Lecture October 2013 Most of this lecture taken from Chapters 6,7 of Rolfes et al(Understanding Normal and Clinical Nutrition (Nutrition 2104/2106 text)

Lecture October 2013 Protein metabolism and regulation

Outline of lecture 6 Amino acids Definition of amino acid Structure of amino acid Non-essential amino acids Essential amino acids Conditionally essential amino acids Class exercise

Outline of lecture 6 Proteins Definition of protein Amino acid chains Amino acid sequence Protein shapes Protein functions Protein denaturation Digestion Absorption Transport

Outline of lecture 6 Metabolism Amino acid anabolism Protein anabolism Protein catabolism Amino acid catabolism Nitrogen balance Regulation of amino acid and protein metabolism

More detailed comments

Amino acids Definition of amino acid -building blocks of proteins Structure of amino acid -each amino acid has an amino group(NH 2 ), an acid group(COOH), a hydrogen atom, and a distinctive side group all of which are attached to central carbon atom -some amino acids also contain sulphur

Amino acids Non-essential amino acids -body can synthesise these for itself -foods usually deliver these to the body but it is not essential for food to deliver these amino acids-usually

Amino acids Essential amino acids -cannot make on own or cannot make sufficient amounts of these amino acids -therefore they are required in the diet

Amino acids Conditionally essential amino acids -sometimes a non-essential amino acid becomes essential -two reasons for conditional essentiality

Class exercise -find all essential amino acids -find all non-essential amino acids -find an example of a conditionally essential amino acid -what foods contain all essential amino acids? -what foods are lacking in one or more essential amino acids? -how does one overcome issue of diet lacking in one or more essential amino acids?

Class exercise Essential amino acids Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

Class exercise Non- Essential amino acids Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Proline Serine Tyrosine

Class exercise Conditionally Essential amino acids Phenylalanine makes tyrosine If not enough phenylalanine in diet or conversion is reduced then tyrosine becomes essential

Proteins Definition of protein -compounds composed of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur atoms, arranged into amino acids linked in a chain

Proteins Amino acid chains -dipeptides, tripeptides, polypeptides

Proteins Amino acid sequence -20 amino acids give tremendous variability unlike starch

Proteins -Protein shapes -side groups- attract or repel water -attract or repel other side groups on amino acids in amino acid sequence

Proteins Protein denaturation -if change protein structure lose function

Proteins Digestion mouth-no digestion stomach-acid digestion leads to denaturation -acid converts pepsinogen to pepsin -pepsin makes large polypeptides into smaller polypeptides and some amino acids

Proteins Digestion small intestine-pancreatic and intestinal proteases digest polypeptides to: oligopeptides ( oligo means few; one definition suggests 2-40 amino acids though this definition varies), tripeptides, dipeptides and amino acids -peptidases split most of dipeptides and tripeptides to single amino acids

Proteins Digestibility Proteins vary in their digestibility due to variable dietary protein structures as well as other food ingredients and hence accessibility to protein digestive enzyme active sites Animal proteins are generally very digestible and plant proteins are generally less digestible than animal proteins Complete plant proteins -soy - very digestible - close to many animal proteins’ digestibility -quinoa - about 10 % less digestible than soy

Proteins Digestibility Digestibility affects availability (WWFQ) of essential and non-essential and conditionally essential amino acids

Proteins Digestibility Current gold standard for protein digestibility is: Protein Digestibility Corrected Amino Acid Score (PDCAAS) PDCAAS = mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x true digestibility percentage. True digestibility = human digestibility - faecal digestibility e.g. of reference protein = milk protein = 100

Proteins Digestibility FAO has recently proposed a new gold standard for protein digestibility -Digestible Indispensable Amino Acid Score (DIAAS) DIAAS % = 100 x [(mg of digestible indispensable amino acid in 1 g of dietary protein)/(mg of the same indispensable amino acid in 1 g of reference protein)]

Proteins Absorption -specific carriers move amino acids and a few dipeptides and tripeptides into intestinal cells -once inside intestinal cells amino acids can be used for energy or to synthesise some proteins

Proteins Transport -rest of amino acids put directly into blood and taken to liver -are amino acid carriers required for free amino acids to transport those free amino acids in the blood?

Proteins Class exercise -what happens to protein functions if there are insufficient: a) essential amino acids in the diet? why? b) non-essential amino acids in the diet? Explain -what happens to protein functions if there are sufficient? c) essential amino acids in the diet? explain

Metabolism Protein anabolism amino acids joined to amino acids figure 6-7 Rolfes et al

Fig. 6-7, p. 188

Metabolism Protein catabolism -digestion in stomach and small intestine -non gi tract catabolism

Metabolism Amino acid catabolism -figure 7-13 Rolfes -figure 7.24 Gropper - get urea which is excreted in urine

© 2009 Cengage - Wadsworth

Metabolism Nitrogen balance -equilibrium N in = N out healthy adult -negative nitrogen balance N in < N out illness, starvation -positive nitrogen balance N in > N out -person recovering from illness -growing child

Regulation of amino acid and protein metabolism -demand for amino acid and protein anabolism -eg if need positive N balance or to keep in N equilibrium -if lots of glucose available -demand for amino acid and protein catabolism-eg if in negative N balance or to keep in N equilibrium -if short of glucose

Relation of protein metabolism to carbohydrate and lipid metabolism -figure 7-8 Rolfes et al.

© 2009 Cengage - Wadsworth

Class exercise Explain the importance of dietary carbohydrate to protein metabolism Explain the importance of dietary lipid to protein metabolism Explain the importance of dietary protein to protein metabolism