Protein

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Protein
Human Nutrition HLTH 2001 Random Facts

• Health claim states 25 grams of soy protein
  daily in the diet is needed to show a significant
  cholesterol lowering effect

• Tofu, also known as soybean curd, is a soft,
  cheese-like food made by curdling fresh hot
  soymilk with a coagulant
• 3 Serves of tofu 1 ½ cups of tofu to get 25
  grams

http//www.soyfoods.org/
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Lecture 5. Macronutrients Protein
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Amino Acid structure

• H
• central carbon atom
• H C H
• H H H O
• H C C C C C O H
• organic acid group
• H H H N Carboxyl group
• side group H H
• amino group (NH2)

(alpha carbon)
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Amino Acids

• 20 common amino acids in food
• 2 additional less common forms
• each has a different side group
• Figure 6.2 (p. 183) Examples of Amino Acids.
  Whitney Rolfes 10th Ed.

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Amino Acids
Leucine Lysine Methionine PhenylalanineProline
Serine Threonine Tryptophan Tyrosine Valine




Link for each Amino acid to structures- Click
here for a quick link to the structures of the
various amino acids
The 11 amino acids that we can produce.
Histidine cant be made by infants
http//www.biology.arizona.edu
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Peptides

• Peptide bonds links the amino acids together
• Condensation reactions connect amino acids
• 2 amino acids bonded together form a dipeptide,
• if 3 join then a tripeptide,
• if more then a polypeptide
• Most proteins are several hundred amino acids long

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Protein Structures

• Protein POLYPEPTIDE of 50-300 amino acids
• eg. human Insulin has 51 amino acids (very small)
  
• Figures 6-4 (p. 184), Structures of Insulin.
  Whitney Rolfes 10th Ed.
• more complex larger molecules than CHO
• due to side group

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Haemoglobin
Picture from University of Miami Biology Dept
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Protein Structures

• constituent amino acids characterize a PROTEIN
• eg. protein of BEEF muscle different to protein
  of PORK muscle

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Amino Acids structural functional roles

• cell membrane
• connective tissue
• (collagen elastin)
• inert protein
• (hair nails)
• Enzymes
• Hormones
• (insulin)
• Fluid balance
• (aquaporins)

• blood proteins
• (albumin haemoglobin)
• skeletal smooth muscle
• antibodies
• 20 energy source
• Acid- base regulator
• Transporters
• (Glut4)

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Function summary
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Protein

• AAs continually synthesised catabolised in the
  body
• daily turnover ?3 4 g/kg body weight/day
• dietary intake ? ¼ - ½ this amount

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• MOST Protein made from recycling amino acids

essential, from food or already in body
Synthesise new proteins
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Essential (indispensable) amino acids

• new protein synthesis requires full complement of
  amino acids
• cannot make part proteins
• other AAs are wasted (deaminated)
• most amino acids synthesised in the body
• need Nitrogen for amine group
• C-fragments H atoms from CHO or Fat molecules
  AND/OR from degraded AAs in the body

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Essential (indispensable) amino acids

• 8 (9 in children) cannot be synthesised in the
  body
• ? MUST BE SUPPLIED FROM FOOD

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Essential (indispensable) amino acids

• Histidine (in children)
• Isoleucine
• Leucine
• Lysine
• Methionine

• Phenylalanine
• Threonine
• Tryptophan
• Valine
• branched chain
• amino acids

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Protein Quality

• Definition
• the amount of protein in a particular food its
  supply of essential amino acids
• Quality is based on digestibility and amino acid
  composition
• ANIMAL protein BEST QUALITY
• supplies ALL 8(9) essential amino acids
• usually the HIGHEST concentration

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Protein Quality

• PLANT protein LESSER quality
• doesnt supply ALL essential amino acids
• LOWER concentration
• exception SOY PROTEIN

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Plant protein cont...

• combining LEGUME CEREAL protein will ensure ALL
  essential amino acids
• each food contributes the essential AAs missing
  in the other food
• COMPLEMENTARY PROTEINS
• (Vegans)

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Complementary proteins
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Protein Quality

• eg. Complementary proteins
• black beans and rice
• peanut butter on bread (wheat)
• refried beans Tacos (corn)
• stir-fried vegetables rice

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Protein requirements

• 1 gram protein supplies 17kJ
• sedentary individuals
• balanced diet 10-15 of Etotal from protein
• athletes
• balanced diet 12-17 of Etotal from protein

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• Sedentary individuals
• or 0.8g - 1.0g protein/kg body weight/day
• if weight 70kg
• protein requirement will be
• between 70 x 0.8 56g protein/day
• and 70 x 1.0 70g protein/day

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• Athletes
• elite endurance athletes
• 1.2 - 1.4g protein/kg body mass/day
• oxidisable fuel when CHO stores depleted
• strength power athletes
• 1.2 - 1.7g protein/kg body mass/day
• maintains ve Nitrogen balance
• AAs can be synthesised incorporated into
  required protein

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Protein from food

• Food Protein g/100g
• HIGH CONTENT
• Beef lamb 28
• Cheese 26
• Chicken 25
• Fish 18
• Eggs 12
• Beans 7
• Peas 5
• Milk 3.3

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• Food Protein g/100g
• MEDIUM CONTENT
• Cornflakes 8.6
• Bread (white) 7.8
• Spaghetti 4.2
• Sweetcorn 4.1
• Rice 2.2
• Cauliflower 1.6
• Potatoes 1.6
• Cabbage 1.3

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• Food Protein g/100g
• LOW CONTENT
• Apples 0.3
• Honey 0.5
• Butter margarine lt0.4
• Wine 0.1
• Soft drink 0

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HOMEWORK

• Sedentary individual (70kg body mass)
• 56 - 70g protein/day protein FOOD
• Endurance athlete (75kg body mass)
• 90 - 105g protein/day protein FOOD
• Strength Power athlete (100 kg body mass)
• 120 - 170g protein/day protein FOOD

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Recommended Reading

• Whitney Rolfes (2005)
• Understanding Nutrition 10th Ed.
• Chapter 6 Protein Amino Acids
• ENTIRE CHAPTER
• AND/OR
• Wahlqvist (2002)
• Food Nutrition
• Chapter 14 Protein
• ENTIRE CHAPTER