Unit 6: Protein; Amino Acids Flashcards
Define Amino Acid
The nitrogen atoms give the name amino (nitrogen containing) to the amino acids–links in the chains of proteins
Describe the basic structure of an amino acid
- Central carbon with a Hydrogen atom
- Amino group (NH2)
- Acid group (COOH)
- Unique R-side group
What distinguishes one amino acid from the next? Makes proteins more complex than lipids or carbohydrates.
Unique R-side group
Define Protein
Cells link amino acids end-to-end in a variety of sequences to form thousands of different proteins.
Approximately how many amino acids make up a protein?
20
What links amino acids together to form a protein?
Peptide bonds
Describe a Peptide bond
-Condensation reaction (produces H2O)
Two amino acids bonded form a?
Dipeptide
3 amino acids bonded together form a?
Tripeptide
More than 3 amino acids bonded together form a?
Polypeptide
Amino Acid Sequence–Primary structure is determined how?
By the sequence of amino acids, to form a chain
Polypeptide Shapes-Secondary Structure is determined how?
By the weak electrical attractions within the polypeptide chain. Positively charged hydrogens attract negatively charged oxygens and the chain twists to a helix or a pleated sheet
What does secondary structure (helix/pleated sheet) do for protein?
Provides strength and rigidity
Polypeptide Tangles-Tertiary Structure are determined how?
Occurs has long polypeptide chains twist/fold into complex tangled shapes. Unique side groups give characteristics that attract or replenish from surrounding fluids and other amino acids
Hydrophobic
Hydrophilic
Disulphides bridges
For shapes such as globular/spherical or linear structures
What does the tertiary structure do for protein?
- Enable them to perform various tasks
- Give maximum stability and shape must be retained to remain functional
Define Hydrophillic
Attracted to water
Define Hydrophobic
Repelled by water
Multiple Polypeptide Interactions-Quaternary Structure is determined by what?
Involves interactions between 2 or more polypeptides. Form a functional protein
Define Denaturation
Protein subject to heat, acid, (other conditions to disturb stability) uncoil and lose their shape. Therefore, their ability to function. Past a certain point denaturation is irreversible. Proteins are denatured when exposed to stomach acid allowing them to be digestible
Nonessential (Dispensable) Amino Acids: can be synthesized by the body. What are they?
Alanine Asparagine Aspartic Acid Glutamic Acid Serine
Essential (Indispensable) Amino Acids: (9) must be supplied by the diet, as the body cannot synthesize/adequately synthesize them. What are they?
Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
Conditionally Essential Amino Acids: are sometimes nonessential but become essential under special circumstances. What are they?
Arginine Cysteine Glutamine Glycine Proline Tyrosine
Protein digestion in the mouth
Chewing and crushing moisten protein-rich foods and mix them with saliva
Protein Digestion in the Stomach
Hydrochloric acid (HCl) uncoils protein strands and activates stomach enzymes
Protein –> Pepsin, HCl –> Smaller polypeptides
Protein digestion in the Small Intestine
Pancreatic and small intestinal enzymes split polypeptides further
Polypeptides –> Pancreatic/Intestinal Protease –> Tripeptides, dipeptides and amino acids
Enzymes on the surface of the small intestinal cells hydrolyze these peptides and the cells absorb them
Peptides –> Intestinal tripeptidases/Dipeptidases –> Amino Acids (absorbed)
Only free amino acids enter the general blood circulation at the portal vein. What is an exception to this?
Newborn infants receive immunity from mother’s when intact protein antibodies present in human colostrum enter the mucosa. A few days after birth the mucosal cells are closed to whole proteins
Digestive enzymes in the stomach are? (2)
Hydrochloric Acid (HCl): denatures protein structure, activates Pepsinogen to pepsin
Pepsin: C;eaves proteins to smaller polypeptides and some free amino acids. Inhibits pepsinogen synthesis
A proenzyme (or zymogen) is the inactive form of an enzyme. What is the inactive form of pepsin?
Pepsinogen
A string of 4-9 amino acids is known as a?
Oligopeptide
Pepsin works best in the low pH of the stomach. When it enters to small intestine (higher pH) what happens?
Becomes inactive and is digested
Once inside intestinal cells amino acids are used for? If they are not used for this what happens?
-Energy
-Synthesize needed compounds
If not used for this:
-Transported across cell membrane into surrounding fluid where they enter the capillaries on their way to the liver
Enzymes in the small intestine are? (8)
Enteropeptidase Trypsin Chymotrypsin Carboxpeptidases Elastase and collage are Intestinal Tripeptidases Intestinal Dipeptidases Intestinal Aminopeptidases
What 2 factors determine protein quality?
- Amino Acid Composition (especially essential amino acids)
2. Digestibility of the protein
Proteins that occur naturally in food are balanced in terms of amino acids, because they are biologically similar to human proteins and so…
Competition for absorption is not significant
Define Complete Protein
A protein containing all the essential amino acids in amounts and proportions required by humans.
Define Incomplete Protein
Lacks one or more essential amino acid
Ex. Plant proteins (corn)
Define high-quality protein
A complete protein that provides all essential amino acids in amounts and proportions
Define Limiting Amino Acid
An essential amino acid supplied in less than the amount needed to support protein synthesis.
If one amino acid is missing protein synthesis stops
Define Complementary Proteins
Amino acids in different food complement each other to form a complete protein Ex. Animal + plant protein Ex. Grains + legumes Ex. Legumes + seeds Ex. Leafy vegetables + grains
Is it necessary to balance amino acids in each meal? (Complementary amino acids must be consumed at the same time)
NO
As long as protein intake is varied and energy intake is sufficient
Protein Function 1: Structural Growth and Maintenance of Body Tissues
Primary function of proteins because they are building blocks of a cell
Ex.
Collagen – formation of scars, tendons, ligaments, bones, teeth
Contractile Proteins – formation of muscle tissues
Cell Membrane Proteins – formation of barrier around cells
Protein Function 2: Regulation of Body Functions
Enzymes – catalysts for metabolic reactions
Proteins in blood and lymph – fluid and acid-base balance
Antibodies – Immunity
Some hormones:
Insulin – regulation of blood glucose
Thyroid Hormone – regulation of metabolic weight
Transport Proteins:
Hemoglobin – oxygen transport in blood
Lipoproteins – fat transport
Transferrin – iron transport
Prothrombin, Fibrin – clotting of blood
Opsin – vision
Some neurotransmitters – nerve impulse transmission
Protein Function 3: Source of Energy
Not a primary function but in instances of carb/fat shortage protein is broken down for energy. The nitrogen part of amino acids is secreted as urea via urine and remaining carbon-containing element is metabolized to produce energy, can also be converted to glucose or stored as fat
Explain Nitrogen Balance
Proteins are the only nitrogen containing nutrient (16%).
Nitrogen balance can be determined by analyzing the intake of nitrogen (food consumed over a period of time) and the nitrogen loss (urine, feces, skin, hair, nails, sweat, tears, menses, mucus etc.)
Generally only urine and feces nitrogen loss is measured.
Define Nitrogen Equilibrium
Intake of nitrogen = loss of nitrogen Healthy adults (neither gaining/losing weight or pregnant) When protein intake is high the body excretes more nitrogen to maintain equilibrium because protein cannot be stored
Define Positive Nitrogen Balance
Greater input than output
Growing children, pregnant women, patients recovering from illness or tissue injury
Define Negative Nitrogen Balance
Input less than output
Fasting, illness, tissue injury/breakdown, cancers, burns, surgery, infection, stress, prolonged immobilization, poor quality/quantity proteins in diet
Define Protein Turnover
Continuous creation and breakdown of proteins in a cell. When proteins break down they free amino acids. These amino acids mix with dietary amino acids to form a small amino acid pool
Define Endogenous Amino Acids
Derived from within the body
Define exogenous amino acids
Derived from foods
Define acidosis
Above-normal acidity in the body
Define Alkalosis
Above-normal alkalinity (base) in the blood and body fluids
Define Edema and the cause
In critical illness and protein malnutrition, blood vessels become “leaky” and allow plasma proteins to move into the tissues. Because proteins are attracted to water, the tissues swell
Define Buffer
Compounds that keep a solution’s pH constant when acids or bases are added
Protein-Energy Malnutrition (PEM)
When protein intake falls below required level the body becomes more efficient. Once it falls below a critical level PEM occurs. Results in swelling, weakness, increased risk of infection. More common in children than adults because in relation to body weight children have higher protein requirements. Occurs in developing countries, areas of poverty in North America, patients with tuberculosis, cancer, GU tract disease, anorexia nervosa
Protein Excess can result in:
Severe dehydration (especially in children) because the kidney cannot concentrate urine and water is excreted with urea
Protein-Energy Undernutrition (PEU) previously called PEM is divided into 2 groups. What are they?
Marasmus and Kwashiorkor
A child underweight for their height might be suffering from:
Acute PEU
A child short for their age might have experienced what:
Chronic PEU
Explain Marasmus
Infancy (less than 2 years) Severe deprivation, impaired absorption of protein, energy, minerals, vitamins Chronic PEU (slow development) Severe weight loss Muscle wasting (no body fat) Growth <60% weight-age No detectable edema No fatty liver Anxiety, apathy Good appetite possible Hair sparse, dry, thin, easy to pull out Skin dry, thin, wrinkles
Explain Kwashiorkor
Older infants/children (1-3) Inadequate protein intake or infections Rapid onset (Acute PEU) Some weight loss Some muscle wasting with retention of body fat Growth: 60-89% weight-age Edema Enlarged fatty liver Apathy, misery, irritability, sadness Loss of appetite Hair is dry, brittle, easy to pull out, changes coulour, becomes straight Skin develops lesions
Explain Marasmus-Kwashiorkor Mix
Combination of symptoms. Characterized by edema of kwashiorkor with wasting of marasmus. Effects of both malnutrition and infections
Vegetarian diets are superior from an environmental perspective as they:
Require less energy and water
Define Lacto-vegetarians
People who include milk and milk products but exclude meat, poultry, fish, seafood, and eggs from their diet
Define Lacto-ovo-vegetarian
People who include milk, milk products, and eggs but exclude meat, poultry, fish, and seafood
Define Vegetarian
General term used to describe people who exclude meat, poultry, fish, or other animal derived products from their diet
Define Vegan
People who exclude all animal-derived products (meat, poultry, fish, eggs, dairy products) Also called pure, strict, or total vegetarians
Benefits of vegetarian Diets
-May increase life expectancy
-reduce obesity (lower body weight)
-reduce risk of diabetes
-decrease hypertensions
-decrease risk of heart disease (fats common in plant-based diets-monounsaturated)
-lower cancer rates (high intake of vegetables)
_Osteoporosis, diverticular disease, gallstones, rheumatoid arthritis
Risk of Vegetarian diet and how to solve them
- lack of protein, vitamins, minerals (iron, zinc, B12)
- ensure a well planned diet with meat alternatives and fortified milk/soy beverages
What are the factors considered when establishing the RDA for protein?
- Age/physiological state (requirements are highest during first year of life, adolescence, pregnancy, lactation)
- Lean body mass (protein need increases as muscle mass increases)
- Protein quality
- Energy intake (Protein can only be used efficiently when adequate energy from carbs/fats is available)
- Health status (physiological/psychological stress increases protein requirements)
- Individual variation (protein requirements are established with margin of 30% above to allow for individual variation)
What is the RDA for adults per kilogram of body weight per day?
0.8 grams/kilogram of body weight/day
Substantially overweight/underweight base your calculation on appropriate weight for your height
What percent of energy intake should protein be?
10-35% of energy intake
What is the protein recommendation for athletes?
1.2-1.7 grams/kilogram of body weight/day
In Canada high protein content in food means the average consumption exceeds the recommended levels. TRUE OR FALSE?
TRUE
Protein from animal sources is a major source in Canadian diets. So the Food Guide has done what?
Put an emphasis on vegetables, fruit and grain products to encourage a shift to eating less meat
What segment of Canada’s population may have inadequate protein intake?
Women over 65 (0.78 grams/kilogram body weight/day)
High protein intake can be harmful in connection to…
Bone loss (But bone loss is also associated with low protein intakes especially, in the elderly)
Protein intake should be moderate in persons with:
Kidney Disease
