cells perform fermentation?

To regenerate NAD+ from NADH so glycolysis can continue when respiration cannot oxidize NADH fast enough.

Why does glycolysis stop if NAD+ is not regenerated?

NAD+ is required to accept electrons during glycolysis; without it, that pathway cannot continue.

How much ATP do glycolysis plus fermentation yield per glucose?

2 net ATP, all produced by glycolysis. Fermentation adds no additional ATP.

What happens during lactic acid fermentation?

Pyruvate receives electrons from NADH and becomes lactate, regenerating NAD+.

Where does lactic acid fermentation occur?

In human muscle cells during high demand and in some bacteria.

What happens during alcoholic fermentation?

Pyruvate loses CO2 to become acetaldehyde; acetaldehyde receives electrons from NADH to form ethanol, regenerating NAD+.

What are the end products of alcoholic fermentation?

Ethanol and CO2.

Which organisms commonly perform alcoholic fermentation?

Yeast and some other microorganisms.

What do lactic acid and alcoholic fermentation have in common?

Both regenerate NAD+ and allow glycolysis to continue; both yield only the 2 net ATP per glucose made by glycolysis.

What is a facultative anaerobe?

An organism that can grow with or without oxygen, using aerobic respiration when oxygen is present and fermentation or anaerobic respiration when it is absent.

What is an obligate anaerobe?

An organism that grows without oxygen and is harmed by oxygen.

How does fermentation differ from anaerobic respiration?

Fermentation uses no electron transport chain. Anaerobic respiration uses a chain with a final electron acceptor other than oxygen.

Do plants perform cellular respiration?

Yes. Plants use cellular respiration to make ATP from organic molecules, including sugars made through photosynthesis.

How do autotrophs and heterotrophs differ in their carbon source?

Autotrophs build organic molecules from inorganic carbon such as CO2; heterotrophs obtain organic carbon by consuming or absorbing existing organic molecules.

What are examples of autotrophs?

Most plants, many algae, cyanobacteria, and some other bacteria and archaea.

What is a chemoautotroph?

An autotroph that uses energy from inorganic chemicals rather than light to make organic molecules from inorganic carbon.

What organelle performs photosynthesis in plants and algae?

The chloroplast.

Do cyanobacteria have chloroplasts?

No. They photosynthesize using internal membranes without having chloroplasts.

What structures should you label on a chloroplast diagram?

Outer membrane, inner membrane, stroma, a granum or grana, thylakoid membrane, and thylakoid lumen.

How many membranes form the chloroplast envelope?

Two: an outer membrane and an inner membrane.

What is the thylakoid lumen?

The space inside a thylakoid, where H+ accumulates during the light reactions.

What is the plural of granum?

Grana; each granum is a stack of thylakoids.

How do gases enter and leave a leaf?

They diffuse through stomata. During net photosynthesis, CO2 generally enters and O2 leaves.

What do guard cells do?

Regulate the opening and closing of stomata, balancing gas exchange with water loss.

What substance besides oxygen leaves a leaf through stomata?

Water vapor; this loss is part of transpiration.

What is the simplified balanced equation for photosynthesis?

6 CO2 + 6 H2O + light energy -> C6H12O6 + 6 O2.

Where does the O2 released during photosynthesis come from?

From splitting water during the light-dependent reactions, not from CO2.

Where does the carbon in photosynthetic sugars come from?

From CO2 fixed during the Calvin cycle.

How are the simplified photosynthesis and respiration equations related?

Their reactants and products are reversed. Photosynthesis stores light energy in organic molecules; respiration releases energy from those molecules to make ATP.

What are the two main stages of photosynthesis?

The light-dependent reactions and the Calvin cycle.

Where do the light-dependent reactions occur?

In the thylakoid membrane of the chloroplast.

What are the main inputs and outputs of the light-dependent reactions?

Inputs: light, water, ADP, Pi, and NADP+. Outputs: O2, ATP, and NADPH.

Where does the Calvin cycle occur?

In the chloroplast stroma.

What are the main inputs and net carbon output of the Calvin cycle?

Inputs: CO2, ATP, and NADPH. Net carbon output: G3P, a three-carbon sugar.

What wavelengths does chlorophyll absorb especially well?

Blue and red light. Green light is mostly reflected or transmitted.

What happens when a photosystem absorbs light?

Pigments transfer excitation energy to reaction-center chlorophyll, which passes an excited electron to a primary electron acceptor.

Which photosystem acts first in linear electron flow?

Photosystem II (PSII), followed by photosystem I (PSI), despite their numbering.

What replaces the electrons lost by photosystem II?

Electrons from water splitting. Splitting 2 H2O provides 4 electrons and releases O2 and 4 H+.

What connects photosystem II to photosystem I?

An electron transport chain; electron transfers help build the H+ gradient across the thylakoid membrane.

What happens to electrons when they reach photosystem I?

Light excites them again; they pass to ferredoxin and then to NADP+ reductase.

What is the basic electron path in the light reactions?

Water -> PSII -> electron transport chain -> PSI -> ferredoxin -> NADP+ reductase -> NADPH.

Where do H+ ions accumulate in the chloroplast during light reactions?

In the thylakoid lumen, due to water splitting and electron transport.

In which direction do H+ ions flow through chloroplast ATP synthase?

From the thylakoid lumen into the stroma, driving ATP production.

What is photophosphorylation?

Light-powered ATP production from ADP and Pi, using a proton gradient and ATP synthase.

How is NADPH produced in the light reactions?

NADP+ reductase combines NADP+, 2 electrons, and H+ to form NADPH on the stroma side.

What do ATP and NADPH supply to the Calvin cycle?

ATP supplies energy; NADPH supplies high-energy electrons, or reducing power.

What are the three phases of the Calvin cycle?

Carbon fixation, reduction, and regeneration of RuBP.