2005-2006AP Biology

Proteins

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Proteins Most structurally & functionally diverse

group of biomolecules Function:

involved in almost everything enzymes structure (keratin, collagen) carriers & transport (membrane channels) receptors & binding (defense) contraction (actin & myosin) signaling (hormones) storage (bean seed proteins)

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Proteins Structure:

monomer = amino acids 20 different amino acids

polymer = polypeptide protein can be 1 or more polypeptide

chains folded & bonded together large & complex molecules complex 3-D shape

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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

H

H|

—C—|

C—OH

||O

R

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Nonpolar amino acids nonpolar & hydrophobic

Why are these nonpolar & hydrophobic?

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Polar amino acids polar or charged & hydrophilic

Why are these polar & hydrophillic?

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Sulfur containing amino acids Disulfide bridges

cysteines form cross links

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Building proteins Peptide bonds: dehydration synthesis

linking NH2 of 1 amino acid to COOH of another

C–N bond

peptidebond

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Building proteins Polypeptide chains

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

polypeptide backbone 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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Protein structure & function function depends on structure

all starts with the order of amino acids what determines that order of

amino acids?

lysozyme: enzyme in tears & mucus that kills bacteriathe 10 glycolytic enzymes

used to breakdown glucose to make ATP

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Primary (1°) structure Order of amino acids in chain

amino acid sequence determined by 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!

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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

-helix -pleated sheet

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Secondary (2°) structure

The Alpha Helix

Beta-Pleated Sheets

18

Representations of Protein Secondary Structure

lysozyme

19

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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)

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Quaternary (4°) structure Joins together more than 1 polypeptide chain

only then is it a functional protein

hemoglobin

collagen = skin & tendons

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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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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

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Denature a protein Disrupt 3° structure

pH salt temperature

unravel or denature protein disrupts H bonds, ionic bonds &

disulfide bridges Some proteins can

return to their functional shape after denaturation, many cannot

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Let’s build some

Insulin!

AP Biology

The insulin protein has two chains, with a total of 53 amino acids

The two chains are connected by disulfide bridges from cysteine molecules

After you link together the primary sequence through dehydration synthesis, you can join the cysteines together!

Each side of the room will build an insulin molecule

The abbreviations for the 20 amino acids are found in the table

The amino acids are color coded by side group: non-polar, polar, acidic, and basic

Water molecules need to be removed by dehydration synthesis

Join the amino acids together, then work on the cysteines (part of tertiary structure)

Ribosome Animations of Protein Synthesis

Real TimeSlo-moOlder – Gumby-LikeShows secondary structure of ribosome in action

Bonus Question(1st group to answer gets

candy)

Some of the 20 amino acids are missing from insulin – name them all!