BIOL Chap 4

What is energy?

The ability to do work or bring about change.

Why do cells need energy?

To grow, develop, repair, reproduce, send signals, and keep reactions going.

What are examples of forms of energy?

Mechanical energy, chemical energy, light energy, and heat energy.

What is potential energy?

Stored energy.

How is matter related to energy?

Matter can contain potential energy, such as food, wood, coal, or gasoline.

What is kinetic energy?

Energy in motion or released energy.

What are examples of kinetic energy?

Light, electricity, movement, and heat.

What is the first law of thermodynamics?

Energy cannot be created or destroyed; it can only change forms.

What does it mean that energy is conserved?

The total amount of energy stays constant even when it changes form.

In eukaryotic cells, what organelle converts energy from organic molecules into ATP?

Mitochondria.

What is the second law of thermodynamics?

When energy is converted from one form to another, some usable energy is lost as heat.

Why is no energy conversion 100% efficient?

Some useful energy is always lost as heat.

Why haven’t living things run out of energy?

The sun provides a continuing source of energy.

What are autotrophs?

Organisms that convert sunlight into chemical energy stored in carbohydrates.

What process do autotrophs use to convert sunlight into chemical energy?

Photosynthesis.

What are examples of autotrophs discussed in lecture?

Plants and cyanobacteria.

What are heterotrophs?

Organisms that depend on food produced by autotrophs.

Are humans autotrophs or heterotrophs?

Heterotrophs.

What are producers in an ecosystem?

Autotrophs that convert sunlight into usable stored energy.

What happens to energy at each step of an ecosystem food chain?

Energy is lost, mostly as heat.

About how much energy passes from one trophic level to the next?

About 10%.

What is ATP?

Adenosine triphosphate, the usable form of energy inside cells.

What does ATP stand for?

Adenosine triphosphate.

What are the three main parts of ATP?

Adenine, ribose, and three phosphate groups.

What does triphosphate mean?

Three phosphate groups.

What part of ATP stores energy cells can directly use?

The final phosphate-phosphate bond.

What is ADP?

Adenosine diphosphate, ATP after one phosphate group has been removed.

What is AMP?

Adenosine monophosphate, a molecule with one phosphate group attached.

What is inorganic phosphate often written as?

Pi.

What kinds of work does ATP power in cells?

Anabolic reactions, active transport, muscle contractions, and movement of cilia and flagella.

Can cells directly use the energy stored in glucose’s carbon-carbon bonds?

No. They convert that energy into ATP first.

What is an exergonic reaction?

An energetically favorable reaction that releases energy.

Do exergonic reactions require energy overall?

No, they release energy overall.

What is an endergonic reaction?

An energetically unfavorable reaction that requires energy.

Do endergonic reactions require energy?

Yes.

What is metabolism?

All biochemical reactions that occur within a cell or body.

What are the two main types of metabolic reactions?

Catabolic reactions and anabolic reactions.

What are catabolic reactions?

Breakdown reactions that degrade larger molecules into smaller ones.

What are anabolic reactions?

Build-up reactions that synthesize larger molecules from smaller ones.

What type of energy change is associated with catabolism?

Catabolism releases energy.

What type of energy change is associated with anabolism?

Anabolism requires energy.

What is hydrolysis associated with?

Catabolic breakdown reactions.

What is dehydration synthesis associated with?

Anabolic build-up reactions.

What is oxidation associated with in metabolism?

Catabolic reactions and loss of electrons or hydrogen atoms.

What is reduction associated with in metabolism?

Anabolic reactions and gain of electrons or hydrogen atoms.

What is another term for energy-releasing reactions?

Exergonic or exothermic.

What is another term for energy-consuming reactions?

Endergonic or endothermic.

How can catabolic reactions power anabolic reactions?

Energy released from breakdown reactions can be used to build larger molecules.

Why does the professor compare ATP to cash?

ATP can be used for many different types of cellular work, like cash can be spent in many places.

What is an enzyme?

A protein that speeds up a chemical reaction.

What are enzymes also called?

Biological catalysts.

What suffix do many enzyme names end in?

-ase.

What happens if an enzyme in a metabolic pathway is missing?

The pathway may stop, and the final product may not be produced.

What is activation energy?

The energy needed to start a reaction.

How do enzymes affect activation energy?

They lower the activation energy needed to start a reaction.

Do enzymes change the final products of a reaction?

No. They make the reaction happen faster or with less starting energy.

What is a substrate?

The reactant that an enzyme acts on.

What is the active site?

The region of an enzyme where the substrate binds.

What is the enzyme-substrate complex?

The temporary complex formed when an enzyme binds to its substrate.

What does enzyme specificity mean?

Each enzyme recognizes and acts on a specific substrate.

What model describes enzyme specificity?

The lock-and-key model.

What happens when an enzyme-substrate complex breaks apart?

Product is released.

What factors can affect enzyme function?

Substrate amount, temperature, pH, acids/bases, UV light, and inhibitors.

What happens when substrate concentration increases?

The reaction rate increases until the enzyme active sites are saturated.

What is the point of saturation?

The point where all enzyme active sites are full and adding more substrate no longer speeds the reaction.

How does temperature affect enzyme activity?

Activity increases up to an optimal temperature, then decreases if the enzyme denatures.

Why can high temperature reduce enzyme activity?

It can denature the enzyme and alter its shape.

What does denaturation mean?

A protein loses its shape and therefore loses its function.

Why does enzyme shape matter?

Structure determines function; the active site must keep the correct shape for the substrate to bind.

How does pH affect enzymes?

Changes in pH can disrupt bonds in the enzyme and alter the active site.

What is an enzyme’s optimal pH?

The pH where the enzyme works best.

What pH do many human cell enzymes work best around?

Around pH 7.4.

What enzyme works well in the acidic stomach?

Pepsin.

What enzyme works best around the pH of the upper intestine?

Trypsin.

What bacterium mentioned can function in the acidic stomach?

Helicobacter pylori.

What are enzyme inhibitors?

Molecules that decrease enzyme activity.

What is a competitive inhibitor?

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

What is a noncompetitive inhibitor?

An inhibitor that binds somewhere other than the active site and changes the enzyme’s shape.

How do competitive inhibitors affect reaction rate?

They slow the reaction by blocking substrate binding at the active site.

Are competitive inhibitors often reversible?

Yes.

How does a noncompetitive inhibitor prevent substrate binding?

It changes the shape of the enzyme or active site.

What is a metabolic pathway?

A series of linked reactions where products of one step become reactants for later steps.

What is a reactant?

A starting molecule in a reaction.

What is a product?

The molecule produced by a reaction.

What are intermediates in a metabolic pathway?

Molecules formed between the initial reactant and final end product.

What is negative feedback?

A pathway product inhibits an earlier enzyme to turn down or stop the pathway.

Why is negative feedback useful?

It prevents the cell from making too much of a product it already has enough of.

In the histidine example, what does excess histidine do?

It inhibits the first enzyme in the pathway.

What is allosteric feedback inhibition?

An end product binds to an allosteric site and changes enzyme shape, reducing enzyme activity.

What is an allosteric site?

A site on an enzyme other than the active site where a regulator can bind.

How is allosteric inhibition similar to noncompetitive inhibition?

Both involve binding away from the active site and changing enzyme shape.

What is phosphorylation?

The addition of a phosphate group to a molecule such as an enzyme.

What is dephosphorylation?

The removal of a phosphate group.

Can phosphorylation activate or inhibit an enzyme?

Yes. It depends on the enzyme.

What is oxidative phosphorylation?

Production of ATP using energy from electron transfer in an electron transport system.

What is photophosphorylation?

Production of ATP using energy from sunlight.

What are enzyme cofactors?

Helper molecules that enzymes may need to function.

What is a coenzyme?

An organic cofactor that assists an enzyme.

What are examples of coenzymes or electron carriers?

NAD, FAD, and NADP.

What is a redox reaction?

A reaction involving both reduction and oxidation.