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Flashcards in Lecture 10 Deck (36):

What are the 3 cellular energy considerations

1. ATP (adenosine triphosphate)
2. Exergonic vs. Endergonic reactions
3. Change in free energy


What is the role of enzymes?

catalyze biochemical reactions in a living organism, usually a protein


What are enzymes made of?

Enzymes are made from living cells, but could still remain and function, once the cells from which they were made were broken down


What are proteins manufactured from

manufactured from genes through the process of protein synthesis


Enzyme size and fit

Enzymes are larger than the substances (substrates) upon which they act. Enzymes have a location known as the active or catalytic site where the substrates will fit.



improve the efficiency of reactions. They speed up reactions that would otherwise occur in nature very slowly without these enzymes.


How do enzymes help metabolism in cells? 2 ways

a. Enzymes lower the activation energy that is necessary to initiate a reaction.
b. Enzymatic reactions allow for energy to be released in increments, thus allowing for a more
efficient capture and usage of the energy.


Can enzymes be recycled?



active or catalytic site

Enzymes come into a close and
intimate 3D contact with their substrates at the active or catalytic site- this specific interaction is
sometimes described by a lock and key type hypothesis and as complimentary steric specificity


allosteric sites

Enzymes have sites for chemical bonding away from the active or catalytic site. These sites are
known as allosteric sites.


Competitive inhibitors

act to compete with the substrate at the active site


non-competitive inhibitors

act at allosteric sites



protein portion



nonprotein portion


The apoenzyme and the cofactor together make up

the complete and active whole enzyme known as a holoenzyme


The cofactor can be

a metal ion, or if it is a low molecular weight and complex organic molecule it is called a coenzyme


Metal ion such as? bind where?
what do they do?

such as iron, zinc, magnesium and calcium will bind at allosteric sites
Metal ion cofactors will bind to allosteric sites and alter the configuration of the active sites.


Coenzymes bind?

will bind at the active or catalytic site


Coenzymes assist the enzymes by and are derived from?

by accepting atoms removed by the substrate or
by donating atoms required by the substrate. Many coenzymes are derived from vitamins.


NAD (nicotinamide adenine dinucleotide)

transfers hydrogen pairs (2H) and is derived from
the B complex vitamin, niacin


FAD (flavin adenine dinucleotide)

transfers hydrogen pairs (2H) and is derived from the B
complex vitamin, riboflavin.


CoA (coenzyme A)

transfers a 2 carbon unit (acetyl group) and is derived from the B complex vitamin, pantothenic acid


Folic acid-transfers carbon

derived from the vitamin called THFA (tetrahydrofolic acid)


PABA (para-aminobenzoic acid)

Bacteria uniquely need PABA (para-aminobenzoic acid) to make folic acid. Antibiotics known as sulfanilamides will block the activity of PABA, preventing the synthesis of folic acid and thereby inhibiting bacterial metabolism


Enzyme activity can be affected by
does size affect it?

enzyme concentration, substrate (reactant) concentration,
product concentration, temperature and pH. Actual size variations amongst different enzymes have little effect on enzyme activity


oxidoreductase group

An enzyme class known as the oxidoreductase group is involved in oxidation and reduction reactions


An oxidation reaction results in

the loss of hydrogens, loss of electrons, or the gain of oxygen


A reduction reaction results in

the gain of hydrogens, gain of electrons or the loss of oxygen


A dehydrogenase is a

type of oxidoreductase enzyme that removes hydrogen


Enzyme control at the level of synthesis (formation)
Inducible enzymes

Some enzymes are only made in the presence of their substrates. These are known as inducible (adaptive) enzymes.


Repressible enzymes

are no longer made when specific products of a reaction are present in appropriate amounts.


Where are repressible and unducible enzymes controlled

Induced and repressed enzymes are controlled at the gene level.


When are genes on and off

Genes are turned on (enzymes are made from protein synthesis process) to produce inducible enzymes, while genes are turned off (enzymes are not made from protein
synthesis process) to not produce repressible enzymes.


Enzyme control of pre-synthesized (constitutive) enzymes

the activities of pre-synthesized (already present in the cell) enzymes can be controlled through competitive and noncompetitive inhibition.


In competitive inhibition

the inhibitor is generally an organic compound that resembles the substrate. It will fight or compete for the active (catalytic) site. The effectiveness of the inhibitor is related to the concentration of the inhibitor, the concentration of the substrate and the relative affinity (ability to bind) of the enzyme to the substrate or the inhibitor


In noncompetitive inhibition

the inhibitors react with the allosteric sites, and look
nothing like the original substrate. In feedback (end-product) inhibition, final products of a reaction will bind on allosteric sites of an original enzyme in the reaction chain to shut down a reaction. In branched pathways, the product will generally inhibit the activity of the first unique enzyme in the pathway. This will shut down the unneeded