Transcript CHM 103 Lecture 36 S07

Announcements & Agenda (04/25/07)
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

Indicate 2 times you can meet for review next week
Choices: T @ 4, T @ 5, T @ 7
W @ 4, W @ 5, W @ 7
FINAL EXAM TIME: Thursday @ 10:30 am!!!

Cumulative with 10-15 % New Stuff
Exam 3 back Fri 
Complete HCTA: If >85 % Do Before Exam,
You ALL get 2 extra credit points
Today
 Protein Structure (16.5)
 Enzymes (16.6-16.8)
 Coenzymes (16.9)
NO 3pm Review
Today 
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CH 16 Practice Problems
(MUST DO 10 OF THESE BY FRI)
Will be counted as FINAL QUIZ! (EASY PTS)
16.01, 16.07, 16.11, 16.21, 16.25, 16.27,
16.29, 16.31, 16.33, 16.35, 16.37, 16.39,
16.41, 16.43, 16.49, 16.51, 16.55, 16.61,
16.63, 16.67, 16.69, 16.77, 16.81
Useful for Exam Prep on CH 16!
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Last Time: Functions of Proteins
Proteins perform many different functions in the body.
KNOW THE CLASSES!
Function of proteins determined by amino acids used
and how they are put together in 2-D and 3-D
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Last Time: Types of Amino Acids
Nonpolar
Polar
4 main kinds:
• nonpolar (hydrophobic)
with hydrocarbon side
chains.
• polar (hydrophilic) with
polar or ionic side chains.
• acidic (hydrophilic) with
acidic side chains.
• basic (hydrophilic) with
–NH2 side chains.
Acidic
Basic
Be able to recognize these 4 kinds, no need to memorize
all 20 for the Final Exam!!!!!!!!!!!!!!!!!
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Last Time: Formation of Proteins
The Peptide Bond
• The peptide bond is an amide bond.
• forms between the carboxyl group of one amino acid
and the amino group of the next amino acid.
O
+
||
H3N—CH2—C—O– +
CH3 O
|
||
+
H3N—CH—C—O–
O H CH3 O
|| | |
||
+
H3N—CH2—C—N—CH—C—O–
peptide bond
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Tour of Protein Structure…
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Last Time: Primary Structures
• The nonapeptides oxytocin and vasopressin
have similar primary structures.
• Only the amino acids at positions 3 and 8 differ.
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Primary Structure of Insulin
Insulin
• was the first protein to have
its primary structure
determined.
• has a primary structure of
two polypeptide chains linked
by disulfide bonds.
• has a chain A with 21 amino
acids and a chain B with 30
amino acids.
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Modification of insulin
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Secondary Structure Elements
• a 3-D arrangement of amino
acids in a polypeptide chain.
• result from intermolecular forces
such as hydrogen bonding
• Several types of secondary
structure
•
•
•
•
Alpha helices
Beta sheets
Triple helices
Many more…
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Secondary Structure – Alpha Helix
• a 3-D spatial arrangement of
amino acids in a polypeptide
chain.
• held by H bonds between the
H of –N-H group and the O of
C=O of the fourth amino acid
down the chain.
• a corkscrew shape that looks
like a coiled “telephone cord”.
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Beta Pleated Sheet
•
•
•
•
polypeptide chains side by side.
hydrogen bonds between chains.
has R groups above and below the sheet.
is typical of fibrous proteins such as silk, betakeratin, etc.
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Secondary Structure – Triple Helix
• three polypeptide
chains woven
together.
• typical of collagen,
connective tissue,
skin, tendons, and
cartilage.
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Tertiary Structure
• overall 3-D shape.
• determined by
attractions &
repulsions between
side chains of amino
acids
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Crosslinks in Tertiary Structures
involve attractions
and repulsions
between the side
chains of the
amino acids in the
polypeptide chain.
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Example: Globular Proteins
• have compact,
spherical shapes.
• carry out synthesis,
transport, and
metabolism in the
cells.
• such as myoglobin
store and transport
oxygen in muscle.
Myoglobin
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Quaternary Structure
• combination of 2 or
more protein units.
• Example: hemoglobin
consists of 4 subunits.
• stabilized by the same
interactions found in
tertiary structures.
Hemoglobin
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Summary of Protein Structure
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Denaturation
• the disruption of bonds in the secondary, tertiary
and quaternary protein structures.
• heat and organic compounds: break apart H
bonds and disrupt hydrophobic interactions.
• acids and bases: break H bonds between polar
R groups and disrupt ionic bonds.
• heavy metal ions: react with S-S bonds to form
solids (among many other things)
• agitation such as whipping that stretches
peptide chains until bonds break.
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Applications of Denaturation
• cooking.
• the skin is wiped
with alcohol.
• heat is used to
cauterize blood
vessels.
• instruments are
sterilized in
autoclaves.
http://www.lifehouseproductions.com/remorgida.html
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Enzymes: Biological Catalysts (16.6)
• Catalyze nearly all
chemical reactions
taking place in the cells
of the body.
• Increase the rate of
reaction by lowering
the energy of
activation.
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Classification of Enzymes
- classified by the reaction they catalyze.
- names usually end in –ase & often identify reactant
(substrate) and function of enzyme
Class
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
Type of Reactions catalyzed
Oxidation-reduction
Transfer groups of atoms
Hydrolysis
Add atoms/remove atoms to or
from a double bond
Rearrange atoms
Use ATP to combine small molecules
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How They Work!!!
In an enzyme-catalyzed reaction:
• a substrate attaches to active site.
• an enzyme-substrate (ES) complex
forms.
• Lock & key model (OLD, RIGID MODEL)
• Induced-fit model (CURRENT MODEL)
• reaction occurs, products released
• an enzyme is used over and over.
• Known functions of enzymes
important in medical analyses
E+S
ES
E+ P
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Diagnostic Enzymes
• often determine
the amount of
damage in
tissues.
• that are elevated
may indicate
damage or
disease in a
particular organ.
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Diagnostic Enzymes Example
Levels of enzymes
CK, LDH, & AST
• are elevated
following a heart
attack.
• are used to
determine the
severity of the
attack.
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Factors Affecting Enzyme Activity!
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Temperature
Enzymes
• are most active at an
optimum temperature
(usually 37°C in
humans).
• show little activity at
low temperatures.
• lose activity at high
temperatures as
denaturation occurs.
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pH
Enzymes
• are most active at
optimum pH.
• contain R groups
of amino acids
with proper
charges at
optimum pH.
• lose activity in low
or high pH as
tertiary structure is
disrupted.
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Optimum pH Values
Most Enzymes in
• the body have an optimum pH of about 7.4.
• certain organs, enzymes operate at lower and higher
optimum pH values.
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Substrate Concentration
As substrate
concentration increases,
• the rate of reaction
increases (at constant
enzyme concentration).
• the enzyme eventually
becomes saturated
giving maximum activity.
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Enzyme Inhibitors
• are molecules that cause a loss of catalytic
activity.
• prevent substrates from fitting into the active
sites.
E+S
E+I
ES
EI
E+P
no P
Natural & Synthetic: Lots of drugs
work by acting as inhibitors
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Coenzymes (16.9)
Coenzyme: a molecule which is ‘associated’ with
the enzyme (but in not part of the amino acid
sequence) that helps enzymes prepare the
active site for catalytic activity.
- many coenzymes derived from vitamins
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Water-Soluble Vitamins
• soluble in aqueous solutions.
• cofactors for many enzymes.
• not stored in the body.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Fat-Soluble Vitamins
• are A, D, E, and K.
• are soluble in lipids, but not in aqueous solutions.
• are important in vision, bone formation,
antioxidants, and blood clotting.
• are stored in the body.
More on these on Friday!
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