# Nutrition 251 Study Questions Exam #2 PSU

How is the chemical structure of protein different and similar to that of complex carbohydrates? (Ex. they are both long chains of building block units.) How is the chemical structure of a monosaccharide different from that of an amino acid, just in general terms? (Chpt 6 and Lesson 4)
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Protein: composed of carbon, hydrogen, oxygen and nitrogen atoms arranged into amino acids linked in a chain
- the nitrogen group is the amino group, allowing the protein to link
Carbohydrate: composed of carbon, oxygen, and hydrogen arranged as monosaccharides or multiples of monosaccharides
- carbs are linked as many of the SAME molecules, unlike amino groups which are different
1. Mouth - chewing crushes and tears protein-containing foods and mixes them with saliva before swallowing
2. Stomach - HCl denatures protein and also activates pepsinogen to pepsin, a protease which breaks large proteins into smaller polypeptides.
-disrupts the bonds in proteins which increases surface area for the enzymes in the stomach to act
3. Pancreas - Pancreatic proteases are secreted into the duodenum
4. Small Intestine - Proteases derived from the pancreas and small intestinal cells do the final digestion of polypeptides to amino acids. Amino acids and some dipeptides and tripeptides are then absorbed across the small intestinal membrane into the circulatory system.
-absorbed by active transport, are water soluble so go to liver through the circulatory system
An amino acid is a precursor molecule because it precedes other molecules, meaning its components can be used for other molecules in the body.
4 functions:
1. Turn protein's carbon into glucose thru gluconeogenesis. Amino acid known as glucogenic afterwards.
2. Amino acid used as fuel (less of a fuel compared to fatty acids and glucose)
3. Stored as fatty acids when cal. intake is high
4. Essential A.A. turned into nonessential A.A.
-phenylalanine as a precursor to tyrosine
-Tryptophan is enzymatically converted to niacin, a B vitamin and serotonin.
1. Collagen protein vital to the framework for laying down the crystalline structures of bone and teeth; "glue" that holds cells together and basic structure of skin, blood vessels, and organs
2. In blood and fluid compartments-
-regulate fluid balance - R groups of AAs can attract water
-maintain acid-base balance - R groups have buffering capacity
-transport nutrients to cells
-function in immunity - antibodies are proteins
-are hormones - insulin and gastrin are examples
3. Proteins are enzymes - thousands of enzymes catalyze reactions in the body
4. Proteins are transporters in membranes - recognize specific molecules to transport them across a membrane
Deamination (in AAs) - the removal of the amino group (NH2) from the amino acid
Ammonia is a product of deamination. Ammonia is toxic b/c it disrupts blood's acid-base balance in excessive amounts since its a base. Liver combines ammonia with CO2 to make urea. The kidneys filter the urea out of the blood for excretion in the urine.
4 essential AAs:
-Phenylalanine -Methionine -Tryptophan -Lysine
20AAs, 9 are essential, 11 are nonessential.
The amino acid pool is the availability of all AAs in the fluid compartment of the cell. It contains essential and non-essential AAs.
The sources are the diet, the degradation of cellular proteins to AAs, and (for non-essential AAs) synthesis from other molecules.
The AA pool must be balanced to have more effective protein synthesis. If the pool is low, protein syn. is slowed.
Protein quality by:
1. Digestibility of proteins: high quality are more digestible than low quality; animal proteins > legume proteins > vegetable proteins
- complementing proteins - low quality proteins good source of protein when mixed together or mixed with animal protein
2. Amino Acid composition: depends on amounts and profile of essential AAs per gram of protein; animal protein has essential AAs in adequate amounts; plant proteins have at least 1 essential AA in low amounts
- limiting AA - the essential AA found in the shortest supply relative to the amounts needed for protein synthesis in the body - 4 likely AAs: lysine, methionine, threonine, tryptophan
- reference protein - a standard against which to measure the quality of other proteins
Can measure digestibility by measuring the amount of protein that is consumed (before you actually eat it) and then measuring the amount of protein excreted in feces. Depending on how much protein there is in the feces, this will tell you how much protein was digested.
Egg has the highest digestibility because it is an animal protein.