NUTR Ch 6: Digestion/Importance of Proteins

How does protein help maintain the acid-base balance?

act as buffers; protein buffers pick up hydrogens (acid) when there is too much and release them again when there is too few

Hormones and amino acids

many hormones are made from amino acids

3 ways the body uses residues of amino acids

meet immediate energy needs, make glucose for storage as glycogen, or make fat for energy storage

Structure of most proteins by the time they pass from the stomach into the small intestine

most are denatured and cleaved into smaller pieces. A few are singly amino acids, but the majority remain in polypeptides

Muscle protein structures

40% of the body's protein exists in muscle tissue. Specialized muscle protein structures allow the body to move, some can release some of their amino acids, should the need for energy become dire

Larger peptide molecules and digestion/absorption

A few larger peptide molecules can escape the digestive process and enter the bloodstream intact; scientists believe they may act as hormones

3 ways an amino acid can be used by a cell

as-is to build a part of a growing protein, be altered to make another needed compound, or be dismantled to use its amine group to build a different amino acid, the remainder of which can be used for fuel

How is fluid held in blood vessels?

b proteins too large to move freely across the capillary walls. Those proteins attract water and hold it in the vessels, preventing it from flowing freely into spaces between the cells (which would cause edema)

How do proteins help maintain the fluid and electrolyte balance?

by regulating the quantity of fluids in the compartments of the body

What do antibodies do?

distinguish foreign particles (usually proteins) from proteins that belong in the body, and mark it as a target for attack. Each one is designed to destroy one specific type of invader

What happens to protein in the small intestine?

enzymes from the pancreas and the intestine split peptide strands into tripeptides, dipeptides, and amino acids

How does the body dismantle its tissue proteins to obtain amino acids for building essential proteins/energy?

first, small proteins from the blood, and then proteins from the muscles

How does protein help blood clot?

forms a stringy net that traps blood cells to form a clot

tyrosine functions

forms part of neurotransmitters epinephrine and norepinephrine, to make brown pigment melanin, and is converted into the thyroid hormone thyroxine, which regulates the body's metabolism

2 examples of transport proteins/their functions

hemoglobin, which carries oxygen from the lungs to the cells, and lipoproteins that transport lipids in the blood

What happens when a cell is starved for energy and has no glucose or fatty aids?

it strips the amino acid of its amine group (nitrogen part) and uses the remainder for energy. Amine group is excreted from the cell and then the body in the urine

What do other body cells do with amino acids?

link them together to make proteins that they keep for their own use or liberate them into lymph or blood for other uses

tryptophan function

serves as starting material for serotonin and the vitamin niacin

Sites of amino acid absorption in the small intestine

small intestine cells contain separate sites for absorbing different types of amino acids - those of the same type compete for the absorption site (so when you ingest a large dose of any single amino acid, that AA may limit absorption of others of its general type)

Edema

swelling of body tissue caused by leakage of fluid from the blood vessels; seen in protein deficiency and other conditions

What happens when amino acids are oversupplied?

the body can't store them and has no choice but to remove and excrete their amine groups and use the residues in one of three ways: meet immediate energy needs, make glucose for storage as glycogen, or make fat for energy storage

What happens to amino acids after protein is digested?

the cells along the small intestine absorb single amino acids and dipeptides and tripeptides are split into single amino acids, which are then absorbed as well

Protein turnover

the entire process of breakdown, recovery, and synthesis of proteins

What happens to Amino acids once they are circulating in the bloodstream?

they are brought to the liver, where they may be used or released into the blood to be taken up by other cells of the body

how do proteins help cells regulate fluid amounts?

when cells maintain stores of internal proteins and some minerals, they retain the fluid they need

What happens to protein in the stomach?

when swallowed food arrives in the stomach, hydrochloric acid denatures the protein strands, and an enzyme cleaves amino acid strands into polypeptides and a few amino acids

conditions under which amino acids are "wasted"

when the body lacks energy from other sources, when diet supplies more protein than the body needs, when the body has too much of any single amino acid, and when the diet provides protein of low quality, with too few essential amino acids

What happens to the tripeptides, dipeptides, and amino acids that were split in the small intestine?

while in the small intestine, enzymes on the surface of the lining and within the absorptive cells split tripeptides and dipeptides. The intestinal cells absorb and transfer amino acids into the bloodstream

Enzymes

work as catalysts, speeds up a reaction. Thousands are inside a single cell, and each one facilitates a specific chemical reaction

Amino/fatty acid glucose conversion

ð amino acids can be converted to glucose, fatty acids cannot

Urea

ð the principal nitrogen-excretion product of protein metabolism; generated mostly by removal of amine groups from unneeded amino acids or from amino acids being sacrificed for energy