BPK 110 Lecture Notes - Lecture 6: Veganism, Diverticulosis, Kwashiorkor
10 Jul 2016
School
Department
Course
Professor
Chapter 6
Proteins and Amino Acids
Proteins• Composed of long, folded chains of amino acids (aa)
– Combinations of these 20 aa’s make up all the proteins found in nature
• 9 of these aa’s are essential– Complete proteins have all 9 essential aa’s – Incomplete
proteins lack 1+ essen:al aa’s
Note: you do not need to know this chart
• Each aa contains an amino group, an acid group and a unique side chain
Animal Sources of Protein
•• Are complete proteins
•• Are typically higher in total protein content
•• Have B vitamins, iron, zinc, calcium
•• Tend to be low in fiber, high in saturated fat and cholesterol – Increase risk of heart
disease
Plant Sources of Protein
•• Are typically incomplete proteins (ex. Legumes)
•• Contain some B vitamins, iron, zinc, calcium – but they are less available in the body
• These sources tend to be high in fiber, unsat fats and phytochemicals
Ask yourself:Which are be=er: animal or plant proteins?
Which are be=er: animal or plant proteins?
•• Answer: “better” is a subjective term. Many different types of diets can be healthy, this
includes both diets that include animal products and ones that don’t. A diet high in animal
protein and low in plant protein is higher in total protein (but protein deficiency is rare in
Canada), has all the essential amino acids and is rich in various minerals and vitamins. On the
find more resources at oneclass.com
find more resources at oneclass.com
other hand, it is potentially high in saturated fat and low in fibre, phytochemicals and
antioxidants, which may increase risk of disease in the individual.
•• A diet rich in plant proteins is high in fibre, phytochemicals and antioxidants, all of
which may decrease risk of disease, but it may be deficient in certain vitamins and minerals. It is
also more likely to lack one or more essential amino acid.
•• Take home message: both diets that include animal protein and those that don’t can be
healthy, but they both have to be well-planned, varied, moderate and balanced to promote health,
reduce risk of deficiency and/ or reduce risk of disease. It is probably healthier though to in
general to favour plants over animals in your food decisions.
Protein structure
•• Proteins are composed of long chains of amino acids folded into very specific patterns
•• Amino acids, unlike sugars/fatty acids, have nitrogen
•• Amino acids are linked together by peptide bonds to form polypeptides. – All
proteins are polypeptides, but not all polypeptides are proteins • To be a functional protein, a
polypeptide needs to fold into a specific structure with 3 or 4 levels of organization (next slide) •
The shape of a protein is essential to its function
The 4 Levels of Protein Structure
The polypeptide chain is the primary structure of the protein
Hydrogen bonds between side chains in the polypeptide help form alpha-helices and beta
pleated sheets which form its secondary structure
The 4 Levels of Protein Structure
Disulphide, hydrogen bonds etc. between side chains form the tertiary structure
Quaternary structure is the binding of 2+ polypeptide chains together
Ex. The Quaternary Structure of Hemoglobin (blood protein that carries oxygen)
Denaturation
• Denaturation refers to the alteraon of a protein’s 3D structure
– Heat, acid, agitaon can denature a protein • Ex. Cooking an egg
find more resources at oneclass.com
find more resources at oneclass.com
• When a protein loses its 3D structure, it loses its original function
Ex. When you add heat to an egg, you are changing the nature of egg protein (“denaturation”),
this is evidence by a change in the colour and texture of the egg
Protein Digestion and Absorption
•• The protein’s 3D structure is denatured during the process of digestion and the
remaining polypeptide is typically broken down into individual aa’s, which can then be absorbed
•• aa’s are then absorbed into the SI by acAve transport – Similar aa’s sometimes use the
same transporter, therefore if there is an overabundance of one aa, it may block the absorption of
another! • Some single amino acids are sold as supplements. If these are consumed in excess, it
may lead to a deficiency of another essential amino acid
Protein Digestion and Absorption
The chemical digestion of protein begins in the stomach (recall the role of HCl, pepsin), but
primarily takes place in the small intestine. In the small intestine, proteins are finally broken
down into their subunits, amino acids, which can then be absorbed into the blood.
Protein SynthesisMaking body proteins from available amino acids in the body
•• While we can use amino acids to produce ATP (energy), recall that we primarily eat
protein to get amino acids that we can then, in turn, use to make body proteins – But how do we
know how to make specific body proteins (ex. muscle proteins) from amino acids?
•• Our DNA contains the ‘recipe’ for how to make all of our body proteins • Certain
genes (specific segments of DNA with specific functions) are turned on/off to drive/halt protein
synthesis
Both dietary proteins and the breakdown of body proteins can contribute to the “pool” of amino
acids available for use in the body
This “amino acid pool” can then be used for energy production, or the synthesis of glucose, fatty
acids or non-protein molecules. However, we are most likely to use the ‘amino acid pool’ to
make body proteins
Protein Synthesis
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Proteins composed of long, folded chains of amino acids (aa) Combinations of these 20 aa"s make up all the proteins found in nature: 9 of these aa"s are essential complete proteins have all 9 essential aa"s incomplete proteins lack 1+ essen:al aa"s. Note: you do not need to know this chart: each aa contains an amino group, an acid group and a unique side chain. Animal sources of protein: are complete proteins, are typically higher in total protein content, have b vitamins, iron, zinc, calcium, tend to be low in fiber, high in saturated fat and cholesterol increase risk of heart disease. Plant sources of protein: are typically incomplete proteins (ex. Legumes: contain some b vitamins, iron, zinc, calcium but they are less available in the body, these sources tend to be high in fiber, unsat fats and phytochemicals. Which are be=er: animal or plant proteins: answer: better is a subjective term.
