Enzymes
A cell’s toolbox (Ch 6.4)
Enzymes are:
65%
1.
2.
3.
4.
5.
Proteins
Carbohydrates
Lipids
Nucleic acids
Depends on the
enzyme
21%
6%
9%
0%
1
2
3
4
5
high
activation energy
without catalyst
energy
content
of
molecules
activation energy
with catalyst
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
active site
enzyme
Many enzymes have both
active sites and allosteric
regulatory sites.
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?
75%
1. Other proteins
2. DNA
3. Depends on the
enzyme
14%
11%
1
2
3
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
Pepsin is a protease which
breaks apart protein chains
into smaller chains or
single amino acids.
If enzymes are
proteins, can
pepsin digest
itself?
Hair and feathers
are keratin protein.
Why aren’t they
digestible?
• 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?
W
O
R
K
T
O
G
E
T
H
E
R
The monomers of enzymes are
always:
25%
1.
2.
3.
4.
25%
25%
2
3
25%
Amino acids
Nucleic acids
Fatty acids
Simple sugars
1
4
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 noncompetitive 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.
More information on the MTHFR gene
on:
•http://www.stopthethyroidmadness.co
m/mthfr/
•http://ghr.nlm.nih.gov/gene/MTHFR
• 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.
Which of the following can inhibit
enzyme function?
25%
1.
2.
3.
4.
25%
25%
2
3
25%
Temperature
pH
The genetic code
All of these
1
4
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
Enzyme activity
increases
enzyme
activity
Maximum activity at
optimal temperature.
High temperatures
distort enzyme
structure.
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.