1. Chemistry 24.3

2. Amino Acids and Their Polymers
Many people are lactose intolerant. These people cannot digest milk products because their bodies do not produce enough of the enzyme lactase to digest lactose, the sugar found in milk. You will learn what enzymes are and what function they serve in the body.

3. Amino Acids What is the general structure of an amino acid?

4. Amino Acids
An amino acid is any compound that contains an amino group (—NH2) and a carboxyl group (—COOH) in the same molecule.

5. Amino Acids
Amino acids have a skeleton that consists of a carboxyl group and an amino group, both of which are covalently bonded to a central carbon atom. The remaining two groups on the central carbon atom are hydrogen and an R group that constitutes the amino acid side chain.

6. Amino Acids

7. Peptides
Peptides
Which functional groups are always involved in amide bonds between amino acids?

8. Peptides
A peptide is any combination of amino acids in which the amino group of one amino acid is united with the carboxyl group of another amino acid.

9. Peptides
The amide bond between the carboxyl group of one amino acid and the nitrogen in the amino group of the next amino acid in the peptide chain is called a peptide bond.

10. Peptides
The amide bonds between amino acids always involve the central amino and central carboxyl groups. The side chains are not involved in the bonding.

11. Proteins
Proteins
What determines the differences in the chemical and physiological properties of peptides and proteins?

12. A peptide with more than about 100 amino acids is called a protein.
Proteins
A peptide with more than about 100 amino acids is called a protein.
Your skin, hair, nails, and muscles are made of protein.
Proteins are needed for almost all chemical reactions that take place in the body.

13. Amino Acids in a Peptide Chain
Proteins
Amino Acids in a Peptide Chain
Peptides form three-dimensional shapes. a) This is a representation of amino acids in a peptide chain. b) The chain may coil into a helix. c) Two peptide chains may become arranged in a pleated, sheet-like structure. Applying Concepts What types of bonds determine the three-dimensional shape of a protein?

14. Proteins
Sections of a peptide chain may coil into a regular spiral, known as a helix.
Peptides form three-dimensional shapes. a) This is a representation of amino acids in a peptide chain. b) The chain may coil into a helix. c) Two peptide chains may become arranged in a pleated, sheet-like structure. Applying Concepts What types of bonds determine the three-dimensional shape of a protein?

15. Proteins
Peptide chains may also be arranged side by side to form a pleated sheet.
Peptides form three-dimensional shapes. a) This is a representation of amino acids in a peptide chain. b) The chain may coil into a helix. c) Two peptide chains may become arranged in a pleated, sheet-like structure. Applying Concepts What types of bonds determine the three-dimensional shape of a protein?

16. Proteins
Differences in the chemical and physiological properties of peptides and proteins result from differences in the amino acid sequence.

17. The Shape of Myoglobin Proteins
The three-dimensional structure of myoglobin, the oxygen storage protein of this muscle tissue, is shown here. Most of the peptide chain of myoglobin is wound into helixes. Myoglobin also contains a nonprotein structure called heme. The heme group is shown as a disk in the myoglobin structure. Heme contains four linked rings with an iron(II) ion (Fe2+) at the center. Molecular oxygen binds to the heme iron.

18. Enzymes How do enzymes affect the rates of reactions in living things?

19. Enzymes are proteins that act as biological catalysts.
Enzymes increase the rates of chemical reactions in living things.

20. Enzymes
The enzyme urease hydrolyzes urea, a constituent of urine, into ammonia and carbon dioxide.

21. Enzymes catalyze most of the chemical changes that occur in the cell.
How Enzymes Work
Enzymes catalyze most of the chemical changes that occur in the cell.
Substrates are the molecules on which an enzyme acts.
The place on an enzyme where a substrate binds is called the active site.

22. Enzymes
In a typical enzymatic reaction, the substrate interacts with side chains of the amino acids on the enzyme. These interactions cause the making and breaking of bonds.
A substrate fits into a distinctively shaped active site on an enzyme. Bond-breaking occurs at the active site to produce the products of the reaction. Predicting What would happen if access to the active site were blocked by another molecule?

23. Enzymes
An HIV particle (red) infects a human white blood cell (orange). The diagram models the enzyme HIV protease.
This color-enhanced scanning electron micrograph shows HIV (red particle) infecting a human white blood cell (orange). The diagram models the enzyme HIV protease. The green and yellow ribbons trace the two peptide chains of the enzyme. A substrate molecule (purple) is embedded in the active site formed between the two peptide chains.

24. Enzymes
The enzyme carbonic anhydrase catalyzes the reversible breakdown of carbonic acid to carbon dioxide and water.

25. Enzymes
Coenzymes
Coenzymes are metal ions or small organic molecules that must be present for an enzyme- catalyzed reaction to occur.

26. Enzymes
The enzyme catalase includes an iron(III) ion in its structure. Catalase catalyzes the breakdown of hydrogen peroxide to water and oxygen.

27. 24.3 Section Quiz.
24.3.

28. 24.3 Section Quiz.
1. Choose the correct words for the spaces. An amino acid is a compound having the ________ group and the _________ group bonded to a central carbon atom.
carboxyl, amino
carbonyl, amide
amino, peptide
carbohydrate, amide

29. 24.3 Section Quiz.
2. Choose the correct words for the space. A protein is a peptide with ___________ amino acids linked in a chain.
more than about 100
less than about 100
two
zero

30. 24.3 Section Quiz.
3. Enzymes affect biochemical reactions by
changing the equilibrium position of the system.
acting as catalysts to speed up the reaction.
being consumed as the reaction progresses.
decreasing the size of competing substrates.

31. 24.3 Section Quiz.
4. Some vitamins participate in biological processes as
peptides.
amino acids.
enzymes.
coenzymes.

32. END OF SHOW