Structure of proteins
- Amino Acids
- Supplied by protein containing food
- Body requires 20 different amino acids to function, 9 of which needed to be obtained through diets
Non essential AA
amino acids our bodies make in sufficient amounts
Essential AA
amino acids our bodies do not make in sufficient amounts and therefore must be obtained through diet
Synthesis of Nonessential AA by Body:
transamination: transferring an amino group from 1 amino acid to a carbon skeleton to form a new amino acid
Deamination
process of losing an amino acid without it being transferred to another carbon skeleton
- Lost amino acids are incorporated into urea in the liver which is excreted in urine
Complete Proteins
protein sources containing all 9 essential amino acids
- All animal sources of protein are complete
- Also plant sources such as soy, buckwheat and quinoa
Incomplete Proteins
protein sources that do not contain all 9 essential amino acids
- Most plant sources are low in at least 1 of the 9 aa
Complementary Proteins
when 2 or more plant proteins are combined to compensate for their individual differences in essential amino acid contents
Limiting Amino Acid
limits the amount of protein the body can synthesize due to it being the essential amino acid in smallest supply
- Body cells require a pool of essential aa for the synthesis of body proteins - A single plant protein cannot support the synthesis of body protein if it’s the sole source, therefore proteins cannot be made and remaining aa are converted to carbs or fat
Synthesis of Proteins
through transcription and translation amino acids are produced and linked by peptide bonds
size of Protein Chains
- Dipeptides:
- Tripeptides: joining of 3 amino acids
- Oligopeptides: joining of 4-9 amino acids
- Polypeptides: joining of 10 or more amino acids
Sources of Protein
- high protein food sources
- recycling of amino acids by breakdown of body protein
How the body recycles body protein
- Digestive tract constantly sheds off the lining, which is treated like food particles and it releases amino acids during digestion.
- The amino acids that are picked up are then reabsorbed and added to the pool of aa
- Adults make and degrade 250-300g of protein per day
- Dietary protein is needed to replenish and maintain an adequate amount
Biological Value
a measure of how efficiently the absorbed food protein is converted into body tissue protein
- Determined by comparing nitrogen retention with the nitrogen content of the food protein
- The higher the match, the greater the BV
Protein Efficiency Ratio
assesses a foods protein quality by comparing the amount of weight gain by a growing lab animal consuming a specifc amount of the protein source
Chemical Score
also known as the amino acid score which the amount of each essential aa in a gram of the food protein being tested is divided by the ideal amount of that aa in a gram of reference protein(egg)
Protein Digestibility Corrected Amino Acid Score
multiplies a foods chemical score by its digestibility
Nitrogen Balance
- Healthy people not in periods of growth or recovering from illness or injury or are athletes need to consume protein in an amount that replaces protein lost in urine, sweat, feces, skin cells and hair and nails
Recommended Intakes of Protein
- 0.8g/kg of body weight
- AMDR is between 10-35%
Protein Digestion
- Protein digestion begins during cooking as heat denatures proteins and softens the tough connective tissue in meat
Protein digestion:
- Begins in the stomach by HCI
- Pepsin unravels polypeptides
- Partially digested proteins move into the SI
- CCK released from SI which travels to the pancreases and forces the release of proteases
- These enzymes break down proteins into short amino acids which can be absorbed
Protein Absorption
- Short chain AA are absorbed by villi which are completely broken down into single amino acids
- Portal vein takes them to the liver
- Either stored, combined to form needed proteins or converted to fat
Function of Proteins
- support the development of body tissues and structures
- Albumin and globulin blood proteins are important in maintaining fluid balance
- Proteins located in cell membranes pump chemical ions into and out of cells which help keep the blood slightly alkalinic
- Proteins act as good buffers
- Amino acids are required for the synthesis of most hormones in the body
- transporters carrying them through the bloodstream to cells and across cell membranes
- Antibody proteins are key components in the immune system as they bind to foreign proteins that invade the body, preventing attacks
- Amino acids can also be turned into glucose as a back up energy system
Protein Energy Malnutrition
protein deficiency rarely developing as an isolated condition but in combination with deficiencies in other nutrients
- Occurs in the disease form as: - Marasmus: severe energy deficiency leading to extreme weight loss, muscle and fat loss Kwashiorkor: underlying infections or disease due to severe protein deficits
Issue with High Protein Diets
- High protein diets can overburden people with impaired kidney functions, limiting their ability to excrete excessive nitrogen as ureaI
