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EnzymesA cell’s toolbox (Ch 6.4)
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progress of reactionlow
high
energycontent
ofmolecules
products
reactants
activation energywithout catalyst
activation energywith catalyst
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• An enzyme is a protein that
• catalyzes a chemical reaction in living cells.
• is not consumed in the reaction.
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Enzyme structure
allostericregulatory site
Many enzymes have bothactive sites and allostericregulatory sites.
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3 Substrates, bondedtogether, leave enzyme;enzyme ready for newset of substrates.
active siteof enzyme
enzyme
1 Substrates enteractive site in aspecific orientation.
2 Substrates and activesite change shape,promoting reactionbetween substrates.
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Lactase
Lactose (milk sugar) is a
disaccharide.
Lactase breaks lactose down into two
monosaccharides, which can be absorbed in the
small intestine.
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Why would the genetic “error” causing lactose tolerance (the ability to drink milk all your life) be selected for in some parts of the world and not in others?
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Amylase
Amylase breaks ________ (amylose)
apart into monosaccharides
Iodine turns black when ______ is
present. How does the test in this picture
demonstrate amylase activity?
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Pepsin Pepsin is a protease which breaks apart _______ chains into
smaller chains or single _____ ______.
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allostericregulatormolecule
An allosteric regulatormolecule causes the activesite to change shape, so thesubstrate no longer fits.
Allosteric inhibition
A competitive inhibitor moleculeoccupies the active site andblocks entry of the substrate.
Competitive inhibition
Enzyme regulation
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Regulation controls enzyme pathways.
If one enzyme in the chain were missing, could the end product, G, be made?
If Product G came from another source, such as from consumed food, what would be its effect on
this system?
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Regulation may be through competitive or non-competitive inhibition.
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MTHFR gene: methylenetetrahydrofolate reductase
enzyme.
Located on the p arm of chromosome 1 in humans, this gene codes for an enzyme involved in the methylation of folic acid, a necessary B vitamin. Methylated (folate) and non-methylated (folic acid) forms are found in leafy greens, beans, and whole grains.
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MTHFR is just one enzyme among many that convert certain nutrients into usable forms
and convert waste into non-toxic forms.
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• Lack of the MTHFR enzyme causes buildup of homocysteine and/or folic acid, which can cause damage to the heart, blood vessels, and thyroid over time.
• Homocysteine is normally converted to glutathione, one of the body’s chief antioxidants. People with a defective MTHFR enzyme lose the protection of this important antioxidant.
More information on the MTHFR gene on:
•http://www.stopthethyroidmadness.com/mthfr/
•http://ghr.nlm.nih.gov/gene/MTHFR
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pH influences enzyme activity
enzymeactivity
acidic
pepsin
salivaryamylase
basicpH
If you ate a lot of antacids, could that affect your digestion? Why?
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enzymeactivity
Enzyme activityincreases
temperature
Maximum activity atoptimal temperature.
High temperaturesdistort enzymestructure.
Temperature influences enzyme activity
What is one reason why high fevers can be dangerous?
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Recap
• Enzymes are proteins that catalyze chemical reactions in living systems.
• Each enzyme does one job, but does that job over and over again. This is referred to as enzyme specificity.