Introduction to Cell Biology and Genetics - Ch. 6

First Law of Thermodynamics

Energy can be transferred or transformed but not created or destroyed.

Second Law of Thermodynamics

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

Metabolism

The totality of an organism’s chemical reactions.

(Cont.) Energy is fundamental to these processes.

An emergent property that arises from orderly interactions between molecules.

Metabolic Pathway

Begins with a specific molecule and ends with a product.

Each step is catalyzed by a specific enzyme.

Two types: Catabolic and Anabolic.

Catabolic Pathways

Energy is released by breaking down complex molecules into simpler compounds.

The energy is then available to do cellular work.

Anabolic (A.K.A. Biosynthetic) Pathways

Energy is consumed to build complex molecules from simpler ones.

Energy

The capacity to cause change.

Exists in various forms, some of which can perform work.

(Can be converted from one form to another)

Potential Energy

_____ that matter possesses because of its location or structure.

Kinetic Energy

Associated with motion.

Thermal Energy

Kinetic energy associated with random movements of atoms or molecules.

Heat

The thermal energy transfer of one object to another.

Light

Another type of energy that can be harnessed to perform work.

(Hint: Photosynthesis)

Chemical Energy

Potential energy available for release in a _____ reaction.

Thermodynamics

The study of energy transformations.

(Cont.)
Open System: energy and matter can be transferred between the system and its surroundings

Isolated System: exchange with the surroundings cannot occur

Entropy

A measure of molecular disorder, or randomness.

Increased by energy transfers and transformations because some energy is always lost to its surroundings as heat.

Spontaneous Processes

Occur without energy input; they can happen quickly or slowly.

Increases entropy of the universe.

Nonspontaneous Processes

Energy is required, and in turn lowers the entropy of the universe.

Free Energy (G)

The portion of a system’s energy that can do work when temperature and pressure are uniform throughout.

ΔG = G_{final state} - G_{initial state}

(Only reactions with negative Δ are spontaneous)

A measure of a system’s instability, its tendency to change to a more stable state. 

Unstable systems (Higher Δ) tend to change so they become more stable (Lower Δ)

Exergonic Reaction

Proceeds with a net release of free energy and is spontaneous; ΔG is negative

(Ex. overall reaction for Cellular Respiration)

Endergonic Reaction

Absorbs free energy from its surroundings and is not spontaneous; ΔG is positive.

(Ex. photosynthesis, the reverse process of cellular respiration)

Work

A cell does three kinds:

Chemical - pushing endergonic reactions

Transport - pumping substances across membranes against the direction of spontaneous movement

Mechanical - such as beating cilia or contracting muscle cells

Energy Coupling

The use of an exergonic process to drive an endergonic one, to do work

ATP

Composed of ribose, adenine and a chain of 3 phosphate groups.

Used in energy coupling and to make RNA.

Hydrolysis of this releases energy and produced ADP and inorganic phosphate.

A renewable resource produced by addition of a phosphate group to ADP.

Catalyst

A chemical reaction that speeds up a reaction without being consumed by the reaction.

Enzyme

A macromolecule that acts as a catalyst; most of these are proteins.

Speeds up reactions without being consumed.

Specific for the reactions they catalyze.

Activation Energy

The energy required to start a reaction by contorting reactant molecules so the bonds can break.

Substrate

The reactant molecule on which an enzyme acts.

Becomes an enzyme-substrate complex when bound to an enzyme.

Active Site

The region of the enzyme to which the substrate binds.

Enzymes change shape due to chemical interactions with the substrate.

Induced fit brings chemical groups of the active site together.

Cofactors

Non-protein molecules that help carry out processes that are difficult for amino acids.

May be organic or inorganic.

An organic _____ is called a coenzyme.

Competitive Inhibitors

Bind to the active site of an enzyme and prevent the substrate from binding.

Noncompetitive Inhibitors 

Bind to an alternate site on the enzyme, causing the active site to change shape and become less effective.

Allosteric Regulation

Occurs when a protein’s function at one site is affected by the binding of a regulatory molecule to a seperate site.

Cooperativity

The binding of one substrate molecule to the active site of subunit locks all other subunits into the active shape.

(Amplifies the response of enzymes to substrates.)

Feedback Inhibition

The end product of a metabolic pathway shuts down the pathway by inhibiting an enzyme that functions early in the pathway.

(Prevents the cell from wasting chemical resources by synthesizing more product than is needed)