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Learn about enzymes, the proteins that catalyze chemical reactions in living cells. Understand enzyme structure, substrate binding, and enzyme specificity. Explore enzyme regulation and the factors that influence enzyme activity.
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Enzymes • A cell’s toolbox (Ch 6.4)
Enzymes are: • Proteins • Carbohydrates • Lipids • Nucleic acids • Depends on the enzyme
high activation energy without catalyst activation energy with catalyst energy content of molecules reactants products low progress of reaction
An enzyme is a protein that • catalyzes a chemical reaction in living cells. • is not consumed in the reaction.
Enzyme structure substrate Many enzymes have both active sites and allosteric regulatory sites. active site enzyme allosteric regulatory site
substrates active site of enzyme enzyme 1 Substrates enter active site in a specific orientation. 3 Substrates, bonded together, leave enzyme; enzyme ready for new set of substrates. 2 Substrates and active site change shape, promoting reaction between substrates.
If enzymes are proteins, which type of molecule contains the instructions for making enzymes? • Other proteins • DNA • Depends on the enzyme
Lactase Lactose (milk sugar) is a disaccharide. Lactase breaks lactose down into two monosaccharides, which can be absorbed in the small intestine.
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?
Amylase Amylase breaks starch (amylose) apart into monosaccharides Iodine turns black when starch is present. How does the test in this picture demonstrate amylase activity?
Pepsin is a protease which breaks apart protein chains into smaller chains or single amino acids. Pepsin If enzymes are proteins, can pepsin digest itself? Hair and feathers are keratin protein. Why aren’t they digestible?
W O R K T O G E T H E R • If the enzyme amylase were broken down into its monomers by another enzyme, what would those monomers be? • What would be the monomers of the enzyme lactase? • What about the monomers of the enzyme pepsin?
The monomers of enzymes are always: • Amino acids • Nucleic acids • Fatty acids • Simple sugars
Enzyme regulation Allosteric inhibition Competitive inhibition allosteric regulator molecule An allosteric regulator molecule causes the active site to change shape, so the substrate no longer fits. A competitive inhibitor molecule occupies the active site and blocks entry of the substrate.
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?
Regulation may be through competitive or non-competitive inhibition.
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.
MTHFR is just one enzyme among many that convert certain nutrients into usable forms and convert waste into non-toxic forms.
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
Which of the following can inhibit enzyme function? • Temperature • pH • The genetic code • All of these
pH influences enzyme activity salivary amylase pepsin enzyme activity acidic pH basic If you ate a lot of antacids, could that affect your digestion? Why?
Temperature influences enzyme activity Maximum activity at optimal temperature. Enzyme activity increases High temperatures distort enzyme structure. enzyme activity temperature What is one reason why high fevers can be dangerous?
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.
