The most diverse molecules in living organisms and among the most important: gelatin, desserts, hair, antibodies, spider webs, blood clots, egg whites, tofu, and fingernails, etc.

Make up 50% of dry mass of most cells. ◦ Structural building blocks◦ Functional molecules◦ Involved in almost anything that cells do. ◦ 3D shape is directly related to their function.◦ Enzymes: catalysts speed up chemical reactions so cells can sustain

life.◦ Immunoglobins: protect animals against foreign microbes and cancer

cells. ◦ Hemoglobin: transports oxygen. ◦ Protein carriers: move substances across cell membranes.◦ And much more!

Proteins (in detail) (Pg. 40)

Genetic information in DNA codes specifically for production of proteins and nothing else.

All copies of the same gene produce the same protein.

DNA to PROTEIN

Monomer: amino acid. ◦ Central carbon atom with an amino group, a carboxyl

group, a hydrogen atom, and a side chain (R). ◦ 20 different R groups, therefore 20 different AAs. ◦ Amphiprotic: both acidic (carboxyl) and basic (amino)

functional group. When dissolved in water, carboxyl group donates an H+

ion to the amino group Causes the carboxyl group to become (-) and amino (+). Amino acids may have side chains that are polar (hydrophillic)

or nonpolar (hydrophobic), acidic (contain a carboxyl) or basic (amino).

Protein Structure

Nonpolar amino acids

Polar Amino Acids

Electrically charged (acidic/basic) amino acids

Note: there are 8 essential amino acids: body cannot synthesize from simpler compounds:Tryptophan, methionine, valine, threonine, phenylalanine, leucine, isoleucine, lysine.

HW (to do for Monday):Amino Acid Memory Cards 1) take a cue card and place it in `portrait` orientation towards

you. 2) fold the top down and bottom up about 1 inch from the

edges. 3) Draw an amino acid on the blank side of the cue card. 4) write the name of the amino acid on one of the folded parts,

and the short-hand notation on the other fold. 5) write a few things about the amino acid on the side with

lines. 6) use these cue cards to study. Do not lose them! (attach

them to your binder, put them in your pencil case, etc). You will be required to know all of the amino acids as well as their properties.

Proteins consist of one or more amino acid polymers (polypeptides) that have twisted and coiled into a specific shape. ◦ Final shape: conformation determined by the

sequence of amino acids it contains. ◦ Peptide bond: condensation reaction between

amino group of one amino acid and carboxyl group of another amino acid, forming an amide Functional group linkage is called an amide bond.

◦ Polypeptides: constructed in the cytoplasm of cells through process called protein synthesis.

Formation of a Polypeptide

Amino terminus: amino group at one end. Carboxyl terminus: carboxyl group at other

end. Can be between a few to more than a thousand

amino acids. Sequence determines polypeptide’s 3D

conformation determines function.◦ Structural proteins: roughly linear: forms strands or

sheets.◦ Globular proteins: 1+ polypeptide chains that coil and

bend to form rounded, spherical shape Many enzymes are globular.

Polypeptides

Primary Structure: unique sequence of amino acids in a polypeptide chain. ◦ Amino acid referred to as a ‘residue.’◦ First protein to be ‘decoded’ in terms of residue

was insulin: Fredrick Sanger, 1958.◦ Determined by the nucleotide sequence of DNA. ◦ Possible arrangement of polypeptides:

The number of possible arrangements of residues in a polypeptide are 20n .

Example: How many different 40- residue polypeptides are possible?

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Primary Structure

Changing the sequence by one amino acid could alter the 3D shape protein loses it’s function, is rendered useless, or has a different function (rare). ◦ Ex// Sickle cell anemia: single AA change in hemoglobin causes

red blood cell to change shaped: flow is hindered, vessels clog.

Changing the sequence.

During protein synthesis, AAs added to growing chain one at a time coils, folds, bends at various locations.

Two main shapes form:◦ α-helix & β-pleated sheet.

Secondary Structure

α-helix: hydrogen bond forms between the electronegative O of (C=O) of one peptide bond and the electropositive hydrogen of the amino group (N-H) four peptide bonds away

Ex// fibrous proteins - α-keratin: protein in hair.

α-helix

Two parts of polypeptide chain lie parallel to one another. Hydrogen bonds form between oxygen atoms of C=O on one

strand and hydrogen atoms of amino groups on adjacent strand.

β-pleated sheet

Spiders are Crazy Cool!• silk contains large amounts of betapleated sheets spiders secrete silkin liquid form and then solidify when exposedto air. Many H-bonds. Strength!

Strong forces of attraction and repulsion between the polypeptide and its environment force it to undergo additional folding.

Chaperone proteins: aid growing polypeptide to fold into tertiary structure: deficiency: cystic fibrosis.◦ AAs with polar R groups (ex// serine, tyrosine, and glutamine) are attracted

to water.◦ AAs containing nonpolar R groups (ex//valine and phenylalanine) are

‘repelled’ by water. Congregate in the interior of folded polypeptide, away from water.

◦ Structure stabilized by number of R-group interactions. H-bonds ionic bonds (between oppositely charged side chains) van der Waals forces between nonplar R groups. Disulfide bridges: covalent bond between sulfur-containing R groups of

cysteine residues. Proline kinks: R group is attached to the amino group forms a kink in the

polypeptide.

Tertiary Structure

Sometimes 2+ polypeptide subunits combine to form a functional protein. ◦ Collagen (skin, bones,

tendons, ligaments)◦ Keratin (hair)◦ Hemoglobin (transports

oxygen): four polypeptides in quaternary structure.

Quaternary Structure

Proteins are made within a cell, in a mostly neutral pH.

Different environmental conditions may cause unravelling.◦ pH◦ temperature◦ Salt concentrations

Various chemicals and heat disrupt:◦ Hydrogen bonds◦ Ionic bonds◦ Disulfide bridges◦ Hydrophobic interactions

Will usually return to original orientation if denaturing agent is removed.

Denaturation

Enzymes work within specific ranges of conditions◦ Thermophiles: (archaebacteria: live in water at about 100

degrees celcius) Would die at room temperature enzymes would denature.

◦ Gastrin: digestive enzyme in the stomach works best at pH = 2, and denatured in small intestine where the pH = 10.

◦ Fevers: prolonged fevers can denature proteins in brain and lead to seizures/death.

◦ Preservatives: salt, sugar, curry, pickling denatures proteins in bacteria that spoil food.

◦ Straitening hair: temporarily denaturing proteins with heat.◦ Cooking meat: to denature fibrous proteins in muscle

tissue.

Denaturing (2)

PPs, Page 50. #19-29

ON MONDAY, MAKE SURE YOU HAVE THE FOLLOWING COMPLETED:

Any PPs from the text that I have assigned throughout the powerpoint.

Carbohydrate worksheet Lipid worksheet.

MONDAY: quiz on Carbohydrates and Proteins.