Unit 3: Cellular Energetics (AP BIO)

Chapters 8, 9, 10

Kinetic Energy

Energy of things in motion

Potential Energy

Energy that things NOT in motion have

Kinetic Energy

Energy of things in motion

Potential Energy

Energy that things NOT in motion have

Exergonic

Net release of free energy

Endergonic

Absorbs free energy from its surroundings

Free energy

energy available in the system to do the work

Energy Coupling

using the energy released by exergonic reaction to power the uphill motion of endergonic reaction

Enzymes

typically made of proteins, can speed up reactions by holding substrates in optimal position for the

Catabolic

The break down of complex molecules to simpler compounds which results in a net release of energy

Anabolic

Build complicated molecules from simpler ones which results in a net input/consumption of energy

Feedback Inhibition

• Ex. ATP inhibits catabolism, ADP activates it

The end product of a metabolic pathway influences the continuation of that pathway by interacting with an enzyme that catalyzes an earlier step in the pathway.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed. Living systems need to continually acquire and transform energy in order to remain alive.

Second Law of Thermodynamics

Every time energy is transformed there is a loss of usable energy as heat to the surroundings, and the entropy (“disorder”) of the universe increases.

Spontaneity

“energy favorable”

Catalysts

Substances that increase the rate of a chemical reaction by lowering the activation energy of the reaction, without participating in the reaction.

Activation Energy

the initial investment of energy for a starting reaction in order to break bonds.

Co-factors/ co-enzymes

• organic (co-enzymes: “vitamins”) or inorganic (co-factors: “minerals”)

“Little helpers” that many enzymes require (groups of atoms to be bound to the enzyme.) Involved in allosteric interactions.

Competitive Inhibition

Refers to any substance that occupies the active site of an enzyme that is not the substrate of that enzyme.

Non-Competitive Inhibition or “Allosteric Inhibition”

Affects enzyme structure and function through binding away from the active site (usually changes the shape of the active site).

Allosteric inhibitors

modify the active site of the enzyme so that substrate binding is reduced or prevented.

Allosteric activators

modify the active site of the enzyme so that the affinity for the substrate increases.

Allosteric Regulators

This often happens through cooperativity:

Binding of first substrate increases the affinity for all of the other substrates to bind.

Redox reactions (oxidation-reduction)

atom are oxidized (loss of e-), then reduced (addition of e-)

Electron Shuttles

molecules which can hold electrons when they are taken from molecules and release them to other molecules when needed.

ATP

• Free energy from metabolism is used to turn a molecule of ADP (2 phosphates) into a molecule of ATP (3 phosphates).

• The bond between the 2nd and 3rd phosphate is easily broken.

• The free energy that is released from bonds formed (between water and phosphate) is used to power cellular work.

short-term free energy storage molecule used in all biological systems.

NADH/NAD+ & FAD/FADH2 & NADP+/NADPH

• Helps with biological energy production by starting redox reactions

Electron shuttles - can hold electrons when they are taken from molecules and release them to other molecules when needed. This transfer of electrons also brings protons along for the ride.

Fermentation

• Occurs: in the cytoplasm of all anaerobically respiring cells

• Uses: 2 Pyruvate, 2 NADH

  Produces: A variety of organic molecules depending on the organism, and 2 NAD+

  • Examples of products + 2 NAD+:

    Yeast – ethanol (2 Carbon) and CO2

    Mammalian Muscle Cells – Lactic Acid (3 Carbon)

Fermentation pathways allow cells to oxidize NADH back to NAD+ in order to continue anaerobic cellular respiration. Pyruvate is reduced into one of a variety of molecules.

Glycolysis

Occurs: in the cytoplasm of all cells

Uses: Glucose (6 Carbon), 2 ATP, 2 NAD+

Produces: 2 Pyruvate (3 Carbon), 4 ATP, 2 NADH

1 Glucose is broken into 2 (three carbon) pyruvates.

Pyruvate Oxidation (Link RXN)

1 pyruvate is oxidized (loses e-) to become acetyl CoA, producing one molecule of Co2 (removes one carbon from pyruvate) and 1 NADH

Citric Acid Cycle (Kreb cycle)

Occurs: In the matrix of the mitochondria.

Uses: A molecule of Acetyl-CoA (2 Carbon), 3 NAD+, 1 FAD, and 1 ADP

Produces: 2 CO2, 3 NADH, 1 FADH2, 1 ATP

Note: This happens twice per every 1 glucose.

Stores energy from glucose into electron carriers (NADH and FADH2) to be used in oxidative phosphorylation. Remaining 4 carbons will be released as Co2.

Oxidative Phosphorylation

Occurs: At the inner membrane of the mitochondria

Uses: Oxygen, and all NADH and FADH2 produced in glycolysis (2 NADH), link reaction (2 NADH per glucose), and the citric acid cycle (6 NADH and 2 FADH2 per glucose)

Produces: Water, NAD+, FAD, and >30 ATP

What’s oxidized: NADH and FADH2

What’s produced: ATP and Water

Electron Transport Chain

Electron carriers drop off e-, passes e- across proteins as they are attracted to electronegative o2 at the end of the chain. In the process, H+ ions are sucked through the channel (active transport) because they are attracted to the e- moving through the ETC. The e- are oxidized and reduced until they reach o2 (electron acceptor) which becomes H20.

Chemiosmosis

ATP Synthase (protein channel) takes energy from e- crossing bilayer (passive transport) to turn ADP + Pi (inorganic phosphate) into ATP

Light-dependant reactions

Occurs: photosystems in the thylakoid membrane of chloroplasts

Uses: H20, light, NADP+, ADP

Produces: O2 (waste product), NADPH and ATP (travel to Calvin cycle/light-independent reactions)

Equation of photosynthesis

6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂

(Carbon dioxide + water + light → glucose + oxygen)

Role of H20 in the light independent reactions

Water (H₂O) is split (photolysis), releasing oxygen (O₂), electrons, and protons (H⁺)

Calvin Cycle (dark reactions//light-independent reactions)

Occurs: stroma of the chloroplast

Uses: CO₂, ATP, NADPH

Outputs: G3P (used to form glucose, takes 3 turns to produce 1), ADP + Pi, NADP⁺

Carbon fixation

process of incorporating CO₂ into organic molecules (first step of the Calvin Cycle, catalyzed by the enzyme RuBisCO)

G3P (glyceraldehyde-3-phosphate)

Product of the Calvin Cycle that can be used to make glucose

Stomata

Pores on the leaf surface that allow gas exchange: Co2 INSIDE, O2 OUT

Reduction

PGA is phosphorylated by ATP, forming the intermediate 1,3-biphosphoglycerate.

1,3-BPG is reduced by NADPH (from the light reactions) and loses a phosphate group to form G3P.

Regeneration

1 net G3p from the Reduction phase is produced. ATP is used to convert the remaining five 3-carbon G3P’s back into three 5-carbon RuBP molecules to begin the cycle again.

Photorespiration

Wasteful pathway that occurs when Calvin Cycle enzyme (RuBisCo) reacts with oxygen rather than carbon dioxide.

Does no good for the plant, but it happens because of the differing Co2 and O2 levels or when temperature increases.