Download Proteins are made of chains of amino acids

1. What makes an enzyme specific to one
type of reaction (in other words, what
determines the function of a protein)?
– SHAPE determines the function of a protein
and makes enzymes specific to one reaction
2. How does heating (boiling) affect the
ability of an enzyme to perform its
function?
– Heating/boiling denatures enzymes (unfolds
them) and makes them lose their function
What will we learn today?
HOW is the shape of a protein determined?
WHY does heating/boiling denature
enzymes and make them lose their
function?
Also:
• What makes hair straight or curly and how do
perms work?
• Why is it important to eat different types of food
to supply our protein needs?
Proteins are made of
chains of amino acids
What are amino acids?
Link to amino acid 3-D models
There are 20 different amino acids.
All have the same general form.
H
Amino
group
H2N
C
R
O
Carboxyl
group
C
OH
Side chain
Non-ionized form
Each amino acid has a different side chain.
H
H3N+
C C
H
H
O
–
O
Glycine (G)
Gly
H3N+
H
O
C C
–
CH3 O
Alanine (A)
Ala
C C –
CH O
H3C CH3
H3N+
Valine (V)
Val
H
O
H
O
H
O
O
C C –
CH2 O
CH
H3C CH3
H3N+
N+
Leucine (L)
Leu
Isoleucine (I)
Ile
Proline (P)
Pro
H3N+
C C – H2
C C –
O
O
H3C CH
H2C CH2
CH2
CH2
CH3
These side chains contain only carbon and/or hydrogen
Each amino acid has a different side chain.
H
H
O
H3N+
C
H3N+
C
C
CH2
H3N+
C
–
O
H
O
C
O
C
–
CH2
O
–
O
CH2
NH
OH
Phenylalanine (F)
Phe
Tyrosine (Y)
Tyr
Side chains contain ring structures
Tryptophan (W)
Trp
Each amino acid has a different side chain.
H
H3N+
C
H
O
H3N+
C
C
O
C
–
–
CH2
O
CH2
O
CH2
SH
S
CH3
Methionine (M)
Met
Side chains contain sulfur
Cysteine (C)
Cys
Each amino acid has a different side chain.
H
H
O
H3N+
C
O
H3N+
C
C
C
–
–
O
O
CH2
OH
Serine (S)
Ser
CH
HO
CH3
Threonine (T)
Thr
Side chains contain hydroxyl [OH] functional groups
Each amino acid has a different side chain.
H
H
H3N+
O
O
C
H3N+
C
C
C
–
–
CH2
O
CH2
C
H2N
CH2
O
C
H2N
Asparagine (N)
Asn
O
Glutamine (Q)
Gln
Side chains contain amino [NH2] functional groups
O
Each amino acid has a different side chain.
H
H3N+
O
C
H3N+
C
H
H
C
CH2
NH
+NH
H3N+
C
C
–
–
O
O
O
CH2
O
–
CH2
CH2
CH2
CH2
CH2
CH2
NH
+NH
3
C
C
O
+NH
2
NH2
Histidine (H)
His
Lysine (K)
Lys
Basic side chains
Arginine (R)
Arg
Each amino acid has a different side chain.
H
H3N+
H
O
C
H3N+
C
O
C
C
–
–
CH2
O
CH2
C
–
O
CH2
O
C
–
O
Aspartate (D)
Asp
O
Glutamate (E)
Glu
Acidic side chains
O
Proteins are chains of amino acids
H
H2N
H
O
+
C
C
H
OH
Carboxyl
group
H2N
Amino
group
C
O
H2N
C
CH3
OH
H
O
H
H
C
C
N
C
H
Peptide
bond
O
C
+
OH
CH3
C-terminus
N-terminus
H
H2O
H
H
O
H
H
O
H
H
O
H
H
O
H
H
O
H
H
O
H
H
O
H
H
O
N
C
C
N
C
C
N
C
C
N
C
C
N
C
C
N
C
C
N
C
C
N
C
C
CH3
H
CH2
CH2
OH
C
CH2
CH
H3C
OH
CH2
CH3
OH
CH2
SH
O
OH
N-terminus
H2N
C-terminus
Gly
Ala
Ser
Asp
Phe
Val
Tyr
Cys
1
2
3
4
5
6
7
8
COOH
Amino Acid sequence determines
the 3-D protein shape
• Interactions between amino acids cause
folding and bending of the chain
Examples:
– positive (+) and negative (-) parts of amino
acids are attracted to each other.
– hydrophobic regions are attracted to each other
• Folding
http://www.stolaf.edu/people/giannini/flashanimat/proteins/hydrophobic%20force.swf
•
Structure levels
http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein structure.swf
Figure 3.11a
Interactions that determine the structure of proteins
H N
C O
Hydrogen bond
between peptide
groups
CH2 OH
O C
Hydrogen bond between
side chain and peptide group
H
CH2 OH
CH3
O
H3C
CH2CH
(CH2)4
CHCH2
CH3
H3C
NH3+
Ionic bond
Hydrophobic
interaction
O
N CH2C
H
Hydrogen bond between
two side chains
–O
CH2
S
S CH2
Disulfide bond
CCCH2
Figure 3.11b
Tertiary structures are diverse.
A tertiary structure
composed mostly of
a-helices
A tertiary structure
composed mostly of
b-pleated sheets
A tertiary structure
rich in disulfide bonds
Paper polypeptides activity
Peptides are chains of amino acids and
sometimes used as another word for
protein.
Follow the instructions of your teacher to
build peptides using the paper amino acid
models.
Straight, curly, and “permed” hair
Explain the connection between
the order of the amino acids
and the shape of the protein.
Why did the boiled lactase not
work any more? (base your
answer on the paper model)
ESSENTIAL
AMINO ACIDS
Essential amino acids and nutrition
• Consider why protein is needed and what amino acids and proteins are
used for in the body. Describe the symptoms you would expect a person
with protein deficiency to have.
• Look at Table 1. Which amino acids does corn lack (not have)? Which
amino acids do beans and legumes lack (not have)?
• Vegans are vegetarians that do not eat any food from animals, including
milk and eggs. Why must vegans combine foods from a variety of plant
sources to avoid protein deficiency (for example rice and beans instead
of only beans)?
• A new protein supplement for athletes and weightlifters advertises that it
is the best because it is made of “100% natural organic corn protein”.
Why would this not be a good product for athletes and weightlifters?