AP Biology Chemical Building Blocks 3.4 Proteins.

AP Biology

Chemical Building Blocks 3.4 Proteins

AP Biology

Proteins

AP Biology 2006-2007

ProteinsMultipurpose

molecules

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Proteins Most structurally & functionally diverse

group of biomolecules Function:

involved in almost everything enzymes (pepsin, polymerase, etc.) structure (keratin, collagen) carriers & transport (membrane channels) receptors & binding (defense: antibodies) contraction (actin & myosin) signaling (hormones: insulin) 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

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Amino acids Structure:

central carbon amino group carboxyl group (acid) R group (side chain)

variable group confers unique

chemical properties of the amino acid —N—

H

HC—OH

||O

R

|—C—

|

H

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Nonpolar amino acids nonpolar & hydrophobic

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

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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

cross links betweens sulfurs in amino acids

You wonderedwhy perms

smelled like rotten eggs?

H-S – S-HH-S – S-H

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Building proteins Peptide bonds

linking NH2 of one amino acid to COOH of another

C–N bond

peptidebond

dehydration synthesis

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Building proteins Polypeptide chains

N-terminus = NH2 end C-terminus = COOH end repeated sequence (N-C-C) is the

polypeptide 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 acid sequence can affect protein’s structure & it’s function even just one amino acid change

can make all the difference!

lysozyme: enzyme in tears & mucus that kills bacteria

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Sickle cell anemia

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Secondary (2°) structure “Local folding”

folding along short sections of polypeptide interaction between

adjacent amino acids

H bonds between R groups

-helix -pleated sheet

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Secondary (2°) structure

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Tertiary (3°) structure “Whole molecule folding”

determined by interactions between R groups hydrophobic

interactionseffect of water

in cell anchored by

disulfide bridges(H & ionic bonds)

Van der Waals Force (velcro)

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Quaternary (4°) structure More than one polypeptide chain

joined together only then is it a functional protein

hydrophobic interactions

hemoglobin

collagen = skin & tendons

“Let’s go to the video tape!”(play movie here)

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Protein structure (review)

1°

2°

3°

4°

aa sequencepeptide bonds

R groupsH bonds

R groups hydrophobic interactions,

disulfide bridges

determinedby DNA

multiplepolypeptideshydrophobic interactions

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Denature a protein Unfolding a protein

disrupt 3° structure pH salt temperature

unravels or denatures protein disrupts H bonds, ionic bonds &

disulfide bridges destroys functionality

Some proteins can return to their functional shape after denaturation, many cannot

In Biology,size doesn’t matter,

SHAPE matters!

AP Biology 2006-2007

Let’s build some

Proteins!

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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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Diseases as a result Cystic fibrosis; disables vital proteins

from moving ions across membranes Alzheimers; protein clumping in brain

cells Chaperone does fails to create correct

folding.

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Protein models Protein structure visualized by

X-ray crystallography extrapolating from amino acid sequence computer modelling

lysozyme