FUNCTIONS OF PROTEINS

By: Alec Hoover, Katie Klick, and Cory Yerger(14.1-14.4)

Functions of Proteins

Structural support Animals have structural proteins. These are chief

constituents in skin, bones, hair, and nails. Two important proteins are:

Collagen and keratin Catalysis

All reactions that take place in living organisms are catalyzed by proteins called enzymes

Without enzymes reactions would be slow and useless

Continued…

Movement Muscle are made up of protein molecules

Myosin and actin Transport

Hemoglobin in the blood carries oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs Move molecules across the cell brain

Continued…

Hormones Many hormones are protein

insulin, erythropoietin, human growth hormone Protection

The body makes proteins called antibodies to counteract foreign proteins

This is one of the major mechanisms used by the body to fight off diseases

Fibrinogen is the protein used in blood clotting

Continued…

Storage Proteins store material

Example: casein in milk and ovalbumin in eggs store nutrients for newborn mammals and birds.

Ferritin: protein in the liver that stores iron. Regulation

Control the expression of genes Regulate the kind of proteins synthesized in a

particular cell Dictate when it is controlled

Continued… A typical cell contains about 9000 different

proteins; the entire human body has 100,000 different proteins

Classified by two major types: Fibrous proteins

Insoluble in water and used mainly for structural purposes Globular proteins

More or less soluble in water and used mainly for nonstructural purposes

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Side Chains Side chains are responsible for the

characteristics and functions of amino acids

Some amino acids have charged side chains EX: Glutamic Acid & Aspartic Acid

Cysteine Two identical cystine monomers make up

cysteine Unique because its side chain ( -SH) can

form disulfide bridges with another cysteine

Charged Amino Acids When an amino acid has an additional

carboxyl group it loses a proton and forms a corresponding carboxylate anion EX: Glutamic Acid Glutamate Side chain is negatively charges at neutral

pH Histidine, Lysine, & Arginine have basic

side chains Lysine & Arginine have side chains that

are positively charges at or near neutral pH

Aromatic Rings Phenylalanine, Tryptophan, & Tyrosine

have aromatic rings in their side chains Allow us to locate and measure proteins

because the aromatic rings absorb strongly

Can be detected using a spectrophotometer

Key precursors to neurotransmitters (substances involved in the transmission of nerve impulses)

Serotonin Tryptophan is converted to serotonin,

calming agent Low levels of serotonin are associated

with depression High levels produce a hyper condition Bipolar disorder can be managed by

controlling levels of serotonin

L-dopa L-Dihydroxyphenylalanine = L-dopa Low levels of L-dopa are involved in

Parkinson’s disease Tyrosine or phenylalanine supplements

increase levels of dopamine because it passes into the brain quickly through brain-blood barrier

Hormones Tyrosine and Phenylalanine are

transformed into norepinephrine and epinephrine, stimulants

Epinephrine is the “Flight or Fight” hormone Causes the release of glucose and other

nutrients into the blood Stimulates brain function

Side Effects Tyrosine & Phenylalanine may have

unexpected effects in some people Some people get headaches from the

phenylalanine in aspartame, artificial sweetener in diet soft drinks

Tyrosine gives some people a morning lift

Tryptophan helps you sleep at night Milk proteins are an aid in inducing sleep

What Are Amino Acids? Contains amino and carboxyl groups.

Structure: (side chain)

What Are Amino Acids? Form chains that make up proteins

20 common amino acids found in nature Called alpha amino acids

Listed on page 303 in figure 14.1

How do we categorize them? Classified into four groups based off of their

polarity. Non-polar Polar But Neutral Acidic Basic

Non-polar side chains are hydrophobic and the side chains of the rest are hydrophilic.

Side chains are responsible for determining both the structure and function of each protein molecules.

What are Zwitterions? Compounds with a positive charge on one

atom and a negative charge on another are known as zwitterions.

Zwitterions Zwitter is a German word meaning “hybrid” Amino acids are zwitterions in a water

solution and in the solid state As the pH is changed in the solution, the

amount of positive and negative charges in the molecules change.

When the pH is at the level where the positive and negative charges are balanced, it is known as the isoelectric point.