Regents Biology

Proteins

2006-2007 Regents Biology

Proteins:

Multipurpose molecules

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Proteins

insulin

collagen (skin)

hemoglobin

Examples muscle fingernails, claws skin hair enzymes

example: pepsin

hormones example: insulin

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Proteins Function:

many, many functions hormones

insulin

movementmuscle

immune systemprotect against germs

enzymeshelp chemical reactions

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Proteins

Building block =

aminoacid

aminoacid–

aminoacid–

aminoacid–

aminoacid–

—N—H

H

H|

—C—|

C—OH

||O

variable group

amino acids

20 different amino acids

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Amino acid chains Proteins

amino acids chained into a polymer

Each amino acid is different some “like” water & dissolve in it

some “fear” water & separate from it

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Water-fearing amino acids Hydrophobic

“water fearing” amino acids try to get away from water in cell

the protein folds

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Water-loving amino acids Hydrophillic

“water loving” amino acids try to stay in water in cell

the protein folds

Regents Biology pepsin

3-D protein structure

collagen

Proteins fold & twist into 3-D shape

hemoglobingrowthhormone

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Proteins (Polypeptides)Proteins (Polypeptides)

Four levels of protein Four levels of protein structure:structure:

A.A. Primary StructurePrimary Structure

B.B. Secondary Structure Secondary Structure

C.C. Tertiary Structure Tertiary Structure

D.D. Quaternary Structure Quaternary Structure

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Primary Structure

Amino acids bonded together by peptide bonds peptide bonds (straight chains)(straight chains)

aa1 aa2 aa3 aa4 aa5 aa6

Peptide Bonds

Amino Acids (aa)

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Secondary StructureSecondary Structure3-dimensional folding

arrangement of a primary primary structurestructure into coilscoils and pleatspleats held together by hydrogen hydrogen bondsbonds.

Two examples:Two examples:Alpha HelixAlpha Helix

Beta Pleated SheetBeta Pleated Sheet

Hydrogen BondsHydrogen Bonds

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Tertiary StructureTertiary StructureSecondary structuresSecondary structures bentbent and

foldedfolded into a more complex 3-D more complex 3-D arrangementarrangement of linked polypeptides

Bonds: H-bonds, ionic, disulfide Bonds: H-bonds, ionic, disulfide bridges (S-S)bridges (S-S)

Call a “subunit”.“subunit”.Alpha HelixAlpha Helix

Beta Pleated SheetBeta Pleated Sheet

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Quaternary StructureQuaternary StructureComposed of 2 or more “subunits”Globular in shapeForm in Aqueous environmentsExample: enzymes (hemoglobin)enzymes (hemoglobin)

subunitssubunits

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Its shape that matters! Proteins do their jobs, because

of their shape Unfolding a protein destroys its shape

wrong shape = can’t do its job unfolding proteins = “denature”

temperature pH (acidity) folded

unfolded“denatured”