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