Bio 93 Quiz 3: Energy Transfer and Metabolic Pathways in Cells

Energy

The capacity to cause change.

Kinetic energy

Energy associated with motion.

Heat (thermal energy)

Kinetic energy associated with random movement of atoms or molecules.

Potential energy

Energy that matter possesses because of its location or structure.

Chemical energy

Potential energy available for release in a chemical reaction.

First law of thermodynamics

Energy of the universe is constant; can be transferred or transformed but cannot be created or destroyed.

Second law of thermodynamics

Every energy transfer or transformation increases the entropy (disorder) of the universe.

Entropy

A measure of disorder in a system.

Spontaneous processes

Processes that occur without energy input; they can happen quickly or slowly.

Anabolic reactions

Small molecules assembled into large ones; require energy.

Catabolic reactions

Large molecules are broken down into small ones; generate energy.

Change in free energy (ΔG)

Related to the change in enthalpy/total energy (ΔH), change in entropy (ΔS), and temperature in Kelvin (T).

Exergonic reaction

Releases energy, spontaneous, from high energy to low energy.

Endergonic reaction

Requires energy, non-spontaneous, from low energy to high energy.

ATP

Cell's energy shuttle that mediates energy coupling.

Components of ATP

Composed of ribose, adenine, and 2 phosphate groups.

Hydrolysis of ATP

Powers the three types of cellular work: mechanical, transport, and chemical.

ATP cycle

Acts like a revolving door for energy; ATP is regenerated by addition of a phosphate group to adenosine diphosphate (ADP).

Phosphorylation

ATP donates a phosphate and changes the shape of that protein.

Sodium and potassium pump

Energy derived from exergonic ATP hydrolysis is used to pump sodium and potassium ions across the cell membrane.

Net ΔG

If the first reaction has a positive ΔG, it won't happen on its own; coupling it with ATP can drive the reaction forward.

Renewable energy resource

ATP is regenerated by addition of a phosphate group to ADP, with energy coming from catabolic reactions in the cell.

Catalyst

a chemical agent that speeds up a reaction without being consumed by the reaction

Enzyme

a catalytic protein

Activation energy (Ea)

the initial energy needed to start a chemical reaction

Substrate

reactant that an enzyme acts on

Enzyme-substrate

this is formed when the enzyme binds to its substrate

Active site

region on the enzyme where the substrate binds

Induced fit

the process where the substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

Cofactors

non-protein enzyme helpers

Inorganic cofactors

metal in ionic form

Coenzymes

organic cofactors, i.e., vitamins

Competitive inhibitor

binds to the active site of an enzyme competing with the substrate

Non-competitive inhibitor

binds to another part of the enzyme, causing it to change shape and making the active site less effective

Allosteric regulation

either inhibit or stimulate an enzyme's activity; occurs when a regulatory molecule binds to a protein at one site and affects the protein's function at another

Metabolic pathways

a series of reactions catalyzed by multiple enzymes

Feedback inhibition

where the end product of the pathway inhibits an upstream step

If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down

Cellular respiration

includes both aerobic and anaerobic but is often used to refer to aerobic respiration

Anaerobic respiration

doesn't use oxygen and produces lactic acid as a byproduct

Glucose is still broken down but not as efficiently

Photosynthesis

generates O2, glucose, organic molecules, which are used in cellular respiration

Thermal energy

often supplied to the reactant molecules to start a chemical reaction

Optimal conditions

allow the most active shape for the enzyme molecule

Taq polymerase

an enzyme used in PCR (Polymerase Chain Reaction) that can withstand high temperatures

Lactic acid

the byproduct of anaerobic respiration that can lead to muscle fatigue or cramps

OIL RIG

Oxidation is loss, reduction is gain.

Oxidation

Loses electrons and is oxidized.

Reduction

Gains electrons and is reduced (the amount of positive charge is reduced).

Reducing agent

Electron donor.

Oxidizing agent

Electron acceptor.

Redox reactions

Chemical reactions that transfer electrons between reactants.

NAD+ in cellular respiration

A coenzyme that functions as an oxidizing agent during cellular respiration.

NADH in cellular respiration

The reduced form of NAD+ that represents stored energy for ATP synthesis.

Glycolysis

The process that breaks down glucose into two molecules of pyruvate, occurring in the cytoplasm. Electrons carried via NADH. Occurs in the cytoplasm.

Citric Acid Cycle

Completes the breakdown of glucose, occurring in the mitochondria. Electrons carried via NADH, FADH2

Oxidative Phosphorylation

Accounts for most of the ATP synthesis by harvesting electrons to create a big electrochemical gradient.

Energy Investment Phase

The phase of glycolysis that requires initial energy, adding 2 ATP to start the process.

uses two ATP molecules in the phosphorylation of glucose → two three-carbon molecules

Energy Payoff Phase

The second half of glycolysis that involves phosphorylation with ATP investment, produces 4 ATP and 2 NADH.

This phase happens 2x for every glucose we end up splitting

Net ATP from Glycolysis

2 ATP net, 2 NADH, and 2 pyruvate per glucose molecule.

Acetyl CoA

The molecule that pyruvate is converted into before entering the Citric Acid Cycle.

Krebs Cycle

Another name for the Citric Acid Cycle, which completes the breakdown of pyruvate to CO2.

Glyceraldehyde 3-phosphate

The molecule that feeds into the payoff phase of glycolysis.

Carbon dioxide release

Occurs when pyruvate is converted to acetyl CoA.

Multienzyme complex

Catalyzes the conversion of pyruvate to acetyl CoA.

ATP synthesis

The process of producing ATP, primarily occurring during oxidative phosphorylation.

FADH2

An electron carrier produced during the Citric Acid Cycle.

Oxaloacetate

The final compound that regenerates to start the cycle again as long as pyruvate is available.

Electron Transport Chain

A series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH2.

Chemiosmosis

The process of protons moving down their concentration gradient to generate ATP.

This is where ATP Synthase is making ATP.

ATP Synthase

An enzyme that synthesizes ATP as protons flow through it, functioning like a turbine.

As electrons move down the chain, protons (H⁺) are pumped into the intermembrane space, creating a gradient. This gradient powers ATP synthase, which makes ATP — this process is called oxidative phosphorylation.

Free Energy

The energy that electrons lose as they move down the electron transport chain.

Oxygen

The final electron acceptor in the electron transport chain, forming water.

Without oxygen, there would be no electron transport chain, no protein gradient, no ATP synthase.

ATP Production Summary

Glycolysis produces 2 ATP, Citric Acid Cycle produces 2 ATP, and Oxidative Phosphorylation produces 26-28 ATP. Total: 30-32 ATP

Protein Gradient

A concentration gradient of protons created during oxidative phosphorylation, essential for ATP synthesis.

Alcohol Fermentation

A process where pyruvate is converted to ethanol in two steps, with the first releasing O2, used in brewing, winemaking, and baking.

Pyruvate in Alcohol Fermentation

The product of glycolysis that is converted to acetaldehyde, releasing CO₂.

Acetaldehyde

The compound that accepts electrons from NADH, converting it back to NAD⁺ and becomes ethanol.

Lactic Acid Fermentation

A process where pyruvate is reduced by NADH, forming lactate as an end product, with no release of CO₂.

Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

GLUT4

A glucose transporter stored in vesicles that fuses with the plasma membrane upon insulin binding to transport glucose into the cell.

Light Dependent Reactions

The first stage of photosynthesis occurring in thylakoids, using light energy to make ATP and NADPH.

Calvin Cycle

The second stage of photosynthesis occurring in the stroma, using energy from ATP and NADPH to make GA3P from CO₂.

Chloroplasts

Organelles where photosynthesis occurs, containing chlorophyll and found mainly in mesophyll cells.

Stomata

Microscopic pores in leaves through which CO₂ enters and O₂ exits.

Heterotrophs

Organisms that obtain their organic material from other organisms, including humans.

Fossil Fuels

Energy stores formed from the remains of organisms that died hundreds of millions of years ago.

ATP Generation in Glycolysis

Glycolysis produces a net gain of 2 ATP.

Oxygen in Photosynthesis

A byproduct of photosynthesis produced when chloroplasts split H₂O.

Chlorophyll

The green pigment in chloroplasts responsible for capturing light energy.

Located in the membranes of the thylakoids.

Where green color of leaves come from?

Mesophyll

The interior tissue of the leaf where chloroplasts are primarily located.

Light

A form of electromagnetic energy, also called electromagnetic radiation.

Wavelength

The distance between crests of waves, determining the type of electromagnetic energy.

Pigments

Substances that absorb visible light. Different pigments absorb different wavelengths

Wavelengths that aren’t absorbed are reflected or transmitted

Leaves appear green because chlorophyll reflects and transmits green light

Chlorophyll a

The main photosynthetic pigment, functioning in 'normal light'.

Accessory Pigments

Pigments such as chlorophyll b that broaden the spectrum used for photosynthesis. (“low light”)

Carotenoids

Accessory pigments that absorb excessive light that would damage chlorophyll ("bright ass light")

Excited State

The unstable state of a pigment after absorbing light.

When a pigment absorbs light, it goes from ground state to an excited state, which is unstable

Fluorescence

The afterglow given off when excited electrons fall back to the ground state and photons are given off

Photosystem

A structure consisting of a reaction-center complex surrounded by light harvesting complexes.

Primary Electron Acceptor

A component in the reaction center that accepts excited electrons and is reduced.

Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of light reactions

Photosystem II (PSII)

The first functioning photosystem, best at absorbing a wavelength of 680nm.

P680

The reaction center chlorophyll a of Photosystem II.