ProteinsProteins

ObjectivesObjectives

Write the general formula for an Write the general formula for an amino acid.amino acid.

Define a peptide bond and write a Define a peptide bond and write a formula that shows what this bond formula that shows what this bond looks like.looks like.

Define and show the relationship Define and show the relationship between a protein and polypeptide.between a protein and polypeptide.

Define Define essential amino acidsessential amino acids and and complete proteinscomplete proteins..

ObjectivesObjectives

Write formulas and/or structures that Write formulas and/or structures that will illustrate what is meant by will illustrate what is meant by primary, secondary and tertiary primary, secondary and tertiary structure of a protein.structure of a protein.

Explain what denaturation is and how Explain what denaturation is and how it can be produced.it can be produced.

Describe at least two human diseases Describe at least two human diseases that result from improper protein that result from improper protein nutritional practices.nutritional practices.

ProteinProtein“Prime importance”

Found in:

Cells (2/3 of dry cell weight )

Tissues

All body fluids except urine and bile

Not stored for future use (like carbohydrates and lipids)

Proteins Proteins Major components of:

Skin, nails, claws, hair, wool, feathers, hooves, muscles, tendons and cartilage.

ProteinsProteins Essential FunctionsEssential Functions

Support (keratin/collagen)Support (keratin/collagen) Enzymes (specific catalysts)Enzymes (specific catalysts) Transport (channel proteins/hemoglobin)Transport (channel proteins/hemoglobin) Defense (antibodies)Defense (antibodies) Hormones (regulatory - insulin)Hormones (regulatory - insulin) Motion Motion (actin/myosin)(actin/myosin)

Protein CompositionProtein Composition

PolymersPolymers

Amino Acid MonomersAmino Acid Monomers

20 amino acids in proteins20 amino acids in proteins

Amino AcidsAmino Acids

R C

H

C

NH2

O

OH

acid groupacid groupamino groupamino group

Amino AcidsAmino Acids

Some are chemically neutral.Some are chemically neutral.

Glycine has 1 carboxyl group and 1 basic group.

Amino AcidsAmino Acids

Some are chemically “acidic.”Some are chemically “acidic.”

Glutamic acid has two carboxyl groups only 1 amino acid.

Amino AcidsAmino AcidsSome are chemically “basic.”Some are chemically “basic.”

Lysine has two amino groups and 1 carboxyl.

Amino AcidsAmino Acids

Differ in nature of Differ in nature of R R group. group.

Amino AcidsAmino AcidsSome are Some are hydrophobic.hydrophobic.

Amino AcidsAmino AcidsSome are Some are hydrophilic.hydrophilic.

PeptidePeptide

Two or more amino Two or more amino acids bonded together.acids bonded together.

AA AAX

Peptide BondPeptide Bond• Covalent bond between amino acids.• Electrons shared unevenly (O2 is more electro-negative

than N2).• Polarity permits hydrogen bonding between parts of a

polypeptide.

PolypeptidesPolypeptides

• Chains of many amino acids joined by peptide bonds.

• Proteins may contain more than one polypeptide chain.

• Can have large numbers of amino acids.• Since amino acids differ by R group; proteins differ

by a particular sequence of the R groups.

Protein Functions

• Enzymatic• Structural• Storage• Transport• Hormonal• Receptor• Contractile• Defensive• Regulatory• Sensory

Enzymatic Action

Enzyme(sucrase)

Substrate(sucrose)

Fructose

Glucose

OH

HO

H2O

Protein StructureProtein Structure

Shape determines Shape determines function.function.

Animation: Protein Structure IntroductionAnimation: Protein Structure Introduction

Interactions and Protein Shape

• Hydrogen bonds• Disulfide “bridges”• Ionic bonds• Van der Waals attractions• Hydrophilic/hydrophobic reactions

Interactions and Protein Shape

• R group of cysteine ends with a sulfhydryl group(-SH)

• Enables one chain of amino acids to connect to another by a disulfide bond (-S-S-).

Interactions and Protein Shape

Interactions and Protein Shape

Interactions and Protein Shape

Interactions and Protein Shape

Levels of Protein StructureLevels of Protein StructurePrimaryPrimary

The specific sequence of amino acids joined by peptide bonds.

Animation: Primary Protein StructureAnimation: Primary Protein Structure

Primary StructurePrimary StructureHistorical PerspectiveHistorical Perspective

- Fredrick Sanger determined first protein sequence (insulin).

- Broke into fragments and determined AA sequence of fragments.

- Then determined sequence of fragments.

- Required ten years research; modern automated sequencers analyze sequences in hours.

The specific geometric shape caused by intramolecular and intermolecular hydrogen bonding.

Levels of Protein StructureLevels of Protein StructureSecondarySecondary

Animation: Secondary Protein StructureAnimation: Secondary Protein Structure

Helix

• Discovered by Linus Pauling andRobert Corey.

• Oxygen partially ─, hydrogen partially +.

• Hydrogen bonding between the C=Oof one AA and the N-H of another.

• Hydrogen bonding between every fourthAA acid holds spiral shape of an alpha

helix.• In keratin helices covalently bonded by

disulfide (-S-S-) linkages between twocysteine amino acids.

Levels of Protein StructureLevels of Protein StructureSecondarySecondary

Pleated Sheet

• Polypeptides turn back upon themselves

• Hydrogen bonding between extended lengths.

• keratin includes feathers, hooves, claws, beaks, scales and horns; silk

Levels of Protein StructureLevels of Protein StructureSecondarySecondary

Folds or creases– Beta ribbon– Greek Key– Omega loop– Helix-loop-helix– Zinc finger– Helix-turn-helix– Beta hairpin

Levels of Protein StructureLevels of Protein Structure

MotifsMotifs

Greek Key

4 beta strands folded over into a sandwich shape. It is named for its resemblance to the Greek key meander pattern in art.

Omega Loop

• Named after its shape, the Greek capital letter Omega

• Consists of a loop of any length and any amino acid sequence.

Helix-Loop-Helix

Two α helices connected by a loop. Some of these facilitate DNA binding.

Zinc Finger

Protein (blue) containing three zinc fingers in complex with DNA (orange). The Zinc ions are green. (Transcription Factors)

Helix-Turn-Helix

• Binds to major groove of DNA through hydrogen bonds and various Van der Waals interactions with exposed bases.

• Two α helices joined by a short strand of amino acids

• Found in many proteins that regulate gene expression.

Beta Hairpin

• Two beta strands that look like a hairpin.

• Beta strands are adjacent in primary sequence and oriented in an antiparallel arrangement in the hairpin

Result when proteins of secondary structure are folded, due to various interactions Between R groups of their constituent amino acids.

Levels of Protein StructureLevels of Protein StructureTertiaryTertiary

Animation: Tertiary Protein StructureAnimation: Tertiary Protein Structure

Results when two or more polypeptides combine.

- Hemoglobin is globular protein with a quaternary structure of four polypeptides.

- Collagen is a fibrous protein consisting of three polypeptides coiled like a rope

- Most enzymes have a quaternary structure.

Levels of Protein StructureLevels of Protein StructureQuarternaryQuarternary

Animation: Quaternary Protein StructureAnimation: Quaternary Protein Structure

Sickle-Cell Disease

• Slight change in primary structure can affect a protein’s structure and ability to function

• Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin.

Chaperone Proteins

• Special proteins which help new proteins fold correctly.– Chaperone deficiencies may play a role in

facilitating certain diseases.

Denaturation Of ProteinsDenaturation Of ProteinsLoss of normal configuration – a physical Loss of normal configuration – a physical change.change.

Once a protein loses it normal shape, it cannot Once a protein loses it normal shape, it cannot perform its usual function.perform its usual function.

Sometimes will “renature.”Sometimes will “renature.”

How Proteins Can Be DenaturedHow Proteins Can Be Denatured

• TemperatureCooking an eggAlbumin congeals

• Addition of hydrogen or hydroxide ions (large pH changes)

Adding acid to milkCauses curdling

• Vigorous Shaking• Organic Solvents• Salts of heavy metals (mercury, silver & lead)• Detergents• Ultraviolet Radiation

Essential Amino AcidsEssential Amino Acids

Dietary requirements

Not synthesized

Essential Amino AcidsEssential Amino Acids

methionine or cysteineleucine

isoleucine lysine

phenylalanine (or tyrosine) threonine,typtophan

valine

Complete ProteinsComplete Proteins

Proteins that contain all essential Proteins that contain all essential amino acids. They are usually amino acids. They are usually derived from animal sources.derived from animal sources.

Protein Deficiency DiseasesProtein Deficiency Diseases

Marasmus & KwashiokorMarasmus & Kwashiokor

• Two of the most common children’s diseases Two of the most common children’s diseases worldwide.worldwide.

• Weaned diet deficient in protein.Weaned diet deficient in protein.

KwashiokorKwashiokor

• Sufficient calories, Sufficient calories, insufficientinsufficient protein. protein.• SymptomsSymptoms

– Loss of appetiteLoss of appetite– DiarrheaDiarrhea– Enlarged liverEnlarged liver– Pigmented skinPigmented skin– ApathyApathy– IrritabilityIrritability– Bloated bellyBloated belly

MarasmusMarasmus

• Inadequate calories Inadequate calories and proteinand protein

• Symptoms similar to Symptoms similar to KwashikorKwashikor– Swollen bellySwollen belly– Loss of muscular toneLoss of muscular tone– Rough, leathery skinRough, leathery skin– Generally retarded Generally retarded

physical and mental physical and mental developmentdevelopment