Chapter 6
Proteins and Amino Acids
General Amino Acid Structure
Side Group Varies
H
O
Amino
N C C OH Acid
group
group H
H
Examples of amino acids
O
H
H
H
H O
Glycine
CH3
H
N C C OH
N C C OH
H
H O
Alanine
H
H C H
N C C OH
H
H O
Aspartic
Acid
SH
H
H C H
H
H
H O
Phenylalanine
H
C
CH3
H
N C C OH
N C C OH
H
OH
H O
Cysteine
H
H
C
OH
N C C OH
H
H O
Threonine
Condensation of two amino acids:
Formation of a dipeptide
H
H3C
N C C OH
H
H C H
H O
Alanine
H
+
N C C OH
H
H O
Phenylalanine
+ H2O
H
CH3
N C C
H
H C H
N C C OH
H O H H O
Peptide
Bond
Formation of a Polypeptide
AA1 + AA2 + AA3 + AA4 + AA5 + AA6 + AA7 + AA8 + AA9 + AA10 + AA11 + AA12
11 H2O
AA1---AA2---AA3---AA4---AA5---AA6---AA7---AA8---AA9---AA10---AA11---AA12
Folding and
Shape of Proteins
Essential versus Non-essential Amino Acid
Humans need ALL 20 amino acids to be able to
make proteins.
Glycine
Cysteine
Aspartic Acid
Glutamine
Alanine
Proline
Asparagine
Arginine
Serine
Tyrosine
Glutamic Acid
Valine
Threonine
Tryptophan
Leucine
Methionine
Lysine
Isoleucine
Phenylalanine
Histidine
Essential Amino Acids
Conditionally Essential Amino Acids
OH
H
H C H
Human enzyme
phenylalanine hydroxylase
N C C OH
H
H O
Phenylalanine
H
H C H
N C C OH
H
H O
Tyrosine
Protein digestion in
the GI Tract
Mouth
- moisten and mechanical
crushing
Stomach
- HCl denatures proteins
- HCl also converts
pepsinogen into pepsin
- pepsin acts to cleave
large polypeptides into
smaller polypeptides
Protein digestion in
the GI Tract
Small Intestine
- Trypsin and chymotrypsin
breakdown polypeptides into
smaller and smaller peptides.
- Carboxypeptidases and
aminopeptidases “chew”
along from the ends to
liberate amino acids.
- Di- and tripeptidases
break down dipeptides and
tripeptides to amino acids.
- Free amino acids are
absorbed into the blood
system.
Protein synthesis: Transcription
Making messenger RNA
Cell
mRNA
DNA
Protein synthesis: Translation
Ribosomes “translate” the CODE of the
message utilizing transfer RNAs which
carry individual amino acids
Ribosome
mRNA
Amino Acid
Transfer RNA
Protein synthesis
Growing protein strand
Protein Function Within Our Body
1) Building materials
(e.g.
collagen, elastin, keratin,
myocin, actin)
2) Enzymes
(e.g. lipase, amylase, pepsin)
3) Hormones
(e.g. insulin, glucagon, CCK)
4) Regulators
Fluid balance
5) Transport: i.e. hemoglobin, ferritin
Iron atom
Heme
Normal
versus
Sickle Cells
6th residue
Normal Hemoglobin
Val-His-Leu-Thr-Pro-Glu-Glu-
Sickle Cell Hemoglobin
Val-His-Leu-Thr-Pro-Val-Glu-
A Membrane-bound transport protein
“Sodium - Potassium Pump”
INSIDE CELL
OUTSIDE CELL
6) Acid-Base Regulators
8.0
Death
Alkalosis
7.45
Normal
7.35
Acidosis
6.8
Death
7) Antibodies (Immune system)
8) Energy:
- break down protein to use
the energy.
Grams
Proteins per Serving
In Food Groups
Quality of Proteins
• A COMPLETE protein contains essential
amino acids is relatively the same amounts as
humans need.
(e.g. meat, fish, poultry, eggs, milk)
• However, all proteins do not have the same
proportion of each amino acid.
Legume
Ile
YES
Lys
YES
Met
NO
Trp
NO
Grains
NO
NO
YES
YES
Together
YES
YES
YES
YES
© 2002 Wadsworth Publishing / Thomson Learning™
PEM (Protein-Energy Malnutrition)
• affects 1 out of 4 children in the world.
• accomplice in 50% of the 10.9 million
child deaths each year.
• 70% in Asia, 26% in Africa & 4% in
Latin America
PEM (Marasmus)
• chronic PEM
•6 - 18 months
• inadequate intake
of energy and
protein.
PEM (Kwashiorkor)
• acute PEM
• sets in at 18 months 2 years of age
• inadequate intake of
protein due to a change
from breast milk to
protein poor cereals.
Protein and Amino Acid Supplements
 what is the RDA for protein?
 what happens when more high
protein higher amounts of proteins
are consumed?
 do athletes need to supplement
their diet with higher amounts of
protein or amino acid?
Types of Vegetarianism
Omnivores - people that eat ALL foods
including meat.
Lactoovovegetarians - exclude meat,
poultry, fish, and seafood.
Lactovegetarians - also exclude eggs
Vegan - exclude ALL animal derived foods
Vegetarians obtain their protein from whole
grains, legumes, nuts, vegetables, and, in some
cases, eggs and milk products
Food Pyramids Compared