2 - Dr. Jerry Cronin

2 - Dr. Jerry Cronin

(a) Triglyceride formation Three fatty acid chains are bound to glycerol by dehydration synthesis + Glycerol Copyright 2010 Pearson Education, Inc. 3 fatty acid chains Triglyceride, or neutral fat 3 water molecules Figure 2.16a

Saturation of Fatty Acids Saturated fatty acids Single bonds between C atoms; maximum number of H Solid animal fats, e.g., butter Unsaturated fatty acids One or more double bonds between C atoms Reduced number of H atoms Plant oils, e.g., olive oil Copyright 2010 Pearson Education, Inc. Phospholipids Modified triglycerides: Glycerol + two fatty acids and a phosphorus (P)-containing group

Head and tail regions have different properties Important in cell membrane structure Copyright 2010 Pearson Education, Inc. (b) Typical structure of a phospholipid molecule Two fatty acid chains and a phosphorus-containing group are attached to the glycerol backbone. Example Phosphatidylcholine Polar head Nonpolar tail (schematic

phospholipid) Phosphoruscontaining group (polar head) Copyright 2010 Pearson Education, Inc. Glycerol backbone 2 fatty acid chains (nonpolar tail) Figure 2.16b Steroids Steroidsinterlocking four-ring structure

Cholesterol, vitamin D, steroid hormones, and bile salts Copyright 2010 Pearson Education, Inc. (c) Simplified structure of a steroid Four interlocking hydrocarbon rings form a steroid. Example Cholesterol (cholesterol is the basis for all steroids formed in the body) Copyright 2010 Pearson Education, Inc. Figure 2.16c

Eicosanoids Many different ones Derived from a fatty acid (arachidonic acid) in cell membranes Prostaglandins Copyright 2010 Pearson Education, Inc. Other Lipids in the Body Other fat-soluble vitamins Vitamins A, E, and K Lipoproteins Transport fats in the blood Copyright 2010 Pearson Education, Inc. Proteins

Polymers of amino acids (20 types) Joined by peptide bonds Contain C, H, O, N, and sometimes S and P Copyright 2010 Pearson Education, Inc. Amine group Acid group (a) Generalized structure of all amino acids. Copyright 2010 Pearson Education, Inc.

(b) Glycine is the simplest amino acid. (c) Aspartic acid (d) Lysine (a basic amino acid) (an acidic amino acid) has an amine group has an acid group (NH2) in the R group. (COOH) in the R group. (e) Cysteine (a basic amino acid) has a sulfhydryl (SH)

group in the R group, which suggests that this amino acid is likely to participate in intramolecular bonding. Figure 2.17 Dehydration synthesis: The acid group of one amino acid is bonded to the amine group of the next, with loss of a water molecule. Peptide bond

+ Amino acid Amino acid Dipeptide Hydrolysis: Peptide bonds linking amino acids together are broken when water is added to the bond. Copyright 2010 Pearson Education, Inc. Figure 2.18 Structural Levels of Proteins

PLAY Animation: Introduction to Protein Structure Copyright 2010 Pearson Education, Inc. Amino acid Amino acid Amino acid Amino acid Amino acid (a) Primary structure:

The sequence of amino acids forms the polypeptide chain. PLAY Animation: Primary Structure Copyright 2010 Pearson Education, Inc. Figure 2.19a a-Helix: The primary chain is coiled to form a spiral structure, which is stabilized by hydrogen bonds. b-Sheet: The primary chain zig-zags back and forth forming a pleated sheet. Adjacent strands are held together by hydrogen bonds.

(b) Secondary structure: The primary chain forms spirals (a-helices) and sheets (b-sheets). PLAY Animation: Secondary Structure Copyright 2010 Pearson Education, Inc. Figure 2.19b Tertiary structure of prealbumin (transthyretin), a protein that transports the thyroid hormone thyroxine in serum and cerebrospinal fluid. (c) Tertiary structure: Superimposed on secondary structure. a-Helices and/or b-sheets are

folded up to form a compact globular molecule held together by intramolecular bonds. PLAY Animation: Tertiary Structure Copyright 2010 Pearson Education, Inc. Figure 2.19c Quaternary structure of a functional prealbumin molecule. Two identical prealbumin subunits join head to tail to form the dimer. (d) Quaternary structure:

Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein. PLAY Animation: Quaternary Structure Copyright 2010 Pearson Education, Inc. Figure 2.19d Fibrous and Globular Proteins Fibrous (structural) proteins Strandlike, water insoluble, and stable Examples: keratin, elastin, collagen, and certain contractile fibers Copyright 2010 Pearson Education, Inc.

Fibrous and Globular Proteins Globular (functional) proteins Compact, spherical, water-soluble and sensitive to environmental changes Specific functional regions (active sites) Examples: antibodies, hormones, molecular chaperones, and enzymes Copyright 2010 Pearson Education, Inc. Protein Denaturation Shape change and disruption of active sites due to environmental changes (e.g., decreased pH or increased temperature) Reversible in most cases, if normal conditions are restored Irreversible if extreme changes damage the structure beyond repair (e.g., cooking an egg)

Copyright 2010 Pearson Education, Inc. Molecular Chaperones (Chaperonins) Ensure quick and accurate folding and association of proteins Assist translocation of proteins and ions across membranes Promote breakdown of damaged or denatured proteins Help trigger the immune response Produced in response to stressful stimuli, e.g., O2 deprivation Copyright 2010 Pearson Education, Inc. Enzymes Biological catalysts Lower the activation energy, increase the

speed of a reaction (millions of reactions per minute!) Copyright 2010 Pearson Education, Inc. WITHOUT ENZYME WITH ENZYME Activation energy required Less activation energy required Reactants

Reactants Product PLAY Product Animation: Enzymes Copyright 2010 Pearson Education, Inc. Figure 2.20 Characteristics of Enzymes Often named for the reaction they catalyze; usually end in -ase (e.g., hydrolases, oxidases)

Some functional enzymes (holoenzymes) consist of: Apoenzyme (protein) Cofactor (metal ion) or coenzyme (a vitamin) Copyright 2010 Pearson Education, Inc. Product (P) e.g., dipeptide Substrates (S) e.g., amino acids + Energy is absorbed; bond is formed.

Water is released. H2O Peptide bond Active site Enzyme (E) Copyright 2010 Pearson Education, Inc. Enzyme-substrate complex (E-S) 1 Substrates bind 2 Internal at active site. rearrangements

Enzyme changes leading to shape to hold catalysis occur. substrates in proper position. Enzyme (E) 3 Product is released. Enzyme returns to original shape and is available to catalyze another reaction. Figure 2.21 Substrates (S) e.g., amino acids

+ Active site Enzyme (E) Copyright 2010 Pearson Education, Inc. Enzyme-substrate complex (E-S) 1 Substrates bind at active site. Enzyme changes shape to hold substrates in proper position. Figure 2.21, step 1

Substrates (S) e.g., amino acids + Energy is absorbed; bond is formed. Water is released. H2O Active site Enzyme (E) Copyright 2010 Pearson Education, Inc.

Enzyme-substrate complex (E-S) 1 Substrates bind 2 Internal at active site. rearrangements Enzyme changes leading to shape to hold catalysis occur. substrates in proper position. Figure 2.21, step 2 Product (P) e.g., dipeptide

Substrates (S) e.g., amino acids + Energy is absorbed; bond is formed. Water is released. H2O Peptide bond Active site

Enzyme (E) Copyright 2010 Pearson Education, Inc. Enzyme-substrate complex (E-S) 1 Substrates bind 2 Internal at active site. rearrangements Enzyme changes leading to shape to hold catalysis occur. substrates in proper position. Enzyme (E)

3 Product is released. Enzyme returns to original shape and is available to catalyze another reaction. Figure 2.21, step 3 Summary of Enzyme Action PLAY Animation: How Enzymes Work Copyright 2010 Pearson Education, Inc. Nucleic Acids DNA and RNA

Largest molecules in the body Contain C, O, H, N, and P Building block = nucleotide, composed of Ncontaining base, a pentose sugar, and a phosphate group Copyright 2010 Pearson Education, Inc. Deoxyribonucleic Acid (DNA) Four bases: adenine (A), guanine (G), cytosine (C), and thymine (T) Double-stranded helical molecule in the cell nucleus Provides instructions for protein synthesis Replicates before cell division, ensuring genetic continuity

Copyright 2010 Pearson Education, Inc. Phosphate Sugar: Deoxyribose Base: Adenine (A) Thymine (T) Adenine nucleotide Sugar Phosphate

Thymine nucleotide Hydrogen bond (a) Sugar-phosphate backbone Deoxyribose sugar Phosphate Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

(b) Copyright 2010 Pearson Education, Inc. (c) Computer-generated image of a DNA molecule Figure 2.22 Ribonucleic Acid (RNA) Four bases: adenine (A), guanine (G), cytosine (C), and uracil (U) Single-stranded molecule mostly active outside the nucleus Three varieties of RNA carry out the DNA orders for protein synthesis messenger RNA, transfer RNA, and ribosomal

RNA PLAY Animation: DNA and RNA Copyright 2010 Pearson Education, Inc. Adenosine Triphosphate (ATP) Adenine-containing RNA nucleotide with two additional phosphate groups Copyright 2010 Pearson Education, Inc. High-energy phosphate bonds can be hydrolyzed to release energy. Adenine

Phosphate groups Ribose Adenosine Adenosine monophosphate (AMP) Adenosine diphosphate (ADP) Adenosine triphosphate (ATP) Copyright 2010 Pearson Education, Inc. Figure 2.23 Function of ATP Phosphorylation: Terminal phosphates are enzymatically transferred to and energize other molecules Such primed molecules perform cellular work (life processes) using the phosphate bond energy

Copyright 2010 Pearson Education, Inc. Solute + Membrane protein (a) Transport work: ATP phosphorylates transport proteins, activating them to transport solutes (ions, for example) across cell membranes. + Relaxed smooth muscle cell Contracted smooth

muscle cell (b)Mechanical work: ATP phosphorylates contractile proteins in muscle cells so the cells can shorten. + (c) Chemical work: ATP phosphorylates key reactants, providing energy to drive energy-absorbing chemical reactions. Copyright 2010 Pearson Education, Inc. Figure 2.24

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