The Macronutrients-Proteins Chapter 1. Overview of Protein Body is made up of thousands of protein...
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Transcript of The Macronutrients-Proteins Chapter 1. Overview of Protein Body is made up of thousands of protein...
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 group Acid group
Nitrogen group
NH2 O
R C C OH
H
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
CCCCC
AAAAAAAA CAR CAR CAR
RRRRRR CAR CAR
R
A A A
C is the limiting amino acid in this example
Complementary Protein
Food 1 Food 2 Combined
CC CCCC
AAAA AA CAR CAR CAR
RRR RRR 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 0.8-1.0 g/kg/d• Recreational exercisers 0.8-1.0• Serious RT, early 1.5-1.7• Serious RT, established 1.0-1.2• Serious endurance 1.2-1.6• Adolescent athlete 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