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Proteins

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AP Biology 2008-2009

ProteinsMultipurpose

molecules

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Proteins

Most structurally & functionally diverse group

Function: involved in almost everything

enzymes (pepsin, DNA polymerase)

structure (keratin, collagen) carriers & transport (hemoglobin, aquaporin)

cell communication

signals (insulin & other hormones)

receptors

defense (antibodies)

movement (actin & myosin)

storage (bean seed proteins)

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Proteins

Structure

monomer= amino acids

20 different amino acids

polymer= polypeptide protein can be one or more polypeptide

chains folded & bonded together

large & complex molecules

complex 3-D shape

Rubisco

hemoglobin

growthhormones

H2O

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Amino acids

Structure

central carbon

amino group

carboxyl group (acid)

R group (side chain)

variable group

different for each amino acid

confers unique chemical

properties to each amino acid

like 20 different letters of an

alphabet

can make many words (proteins)

N

H

H

COH||O

R

|

C

|

H

Oh, I get it!amino = NH

2acid = COOH

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Effect of different R groups:

Nonpolar amino acids

Why are these nonpolar & hydrophobic?

Why are these nonpolar & hydrophobic?

nonpolar & hydrophobic

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Effect of different R groups:

Polar amino acids polar or charged & hydrophilic

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 disulfide bridges

covalent cross links betweens sulfhydryls

stabilizes 3-D structure

You wonderedwhy perms

smell likerotten eggs?

H-S S-HH-S S-H

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AP Biology

Building proteins

Peptide bonds

covalent bond between NH2 (amine) ofone amino acid & COOH (carboxyl) ofanother

CN bond

peptidebond

dehydration synthesisH2O

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Building proteins

Polypeptide chains have direction

N-terminus = NH2 end

C-terminus = COOH end

repeated sequence (N-C-C) is thepolypeptide backbone

can only grow in one direction

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Protein structure & function

hemoglobin

Function depends on structure

3-D structure

twisted, folded, coiled into unique shape

collagen

pepsin

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Primary (1) structure

Order of amino acids in chain

amino acid sequence

determined by gene (DNA)

slight change in amino acidsequence can affect proteins

structure & its function

even just one amino acid change

can make all the difference!

lysozyme: enzymein tears & mucusthat kills bacteria

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Sickle cell anemia

Imhydrophilic!

But Imhydrophobic!

Just 1out of 146

amino acids!

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Secondary (2) structure

Local folding

folding along short sections of polypeptide

interactions between

adjacent amino acids H bonds

weak bonds

between R groups

forms sections of3-D structure

E-helix

F-pleated sheet

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Secondary (2) structure

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Tertiary (3) structure

Whole molecule folding

interactions between distant amino acids

hydrophobic interactions

cytoplasm iswater-based

nonpolar amino

acids cluster away

from water

H bonds & ionic bonds

disulfide bridges

covalent bonds between

sulfurs in sulfhydryls (SH)

anchors 3-D shape

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Quaternary (4) structure

More than one polypeptide chain bondedtogether

only then does polypeptide becomefunctional protein

hydrophobic interactions

collagen = skin & tendons hemoglobin

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Protein structure (review)

amino acidsequence

peptide bonds

1

determinedby DNA R groups

H bonds

R groups

hydrophobic interactions

disulfide bridges

(H & ionic bonds)3multiple

polypeptides

hydrophobic

interactions4

2

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Protein denaturation

Unfolding a protein

conditions that disrupt H bonds, ionic

bonds, disulfide bridges

temperature pH

salinity

alter 2 & 3 structure

alter 3-D shape

destroys functionality

some proteins can return to their functional shape

after denaturation, many cannot

In Biology,size doesnt matter,

SHAPE matters!

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AP Biology 2008-2009

Lets build some

Proteins!

EAT

X

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AP Biology 2007-2008

Ghosts of Lectures Past(storage)

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Chaperonin proteins

Guide protein folding

provide shelter for folding polypeptides

keep the new protein segregated from

cytoplasmic influences

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Protein models

Protein structure visualized by

X-ray crystallography

extrapolating from amino acid sequence

computer modelling

lysozyme