Introduction to Introduction to ProteinsProteins

What do proteins do?What do proteins do?

1)1) Structural proteinsStructural proteins Function: Function: SupportSupport Example:Example:

Collagen and Collagen and elastin provide a elastin provide a fibrous framework fibrous framework in animal in animal connective tissues connective tissues such as tendons such as tendons and ligamentsand ligaments► Keratin is the protein Keratin is the protein

of hair, horns, quills, of hair, horns, quills, Collagen injection

Keratin

What do proteins do?What do proteins do?

2) Storage Proteins2) Storage Proteins Function: Function: Storage Storage

of amino acidsof amino acids Example:Example:

Ovalbumin is the Ovalbumin is the protein of egg whitesprotein of egg whites►Casein is the protein Casein is the protein

is mammal milkis mammal milk

What do proteins do?What do proteins do?

3)3) Transport ProteinsTransport Proteins Function: Function:

transport other transport other substancessubstances

Example:Example:hemoglobin hemoglobin transports oxygen transports oxygen from the lungs to from the lungs to the other parts of the other parts of the bodythe body► Other proteins Other proteins

transport molecules transport molecules across cellular across cellular membranesmembranes

What do proteins do?What do proteins do?

4) Hormonal Proteins4) Hormonal Proteins Function: Function:

coordination of coordination of bodily activitiesbodily activities

Example:Example: Insulin Insulin helps control the helps control the concentration of concentration of sugar in bloodsugar in blood

Insulin

What do proteins do?What do proteins do?

5)5) Receptor ProteinsReceptor Proteins Function: Function:

response of cell to response of cell to chemical stimulichemical stimuli

Example:Example: neuron neuron receptors respond receptors respond to chemicals to chemicals released by other released by other nerve cellsnerve cells

What do proteins do?What do proteins do?

6)6) Contractile Contractile proteinsproteins

Function: Function: MovementMovement

Example: Actin Example: Actin and myosin are and myosin are the proteins the proteins responsible for responsible for muscle movementmuscle movement

What do proteins do?What do proteins do?

7)7) Defensive ProteinsDefensive Proteins

Function: Function: Protection against Protection against diseasedisease

Example: Example: Antibodies combat Antibodies combat bacteria and bacteria and virusesviruses

The Immune SystemThe Immune System

What do proteins do?What do proteins do?

8)8) Enzymatic ProteinsEnzymatic Proteins

Function: Speed Function: Speed up chemical up chemical reactionsreactions

Example: amylase Example: amylase hydrolyzes sugar hydrolyzes sugar polymers in food.polymers in food.

What is a protein?What is a protein?

► A protein is a linear chain of amino acidsA protein is a linear chain of amino acids► 20 species of amino acid, properties 20 species of amino acid, properties

dictated by side chain (R)dictated by side chain (R) Polar (hydrophillic): contain O and NPolar (hydrophillic): contain O and N Nonpolar (hydrophobic)Nonpolar (hydrophobic) Acidic: negative chargeAcidic: negative charge Basic: positive chargeBasic: positive charge

C

R

NH3+ COO-

H

AminAmino o AcidsAcids

How Complex are Proteins?How Complex are Proteins?

► Example: Average Example: Average E. Coli E. Coli protein:protein:

300 a.a. long300 a.a. long

20 possible a.a. at each position20 possible a.a. at each position

=20=20300300 possible sequences! possible sequences!

DNA: structure is independent of DNA: structure is independent of sequencesequence

Protein: structure change with sequence Protein: structure change with sequence changechange

Polypeptide ChainsPolypeptide Chains

►Enzymes join the carboxyl of one amino Enzymes join the carboxyl of one amino acid to the amino group of another acid to the amino group of another amino acid amino acid

►Amino acids are joined in a Amino acids are joined in a condensation reaction to form a condensation reaction to form a peptide linkagepeptide linkage

►Polypeptides range in length from a few Polypeptides range in length from a few monomers to thousands of amino acids monomers to thousands of amino acids longlong

Peptide linkagePeptide linkage

Protein CompositionProtein Composition

►Proteins are composed of amino acids Proteins are composed of amino acids covalently linked via polypeptide covalently linked via polypeptide bondsbonds

O

C

C

NH

R

NH C

R

C

O

C

NH

R

C

O

C

R

NH

Peptide Bond Amino Acid Subunit

Protein Have Multiple Levels of Protein Have Multiple Levels of StructureStructure

►PrimaryPrimary

►Secondary Secondary

►TertiaryTertiary

►QuaternaryQuaternary

Protein Have Multiple Levels of Protein Have Multiple Levels of StructureStructure

►PrimaryPrimary Unique sequence of amino acidsUnique sequence of amino acids Even a slight change can affect the Even a slight change can affect the

proteins ability to functionproteins ability to function For example: The disease sickle cell For example: The disease sickle cell

anemia is caused by glutamic acid anemia is caused by glutamic acid changing to valine at position 6changing to valine at position 6

Sickle CellSickle Cell

Proteins Have Multiple Levels of Proteins Have Multiple Levels of StructureStructure

► Secondary Secondary -helices, -helices, -sheets, turns, and random coils -sheets, turns, and random coils Controlled by hydrogen bonding networkControlled by hydrogen bonding network

Protein Have Multiple Levels of Protein Have Multiple Levels of StructureStructure

► TertiaryTertiary Interaction of pieces of Interaction of pieces of

secondary structuresecondary structure Controlled by side chain Controlled by side chain

interactions and include interactions and include hydrogen bonds, ionic hydrogen bonds, ionic bonds, hydrophobic bonds, hydrophobic interactions, and interactions, and covalent bonds in the covalent bonds in the form of disulfide bridgesform of disulfide bridges

Hemoglobin

Protein Have Multiple Levels of Protein Have Multiple Levels of StructureStructure

►QuaternaryQuaternary Interaction of multiple chainsInteraction of multiple chains Interactions are controlled by shape and Interactions are controlled by shape and

chemistrychemistry

HemoglobinHemoglobin An example of quarternary structure An example of quarternary structure