Class Notes (806,588)
Canada (492,340)
NFS284H1 (111)

NFS284 Chapter 6 Review Notes

6 Pages
Unlock Document

University of Toronto St. George
Nutritional Science
Tom Wolever

Nutrition: Science and Applications Chapter 6 – Protein Sources of protein in the diet - Protein deficiency is rare in Canada - CCHS  97% of Canadians’ protein intake is above the AMDR - Canada  dietary protein comes from animal protein (e.g., meat, poultry, fish, eggs, and dairy products) - Most of the world  dietary protein comes from plant protein (e.g., grains, vegetables) - As a country’s economy improves, the proportion of animal protein in the diet tends to increase Proteins - Large complex molecules composed of amino acids o Contain carbon, hydrogen, oxygen, nitrogen o Primary source of nitrogen in the diet o Combination of 20 different amino acids Amino acids - Contain amino group (NH2), acid group (COOH), hydrogen atom (H), and side chain - The side chain is unique to each amino acid - Essential amino acids o Met, Thr, Val, Leu, Ile, Phe, His, Trp, Lys o Not manufactured in the body, so must be consumed in the diet o Carbon skeletons do not normally exist in the body, so transamination is not possible - Conditionally essential amino acids o Under certain circumstances, the body cannot make enough of the amino acid and so it must be consumed in the diet - Non-essential amino acids o Not required to be consumed in the diet o Made in the body by the process of transamination  Amino group from an amino acid is transferred to a carbon skeleton to make another amino acid - Peptide bonds o Amino acids are joined together by peptide bonds o Carbon atom from acid group of one amino acid bonds with nitrogen atom from amino group of another amino acid to form a water molecule (OH from acid group of one amino acid and H from amino group of another amino acid) and a dipeptide molecule - Protein structure o Primary structure = amino acid sequence in polypeptide chain o Secondary structure = alpha-helix and beta-strand o Tertiary structure = 3D structure of a single protein o Quaternary structure = 3D structure of a multi-subunit protein Protein digestion - Mouth o Grinds food into smaller particles - Stomach o HCl denatures protein by disrupting quaternary and tertiary structures o HCl activates pepsinogen to pepsin  Pepsin splits polypeptide chains by breaking the peptide bonds - Small intestine o Pancreatic proteases (e.g., trypsin, chymotrypsin) breakdown polypeptide chains into dipeptides and tripeptides o Intestinal peptidases breakdown dipeptides and tripeptides into amino acids o Amino acids are transported into the small intestinal epithelial cells and secreted into the portal blood stream - Liver o Amino acids are taken up by the liver  Uses the amino acids to make various types of proteins  Holds the amino acids within liver cells to be released as needed Protein function - Dietary amino acids are used to synthesize body proteins (e.g., actin, collagen) - Excess amino acids o Broken down to provide energy to the body o Converted into glucose and stored as glycogen in liver or muscle o Converted into fatty acids and stored as fat in adipose tissue o Used to synthesize other nitrogen containing compounds such as neurotransmitters (e.g., adrenaline, serotonin) Protein synthesis - Gene is transcribed into mRNA - Each stretch of 3 adjacent nucleotides encodes for a different amino acid o With 4 nucleotides, there are 64 different combinations of 3 nucleotides - mRNA leaves the nucleus and travels to ribosomes in the cytosol - mRNA is translated into protein o Each amino acid molecule in the cytosol is bound to a specific molecule of transfer RNA o Each amino acid has a different transfer RNA molecule o Each transfer RNA recognizes and binds to the 3 nucleotide code on the mRNA at the ribosome Genetic disorders - Changes in DNA o Called mutations if they are relatively rare o Called polymorphisms if they are relatively common o If occurs in DNA that controls gene transcription, then may lead to altered gene expression o If occurs in DNA that encodes for protein, then may lead to altered protein structure - Examples o Phenylketonuria (PKU)  Rare (1 in 10,000 = 0.01%) inherited condition  Caused by mutation in the DNA of enzyme that converts phenylalanine into tyrosine  Leads to loss of function of the enzyme  Leads to inability metabolize phenylalanine into tyrosine  Leads to increased blood levels of phenylalanine  Leads to excess phenylalanine being converted into phenylketones, which is toxic to the brain (e.g., brain damage)  Prevented by reducing phenylalanine intake in the diet to a minimum and avoiding artificial sweetener aspartame o Sickle cell anemia  Common in people of African ancestry (1 in 500)  May provide a survival advantage because malaria is endemic in Africa and malaria parasite cannot survive in sickle cells  Caused by a single amino acid change in the hemoglobin protein sequence (GluVal)  Leads to deformation of red blood cells into a sickle shape  Leads to abnormal blood clotting, strokes, bouts of severe pain, and anemia o Cystic fibrosis Interactions between genetic polymorphisms and diet - The effects of diet on health is influenced by our genetic make up - Two examples of diet/gene interactions o The effect of coffee on risk for myocardial infarction (MI)  Polymorphism determines if people are fast or slow metabolizers  High consumption of coffee only increases risk for MI in those people who are slow metabolizers o The effect of diet and exercise to prevent diabetes  Polymorphism determines if lifestyle interventions are effective  Lifestyle intervention is only effective in preventing diabetes in those people who had the A allele Energy production from protein - Amino group must be removed from the amino acid - Carbon skeleton enters metabolism either as pyruvate, acetyl-CoA, or as an intermediate of the citric acid cycle Deamination - Amino group removed from the amino acid becomes ammonia (NH3), which is highly toxic - Liver o 2 NH3 + CO2  urea o Urea is a water soluble compound - Kidney o Urea is excreted into the urine Functions of proteins - Cell growth, repair, and maintenance - Enzymes o Facilitate chemical reactions but are themselves not changed by the reaction - Transport o Assist in the transport and metabolism of compounds around the body as membrane transporters (which move things into and out of cells and organelles within cells), binding proteins, lipoproteins (which allow the transport of fat in the blood stream) - Antibodies to protect against disease o Produced by white blood cells and cells in the intestine o Neutralize harmful effects of foreign material - Contractile proteins o Actin and myosin act together to form the contractile tissue in muscles o Actin molecules slide along myosin molecules to cause muscle contraction - Hormones o Not all hormones are proteins, but many proteins are hormones o Peptide hormones  Insulin  Glucagon  Thyroxine o Neurotransmitters made from amino acids  Epinephrine and norepinephrine are made from tyrosine  Serotonin is made from tryptophan - Fluid and electrolyte balance o By exerting osmotic pressure  Osmotic pressure is created by the number of particles in solution, not the size of the particles  Malnutrition  ↓ plasma protein  ↓ osmotic pressure of the blood  water moves out of the blood and into interstitial fluid  water accumulates in the feet and legs  edema o By functioning as transporters of electrolytes  Some proteins are active transporters  Concentration gradient of K+ and Na+ is maintained by Na+/K+ ATPase, which uses ATP to pump Na+ out and K+ in  [K+] inside > [K+] outside  [Na+] outside < [Na+] inside - pH balance o Act a
More Less

Related notes for NFS284H1

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.