Chapter 14 Proteins
Sections: 1-4
By: Kelsi Myer and Rachel Dailey
Section 1 What are the Many
Functions of Proteins?
 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
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?
 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)
General protein
formula
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 german zwitter
 “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