AP Biology Proteins AP Biology 2008-2009 Proteins _______________

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Proteins

AP Biology 2008-2009

Proteins______________________________

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Proteins Most structurally & functionally diverse group Function: involved in almost everything

(pepsin, DNA polymerase) (keratin, collagen) (hemoglobin, aquaporin)

(insulin & other hormones)

(antibodies) (actin & myosin) (bean seed proteins)

AP Biology

Proteins Structure

monomer = 20 different amino acids

polymer = protein can be one or more polypeptide

chains folded & bonded together

Rubisco

hemoglobin

growthhormones

H2O

AP Biology

Amino acids Structure

(acid) (side chain)

variable group different for each amino acid

like 20 different letters of an alphabet

can make many words (proteins)

—N—H

HC—OH

||O

R

|—C—

|

H

Oh, I get it!amino = NH2 acid = COOH

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Effect of different R groups:Nonpolar amino acids

Why are these nonpolar & hydrophobic?Why are these nonpolar & hydrophobic?

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Effect of different R groups:Polar amino acids

Why are these polar & hydrophillic?Why are these polar & hydrophillic?

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Ionizing in cellular waters H+ donorsH+ donors

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Ionizing in cellular waters H+ acceptorsH+ acceptors

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Sulfur containing amino acids Form

covalent cross links betweens sulfhydryls

You wonderedwhy permssmell like

rotten eggs?

H-S – S-HH-S – S-H

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Building proteins Peptide bonds

C–N bond

peptidebond

dehydration synthesisH2O

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Building proteins Polypeptide chains have direction

repeated sequence (N-C-C) is the

_____________________ can only grow in one direction

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Protein structure & function

hemoglobin

3-D structure

twisted, folded, coiled into unique shape

collagen

pepsin

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Primary (1°) structure

slight change in amino acid sequence can affect protein’s structure & its function

lysozyme: enzyme in tears & mucus that kills bacteria

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Sickle cell anemiaJust 1

out of 146amino acids!

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Secondary (2°) structure “ ”

folding along short sections of polypeptide

weak bonds

between R groups

-helix -pleated sheet

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Secondary (2°) structure

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Tertiary (3°) structure “ ”

interactions between distant amino acids

cytoplasm is water-based

nonpolar amino acids cluster away from water

covalent bonds between sulfurs in sulfhydryls (S–H)

anchors 3-D shape

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Quaternary (4°) structure

only then does polypeptide become functional protein hydrophobic interactions

collagen = skin & tendons hemoglobin

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Protein structure (review)

amino acid sequence

peptide bonds

1°

determinedby DNA R groups

H bonds

R groupshydrophobic interactions

disulfide bridges(H & ionic bonds)

3°multiple

polypeptideshydrophobic interactions

4°

2°

AP Biology

Protein denaturation

conditions that disrupt H bonds, ionic bonds, disulfide bridges

alter 2° & 3° structure

destroys functionality

In Biology,size doesn’t matter,

SHAPE matters!