Flashcards in Lecture 10 Deck (36):
1
What are the 3 cellular energy considerations
1. ATP (adenosine triphosphate)
2. Exergonic vs. Endergonic reactions
3. Change in free energy
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What is the role of enzymes?
catalyze biochemical reactions in a living organism, usually a protein
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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
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What are proteins manufactured from
manufactured from genes through the process of protein synthesis
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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.
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Catalysts
improve the efficiency of reactions. They speed up reactions that would otherwise occur in nature very slowly without these enzymes.
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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.
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Can enzymes be recycled?
Yes
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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
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allosteric sites
Enzymes have sites for chemical bonding away from the active or catalytic site. These sites are
known as allosteric sites.
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Competitive inhibitors
act to compete with the substrate at the active site
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non-competitive inhibitors
act at allosteric sites
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apoenzyme
protein portion
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cofactor
nonprotein portion
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The apoenzyme and the cofactor together make up
the complete and active whole enzyme known as a holoenzyme
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The cofactor can be
a metal ion, or if it is a low molecular weight and complex organic molecule it is called a coenzyme
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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.
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Coenzymes bind?
will bind at the active or catalytic site
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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.
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NAD (nicotinamide adenine dinucleotide)
transfers hydrogen pairs (2H) and is derived from
the B complex vitamin, niacin
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FAD (flavin adenine dinucleotide)
transfers hydrogen pairs (2H) and is derived from the B
complex vitamin, riboflavin.
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CoA (coenzyme A)
transfers a 2 carbon unit (acetyl group) and is derived from the B complex vitamin, pantothenic acid
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Folic acid-transfers carbon
derived from the vitamin called THFA (tetrahydrofolic acid)
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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
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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
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oxidoreductase group
An enzyme class known as the oxidoreductase group is involved in oxidation and reduction reactions
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An oxidation reaction results in
the loss of hydrogens, loss of electrons, or the gain of oxygen
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A reduction reaction results in
the gain of hydrogens, gain of electrons or the loss of oxygen
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A dehydrogenase is a
type of oxidoreductase enzyme that removes hydrogen
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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.
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Repressible enzymes
are no longer made when specific products of a reaction are present in appropriate amounts.
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Where are repressible and unducible enzymes controlled
Induced and repressed enzymes are controlled at the gene level.
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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.
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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.
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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
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