Lecture 5 - Macronutrients (PROTEINS) Flashcards
Energy, essential amino acids, and nitrogen (to make non-essential amino acids) are provided by…
Dietary protein
____________ amino acids are nutritionally required in amounts the animal cannot synthesize on its own
Essential
What are some physiological functions that rely on protein?
Enzyme activity, cellular function, barrier/skin function, growth and reproduction
How many types of amino acids are used as building blocks for protein or as free amino acids?
20
True or False: Amino acids consist of an amine group and a carbonyl group, and the type of amino acid is determined by the side chain
True
True or False: Amino acids can never be metabolized from other amino acids
False; SOME amino acids can be metabolized from other amino acids
What are some sources of dietary protein?
Animal proteins (meat/dairy/eggs), plant proteins (legumes/grains), and microbial proteins
True or False: Obligate carnivores, such as cats, tend to have higher protein requirements than most other species
True
Even when protein intake is low, cats cannot regulate deamination of ______ ______ within their bodies to compensate
Amino acids
Why do protein requirements increase in animals that do more strenuous physical activity?
Sufficient protein is needed to build muscle, and lack of protein can lead to physiological complications
A type of non-regenerative anemia in athletes where protein intake is insufficient
Sports anemia
How do proteins and amino acids affect palatability in omnivores and carnivores?
Specific amino acids have a naturally stronger flavor and odor that can drive palatability
Example: methionine
What are the three significant branched chain amino acids (BCAA)?
Valine, leucine, isoleucine
Why is leucine considered “special” amongst the BCAAs?
It promotes muscle-protein synthesis
(Extra info: leucine is abundant in meat products)
What is the Kjeldahl method used to analyze?
Crude protein content in food (specifically provides the weight of nitrogen in all of the analyzed matter)
Where does enzymatic digestion occur in carnivores and omnivores? (2 places in the body)
Stomach and intestines
What occurs during enzymatic digestion and absorption of proteins in omnivores and carnivores?
Proteins are broken down to smaller peptides/amino acids, and amino acids are absorbed via transporters
What happens to undigested amino acids in omnivores and carnivores?
They are converted into ammonia by microbes in the large intestine, which is captured by the liver and catabolized to urea
In forestomach fermenters, what term describes the nitrogenous compounds that pass through the forestomach and are metabolized by microbial organisms?
Degradable Intake Protein (DIP)
True or False: Urea may be metabolized to ammonia and incorporated into bacterial protein in forestomach fermenters
True
Protein that is usually heat-treated and is not digestible by microbial enzymes in forestomach fermenters; bypasses the rumen
Undegradable Intake Protein (UIP)
What happens to UIP after it bypasses the rumen?
Most is digested by abomasal acid/enzymes and the rest by pancreatic enzymes (amino acids are then absorbed by small intestines)
Nitrogen that is metabolized to ammonia in the rumen and can be used by bacteria for amino acid synthesis; supplement provided in the form of urea as a substitute for protein
Non-protein nitrogen (NPN)
Why should you never feed raw whole soybeans and urea supplements together?
Soybeans have an enzyme called urease (breaks down urea into ammonia - TOXIC!)
True or False: Hindgut fermenters absorb highly digestible protein in the small intestines similarly to omnivores
True
Why do hindgut fermenters require dietary protein and essential amino acids in their food, more so than foregut fermenters?
They can only absorb limited amounts of microbial protein in their large intestines
An enzyme complex (pepsin, lipase, rennin) found in neonates that causes milk protein (casein) to temporarily clot in the stomach; also requires acid and calcium
Rennet
What is the main (physiological) problem with using plant-based milk replacers for mammalian neonates?
Vegetable protein is not the same as casein, so it will not clot in the stomach with rennet and will send extra protein to the lower intestines (causing D+)
Amino acids can be used to build new protein, but what happens to amino acids when no additional protein is required?
Deamination, which releases ammonia (carbon skeleton can be used to make acetyl CoA or glucose)
The transference of an amine group from one amino acid to form another amino acid
Transamination
A cycle where muscle protein is degraded to provide more glucose to generate additional ATP for muscle contraction
Glucose-Alanine Cycle
When does the body utilize muscle as a source of alanine (to be metabolized into glucose in the liver)?
During starvation or periods of inadequate energy intake
The ratio between the amount of protein absorbed from the GI tract and the amount of protein that is retained in the body; may be impacted by relative concentrations of amino acids to form a complete protein
Biological value
Protein quality takes into consideration the biological ______ and protein _________.
Value; digestibility
Why are eggs sometimes called the “ideal protein”?
They are a source of protein with a biological value of nearly 100% and very high digestibility
What happens to ingested proteins with low biological value?
They may provide amino acids that will be delaminated and form ammonia, then urea
What happens to ingested proteins with low digestibility?
They will ferment in the large intestines and release ammonia that may be absorbed (will occur regardless of accompanying biological value)
What clinical signs may occur when there is an excess of low digestibility protein in the body?
Diarrhea, and increased ammonia and urea
What are some potential consequences of high ammonia/urea in the body?
- Liver disease (excess ammonia not transformed to urea)
- Kidney disease (excess urea)
- More urea excreted in waste = grass burn!
What are some ways of managing renal and hepatic disease?
Reduce protein, increase in high bio value/high digestibility proteins
(less protein in large intestines = less amino acids to deaminate = less ammonia/urea formation)
What causes this chain of events?
Hypoalbuminemia -> decreased oncotic pressure -> ascites/effusion
Protein deficiency
A type of protein malnutrition that presents with a distinct swollen abdomen and loss of muscle mass, but overall energy intake may be sufficient
Kwashiorkor
A type of protein malnutrition that presents with overall emaciation and insufficient protein AND energy intake
Marasmus
A unique sulfuric free amino acid that can be synthesized from other sulfuric amino acids (like methionine and cysteine); present in high concentrations in retina and cardiac muscle, and can be conjugated to bile acids
Taurine
(Extra note: Essential in cats and human infants!)
What medical complications can taurine deficiency cause?
Heart disease and blindness
Taurine deficiency is unlikely to occur in species where it is not an essential amino acid, unless… (multiple answers)
- low methionine and cysteine intake/bioavailability/digestibility/transformation
- high taurine loss
While taurine is present in high amounts in muscle protein and heart tissue, it is not present in high amounts in plants commonly used as ingredients in pet foods such as…
(2 answers)
Legumes and grains
What are some dietary factors that can cause taurine deficiency in dogs?
- Diet has low methionine and cysteine
- Diet has low digestibility
- Diet has high fiber that changes gut microflora
