Molecules of Life Chapter 3

3.1 Molecules of Life  Molecules of life are synthesized by living cells Carbohydrates Lipids Proteins Nucleic acids

Structure to Function  Molecules of life differ in three-dimensional structure and function Carbon backbone = organic molecules Consist primarily of carbon and hydrogen atoms Carbon atoms bond covalently with up to four other atoms, often in long chains or rings Attached chemical (functional) groups confer properties to biological molecules  Structures give clues to how they function

Functional Groups  Hydroxyl (-OH)  Carboxyl (-COOH)  Amino (-NH 2 )  Phosphate (-PO 4 )

Functional Groups: The Importance of Position

Processes of Metabolism  Metabolism = the sum of all chemical reactions in a cell Synthesis reactions = condensation reactions Decomposition reactions = hydrolysis  Cells use energy to grow and maintain themselves  Enzyme-driven reactions build, rearrange, and split organic molecules Enzymes are catalysts that increase the rate of both synthesis and decomposition reactions

Building Organic Compounds Cells form complex organic molecules Simple sugars → carbohydrates Fatty acids → lipids Amino acids → proteins Nucleotides → nucleic acids  Condensation (dehydration synthesis) reactions combine monomers (subunits) to form polymers Animation:

Condensation and Hydrolysis

3.2 Carbohydrates – The Most Abundant Ones  Three main types of carbohydrates Monosaccharides (simple sugars) Oligosaccharides (short chains) Polysaccharides (complex carbohydrates)  Carbohydrate functions Instant energy sources Structural materials

Oligosaccharides: Sucrose

glucosefructose sucrose Fig. 3.6, p. 38 c Formation of a sucrose molecule

Complex Carbohydrates: Starch, Cellulose, and Glycogen

Fig. 3.8, p. 39 c Glycogen. In animals, this polysaccharide is a storage form for excess glucose. It is especially abundant in the liver and muscles of highly active animals, including fishes and people. Structure of cellulose

Complex Carbohydrates: Chitin

3.3 Greasy, Oily – Must Be Lipids  Lipids Fats, phospholipids, waxes, and sterols Don’t dissolve in water Dissolve in nonpolar substances (other lipids)  Lipid functions Major sources of energy Structural materials Used in cell membranes Chemical messengers (hormones)  Many lipids are composed of glycerol and fatty acid tails

Triglyceride Formation  Animation: 

Phospholipids  Main component of cell membranes Hydrophilic head, hydrophobic tails

Waxes  Firm, pliable, water repelling, lubricating

Sterols: Cholesterol  Membrane components; precursors of other molecules (steroid hormones)

3.4 Proteins – Diversity in Structure and Function  Proteins have many functions Structures Nutrition Enzymes (catalysts) Transportation Communication Defense

Protein Structure  Built from 20 kinds of amino acids

Protein Synthesis

Levels of Protein Structure 1.Primary structure 1.Is the sequence of Amino acids joined by peptide bonds to form a linear polypeptide chain 1.Is what ultimately determines the 3-D structure of a protein molecule  Some proteins have sugar or lipids attached to the polypeptide - Glycoproteins Lipoproteins

Levels of Protein Structure

More about protein structure -  Some proteins are made up of only 1 polypeptide that twists and turns to form a 3-D structure  Other proteins are made up of 2 or more polypeptides that are held together by chemical bonds Insulin is composed of 2 polypeptides

3.5 Why is Protein Structure So Important?  Protein structure dictates function  Sometimes a mutation in DNA results in an amino acid substitution that alters a protein’s structure and compromises its function Example: Hemoglobin and sickle-cell anemia

Normal Hemoglobin Structure

Sickle-Cell Mutation

Fig. 3.19, p. 45 VALINEHISTIDINELEUCINEGLUTAMATEVALINETHREONINEPROLINE sickle cell normal cell b One amino acid substitution results in the abnormal beta chain in HbS molecules. Instead of glutamate, valine was added at the sixth position of the polypeptide chain. c Glutamate has an overall negative charge; valine has no net charge. At low oxygen levels, this difference gives rise to a water-repellent, sticky patch on HbS molecules. They stick together because of that patch, forming rodshaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.)

Clumping of cells in bloodstream Circulatory problems, damage to brain, lungs, heart, skeletal muscles, gut, and kidneys Heart failure, paralysis, pneumonia, rheumatism, gut pain, kidney failure Spleen concentrates sickle cells Spleen enlargement Immune system compromised Rapid destruction of sickle cells Anemia, causing weakness,fatigue, impaired development,heart chamber dilation Impaired brain function, heart failure Fig. 3.19, p. 45 d Melba Moore, celebrity spokes- person for sickle-cell anemia organizations. Right, range of symptoms for a person with two mutated genes for hemoglobin’s beta chain.

Denatured Proteins  If a protein unfolds and loses its three- dimensional shape (denatures), it also loses its function  Denaturation is caused by shifts in pH, temperature, or salt concentrations Disrupts hydrogen bonds and other molecular interactions responsible for protein’s shape Animation:

3.6 Nucleotides, DNA, and RNAs Nucleotide structure, 3 parts: Sugar Phosphate group Nitrogen-containing base

Nucleotide Functions: Reproduction, Metabolism, and Survival  DNA and RNAs are nucleic acids, each composed of four kinds of nucleotide subunits  ATP energizes many kinds of molecules by phosphate-group transfers Image from:

Nucleotides of DNA

The DNA Double-Helix

DNA, RNAs, and Protein Synthesis  DNA (double-stranded) Encodes information about the primary structure of all cell proteins in its nucleotide sequence Nitrogen-bases include thymine, cytosine, guanine, and adenine Nucleotides contain the sugar deoxyribose  RNA molecules (usually single stranded) Different kinds of RNA molecules interact with one another during protein synthesis Nitrogen-bases include uracil, cytosine, guanine, and adenine Nucleotides contain the sugar ribose

DNA vs RNA Structure