Bio exam 3

Kinetic energy

Energy of motion.

Potential energy

Stored energy.

Main energy source for the biosphere

The Sun.

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

First law of thermodynamics

Energy cannot be created or destroyed; it changes form, and some is released as heat during conversions.

Second law of thermodynamics

Entropy in the universe tends to increase.

Entropy

A measure of disorder or energy unavailable to do work.

Free energy equation

$$G = H - TS$$

Change in free energy equation

$$G = H - TS$$

Exergonic reaction

A reaction with negative G that releases free energy and is spontaneous.

Endergonic reaction

A reaction with positive G that requires an energy input.

Activation energy

The energy needed to start a chemical reaction.

Catalyst

A substance that lowers activation energy without changing G.

Can a catalyst make an endergonic reaction spontaneous?

No. A catalyst lowers activation energy but does not change G.

ATP structure

Adenine, ribose, and three phosphate groups.

ATP hydrolysis

Breakdown of ATP that releases energy to help drive cellular work.

Coupled reaction

An energy-releasing reaction, such as ATP hydrolysis, drives an energy-requiring reaction.

Enzyme

A biological catalyst that speeds up a reaction.

What are most enzymes made of?

Protein.

Ribozyme

An RNA molecule that acts as an enzyme.

Active site

The part of an enzyme where its substrate binds.

Enzyme-substrate complex

The temporary structure formed when a substrate binds to an enzyme.

Multi-enzyme complex

A group of enzymes that work together, passing products from one reaction to the next.

What affects enzyme reaction rate?

Enzyme and substrate concentrations, temperature, pH, and conditions that affect enzyme shape.

Competitive inhibitor

An inhibitor that competes with the substrate for the active site.

Noncompetitive inhibitor

An inhibitor that binds away from the active site and changes enzyme function.

Allosteric site

A regulatory site away from an enzyme’s active site.

Allosteric activator

A molecule that binds an allosteric site and increases enzyme activity.

Allosteric inhibitor

A molecule that binds an allosteric site and decreases enzyme activity.

Metabolism

The sum of all chemical reactions in an organism.

Anabolism

Building larger molecules from smaller ones, usually using energy.

Catabolism

Breaking down molecules and releasing usable energy.

Biochemical pathway

A sequence of reactions in which one reaction’s product becomes the next reaction’s substrate.

Feedback inhibition

When a pathway’s end product inhibits an earlier enzyme, slowing or stopping the pathway.

How does feedback inhibition usually work?

The end product binds to an allosteric site on an enzyme and reduces its activity.

Autotroph

An organism that makes organic molecules from inorganic materials, often using photosynthesis.

Heterotroph

An organism that obtains organic molecules by consuming other organisms or their products.

Dehydrogenation

The removal of a hydrogen atom, which carries an electron and a proton.

Cellular respiration equation

$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$$

What is oxidized during aerobic cellular respiration?

Glucose is oxidized to carbon dioxide.

What is reduced during aerobic cellular respiration?

Oxygen is reduced to water.

Aerobic respiration

Respiration that uses oxygen as the final electron acceptor.

Anaerobic respiration

Respiration that uses an inorganic molecule other than oxygen as the final electron acceptor.

NAD+ role

An electron carrier that accepts electrons and a proton to become NADH.

What does NAD+ accept to form NADH?

Two electrons and one proton.

NADH analogy

NADH is an electron “taxi” that carries electrons to the electron transport chain.

Substrate-level phosphorylation

Direct transfer of a phosphate group to ADP to make ATP.

Oxidative phosphorylation

ATP production powered by the proton gradient generated by the electron transport chain.

Four stages of cellular respiration

Glycolysis, pyruvate oxidation, citric acid cycle, and electron transport chain with chemiosmosis.

Where does glycolysis occur?

In the cytoplasm.

How many steps are in glycolysis?

Ten.

Three phases of glycolysis

Energy investment, sugar splitting, and energy payoff.

Energy investment phase of glycolysis

Uses ATP to prepare the sugar for splitting.

Sugar-splitting phase of glycolysis

Splits a six-carbon sugar into two three-carbon molecules.

Energy-payoff phase of glycolysis

Oxidizes molecules and produces ATP and NADH.

Net glycolysis products per glucose

Two pyruvate, two ATP, and two NADH.

Does glycolysis require oxygen?

No. Glycolysis can occur with or without oxygen.

Pyruvate’s fate when oxygen is available

It is oxidized to acetyl-CoA and enters the citric acid cycle.

Pyruvate’s fate when oxygen is unavailable

It can enter fermentation, which regenerates NAD+.

Where does pyruvate oxidation occur in eukaryotic cells?

In the mitochondrial matrix.

Enzyme complex for pyruvate oxidation

Pyruvate dehydrogenase complex.

Pyruvate oxidation products per pyruvate

One carbon dioxide, one NADH, and one acetyl-CoA.

Pyruvate oxidation products per glucose

Two carbon dioxide, two NADH, and two acetyl-CoA.

Where does the citric acid cycle occur?

In the mitochondrial matrix.

Three segments of the citric acid cycle

Citrate formation, citrate rearrangement and decarboxylation, and oxaloacetate regeneration.

What combines to form citrate?

Acetyl-CoA and oxaloacetate.

Citric acid cycle products per acetyl-CoA

Two CO2, three NADH, one FADH2, and one ATP.

Total products after the citric acid cycle per glucose

Six CO2, four ATP, ten NADH, and two FADH2.

Where is the mitochondrial electron transport chain?

In the inner mitochondrial membrane.

What delivers electrons to the mitochondrial ETC?

NADH and FADH2.

What do ETC complexes pump?

Protons (H+) into the intermembrane space.

Proton-motive force

The energy stored in the H+ gradient across a membrane.

Chemiosmosis

The movement of H+ down its gradient through ATP synthase, powering ATP production.

What does ATP synthase do?

Uses energy from H+ flow to make ATP from ADP and inorganic phosphate.

Where do mitochondrial protons flow through ATP synthase?

From the intermembrane space into the mitochondrial matrix.

Theoretical ATP yield per glucose in eukaryotes

About 30 ATP.

Theoretical ATP yield per glucose in bacteria

About 32 ATP.

Approximate share of glucose energy transferred to ATP

About 34%.

Energy flow during cellular respiration

Glucose → NADH → electron transport chain → proton-motive force → ATP.

Feedback inhibition in respiration

High levels of pathway products inhibit earlier enzymes and slow respiration.

Key glycolysis control enzyme

Phosphofructokinase.

What inhibits phosphofructokinase?

High ATP and citrate.

Key pyruvate oxidation control enzyme

Pyruvate dehydrogenase.

What inhibits pyruvate dehydrogenase?

High NADH.

Anaerobic respiration’s final electron acceptor

An inorganic molecule other than oxygen, such as nitrate or sulfur.

Fermentation’s final electron acceptor

An organic molecule.

What are the two common types of fermentation?

Ethanol fermentation and lactic acid fermentation.

Main role of fermentation

Regenerate NAD+ so glycolysis can continue without oxygen.

Ethanol fermentation

Converts pyruvate to ethanol and releases CO2; occurs in yeast.

Uses of ethanol fermentation

Brewing, winemaking, and baking.

Lactic acid fermentation

Reduces pyruvate to lactate without releasing CO2.

Where does lactic acid fermentation occur?

In some microbes and in human muscle cells when oxygen is scarce.

ATP yield of fermentation

Two ATP per glucose, produced by glycolysis.

Approximate ATP yield of aerobic respiration

About 30–32 ATP per glucose.

How can carbohydrates enter respiration?

They are broken into sugars that enter glycolysis.

How can fats enter respiration?

Glycerol can enter glycolysis; fatty acids are converted to acetyl-CoA.

How can proteins enter respiration?

After digestion to amino acids, their carbon skeletons can enter glycolysis or the citric acid cycle.

Where does photosynthesis occur in plants?

In chloroplasts.

Thylakoid

An internal chloroplast membrane that contains the light reactions.