Download Contemporary Nutrition

The Macronutrients-Proteins
Chapter 1
Overview of Protein
• Body is made up of thousands of protein
substances
– More than 30,000 different kinds of protein
– Unique structure and function
– Twenty amino acids commonly found in
human protein
– Proteins = 50% of the dry weight of most cells
Overview of Protein
• Made up of amino acids
• Contains carbon, hydrogen, and oxygen
– And at least one N in structures
• N is in the form of an amine group (NH2)
– Carboxyl group (COOH)
– R group: side chain, this is what makes each
amino acid unique
Amino Acid
R
NH2
O
C
C
OH
H
R group
Acid group
Nitrogen group
Overview of Proteins
• Amino acids
– Peptide bonds
– Dipeptide – two amino acids
– Tripeptide – three amino acids
– Polypeptides – multiple amino acids
Protein Organization
• Polypeptide chain
– Twists and bends to native conformation
– Determined by side chains
• Hydrophilic – outer surface
• Hyrophobic - folded inside
Proteins
• Order of amino acids
– Determines shape
• Final shape
– Determines function
– Determines stability
Fig. 02.16a
Proteins
• Denaturation
– Uncoiling – alters function
• Heat
• Stomach acid
• Irreversible
Denaturation of Proteins
Denaturation
• Foods are a means of obtaining amino
acids
• Cooking can make substances available
– Vitamin – biotin (cooked eggs)
Denaturation of Proteins
Heat/acid/alkaline/enzymes
Results in alteration of the protein’s three
dimensional structure
Overview of Protein
• Amino acids-20 required by body
– Essential – indispensable
• Body does not have pathway to synthesize
• Supplied by diet
– Non-essential
• Can be provided through metabolic pathways
– Conditionally essential amino acids
• Under certain conditions
• Typically malnutrition
Dietary Protein
• Animal proteins
– High-quality
– Complete – 8 essential amino acids
• Low-quality
– Incomplete
• Lacks one or more essential amino acids
– Most plant foods
– Cannot meet all amino acid needs
– Greater variety and amount of plant proteins needed
Transamination
• Transfer of an amine
group
– From a donor amino
acid
– To an acceptor amino
acid
• Formation of new
amino acid
Dietary Protein
• All-or-none principle in protein synthesis
– If not all of the amino acids are present,
protein synthesis does not occur
• Limiting amino acids
– Essential amino acid in smallest supply
• Complementary proteins
– Mixed diets – foods containing different amino
acids are combined
Limiting Amino Acid
C is the limiting amino acid in this example
CCCCC
AAAAAAAA
RRRRRR
CAR CAR CAR
CAR CAR
R
A A A
Complementary Protein
Food 1
Food 2
CC
AAAA
RRR
CCCC
AA
RRR
Combined
CAR CAR CAR
CAR CAR CAR
Vegetarians
• Protein requirements
– Variety of plant foods - Complementary
• Grains and legumes
• Soy protein
– Lacto vegetarian
• Milk, milk products
– Ovolactovegetarian
• Eggs
Protein
•
•
•
•
•
•
Sedentary
Recreational exercisers
Serious RT, early
Serious RT, established
Serious endurance
Adolescent athlete
0.8-1.0 g/kg/d
0.8-1.0
1.5-1.7
1.0-1.2
1.2-1.6
1.5-2.0
Role of Proteins
• Protein content of skeletal muscle
– 65% total protein of body
• Component of tissue structures
– Cells
– RNA, DNA
– Electron carriers
• NAD, FAD
Structural Proteins
Structural Proteins
Globular Proteins
Protein Turnover
• Replenishment of protein containing
structures
– Amino acid pool
• Anabolism
– Tissue building
• Catabolism
– Tissue breakdown
Nitrogen Balance
• Positive nitrogen balance
– Intake exceeds excretion
• Synthesis of new tissues
• Negative nitrogen balance
– Protein used for energy
– Uses reserves – skeletal muscle
Protein Metabolism
• Deamination
– Releases amine group
– Urea
• Fate of deaminated carbon compound
– Make new aa
– Converted to CHO or fat
– Catabolized for energy
Additional Roles of Protein
• Nervous and connective tissue
– Not in energy metabolism
• Alanine provides CHO fuel
– Gluconeogenesis – prolonged exercise
• Alanine-glucose cycle provides 40-50%
– From liver’s glucose release
– Provide up to 15% of the total energy
requirement