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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

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Functions of proteins

Functions of Proteins

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

Functions of proteins1
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


  • 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


  • 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


  • 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


  • 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

  • Click Link:

Side chains
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


  • Two identical cystine monomers make up cysteine

  • Unique because its side chain ( -SH) can form disulfide bridges with another cysteine

Charged amino acids
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
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)


  • 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


  • 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
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
What Are Amino Acids?

  • Contains amino and carboxyl groups.

    • Structure: (side chain)

What are amino acids1
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
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
What are Zwitterions?

  • Compounds with a positive charge on one atom and a negative charge on another are known as 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.