Module 4 - Amino acids and Proteins

Amino acids

are the building blocks of protein

Amino acids

contain a carboxylic acid group and an amino group on the a-carbon, the carbon adjacent to the C=O

Amino acids

both have a weak acid and weak base present,, actually exist as a salt

Amino acids

contains a different side group (R)

Amino acids

soluble in water, have either high melting points or decompose upon heating 

Amino acids

act more like inorganic materials than organic compounds

Nonpolar amino acid

amino acid that contains one amino group, one carboxyl group, and a nonpolar side chain

Nonpolar amino acid

found in the interior of proteins, where there is limited contact with water

Tryptophan

a borderline member of this group because water can weakly interact through hydrogen bonding with the NH ring location on the side chain ring structure

Polar neutral amino acid

amino acid that contains one amino group, one carboxyl group, and a side chain that is polar but neutral

Polar neutral amino acid

more soluble in water than the nonpolar amino acids, the R group present can hydrogen-bond in water

neither acidic nor basic

Side chain of a polar neutral amino acid is _______

Polar acidic amino acid

amino acid that contains one amino group and two carboxyl groups, the second carboxyl group being part of the side chain

Polar acidic amino acid

the side chain bears a negative charge; the side-chain carboxyl group has lost its acidic hydrogen atom

Polar basic amino acid

amino acid that contains two amino groups and one carboxyl group the second amino group being a part of the side chain

Polar basic amino acid

the side chain bears a positive charge; the nitrogen atom of the amino group has accepted a proton

Complete dietary protein

contains all of the essential amino acids in the same relative amounts in which the body needs them

Complete dietary protein

may or may not contain all of the nonessential amino acids

Complete dietary protein

protein usually from animal sources

Incomplete dietary protein

protein that does not contain adequate amounts, relative to the body’s needs, of one or more of the essential amino acids

Limiting amino acid

essential amino acid that is missing, or present in inadequate amounts, in an incomplete dietary protein

Casein

from milk and proteins in meat, fish, and eggs are complete dietary proteins

Gelatin

one common incomplete dietary protein that comes from animal sources

Gelatin

a protein in which tryptophan is the limiting amino acid

• Lysine

• Methionine

• Tryptophan

With plant proteins, three amino acids are often limiting:

Lysine

Ex: wheat, rice, oats and corn

Methionine

Ex: beans and peas

Tryptophan

Ex: corn and beans

Methionine and Tryptophan

Both corn and beans have two limiting amino acids:

Soy

only common plant protein that is a complete dietary protein

Complementary dietary protein

two or more incomplete dietary proteins that, when combined provide and adequate amount of all essential amino acids relative to the body’s needs

Glycine

• smallest and simplest amino acid

• responsible for flexibility of protein

• optically inactive

Creatine

formed of three amino acids: L-arginine, glycine, and L-methionine

Creatine

an amino acid located mostly in your body’s muscles, as well as in the brain 

Nephrotoxic drugs

taking high doses of creatine might harm your kidneys, there is concern about combining creatine with drugs that might damage the kidneys

Caffeine and ephedra

combining caffeine with creatine might decrease the efficacy of creatine, combining caffeine with creatine and the supplement ephedra might increase the risk of serious side effects, such as stroke

L isomers

amino acids found in nature and proteins

L isomers

preferred form for amino acids

Histidine

most stable amino acid at physiologic pH

Histidine

can serve as best buffer at pH 7

Histidine

can protonate and deprotonate at neutral pH

Histidine

precursor of histamine

Histamine

an organic nitrogenous compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus

Histamine

involved in the inflammatory response and has a central role as a mediator of itching

Glutamine

storage and transport form of ammonia

Glutamine

removal of ammonia from brain

Glutamine

precursor of purines and pyrimidines

Phenylalanine

precursor of tyrosine

Tyrosine

precursor of Catecholamines, Thyroxine, Melanin

Tyrosine

amino acid that is naturally produced in the body from another amino acid called phenylalanine

Tyrosine

found in many foods,, especially in cheese, where it was first discovered 

Catecholamines

hormones made by your adrenal glands, which are located on top of your kidneys

Catecholamines

what adrenal glands send into your blood when you’re physically or emotionally stressed

• Dopamine

• Norepinephrine

• Epinephrine

Example of Catecholamines:

Dopamine

neurotransmitter, plays a role in how we feel pleasure

Dopamine

a big part of our unique human ability to think and plan

Norepinephrine

released into the blood as a stress hormone when the brain perceives that a stressful event has occurred

Melanin

• skin pigment

• a complex polymer derived from the amino acid tyrosine

Cysteine

can be synthesized in body from methionine (both contain sulphur)

Cysteine

responsible for reducing action of glutathione

Reduced glutathione (GSH)

simply the stable, active form required for good health

Methionine

form S-adenosyl-L-methionine (SAM) which is a major methyl group donor in body

Tryptophan

precursor of niacin and serotonin (which form melatonin)

Tryptophan

60 mg of tryptophan form 1 mg niacin

Arginine

• most basic amino acid

• precursor of nitric oxide 

Nitric oxide

compound in the body that causes blood vessels to widen and stimulates the release of certain hormones such as insulin and human growth hormone

Alanine

transport form of ammonia from muscle

Free ammonia

since ______ is highly toxic, it is never transported in free form in blood

• Transport of Ammonia in the Form of Glutamine

• Transport of Ammonia in the Form of Alanine

Two mechanism are available in humans for the transport of ammonia from the peripheral tissues to the liver for its ultimate conversion to urea:

Zwitterion

has an equal number of -NH₃⁺ and COO^- groups forms when the H from -COOH in an amino acid transfers to the -NH2

Isoelectric point

pH at which amino acid has an overall zero

pH 2.8-10.8

Isoelectric point of amino acids range from

Glycine

with an IP of 6.0 exist as a positively charged species at a pH below 6.0

Aspartic acid

an acidic amino acid, has a IP of 2.8; it is a neutral salt at pH 2.8 forms negative ions with charges -1 and -1 at pH values greater than pH 2.8