MCB100 Introductory Microbiology September 12, 2018

1. MCB100 Introductory Microbiology September 12, 2018 Image from: Brookhaven National Laboratory - US Department of Energy - www.bnl.gov

2. Proteins – polymers of amino acids held together by peptide bonds Lipids – amphipathic molecules that form the matrix of cell membranes – fatty acids and glycerol components are held together by ester bonds Polysaccharides(also known as complex carbohydrates) – polymers of sugars held together by glycosidic bonds Nucleic Acids – polymers of nucleotides held together by phosphodiester bonds

3. Proteins are linear chains of amino acids • Typical proteins consist of 200 – 400 amino acids, but some are smaller than this and others are larger. The key factor that determines the structure and ultimately the function of an enzyme is the sequence of amino acids found in the protein.

4. Structure of amino acids All amino acids contain nitrogen in the form of an amino group. They also always have a carboxylic acid group. The amino groups and the carboxylic acid groups are involved in the formation of the bonds that join amino acids into long chains to make proteins.

5. Formation of a Peptide Bond • The formation of a peptide bond requires a free carboxylic acid group and a free amino group. • A molecule of water is produced when the two amino acids are joined. • Note how the dipeptide has a free amino group and a free carboxylic acid group. Another amino acid can be attached by the formation of another peptide bond.

6. Structure of an Oligopeptide • Since each amino acid has an amino group and a carboxyl group, a linear chain of great length can be made. • The oligopeptide shown is a pentapeptide (oligo = few, penta = 5) • Most proteins are chains of 100 – 1000 amino acids.

7. The Folding of a Protein to Its Final Shape Primary Structure: - The sequence of amino acids in the chain - Determined by the genetic information encoded in the mRNA - Determines the final shape and function of the protein Secondary Structure: - Local folding of a protein chain - Alpha helix and Beta sheet are common motifs - Stabilized by interactions between backbone groups that are fairly close to each other in the primary sequence Tertiary Structure: - Final folding of a single protein chain to its globular form - Stabilized by interactions between groups on side chains that may be far apart in the primary sequence but close together in the final 3-D shape Quaternary Structure: - The noncovalent attraction of two or more separate protein chains to form a functional unit - Stabilized by interactions between groups on side chains that may be far apart in the primary sequence but close together in the final 3-D shape

8. Structure of a Typical Protein Lysozyme: an enzyme that breaks down bacterial & fungal cell walls

9. Protein Functions 1 Which ONE of the following statements about proteins and the roles of proteins in living organisms is FALSE? A. Enzymes are catalysts that make the chemical reactions of life go faster. Most enzymes are proteins. B. Most substances that enter or exit a living cell do so by passing through specific pores in the cytoplasmic membrane. The pores in a cell membrane are made of proteins. C. Living cells contain packets of information called "genes” that must be copied and passed on to the next generation of cells. Genes are made of proteins. D. On the outside surface of some bacterial cells there are rod-like structures called pili that help the bacteria stick to specific surfaces. Pili are made of proteins. E. Some bacteria produce toxins that can cause disease in humans. Many bacterial toxins are proteins.

11. AMINO ACIDS GROUPED BY TYPES OF SIDE CHAINS NON-POLAR (hydrophobic) AROMATIC Glycine (mostly hydrophobic) Alanine Phenylalanine Leucine Tyrosine Isoleucine Tryptophan Valine Proline POLAR (hydroxyl or amide groups)ACIDIC SerineAspartic acid ThreonineGlutamic acid Asparagine Glutamine SULFUR CONTAININGBASIC MethionineLysine CysteineHistidine Arginine

15. Amino Acids Which one of the following amino acids has a basic side chain? A. Cysteine B. Valine C. Asparagine D. Lysine E. Phenylalanine

16. Protein Structure Which one of the following statements about protein structure is TRUE? A. The backbone chain of a typical protein has many branch points that lead to side chains that are several amino acids long. B. The side chains of some amino acids are hydrophobic while other amino acids have hydrophilic side chains. C. Proteins are rich in phosphorous atoms because every amino acid contains at least one phosphate. D. All proteins have quaternary structure because every protein is composed of several peptide chains. E. The first amino acid in any protein chain is an Alanine.

18. DNA – Protein Interactions Some DNA-binding proteins are involved with the regulation of gene expression. A zinc-finger is a motif or fold seen in some DNA binding proteins. Functional groups on the alpha helices of the protein stick to functional groups in the major groove of the DNA double helix. Zinc finger-DNA. Note three alpha helices pointing into the major groove, each recognizing 3 bp of DNA. The Zinc binding domain is a structural element for protein folding, not directly involved in DNA binding.From: kahn@biochem.umd.edu

19. Above: Hemoglobin Right: Cell Membrane Structure

21. Antigen-Antibody Complex

22. The Active Site of a Serine Protease From: www.researchgate.net/profile/Rima_Chauduri