Proteins

1. Proteins
Big Idea 4: Biological Systems Interact

2. 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.

3. • Structural support, storage, transport,
cellular
communications, movement, and defense
against foreigners
• Make up more than 50% of dry mass of cells
Protein Functions!

4. Example: Hemoglobin
• Iron-containing protein found in red
blood cells.
• Transports oxygen to body

5. Antibodies
• Defensive protein  fights
bacteria
Example: Antibodies

6. 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

7. • Hormonal protein: regulates sugar in
blood (tells cells to take it in), pancreas
Example: Insulin

8. Polypeptides
• Polymers built
from same set
of 20 amino
acids
• A protein
consists of
one or more
polypeptides

9. Amino Acid
Monomers

10. Amino Acid
Polymers
• Amino acids are linked by peptide bonds

11. Protein Structure and Function
• Consists of 1/more polypeptides
twisted, folded, and coiled into a
unique shape (determined by amino
acid sequence)

12. Four Levels of
Protein Structure
• Primary,
Secondary,
Tertiary,
Quartenary!
• Watch
Videos!

13. Hollow
cylinder
Cap
Chaperonin
(fully assembled)
Polypeptide
Steps of Chaperonin
Action:
1 An unfolded poly-
peptide enters the
cylinder from one end.
2 The cap attaches, causing the
cylinder to change shape in
such a way that it creates a
hydrophilic environment for
the folding of the polypeptide.
3 The cap comes
off, and the properly
folded protein is
released.
Correctly
folded
protein
•Chaperonins are protein molecules that
assist the proper folding of other proteins

14. Sickle-Cell Disease: A Change in
Primary Structure
• A change in primary structure can affect
a
proteiŶ’s struĐture aŶd aďility to fuŶĐtioŶ
• Ex: Sickle-cell disease: results from a
single

15. Fig. 5-22a
Primary
structure
Secondary
and tertiary
structures
Function
Quaternary
structure
Molecules do
not associate
with one
another; each
carries oxygen.
Normal
hemoglobin
(top view)
subunit
Normal hemoglobin
Val His Leu Thr Pro Glu Glu
1 2 3 4 5 6 7

16. Primary
structure
Secondary
and tertiary
structures
Function
Quaternary
structure
Molecules
interact with one
another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
Sickle-cell
hemoglobin
Fig. 5-22b
Sickle-cell hemoglobin
subunit
Val Glu
6
7
Val His Leu Thr Pro
1 2
3
4
5
Exposed
hydrophobic
region

17. Fig. 5-22c
Normal red
blood cells are
full of individual
hemoglobin
molecules, each
carrying oxygen.
Fibers of abnormal
hemoglobin
deform red blood
cell into sickle
shape.
10 µm 10 µm

18. Messing Up Proteins?
• Alterations in pH, salt concentration,
temp.,
or other environmental factors can cause a
protein to unravel  denaturation 
inactive protein

19. • Acts as a catalyst to speed up
chemical
reactions
• Can perform functions repeatedly 
workhorses!
Enzyme Proteins!

23. Cofactor
s
• A non-protein chemical compound
required for enzyme activity Ex: Fe
• “Helper MoleĐules" that assist iŶ
ďioĐheŵiĐal

24. Coenzym
es
• A protein chemical compound required for
enzyme activity
• “Helper MoleĐules" that assist iŶ
ďioĐheŵiĐal

25. 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

26. Competitive
Inhibitors• Binding of inhibitor molecule to active
site of enzyme prevents binding of the
substrate and vice versa.

28. Allosteric Competition
• Binding of
inhibitor to
another
(allosteric) site
of enzyme
(rather than
active site)
 prevents
binding of

29. 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
eŶzyŵe’s aĐtivity, the disappearaŶĐe of
substrate, and/ or presence of a
competitive inhibitor.