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Amino Acids Proteins, and Amino Acids Proteins, and EnzymesEnzymes

Types of ProteinsAmino Acids

The Peptide Bond

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Types of ProteinsTypes of ProteinsType Examples

Structural tendons, cartilage, hair, nails

Contractile musclesTransport hemoglobinStorage milkHormonal insulin, growth hormoneEnzyme catalyzes reactions in cellsProtection immune response

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Amino AcidsAmino AcidsBuilding blocks of proteinsCarboxylic acid groupAmino groupSide group R gives unique

characteristics

R side chain IH2H—C —COOH I H

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Examples of Amino AcidsExamples of Amino Acids H IH2N—C —COOH I H glycine CH3 IH2N—C —COOH I H alanine

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Types of Amino AcidsTypes of Amino AcidsNonpolar R = H, CH3, alkyl groups,

aromatic O

Polar llR = –CH2OH, –CH2SH, –CH2C–NH2, (polar groups with –O-, -SH, -N-)

Polar/Acidic R = –CH2COOH, or -COOH

Polar/ BasicR = –CH2CH2NH2

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Learning Check AA1Learning Check AA1Identify each as (1) polar or (2) nonpolar

A. NH2–CH2–COOH (Glycine)

CH3 | CH–OH

|B. NH2–CH–COOH (Serine)

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Solution AA1Solution AA1Identify each as (1) polar or (2) nonpolar

A.(2) NH2–CH2–COOH (Glycine)

CH3 | CH–OH |B. (1) NH2–CH–COOH (Serine)

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Essential Amino AcidsEssential Amino Acids10 amino acids not synthesized by the

bodyarg, his, ile, leu, lys, met, phe, thr, trp,

valMust obtain from the dietAll in dairy products 1 or more missing in grains

and vegetables

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Amino Acids as Acids and BasesAmino Acids as Acids and BasesIonization of the –NH2 and the –COOH

groupZwitterion has both a + and – chargeZwitterion is neutral overall

+NH2–CH2–COOH H3N–CH2–COO–

glycine Zwitterion of glycine

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pH and ionizationpH and ionization

H+ OH–

+ +H3N–CH2–COOH H3N–CH2–COO– H2N–CH2–

COO– Positive ion zwitterion Negative

ionLow pH neutral pH High pH

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The Peptide BondThe Peptide BondAmide bond formed by the –COOH of an amino acid and the –NH2 of the next amino acid O CH3

+ | | + |NH3–CH2–COH + H3N–CH–COO– O CH3

+ | | | NH3–CH2–C – N–CH–COO– | peptide bond H

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PeptidesPeptidesAmino acids linked by amide (peptide)

bonds

Gly Lys Phe Arg Ser

H2N-end COOH-end

Peptide bonds

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Learning Check AA3Learning Check AA3

What are the possible tripeptides formed from one each of leucine, glycine, and alanine?

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Solution AA3Solution AA3Tripeptides possible from one each of leucine, glycine, and alanine

Leu-Gly-AlaLeu-Ala-GlyAla-Leu-GlyAla-Gly-LeuGly-Ala-LeuGly-Leu-Ala

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Amino Acids, Proteins, and Amino Acids, Proteins, and EnzymesEnzymes

Primary and Secondary StructureTertiary and Quaternary Structure

Protein Hydrolysis and Denaturation

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Primary Structure of ProteinsPrimary Structure of ProteinsThe particular sequence of amino acids that is the backbone of a peptide chain or protein

H3N CHCH3

CO

NH

CH CO

NH

CH CO

NH

CH C O-OCH

CH CH3

CH3

CH2

SHCH2

CH2

SCH3

+

Ala-Leu-Cys-Met

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Secondary Structure – Alpha Secondary Structure – Alpha HelixHelix

Three-dimensional arrangement of amino acids with the polypeptide chain in a corkscrew shape

Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain

Looks like a coiled “telephone cord”

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Secondary Structure – Beta Secondary Structure – Beta Pleated SheetPleated Sheet

Polypeptide chains are arranged side by side

Hydrogen bonds form between chains

R groups of extend above and below the sheet

Typical of fibrous proteins such as silk

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Secondary Structure – Triple Secondary Structure – Triple HelixHelix

Three polypeptide chains woven together

Glycine, proline, hydroxy proline and hydroxylysine

H bonding between –OH groups gives a strong structure

Typical of collagen, connective tissue, skin, tendons, and cartilage

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Learning Check P1Learning Check P1Indicate the type of structure as(1) primary (2) alpha helix(3) beta pleated sheet (4) triple helix

A. Polypeptide chain held side by side by H bonds

B. Sequence of amino acids in a polypeptide chain

C. Corkscrew shape with H bonds between amino acids

D. Three peptide chains woven like a rope

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Solution P1Solution P1Indicate the type of structure as(1) primary (2) alpha helix(3) beta pleated sheet (4) triple helix

A. 3 Polypeptide chain held side by side by H bonds

B. 1 Sequence of amino acids in a polypeptide chain

C. 2 Corkscrew shape with H bonds between amino acids

D. 4 Three peptide chains woven like a rope

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Tertiary StructureTertiary StructureSpecific overall shape of a proteinCross links between R groups of

amino acids in chaindisulfide –S–S–

+

ionic –COO– H3N–H bonds C=O HO– hydrophobic –CH3 H3C–

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Globular and Fibrous ProteinsGlobular and Fibrous Proteins

Globular proteins Fibrous proteins

“spherical” shape long, thin fibers

Insulin HairHemoglobin WoolEnzymes SkinAntibodies Nails

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Quaternary StructureQuaternary StructureProteins with two or more chains

Example is hemoglobin Carries oxygen in blood

Four polypeptide chainsEach chain has a haem group to

bind oxygen

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Learning Check P3Learning Check P3Identify the level of protein structure1. Primary 2. Secondary3. Tertiary 4. Quaternary

A. Beta pleated sheetB. Order of amino acids in a proteinC. A protein with two or more peptide

chainsD. The shape of a globular proteinE. Disulfide bonds between R groups

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Solution P3Solution P3Identify the level of protein structure1. Primary 2. Secondary3. Tertiary 4. Quaternary

A. 2 Beta pleated sheetB. 1 Order of amino acids in a proteinC. 4 A protein with two or more peptide chainsD. 3 The shape of a globular proteinE. 3 Disulfide bonds between R groups

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Protein HydrolysisProtein HydrolysisBreak down of peptide

bonds Requires acid or base and

heatGives smaller peptides and

amino acids Similar to digestion of

proteins using enzymesOccurs in cells to provide

amino acids to synthesize other proteins and tissues

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Hydrolysis of a DipeptideHydrolysis of a Dipeptide

H3N CHCH3

CO

NH

CH COCH2

OH

OH

+

H3N CHCH3

COHO

+ CH COCH2

OH

OHH3N

H2O, H+

++

heat

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DenaturationDenaturationDisruption of secondary, tertiary and quaternary protein structure byheat/organics Break apart H bonds and disrupt hydrophobic attractions acids/ basesBreak H bonds between polar R groups andionic bondsheavy metal ions React with S-S bonds to form solidsagitation Stretches chains until bonds break

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Applications of DenaturationApplications of DenaturationHard boiling an eggWiping the skin with alcohol swab for

injectionCooking food to destroy E. coli.Heat used to cauterize blood vesselsAutoclave sterilizes instrumentsMilk is heated to make yoghurt

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Learning Check P4Learning Check P4What are the products of the complete hydrolysis of Ala-Ser-Val?

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Solution P4Solution P4The products of the complete hydrolysis of Ala-Ser-Val are

alanineserinevaline

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Learning Check P5Learning Check P5Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events?

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Solution P5Solution P5Acid and heat cause a denaturation of protein. They both break bonds in the secondary and tertiary structure of protein.

DNADNA

DNA RNADNA RNA

DNA RNADNA RNA

DNA RNADNA RNA

DNA Backbone StructureDNA Backbone Structure Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA Backbone StructureDNA Backbone Structure Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA RNADNA RNA

DNA Primary Structure SummaryDNA Primary Structure Summary

DNA RNADNA RNA

DNA Double HelixDNA Double Helix Base pairing by unique hydrogen bonds

C - G and A - T pairs

DNA Double HelixDNA Double Helix Base pairing by unique hydrogen bonds

C - G and A - T pairs

DNADNA

DNA ReplicationDNA ReplicationComplementary base pairs form new strands.

Types of RNATypes of RNAmRNA contains codons which code for amino acids.

DNADNA

Types of RNATypes of RNA rRNA - Ribosome - contains enzymes and keeps everything together

Types of RNATypes of RNA tRNA - Transfer RNA carries amino acid and read codons

on m-RNA through its own anticodons.

Types of RNATypes of RNA tRNA - Transfer RNA carries amino acid and read codons on m-RNA through its own

anticodons.