Chapter 14 Proteins Sections: 1-4

Chapter 14 ProteinsSections: 1-4 By: Kelsi Myer and Rachel Dailey

Section 1 What are the Many Functions of Proteins? keratin • Proteins- are by far the most important of all biological compounds • The word protein is derived from the Greek word proteios meaning “of first importance” • Perform a variety of functions in the body • 1. structure- proteins are the chief constituents of skin, hair, bones, and nails. • Two important structural proteins • Collagen • keratin

Functions continued • 2. Catalysis- most all reactions in the body are catalyzed by enzymes • 3. Movement- muscles are made of protein molecules • Every movement you make, blinking, pointing, walking breathing, can only happen because of the proteins • 2 main • Myosin • Actin • 4. Transport- movement of vital nutrients • Hemoglobin carries oxygen to cells and carbon dioxide to lungs to be expelled • 5. Hormones- many hormones are proteins • Insulin • Erythropoietin • Human growth hormone

Functions Continued • 6. Protection- antibodies are proteins made to counteract proteins of a foreign nature. • Major for fighting disease • Blood clotting (Fibrinogen) • 7. Storage- store materials • Ferritin is found in liver and stores iron • 8. Regulation-control expression of genes and dictate when manufacturing of other proteins take place

Proteins • An average call contains 9000 different proteins • The human body had 100,000 different proteins • Classified into two types • Fibrous proteins • Insoluble in water • Structural purposes • Globular proteins • More or less soluble in water • Used for nonstructural purposes

Section 2 What are Amino Acids? General protein formula • There is a wide variety but they have basically the same structure: they are chains of amino acids. • Contains an amino group and a carboxyl group • 20 common amino acids in nature make up proteins • They are called alpha amino acids • All but one of the 20 fit the formula. It only differs between the R and N bond. • The most important aspect of the R groups is their polarity. • Classified into four groups • Nonpolar ( hydrophobic; repel water) • Polar but neutral (hydrophilic; attracts water) • Acidic (Hydrophilic) • Basic (hydrophilic)

Section 2 continued They are chiral with carbon stereocenters The exception is glycine which is achiral Each amino acid exists as two enantiomers but nature only makes one of the two; usually the L- isomer All the amino acids in your body are the L-isomer. D amino acids are extremely rare but can be found in the cell walls of some bacteria

Section 3: What are Zwitterions? • Amines cannot exists in the presence of a moderately weak acid. • They gain a proton to form ammonium ions • RNM3+ • Has a –COOH group • Has a –NH2 group • Water insoluble • Compounds with a positive charge on one atom have a negative charge on another

Zwitterions • The negatively charged atom is called zwitterions • From germanzwitter • “hybrid” • Amino acids are zwitterions in water solutions and solids • Ionic compounds • Internal salts • Un-ionized ions do NOT exist

Properties • All are solids • Have high melting points • 20 common are all fairly soluble in water • If pH is lowered the zwitterion will turn to a positive ion • -COO gets proton • If pH is raised the zwitterion will turn to negative ion • -NH2 gives proton to –OH • Pretty close isoelectric points • Isoelectric point is where all the molecules have equal positive and negative charges • 15 of 20 are around 6

Proteins • Around isoelectric point amino acids exists in aqueous solution largely as zwitterions • React with either • A strong base • A strong acid

Section 4 What Determines the Characteristics of Amino Acids? • The side chain of an amino acid is responsible for the unique characteristics of these molecules. • The amino acid cysteine has a chemical property not shared by the other 20 amino acids. • Cystine is the dimer of cysteine and can be reduced easily to give two molecule of cysteine. • Many amino acids have acidic or basic properties. • Glutamic acid and aspartic acid and they have carboxyl groups in their side chains, addition to the ones that amino acids all have. • The carboxyl group can lose a proton and for the carboxylate anion. • Because of the carboxylate the side chains of the two amino acids are negatively charged at neutral pH.

Section 4 Continued • Histidine, lysine, and arginine have basic side chains • Lysine and arginine are positively charged or near neutral pH • The pKa values for amino acids depend on the environment and change significantly within the confines of the protein. • Histidine can be found in the protonated or unprotonated forms in proteins and the properties of many proteins depends on whether individual residues are charged or not. • The charged amino acids are found in the active sites of enzymes.

Section 4 Continued • Phenylalanine, tryptophan, and tyrosine have aromatic rings in their side chains • They allow us to locate and measure proteins because the aromatic rings absorb strongly at 280 nm and can be detected using a spectrophotometer. • Important in physiology because they are precursors to neurotransmitters. • Tryptophan is converted to serotonin and has a calming effect • Low levels are associated with depression • High levels produce a manic state

Section 4 Continued Tyrosine (derived from phenylalanine) is converted to the neurotransmitter class called catecholamines Includes adrenalin L-Dihydroxyphenylalanine (L-dopa) is an intermediate of tyrosine Associated with Parkinson’s disease Tyrosine supplements increase the levels of dopamine but L-dopa is usually prescribed because it passes into the brain quickly through the blood-brain barrier.

Section 4 continued • Tyrosine and phenylalanine are precursors to norepinephrine and epinephrine • Both are stimulatory • Epinephrine is known as the “fight or flight” hormone • Releases glucose and nutrients into the blood and stimulates brain function. • Tyrosine is said to give a morning lift • Tryptophan helps sleep at night • Milk proteins have high levels of tryptophan

Chapter 14 Proteins Sections: 1-4