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Proteins
Big Idea 4: Biological Systems Interact
Essential Knowledge
• Essential knowledge 4.B.1: Interactions
between molecules affect their structure and
function.
• a. Change in the structure of a molecular
system may result in a change of the function
of the system.
• b. The shape of enzymes, active sites, and
interaction with specific molecules are
essential for basic functioning of the enzyme.
Protein Functions!
• Structural support, storage, transport, cellular
communications, movement, and defense
against foreigners
• Make up more than 50% of dry mass of cells
Example: Hemoglobin
• Iron-containing protein found in red
blood cells.
• Transports oxygen to body
Example:
Antibodies
Antibodies
• Defensive protein  fights bacteria
and viruses
Example: Lactase, an Enzyme
• Enzyme that helps break down sugar lactose into
galactose and glucose. Speeds up reactions rates:
• Lactose intolerant: Mutation of Chrom. 2.
• Cramps, bloating, flatulence
Example: Insulin
• Hormonal protein: regulates sugar in
blood (tells cells to take it in), pancreas
Polypeptides
• Polymers built
from same set
of 20 amino
acids
• A protein
consists of one
or more
polypeptides
Amino Acid Monomers
Amino Acid Polymers
• Amino acids are linked by peptide bonds
Protein Structure and Function
• Consists of 1/more polypeptides twisted,
folded, and coiled into a unique shape
(determined by amino acid sequence)
Four Levels of
Protein Structure
• Primary,
Secondary,
Tertiary,
Quartenary!
• Watch Videos!
• Chaperonins are protein molecules that
assist the proper folding of other proteins
Polypeptide
Correctly
folded
protein
Cap
Hollow
cylinder
Chaperonin
(fully assembled)
Steps of Chaperonin
2 The cap attaches, causing the
Action:
cylinder to change shape in
such a way that it creates a
1 An unfolded polyhydrophilic environment for
peptide enters the
the folding of the polypeptide.
cylinder from one end.
3 The cap comes
off, and the properly
folded protein is
released.
Sickle-Cell Disease: A Change in
Primary Structure
• A change in primary structure can affect a
protein’s structure and ability to function
• Ex: Sickle-cell disease: results from a single
amino acid substitution in protein
hemoglobin
Fig. 5-22a
Normal hemoglobin
Primary
structure
Val His Leu Thr Pro Glu Glu
1
Secondary
and tertiary
structures
2
3
4
5
6
7
subunit
Quaternary
structure
Normal
hemoglobin
(top view)
Function
Molecules do
not associate
with one
another; each
carries oxygen.
Fig. 5-22b
Sickle-cell hemoglobin
Primary
structure
Secondary
and tertiary
structures
Val His Leu Thr Pro Val Glu
1
2
Exposed
hydrophobic
region
Quaternary
structure
Sickle-cell
hemoglobin
Function
Molecules
interact with
one another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
3
4
5
6
7
subunit
Fig. 5-22c
10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.
Messing Up Proteins?
• Alterations in pH, salt concentration, temp.,
or other environmental factors can cause a
protein to unravel  denaturation 
inactive protein
Enzyme Proteins!
• Acts as a catalyst to speed up chemical
reactions
• Can perform functions repeatedly 
workhorses!
Cofactors
• A non-protein chemical compound required
for enzyme activity Ex: Fe
• “Helper Molecules" that assist in biochemical
transformations.
Coenzymes
• A protein chemical compound required for
enzyme activity
• “Helper Molecules" that assist in biochemical
transformations.
Cofactors and Coenzymes
• Work together to regulate enzyme function.
• Usually the interaction relates to a structural
change that alters the activity rate of the
enzyme
Competitive Inhibitors
• Binding of inhibitor molecule to active
site of enzyme prevents binding of the
substrate and vice versa.
Allosteric Competition
• Binding of
inhibitor to
another
(allosteric) site of
enzyme (rather
than active site)
 prevents
binding of
substrate
Model Interpretations
• The change in function of an enzyme can be
interpreted from data regarding the
concentrations of product or substrate as a
function of time. These representations
demonstrate the relationship between an
enzyme’s activity, the disappearance of
substrate, and/ or presence of a competitive
inhibitor.