1 Functions of Proteins Proteins perform many different functions in the body.

2 Amino Acids Amino acids are the building blocks of proteins. contain a carboxylic acid group and an amino group on the alpha (  ) carbon. are ionized in solution. each contain a different side group (R). R side chain R │ + │ H 2 N—C —COOH H 3 N—C —COO − │ │ H H Zwitterion (ionized form)

3 Examples of Amino Acids H + │ H 3 N—C—COO− │ HGlycine CH 3 + │ H 3 N—C—COO − │ HAlanine

4 must be obtained from the diet. are 10 amino acids not synthesized by the body. are in meat and dairy products. are missing (one or more) in grains and vegetables. Essential Amino Acids Essential amino acids

5 Types of Amino Acids Amino acids are classified as nonpolar (hydrophobic) with hydrocarbon side chains. polar (hydrophilic) with polar or ionic side chains. acidic (hydrophilic) with acidic side chains. basic (hydrophilic) with –NH 2 side chains. Nonpolar Polar Acidic Basic Copyright © 2009 by Pearson Education, Inc.

6 Nonpolar Amino Acids An amino acid is nonpolar when the R group is H, alkyl, or aromatic. Copyright © 2009 by Pearson Education, Inc.

7 Polar Amino Acids An amino acid is polar when the R group is an alcohol, thiol, or amide. Copyright © 2009 by Pearson Education, Inc.

8 Acidic and Basic Amino Acids An amino acid is acidic when the R group is a carboxylic acid. basic when the R group is an amine.

9 Solution Identify each as (1) polar or (2) nonpolar. + A. H 3 N–CH 2 –COO − Glycine (2) nonpolar CH 3 | CH–OH + │ B. H 3 N–CH–COO − Threonine (1) polar

10 A zwitterion has charged −NH 3 + and COO – groups. forms when both the –NH 2 and the –COOH groups in an amino acid ionize in water. has equal + and – charges at the isoelectric point (pI). O O ║ + ║ NH 2 —CH 2 —C—OH H 3 N—CH 2 —C—O – Glycine Zwitterion of glycine Zwitterions

11 In solutions more basic than the pI, the —NH 3 + in the amino acid donates a proton. + OH – H 3 N—CH 2 —COO – H 2 N—CH 2 —COO – ZwitterionNegative ion at pI pH > pI Charge: 0Charge: 1- Amino Acids as Acids

12 In solution more acidic than the pI, the COO – in the amino acid accepts a proton. + H + + H 3 N—CH 2 —COO – H 3 N—CH 2 —COOH Zwitterion Positive ion at pI pH< pI Charge: 0Charge: 1+ Amino Acids as Bases

13 pH and ionization H + OH – + H 3 N–CH 2 –COOH H 3 N–CH 2 –COO – H 2 N–CH 2 –COO – Positive ion Zwitterion Negative ion low pH pI high pH

14 The Peptide Bond A peptide bond is an amide bond. forms between the carboxyl group of one amino acid and the amino group of the next amino acid. O CH 3 O + || + | || H 3 N—CH 2 —C—O – + H 3 N—CH—C—O – O H CH 3 O + || | | || H 3 N—CH 2 —C—N—CH—C—O – peptide bond

15 Formation of a Dipeptide Copyright © 2009 by Pearson Education, Inc.

16 Solution Write the dipeptide Ser-Thr. OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N─CH─C─O – + H 3 N─CH─C─O – Ser Thr OH CH 3 || CH 2 O H HCOH O + | ║ | | ║ NH 3 ─CH─C─N ─CH─ C─O – + H 2 O Ser-Thr

17 Naming Dipeptides A dipeptide is named from the free amine (NH 3 + ) using a -yl ending for the name. names the last amino acid with the free carboxyl group (COO – ) by its amino acid name.

18 Write the names and three-letter abbreviations of the tripeptides that could form from two glycine and one alanine. Glycylglycylalanine Gly-Gly-Ala Glycylalanylglycine Gly-Ala-Gly Alanylglycylglycine Ala-Gly-Gly Solution

19 Solution Tripeptides possible from one each of leucine, glycine, and alanine: Leu-Gly-Ala Leu-Ala-Gly Ala-Leu-Gly Ala-Gly-Leu Gly-Ala-Leu Gly-Leu-Ala

20 Learning Check Write the three-letter abbreviation and name for the following tetrapeptide. CH 3 │ CH 3 S │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–C–O –

21 Solution Ala-Leu-Cys-MetAlanylleucylcysteinylmethionine CH 3 │ CH 3 S │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–C–O – Ala LeuCys Met

22 Primary Structure of Proteins The primary structure of a protein is the particular sequence of amino acids. the backbone of a peptide chain or protein. Ala─Leu ─ Cys ─ Met

23 Primary Structures The nonapeptides oxytocin and vasopressin have similar primary structures. Only the amino acids at positions 3 and 8 differ. Copyright © 2009 by Pearson Education, Inc.

24 Primary Structure of Insulin Insulin was the first protein to have its primary structure determined. has a primary structure of two polypeptide chains linked by disulfide bonds. has a chain A with 21 amino acids and a chain B with 30 amino acids.

25 Secondary Structure–Alpha Helix The secondary structure of an alpha helix is a three-dimensional spatial arrangement of amino acids in a polypeptide chain. held by H bonds between the H of –N-H group and the O of C=O of the fourth amino acid down the chain. a corkscrew shape that looks like a coiled “telephone cord.” Copyright © 2009 by Pearson Education, Inc.

26 Secondary Structure–Beta-Pleated Sheet The secondary structure of a beta-pleated sheet consists of polypeptide chains arranged side by side. has hydrogen bonds between chains. has R groups above and below the sheet. is typical of fibrous proteins, such as silk.

27 Tertiary Structure The tertiary structure of a protein is an overall 3- dimensional shape. is determined by attractions and repulsions between the side chains of the amino acids in a peptide chain.

28 Crosslinks in Tertiary Structures Crosslinks in tertiary structures involve attractions and repulsions between the side chains of the amino acids in the polypeptide chain.

29 Select the type of tertiary interaction. 1) disulfide2) ionic 3) H bonds4) hydrophobic A. leucine and valine B. two cysteines C. aspartic acid and lysine D. serine and threonine Learning check

30 Select the type of tertiary interaction. 1) disulfide2) ionic 3) H bonds4) hydrophobic A. 4 leucine and valine B. 1 two cysteines C. 2 aspartic acid and lysine D. 3 serine and threonine Solution

31 Globular Proteins Globular proteins have compact, spherical shapes. carry out synthesis, transport, and metabolism in the cells. such as myoglobin store and transport oxygen in muscle. Copyright © 2009 by Pearson Education, Inc. Myoglobin

32 Quaternary Structure The quaternary structure is the combination of two or more protein units. of hemoglobin consists of four polypeptide chains as subunits. is stabilized by the same interactions found in tertiary structures. Copyright © 2009 by Pearson Education, Inc.

33 Fibrous Proteins Fibrous proteins consist of long, fiber-like shapes. such as alpha keratins make up hair, wool, skin, and nails. such as feathers contain beta keratins with large amounts of beta-pleated sheet structures.

34 Summary of Protein Structure

35 Summary of Protein Structure

36 Identify the level of protein structure. 1) primary2) secondary 3) tertiary 4) quaternary A. beta-pleated sheet B. order of amino acids in a protein C. a protein with two or more peptide chains D. the shape of a globular protein E. disulfide bonds between R groups Learning Check

37 Identify the level of protein structure. 1) primary2) secondary 3) tertiary 4) quaternary A. 2 beta-pleated sheet B. 1 order of amino acids in a protein C. 4 a protein with two or more peptide chains D. 3 the shape of a globular protein E. 3 disulfide bonds between R groups Solution

38 Denaturation involves the disruption of bonds in the secondary, tertiary, and quaternary protein structures. heat and organic compounds that break apart H bonds and disrupt hydrophobic interactions. acids and bases that break H bonds between polar R groups and disrupt ionic bonds. heavy metal ions that react with S-S bonds to form solids. agitation such as whipping that stretches peptide chains until bonds break. Denaturation

39 Denaturation of protein occurs when an egg is cooked. the skin is wiped with alcohol. heat is used to cauterize blood vessels. instruments are sterilized in autoclaves. Applications of Denaturation Copyright © 2009 by Pearson Education, Inc.

40 Enzymes are Biological Catalysts Enzymes are proteins that Catalyze nearly all the chemical reactions taking place in the cells of the body. Increase the rate of reaction by lowering the energy of activation.

41 Lock-and-Key Model In the lock-and-key model, the active site has a rigid shape. enzyme only binds substrates that exactly fit the active site. enzyme is analogous to a lock. substrate is the key that fits that lock. Copyright © 2009 by Pearson Education, Inc.

42 Induced-Fit Model In the induced-fit model enzyme structure is flexible, not rigid. enzyme and substrate adjust the shape of the active site to bind substrate. the range of substrate specificity increases. shape changes improve catalysis during reaction. Copyright © 2009 by Pearson Education, Inc.

43 The name of an enzyme usually ends in –ase. identifies the reacting substance. For example, sucrase catalyzes the reaction of sucrose. describes the function of the enzyme. For example, oxidases catalyze oxidation. could be a common name, particularly for the digestion enzymes, such as pepsin and trypsin. Names of Enzymes

44 Enzymes are classified by the reaction they catalyze. ClassType of Reactions Catalyzed OxidoreductasesOxidation-reduction TransferasesTransfer groups of atoms Hydrolases Hydrolysis LyasesAdd atoms/remove atoms to or from a double bond IsomerasesRearrange atoms LigasesUse ATP to combine small molecules Classification of Enzymes

45 Match the type of reaction with an enzyme 1) aminase2) dehydrogenase 3) isomerase4) synthetase A. 3 Converts a cis-fatty acid to a trans-fatty acid. B. 2 Removes 2 H atoms to form double bond. C. 4 Combines two molecules to make a new compound. D. 1 Adds NH 3. Solution

46 Enzymes are most active at an optimum temperature (usually 37 °C in humans). show little activity at low temperatures. lose activity at high temperatures as denaturation occurs. Temperature and Enzyme Action

47 Enzymes are most active at optimum pH. contain R groups of amino acids with proper charges at optimum pH. lose activity in low or high pH as tertiary structure is disrupted. pH and Enzyme Action

48 Optimum pH Values Enzymes in the body have an optimum pH of about 7.4. certain organs operate at lower and higher optimum pH values.

49 Substrate Concentration As substrate concentration increases, the rate of reaction increases (at constant enzyme concentration). the enzyme eventually becomes saturated, giving maximum activity.

50 Sucrase has an optimum temperature of 37 °C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction. 1) no change 2) increase 3) decrease A. 2 Increasing the concentration of sucrase B. 3 Changing the pH to 4 C. 3 Running the reaction at 70 °C Solution

51 Inhibitors are molecules that cause a loss of catalytic activity. prevent substrates from fitting into the active sites. E + SESE + P E + I EI no P Enzyme Inhibition

52 Competitive Inhibition A competitive inhibitor has a structure that is similar to that of the substrate. competes with the substrate for the active site. has its effect reversed by increasing substrate concentration.

53 A noncompetitive inhibitor has a structure that is much different than the substrate. distorts the shape of the enzyme, which alters the shape of the active site. prevents the binding of the substrate. cannot have its effect reversed by adding more substrate. Noncompetitive Inhibition Copyright © 2009 by Pearson Education, Inc.

54 Identify each description as an inhibitor that is 1) competitive or 2) noncompetitive. A. 1 Increasing substrate reverses inhibition. B. 2 Binds to enzyme surface, but not to the active site. C. 1 Structure is similar to substrate. D. 2 Inhibition is not reversed by adding more substrate. Solution