Biology 411: Exam 2

Metabolism

the totality of an organism's chemical reaction

Interactions between between molecules in metabolism are

orderly

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Metabolic Pathway

begins with a specific molecule and ends with a product

Each step is catalyzed by a specific enzyme

Catabolic Pathways

release energy by breaking down complex molecules into simpler compounds

Catabolism

breakdown reactions

Are catabolic pathways exergonic or endergonic?

exergonic

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Negative ΔG

Releasing energy from the fuel source and the cell can harness that energy for something useful

Anabolic Pathways

called biosynthetic pathways, consume energy to build complex molecules from simpler ones

Are anabolic pathways exergonic or endergonic?

endergonic

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Do anabolic pathways require ATP

yes

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Energy

the capacity to cause change - perform work

Work

the movement of matter

Kinetic Energy

energy associated with motion

Thermal Energy

kinetic energy associated with random movement of atoms or molecules

Heat

thermal energy in transfer from one object to another

Why do cells lose heat energy?

They can't harness heat and do anything with it

Light energy

can be harnessed to perform work

Photosynthesis

Potential energy

energy that matter possesses because of its location or structure

Chemical energy

potential energy available for release in a chemical reaction

Energy held in the chemical bonds

Can energy be converted from one form to another

yes

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Thermodynamics

the study of energy transformations

Open system

energy and matter can be transferred between the system and its surroundings

Isolated System

exchange with the surroundings cannot occur

Are organisms open or isolated systems

open systems

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first law of thermodynamics

the energy of the universe is constant

Energy can be transferred and transformed, but it cannot be created or destroyed

Principle of conservation of energy

the other term for the first law of thermodynamics

Second law of thermodynamics

Every energy transfer or transformation increases the entropy of the universe

Entropy

measure of molecular disorder

Disorder

how dispersed energy is in a system and how many energy levels are present

How do transformations of energy affect entropy?

Increase entropy

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How does heat affect entropy?

Decrease entropy

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Spontaneous Processes

release energy; spontaneous does not equal fast

How do spontaneous processes affect entropy?

increase entropy

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How do nonspontaneous processes affect entropy?

Decrease entropy

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What happens to energy during a transfer?

Lost into the universe in the form of heat

Does energy input decrease or increase the order of molecules?

increase

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Energy flows into an ecosystem as _______ and leaves as ______

light, heat

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Free Energy

measure of a system's instability (G), its tendency to change to a more stable state

Identifies spontaneous and nonspontaneous reactions

Spontaneous Change

free energy decreases and the stability of a system increases

Energy releasing reaction

Do unstable system have a higher or lower G

higher G

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Unstable systems change so that they become...

more stable

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What is the change in free energy during a chemical reaction?

the difference between the free energy of the final state and the free energy of the initial state

What does it mean if you get a negative ΔG

that amount of energy is being released

Spontaneous reactions

release energy and have a ΔG that releases energy and is a negative number

What does it mean if you get a positive ΔG?

that's the amount of energy needed to perform

Can reactions reach equilibrium?

no

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What is the only time a process is spontaneous and can perform work?

when it is moving toward equilibrium

What would happen if reactions reached equilibrium?

the cells would be dead

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Exergonic reaction

a net release of free energy and is spontaneous (ΔG is negative)

What does the magnitude of ΔG represent?

the maximum amount of work the reaction can perform

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Endergonic reaction

a net input energy and is nonspontaneous (ΔG is positive)

What happens to reactions in an isolated system?

eventually reach equilibrium and can then do no work

Are cells an open or isolated system?

open systems experiencing a constant flow of materials in and out

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One of the defining features of life

the fact that metabolism is never at equilibrium

When are cells at equilibrium

when ΔG = 0

A cell does three main kinds of work

chemical, transport, mechanical

Energy coupling

the use of an exergonic process to drive an endergonic one

What is most energy coupling in cells mediated by?

ATP

Exergonic

energy releasing and the breakdown of organic molecules

Endergonic

energy requiring

ATP (adenosine triphosphate)

ribose (a sugar), adenine (a nitrogenous base), and a chain of three phosphate groups

Why does ATP have high potential energy?

Negatively charged phosphate groups repel each other even though they are bonded in a triphosphate group.

ATP hydrolysis

releases energy and produces ADP (adenosine diphosphate) and inorganic phosphate, and releases due to the repulsive force of the three negatively charged phosphate groups

What is the energy released by the exergonic reaction of ATP hydrolysis used for?

used to drive endergonic reactions

phosphorylated intermediate

A molecule (often a reactant) with a phosphate group covalently bound to it, making it more reactive (less stable) than the unphosphorylated molecule.

What are transport and mechanical work in the cell powered by?

ATP hydrolysis

ATP is renewable and regenerated by..?

addition of a phosphate group to ADP

Where does the energy to phosphorylate ADP come from?

catabolic reactions in the cell

Where does most of the synthesis process in ATP happen?

mitochondria

catalyst

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

Enzyme

macromolecule that acts as a catalyst; most enzymes are proteins

How do you identify enzymes by their names?

end in -ase

Activation energy (Ea)

the energy required to start a reaction by breaking bonds in the reactant molecules

What is activation energy usually supplied by?

heat that reactant molecules absorb from the surroundings

Lower Ea =

faster reaction

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Do enzymes affect the change in free energy (ΔG)?

no

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Why does using an enzyme help the reaction happen faster?

enzymes allow us to lower the activation energy

Substrate

reactant molecule on which an enzyme acts S

Enzyme-substrate complex

formed when the enzyme binds to its substrate ES

Active site

region on the enzyme to which the substrate binds

What does enzyme specificity result from?

the fit between the shape of the active site and the substrate

induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, induced by entry of the substrate.

What are enzymes held to an active site by?

weak interactions such as hydrogen bonds

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How does the active site affect activation energy (Ea)?

lowers the activation energy (Ea) and converts substrates to products

products

The elements or compounds produced by a chemical reaction.

Step one of Catalytic Cycle of an Enzyme

Substrates enter the active site; enzyme changes shape such that its active site enfolds the substrate (induced fit)

Step two of Catalytic Cycle of an Enzyme

Substrates are held in the active site by weak interactions, such as hydrogen bonds and ionic bonds

Step three of catalytic cycle of an enzyme

The active site lowers Ea and speeds up the reaction

Step four of catalytic cycle of an enzyme

Substrates are converted to products

Step five of Catalytic Cycle of an Enzyme

Products are released

Step six of catalytic cycle of an enzyme

Active site is available for two new substrate molecules

What can an enzyme's activity be affected by?

General environmental factors, such as temperature and pH

Chemicals that specifically influence the enzyme

competitive inhibitors

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

What do competitive inhibitors do?

Compete with the substrate for binding at the active site

Can physically block the substrate

Noncompetitive inhibitors

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

What can noncompetitive inhibitors do?

Does not bind to the active site

When we add a noncompetitive inhibitor, it changes the shape of the active site

Reversible inhibitors bind to the enzyme by...?

hydrogen bonds

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Irreversible inhibitors bind to the enzyme by...?

covalent bonds

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What are two examples of irreversible inhibitors

toxins and poisons

Allosteric regulation

may either inhibit or stimulate an enzyme's activity

If we modify one of the subunits, we modify all of the subunits