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Carbon Compounds in Cells Chapter 3 Importance of Carbon Carbon permeates the world of life— from the energy-requiring activities and structural organization of cells, to physical and chemical conditions that span the globe and influence ecosystems everywhere. Humans and Global Warming • Fossil fuels are rich in carbon • Use of fossil fuels releases CO2 into atmosphere • Increased CO2 may contribute to global warming Organic Compounds Hydrogen and other elements covalently bonded to carbon Carbohydrates Lipids Proteins Nucleic Acids Carbon’s Bonding Behavior • Outer shell of carbon has 4 electrons; can hold 8 • Each carbon atom can form covalent bonds with up to 4 atoms Methane: Simplest Organic Compound H H C H Ball-and-stick model H Structural formula Space-filling model Figure 3.2 Page 36 Bonding Arrangements • Carbon atoms can form chains or rings • Other atoms project from the carbon backbone Glucose (ball-and-stick model) In-text figure Page 36 Hemoglobin Molecular Models Ball-and-stick model Space-filling model Ribbon model Figure 3.3 Page 37 Functional Groups • Atoms or clusters of atoms that are covalently bonded to carbon backbone • Give organic compounds their different properties Examples of Functional Groups Methyl group - CH3 Hydroxyl group - OH Amino group - NH3+ Carboxyl group - COOH Phosphate group - PO3- Sulfhydryl group - SH Carbohydrates Monosaccharides (simple sugars) Oligosaccharides (short-chain carbohydrates) Polysaccharides (complex carbohydrates) Lipids • Most include fatty acids – Fats – Phospholipids – Waxes • Sterols and their derivatives have no fatty acids • Tend to be insoluble in water Phospholipids • Main component of cell membranes • Hydrophobic head • Hydrophilic tails Fig. 3.14a,b Page 43 Sterols and Derivatives • No fatty acids • Rigid backbone of four fused-together carbon rings Cholesterol • Cholesterol - most common type in animals Figure 3.15a In-text p43 Waxes • Long-chain fatty acids linked to long-chain alcohols or carbon rings • Firm consistency, repel water • Important in water-proofing Protein Synthesis • Peptide bond – Condensation reaction links amino group of one amino acid with carboxyl group of next Water forms as a by-product Fig. 3.18a Page 45 Primary Structure • Sequence of amino acids • Unique for each protein • Two linked amino acids = dipeptide • Three or more = polypeptide • Backbone of polypeptide has N atoms: -N-C-C-N-C-C-N-C-C-N- Second and Third Levels • Hydrogen bonding produces helix or sheet • Domain formation Tertiary structure Secondary structure Figure 3.19a Page 46 Fourth Level Structure Some proteins are made up of more than one polypeptide chain Figure 3.20 Page 47 HLA-A2 quaternary structure Hemoglobin alpha chain beta chain beta chain alpha chain Nucleotide Structure • Sugar • At least one ATP phosphate group • Nitrogen- containing base Figure 3.23a Page 50 Nucleotide Functions • Energy carriers • Coenzymes • Chemical messengers • Building blocks for nucleic acids DNA • Double-stranded • Sugar-phosphate backbone • Covalent bonds in backbone • H bonds between bases Figure 3.25 Page 51 RNA • Usually single strands • Four types of nucleotides • Unlike DNA, contains the base uracil in place of thymine • Three types are key players in protein synthesis