EnzymesA cell’s toolbox (Ch 6.4)

progress of reactionlow

high

energycontent

ofmolecules

products

reactants

activation energywithout catalyst

activation energywith catalyst

• An enzyme is a protein that

• catalyzes a chemical reaction in living cells.

• is not consumed in the reaction.

Enzyme structure

allostericregulatory site

Many enzymes have bothactive sites and allostericregulatory sites.

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.

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 ________ (amylose)

apart into monosaccharides

Iodine turns black when ______ is

present. How does the test in this picture

demonstrate amylase activity?

Pepsin Pepsin is a protease which breaks apart _______ chains into

smaller chains or single _____ ______.

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

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

pH influences enzyme activity

enzymeactivity

acidic

pepsin

salivaryamylase

basicpH

If you ate a lot of antacids, could that affect your digestion? Why?

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?

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.