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Chapter 3 Biological Molecules
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Why Is Carbon So Important in Biological Molecules?
Organic/inorganic molecules and functional groups Organic refers to molecules containing a carbon skeleton bonded to hydrogen atoms Inorganic refers to carbon dioxide and all molecules without carbon Organisms make and use carbon. Lack carbon or hydrogen
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Why Is Carbon So Important in Biological Molecules?
The carbon atom is key Is versatile because it has four electrons in the outer shell Is stable by forming up to four bonds single, double, or triple covalent Result organic molecules can assume complex shapes: branched chains, rings, sheets, and helices Functional groups in organic molecules Are less stable than the carbon backbone and are more likely to participate in chemical reactions Determine the characteristics and chemical reactivity of organic molecules
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Table 3-1
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Dehydration Synthesis
Small organic molecules (called monomers) are joined to form longer molecules (called polymers) Monomers are joined together through dehydration synthesis, at the site where an H+ and an OH- are removed, resulting in the loss of a water molecule (H2O) The openings in the outer electron shells of the two subunits are filled when the two subunits share electrons, creating a covalent bond dehydration synthesis “removing water to put together”
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Hydrolysis Polymers are broken apart through hydrolysis (“water cutting”) Water is broken into H+ and OH- and is used to break the bond between monomers Digestive enzymes use to break down food hydrolysis Hydro – “water” Lysis – “break apart”
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All contain Carbon, Hydrogen, and generally Oxygen.
Biological Molecules The important organic molecules found in living things: Carbohydrates Lipids Proteins Nucleic Acids Sugar Fat Enzymes Deoxyribonucleic Starch Structural Proteins Ribonucleic Acid Cellulose All contain Carbon, Hydrogen, and generally Oxygen.
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Carbohydrates Carbohydrate molecules are composed of C, H, and O in the ratio of 1:2:1 Monosaccharide - consists of just one sugar molecule Disaccharide - Two linked monosaccharides Polysaccharide - polymer of many monosaccharides Carbohydrate means “carbon plus water” Sacchar means “sugar”
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Carbohydrates Hydrophilic due to the polar OH- functional group
Only mono- and disaccharides Functions: Energy source Combine with other molecules through dehydration synthesis (plasma membrane, cell wall, exoskeletons) 1. OH forms hydrogen bonds with polar H2O
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Carbohydrates There are several monosaccharides with slightly different structures The basic monosaccharide structure is: A backbone of 3–7 carbon atoms Most of the carbon atoms have both a hydrogen (-H) and an hydroxyl group (-OH) attached to them Chemical formula (CH2O)n hydrogen bond hydroxyl group water
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Monosaccharides When dissolved in the cytoplasmic fluid of a cell, the carbon backbone usually forms a ring Glucose (C6H12O6) is the most common monosaccharide in living organisms Fructose (“fruit sugar” found in fruits, corn syrup, and honey) Galactose (“milk sugar” found in lactose) Ribose and deoxyribose (found in RNA and DNA) All end in -ose Note “missing” oxygen atom fructose galactose ribose deoxyribose
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Disaccharides Functions: Examples:
They are used for short-term energy storage When energy is required, they are broken apart by hydrolysis Examples: Sucrose (table sugar) = glucose + fructose Lactose (milk sugar) = glucose + galactose Maltose (malt sugar) = glucose + glucose … especially in plants. Maltose is rare in nature but is part of the break down of polysaccharides in digestive tract. glucose fructose sucrose dehydration synthesis
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Polysaccharides Storage polysaccharides include:
Starch, an energy-storage molecule in plants, formed in roots and seeds Glycogen, an energy-storage molecule in animals, found in the liver and muscles (b) A starch molecule (a) Potato cells (c) Detail of a starch molecule starch grains Polymers of glucose Starch – branched chains of ½ a million glucose subunits
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Polysaccharides Polysaccharides as a structural material
Cellulose (a polymer of glucose) It is found in the cell walls of plants Most abundant organic molecule on Earth It is indigestible for most animals due to the orientation of the bonds between glucose molecules Fiber in your diet
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Polysaccharides Chitin (a polymer of modified glucose units)
Nitrogen-containing functional group The outer coverings (exoskeletons) of insects, crabs, and spiders The cell walls of many fungi
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Review What are carbohydrates used for?
What are the major classes of carbohydrates? What are the types and functions of polysaccharides? Energy and to synthesize larger molecules Monosaccharides, disaccharides, polysaccharides Starch and glycogen – energy storage cellulose – structure chitin – exoskeletons and cell walls of fungi
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Lipids Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbon All lipids contain large chains of non-polar hydrocarbons hydrophobic
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Lipids Lipids are diverse in structure and serve a variety of functions: energy storage waterproof coverings on plant and animal bodies primary component of cellular membranes hormones Lipids are classified into three major groups Oils, fats, and waxes Phospholipids Steroids
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Lipids Oils, fats, and waxes Carbon, hydrogen, oxygen
Made of one or more fatty acid subunits Fats and oils Are used primarily as energy-storage molecules, containing twice as many calories per gram as carbyhydrates and proteins Are formed by dehydration synthesis Three fatty acids + glycerol triglyceride
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Synthesis of a Triglyceride
glycerol fatty acids Dehydration synthesis Fatty acids are long chains of carbon and hydrogen with a carboxyl group (-COOH) on one end. triglyceride Fig. 3-12
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Lipids Oils, fats, and waxes
Fats are solid at room temperature are saturated (the carbon chain has as many hydrogen atoms as possible, and mostly or all C-C bonds); for example, beef fat Produced in animals Straight chains so can pack tightly together. Butter and lard
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Lipids Oils, fats, and waxes
Oils are liquid at room temperature are unsaturated (with fewer hydrogen atoms, and many C=C bonds); for example, corn oil Produced by plants Unsaturated trans fats have been linked to heart disease Kinks so the molecules can’t come close together. Soybean oil, canola oil
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Lipids Oils, fats, and waxes Waxes are similar to fats
Most animals don’t have the enzymes to break them down. Functions: form waterproof coatings such as on: Leaves and stems of land plants Fur in mammals Insect exoskeletons used to build honeycomb structures
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Lipids Phospholipids These form plasma membranes around all cells
Phospholipids consist of two fatty acids + glycerol + a short polar functional group containing nitrogen Hydrophilic polar functional groups form the “head” Hydrophobic non-polar fatty acids form the “tails” polar head glycerol backbone phosphate group variable functional (hydrophilic) (hydrophobic) fatty acid tails 2. One fatty acid is replaced with a phosphate group
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Lipids Steroids Composed of four carbon rings fused together with various functional groups protruding from them Examples: Cholesterol (animal cell membranes) Male and female sex hormones Cholesterol stabilizes membranes, affecting fluidity and reducing permeability affects permeability of the cell high cholesterol content reduces permeability to hydrophilic substances and small molecules that would diffuse through. more control over what substances enter and leave. Cholesterol is used to synthesize other steroids like sex hormones
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Proteins Functions Enzymes are proteins that promote chemical reactions Structural proteins (e.g., elastin, keratin) provide support Hormones Antibodies Toxins
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Proteins Polymers of amino acids joined by peptide bonds
All amino acids have a similar structure All contain amino and carboxyl groups All have a variable “R” group Some R groups are hydrophobic Some are hydrophilic Cysteine R groups can form disulfide bridges 20 unique amino acids The amino acid Cysteine has a sulfhydryl R-group amino group hydrogen variable carboxylic acid group
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Proteins The sequence of amino acids in a protein dictates its function Amino acids are joined to form chains by dehydration synthesis An amino group reacts with a carboxyl group, and water is lost amino acid amino group carboxylic acid peptide water bond dehydration synthesis
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Proteins Amino acids are joined to form chains by dehydration synthesis The covalent bond resulting after the water is lost is a peptide bond, and the resulting chain of two amino acids is called a peptide Long chains of amino acids are known as polypeptides
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Proteins Proteins exhibit up to four levels of structure
Primary structure is the sequence of amino acids Secondary structure is a helix, or a pleated sheet Repeating structure with hydrogen bonds Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds Quaternary structure occurs where multiple polypeptides are linked together Interactions among amino acid R-groups cause twists, folds, and interconnections.
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The Four Levels of Protein Structure
(a) Primary structure: The sequence of amino acids linked by peptide bonds (b) Secondary structure: Usually maintained by hydrogen bonds, which shape this helix leu val heme group lys lys gly his hydrogen bond ala lys val (d) Quaternary structure: Individual polypeptides are linked to one another by hydrogen bonds or disulfide bridges (c) Tertiary structure: Folding of the helix results from hydrogen bonds with surrounding water molecules and disulfide bridges between cysteine amino acids lys helix pro Fig. 3-21
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Proteins The functions of proteins are linked to their three-dimensional structures Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure Disruption of secondary and tertiary bonds leads to denatured proteins and loss of function Extreme heat Extreme changes in pH UV radiation Hair styling Cooking Sterilizing food, water Preserving food
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Nucleotides and Nucleic Acids
Nucleotides act as energy carriers and intracellular messengers Nucleotides are the monomers of nucleic acid chains Three parts: Phosphate group Five-carbon sugar Nitrogen-containing base Deoxyribose Nucleotide sugar phosphate base
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Nucleotides and Nucleic Acids
Nucleotides act as energy carriers Adenosine triphosphate (ATP) is a ribose nucleotide with three phosphate functional groups ADP and cAMP NAD and FAD: electron carriers 3 phosphate groups + ribose (sugar) + Adenine (amino acid) cAMP – intracellular messenger
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Nucleic Acids DNA and RNA, the molecules of heredity
Polymers of nucleotides DNA (deoxyribonucleic acid) is found in chromosomes and carries genetic information needed for protein construction RNA (ribonucleic acid) makes copies of DNA and is used directly in the synthesis of proteins
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Nucleic Acids hydrogen bond Each DNA molecule consists of two chains of millions of nucleotides that form a double helix linked by hydrogen bonds RNA is only one chain of hundreds of nucleotides.
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The Pleated Sheet: An Example of Secondary Structure
hydrogen bond Fig. 3-21 pleated sheet
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