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Chapter 3 The Molecules of Cells
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  1. Chapter 3The Molecules of Cells By Dr. Par Mohammadian Overview: Carbon atom Functional Groups Major Biomolecules

  2. Life’s molecular diversity is based on the properties of carbon • Cell consists mostly of carbon-based molecules • Organic chemistry: Study of carbon compounds Carbon: • It has four electrons in an outer shell that holds eight • Carbon can share its electrons with other atoms to form up to four covalent bonds

  3. These are organic molecules containing only carbon and hydrogen atoms • The simplest hydrocarbon is methane • The simplest organic compounds are hydrocarbons

  4. Functional groups help determine the properties of organic compounds • The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton • These atoms are called functional groups • Functional groups are the groups of atoms that participate in chemical reactions • Hydroxyl groups are characteristic of alcohols • The carboxyl group acts as an acid

  5. Cells make a huge number of large molecules from a small set of small molecules • Most of the large molecules in living things are macromolecules called polymers (e.g. proteins, DNA) • Polymers are long chains of smaller molecular units called monomers • A huge number of different polymers can be made from a small number of monomers

  6. Cells link monomers to form polymers by dehydration synthesis • Polymers are broken down to monomers by the reverse process, hydrolysis

  7. BIOLOGICAL MOLECULES • There are four categories of large molecules in cells • Carbohydrates • Lipids • Proteins • Nucleic acids

  8. Carbohydrates • Carbohydrates include • Small sugar molecules in soft drinks • Long starch molecules in pasta and potatoes Monosaccharides are the simplest carbohydrates • Monosaccharides are simple sugars • The monosaccharides glucose and fructose are isomers • Their atoms are arranged differently

  9. A disaccharide is a double sugar Disaccharides • Disaccharides are joined by the process of dehydration synthesis • It is constructed from two monosaccharides • The most common disaccharide is sucrose, common table sugar • It consists of a glucose linked to a fructose • Sucrose is extracted from sugar cane and the roots of sugar beets • Simple sugars and double sugars dissolve readily in water • They are hydrophilic

  10. Polysaccharides • They are long chains of sugar units • They are polymers of monosaccharides • Complex carbohydrates are called polysaccharides • These large molecules are polymers of hundreds or thousands of monosaccharides linked by dehydration synthesis • Starch and glycogen are polysaccharides that store sugar for later use • Cellulose is a polysaccharide in plant cell walls

  11. Lipids • They do not mix with water • Examples: fats and steroids • Lipids are hydrophobic • Fats are lipids whose main function is energy storage • They are also called triglycerides • A triglyceride molecule consists of one glycerol molecule linked to three fatty acids

  12. These prevent them from solidifying at room temperature • Saturated fats (lard) lack double bonds • They are solid at room temperature • The fatty acids of unsaturated fats (plant oils) contain double bonds

  13. Phospholipids, waxes, and steroids are lipids with a variety of functions • Phospholipids are a major component of cell membranes • Waxes form waterproof coatings • Steroids are often hormones

  14. Steroids • The carbon skeleton is bent to form four fused rings • Cholesterol: your body produces other steroids • Steroids are very different from fats in structure and function

  15. PROTEINS Proteins are essential to the structures and activities of life • Proteins are involved in • cellular structure • movement • defense • transport • communication • Mammalian hair is composed of structural proteins • Enzymes regulate chemical reactions

  16. The Monomers: Amino Acids • All proteins are constructed from a common set of 20 kinds of amino acids • A central carbon atom bonded to four covalent partners • an amino group • a carboxyl group • A side group that is variable among all 20 • Each amino acid consists of

  17. Proteins as Polymers • Your body has tens of thousands of different kinds of protein • Cells link amino acids together by dehydration synthesis • The resulting bond between them is called a peptide bond • The arrangement of amino acids makes each one different

  18. Overview: A protein’s specific shape determines its function • A protein, such as lysozyme, consists of polypeptide chains folded into a unique shape • The shape determines the protein’s function • A protein loses its specific function when its polypeptides unravel

  19. A protein’s primary structure is its amino acid sequence Secondary structure is polypeptide coiling or folding produced by hydrogen bonding Tertiary structure is the overall shape of a polypeptide Quaternary structure is the relationship among multiple polypeptides of a protein

  20. What Determines Protein Structure? • Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape • This is called denaturation • A protein’s shape is sensitive to the surrounding environment

  21. NUCLEIC ACIDS Nucleic acids are information-rich polymers of nucleotides • Nucleic acids such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) serve as the blueprints for proteins • They ultimately control the life of a cell • Nucleic acids are polymers of nucleotides

  22. Each nucleotide is composed of a sugar, phosphate, and nitrogenous base (RNA has A, C, G and instead of T, it has uracil (U). • Each DNA nucleotide has one of the following bases • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C)