PROTEINS-AND-AMINO-ACIDS.pptx.science.Biology

© 2010 Pearson Education, Inc.
PROTEINS AND AMINO ACIDS

I. INTRODUCTION
Proteins
* From Greek word ---> “ of first importance”
* Composed of: C, H, O, N, S
*The most abundant & versatile molecule within the cell
2

II. CELLULAR FUNCTIONS OF PROTEINS
1. Enzymes
2. Antibodies
* Help fight infection
3. Transport Proteins
* Ex.: Transferrin ---> Iron--> bone marrow --> heme
Hemoglobin & myoglobin
4. Regulatory proteins (hormones)
5. Structural proteins
* Ex.: keratin, tendon, & cartilage
6. Movement proteins
* Ex.: actin, myosin , flagellum
7. Nutrient proteins
* egg albumin (for embryos), milk casein ( for infants)
3

: Proteins and Amino Acids

What Are Proteins?
 Large molecules
 Made up of chains of amino acids
 Are found in every cell in the body
 Are involved in most of the body’s functions and life
processes
 The sequence of amino acids is determined by DNA

Structure of Proteins
 Made up of chains of amino acids; classified by number of
amino acids in a chain
• Peptides: fewer than 50 amino acids
- Dipeptides: 2 amino acids
- Tripeptides: 3 amino acids
- Polypeptides: more than 10 amino acids
• Proteins: more than 50 amino acids
- Typically 100 to 10,000 amino acids linked together
 Chains are synthesizes based on specific bodily DNA
 Amino acids are composed of carbon, hydrogen, oxygen,
and nitrogen

Structural Differences Between Carbohydrates,
Lipids, and Proteins
Figure 6.1

The Anatomy of an Amino Acid
Figure 6.2b

Peptide Bonds Link Amino Acids
 Form when the acid group (COOH) of one amino acid joins
with the amine group (NH2) of a second amino acid
 Formed through condensation
 Broken through hydrolysis

Condensation and Hydrolytic Reactions
Figure 6.3

Essential, Nonessential, and Conditional
 Essential – must be consumed in the diet
 Nonessential – can be synthesized in the body
 Conditionally essential – cannot be synthesized due to
illness or lack of necessary precursors
• Premature infants lack sufficient enzymes needed to
create arginine

Structure of the Protein
 Four levels of structure
• Primary structure
• Secondary structure
• Tertiary structure
• Quaternary structure
Any alteration in the structure or sequencing changes
the shape and function of the protein

Denaturing
 Alteration of the protein’s shape and thus functions
through the use of
• Heat
• Acids
• Bases
• Salts
• Mechanical agitation
 Primary structure is unchanged by denaturing

Denaturing a Protein
Figure 6.5

Quick Review
 Proteins are chains of combination of amino acids
 Amino acids contain carbon, hydrogen, oxygen, nitrogen,
and sometimes sulfur
 Unique amino acids consist of a central carbon with a
carboxyl group, a hydrogen, a nitrogen-containing amine
group, and a unique side chain
 There are 20 side chains and 20 unique amino acids
• 9 essential amino acids
• 11 nonessential amino acids
- At time these become conditionally essential
 Amino acids link together with peptide bonds by
condensation and break apart by hydrolysis

Quick Review
 Attractions and interactions between the side chains cause
the proteins to fold into precise three-dimensional shapes
 Protein shape determines its function
 Proteins are denatured and their shapes changed by
• Heat
• Acids
• Bases
• Salts
• Mechanical agitation

III. AMINO ACIDS: THE MONOMERS OF
PROTEINS
General Structures of
Amino acids
1. α-Carbon (central
carbon)
2. α-Carboxylate group
* a carboxyl group that
has lost a proton (-C00-
)
3. α-Amino group
* an amino group that has
gained a proton (-NH3+)
4. Hydrogen atom
5. R group (side chain) 18

In a protein the R groups interact with one another thru a
variety of weak forces. These interactions participate
in folding the protein chain into a precise 3-D shape
that determines its ultimate functions. They also serve
to maintain the 3-D conformation.
19

Enantiomers of Amino
Acids
1. L- amino acids
* α-amino group on the
left side.
2. D- amino acids
* α-amino group on the
right side.
20

Types of Amino Acids Based on the Polarity of the Side chain
Amino acids
Hydrophobic (Non-polar) Amino
Acids
* Prefer contact w/ one another over
water
* Generally found in the interior of
proteins to remain isolated w/
water
Hydrophilic (Polar)
Amino Acids
* Prefer contact w/ water
• Their hydrophilic R groups are
found on the surfaces of proteins
Neutral Amino Acids
* Their R groups
have high affinity
for water, but not
ionic at pH 7
Positively - Charged
Amino Acids
* At pH 7, they have a net + charge
because their R groups have +
groups
* Basic because their R groups react
w/ water to pick up a proton &
release a hydroxide ion
Negatively - Charged Amino
Acids
* At pH 7, they have a net
charge of -1.
* Have ionized carboxyl
groups (Carboxylate) in their
side chains.
* Acidic because ionization of
the carboxylic acid releases a
proton (H+)
21

22

IV. THE PEPTIDE (POLYMER)
1. A peptide is a chain of two or more amino acids connected
together by peptide bonds.
* The number of amino acids is indicated by prefixes di- (2),
tri- (3), tetra- (4), and so forth.
* Long peptides are usually called polypeptides.
* A protein may be composed of one or more peptides.
23

2. A peptide bond (amide bond) is formed when the carboxyl
group (Carboxylate group) of one amino acid is linked to
the amino group of another amino acid.
Illustration:
24

3. A peptide has two ends:
a. Amino(N) – terminal amino acid
* This is the end w/ a free α-NH3
+
b. Carboxy (C) – terminal amino acid
* This is the end w/ free –COO-
Illustration:
25

4. Peptides are named as derivatives of the C-terminal amino
acids, which receives its entire name. For all other amino
acids in a peptide, the ending –ine is changed to –yl.
Example:
26
Glycine Alanine Glycyl-alanine (gly-
ala)

V. WRITING THE STRUCTURES OF
SMALL PEPTIDES
Steps:
1. Note that the backbone of any peptide has the following
repeating sequence from left to right:
N--C--C--N--C--C--N--C--C
1 2 1 2 1 2
2. In the sequence above, consider the following
designations:
N = the amino group
C-1 = the α-carbon, which is always bonded to the hydrogen
atom & the R group.
C-2 = the carbon of the carboxyl group, which is always
bonded to the oxygen atom
27

Example: Draw the structure of the tripeptide alanyl-glycyl-
valine.
Solution:
1. Write the backbone of the said tripeptide. There are three
sets. Remember that the N-terminal amino acids is
written to the left.
28
N--C--C N--C--C
N--C--C
Set 1 Set 3
Set 2

valine.
Solution:
2. Add oxygen to the carboxyl carbon & hydrogens to the
amino nitrogen
N--C--C--N--C--C--N--C--C
29

valine.
Solution:
3. Add the hydrogens to the α-carbon.
N+--C--C--N--C--C--N--C--C--
30
H
H
H O
ll
H
ll
O
H
ll
O
O-
l
l
l
l
--

valine.
Solution:
4. Add the side chains. In the given example, they are CH3, -H, and CH(CH3)2
[from left to right]
N+--C--C--N--C--C--N--C--C--
31
H
H
H O
ll
H
ll
O
H
ll
O
O-
l
l
l
l
--
H H H
l l l

VI. LEVELS OF PROTEIN STRUCTURES
1. Primary structure
* The specific sequence of amino
acids
*Each protein has a unique sequence.
32

2. Secondary structure
* The precise coiling & folding of the
primary structure, resulting from the
hydrogen bonding between amide
hydrogen & carbonyl oxygen
2.1. α-helix
* The coiling of the primary structure
* Ex.: keratin (fibrous) (in hair, fur, wool,
& hoof)
Myosin (fibrous) (in muscles)
2.2. β-pleated sheets
* The folding of the primary structure
* Ex.: silk fibroin (fibrous protein from
silk worm)
NOTE: a protein may be a mixture of α-
helix & β-pleated sheets
33

3. Tertiary structure (3-D structure)
* The further coiling & folding of the secondary
structures, giving the protein its distinct shape.
* Determines the specific functions of a protein
34
Tertiary
structure

4. Quarternary structure
* The association of several polypeptides since many
proteins are not only composed of a single
peptide/polypeptide
* Sometimes, the quarternary structure binds w/ a non-
protein group (prosthetic group) which can modify
the function/s of a protein.
* Ex.: Glycoprotein, lipoprotein, & hemoglobin
35

VII. HEMOGLOBIN VS. MYOGLOBIN
36
Hemoglobin
(a protein w/
iron
Myoglobin
(a protein w/
iron)
RB
C Muscle
To transport
oxygen
To store
oxygen
Myoglobin has greater affinity for oxygen than
hemoglobin! What is the advantage?

VIII. FETAL HEMOGLOBIN VS. ADULT
HEMOGLOBIN
Fetal hemoglobin has greater affinity for O2 than adult
hemoglobin!
What is the advantage?
37

IX. PROTEIN DENATURATION
What is denaturation?
This is a process wherein the coiling & folding of proteins
become disorganized. Denatured proteins lose their
functions.
Can denaturation alter the primary structure of a protein?
No, it can’t!
38

What are the factors (agents) that can contribute to protein
denaturation?
1. Temperature
* High temperature can damage the tertiary (3D) structure
of a protein. Consequently, the protein becomes coagulated.
2. pH
* Very acidic condition --> proteins--> polycations
* Very basic condition --> proteins--> polyanions
39
This is the reason why the blood pH must be maintained.
Under very acidic or basic environment, vital blood
proteins (hemoglobin, immunoglobulin, & fibrinogen)
become denatured.

denaturation?
3. Rubbing alcohol (2-propanol)
* Denatures protein by disrupting the hydrogen bonds w/n the
protein
* Traditionally, a 70% solution of rubbing alcohol has been used
as a disinfectant or antiseptic. However, recent evidences
suggest that it is not an effective agent in this capacity.
4. Detergents
* They can disrupt the hydrophobic interactions, causing the
proteins to unfold.
40

denaturation?
5. Heavy metals (Hg+ and Pb+)
* They interfere with the salt bridges formed between amino
acid R groups of the chain, resulting in the loss of
conformation.
6. Mechanical stresses (stirring, whipping, & shaking)
* They can disrupt the weak interactions that maintain the
protein conformation. This is the reason that whipping egg
white produces a stiff meringue.
41

X. NUTRITIONAL CLASSES OF AMINO
ACIDS
42
Essential A.A.
* Not
synthesized
by the body &
thus required
in the diet
Non - essential
A.A.
* Synthesized
by the body &
thus not
required in
the diet
Semi -
essential A.A.
* Needed by
premature
infants & ill
adults
Isoleucine
Leucine
Lysine
Methionine
Phenylalani
ne
Threonine
Alanine
Arginine
Asparagine
Aspartate
Cysteine
Glutamate
Glycine
Histidine
Proline
Cysteine
Tyrosine
NOTE: Histidine &
arginine are essential
amino acids for
infants, but not for
healthy adults

X. NUTRITIONAL CLASSES OF PROTEINS
43
Therefore, What is
the good source of
protein, animal or
plant?

What is wrong with strict vegetarian diet?
It can’t provide all the essential amino acids! However,
this ca be remedied by succotash diet (staple diet of
native Americans), which is a mixture of corn (rich in
methionine) and bean (rich in lysine & tryptophan).
44

THANK YOU SO MUCH!
45

PROTEINS-AND-AMINO-ACIDS.pptx.science.Biology

Recommended

Recommended

More Related Content

Similar to PROTEINS-AND-AMINO-ACIDS.pptx.science.Biology

Similar to PROTEINS-AND-AMINO-ACIDS.pptx.science.Biology (20)

Recently uploaded

Recently uploaded (20)

PROTEINS-AND-AMINO-ACIDS.pptx.science.Biology