Download Chapter 5: Biological Molecules Molecules of Life • All life made up

Chapter 5: Biological Molecules
Molecules of Life
 All life made up of four classes of large biological molecules
o Lipids, Carbohydrates, Proteins, Nucleic Acids
 Macromolecules
o Large molecules made of thousands of covalently connected atoms
 Polymer – long molecule made of many similar or identical building blocks
 Monomer – small building-block
o 3 of 4 organic classes are polymers
 Carbs, Proteins, & Nucleic acids
Dehydration Reactions
 Two small molecules covalently bonded together w/ loss of water
o Forms polymers, fats, & phospholipids
 Enzyme – protein that speed up reactions & remains unchanged
Hydrolysis Reactions
 ‘Breaking with water’
 Reverse of Dehydration
o Breaks polymers into monomers by adding hydrogen & hydroxyl
 ATP hydrolysis breaks off phosphate releasing energy
Lipids
 Hydrophobic molecules
o Mostly hydrocarbons parts (nonpolar covalent bonds)
 DO NOT form polymers
 Fats (Triglycerides)
o Glycerol (head) w/ 3 Fatty acids (tails) connected via ester linkage
o Energy storage molecules
o Humans & other mammals store fat in adipose cells
 Adipose tissue – cushions vital organs & insulates body
o Fatty Acids
 Vary in length (# carbons), location, & # of double bonds
 Saturated fatty acids – max # of hydrogens (no double bonds)
 Unsaturated fatty acids – 1+ double bonds present
 Trans Fat
 Raises LDL (bad cholesterol)
 Lowers HDL (good cholesterol)
 Phospholipid
o Major component of all cell membranes
o Glycerol w/ phosphate group & 2 fatty acid tails
o Amphipathic molecule
 Hydrophilic head (phosphate)
 2 Hydrophobic tails (fatty acids)
 Steroids
o Lipids characterized by carbon skeleton of 4 fused rings
o Cholesterol – made in liver
 Common part of animal cell membrane
 Precursor to sex hormones (testosterone & estrogen) & bile salts (digestion aid)
Carbohydrates
 Sugars & polymers of sugars
 Fuel & building material for cells
 Monosaccharide (single sugar); Disaccharide (2 sugars); Polysaccharide (many sugars)
o Polymer composed of many sugar monomers
 Monosaccharides
o aka simple sugars
o Always multiples of CH2O
 Glucose (C6H12O6) most common
o
Classified by:
 # of carbons in carbon skeleton
 Location of carbonyl group
 Disaccharides
o 2 monosaccharides linked to transport sugars in organisms
o Sucrose: Fructose/Glucose
o Maltose: Glucose/Glucose
o Lactose: Glucose/Galactose
 Polysaccharides
o aka Complex Carbs
o Polymers of monosaccharides
 Few hundred to few thousand
 Glycosidic linkage connection
o Storage & structural roles
o Plant Polysaccharides
 Starch – energy storage polysacch; made of glucose
 Surplus starch stored as granules in chloroplasts & other plastids
 Cellulose – major structural component of cell wall; made of glucose
 Glycosidic linkages differ b/c two ring forms for glucose: alpha () & beta ()
 Polysaccharide Digestion
 Enzymes digesting starch (hydrolyze -linkage) can’t digest cellulose (hydrolyze
-linkage)
 Humans pass cellulose as insoluble fiber
 Many herbivores have mutualistic relationships w/ microbes that digest cellulose
o Animal Polysaccharides
 Glycogen – energy storage polysacch.
 Humans & other vertebrates store glycogen mainly in liver & muscle cells
 High blood sugar = Insulin (pancreas) released
 Blood sugar uptaken & glycogen formed
 Low blood sugar = Glucagon (pancreas) released
 Glycogen broken down releasing glucose
o Chitin
 Structural polysacch. found in arthropod exoskeletons & fungal cell walls
Proteins
 Account for over 50% of cell’s dry mass
 Functions – enzyme, storage, structural support, transport, movement, cellular communications, & defense
against foreign substances
 Polypeptide
o Polymer built from set of 20 amino acids
o Linked by peptide bonds via dehydration reaction
o Each has unique amino acid sequence; can be a few to more than a thousand
 Amino Acid Structure
o -Carbon bonded to:
 Hydrogen
 Carboxyl group
 Amino group
 Side Chain (R group) – accounts for different properties
 Structure & Function
o Functional protein consists of 1 or more polypeptides coiled, twisted, & folded into a unique shape
o Amino acid order determines protein’s 3-D structure, which determines function
 4 Levels of Protein Folding
o Primary Structure
 Unique sequence of amino acids
 Like letters in a word
 Determined by inherited genetic information (DNA)
o
Secondary Structure
 Found in most proteins; made of coils & folds in chain
 H-bonds form b/w repeating parts of polypeptide backbone
  helix coils
 β pleated sheet folds
o Tertiary Structure
 Final folding of individual polypeptide
 Determined by interactions b/w side chains (R groups)
 H-bonds, ionic bonds, hydrophobic interactions, & van der Waals interactions
 Disulfide bridge – strong covalent bonds that reinforce protein structure
o Quaternary Structure
 Results from 2 or more polypeptide chains forming 1 macromolecule
 Collagen – fibrous protein made of 3 polypeptides coiled like a rope
 Hemoglobin – globular protein made of four polypeptides (2 alpha & 2 beta chains)
 Sickle-Cell Disease
o Inherited blood disorder
o Single amino acid change in protein hemoglobin
 Amino Acid 6 is Valine instead of Glutamic Acid
 Alters shape & function
 Protein Structure
o Physical & chemical conditions affect structure, along w/ primary structure
 Changes in pH, salt, temp, or other environmental factors can cause proteins to unravel
o Denaturation – loss of protein’s native structure; becomes biologically inactive
 Protein Folding
o Most go thru several states on way to a stable structure
o Chaperonin – protein that assists in proper folding of other proteins
 Separate proteins from ‘bad’ influences in cytoplasm during folding
Nucleic Acids
 DNA
o Deoxyribonucleic acid
o Made of genes, which form chromosomes
o Direct amino acid sequence of proteins
o Has directions for DNA replication
 RNA
o Ribonucleic acid
o DNA directs synthesis of messenger RNA (mRNA) = transcription
 mRNA read by ribosomes to make proteins = translation
o rRNA – ribosomal RNA
o tRNA – transfer RNA
 Nucleic Acid Structure
o Polymers – polynucleotides
o Monomers – nucleotides (A, G, T, C, & U)
o Nucleotides made of:
 Phosphate group
 Sugar
 Nitrogenous base
o Nucleotide Monomers
 2 families of nitrogenous bases:
 Pyrimidines – cytosine, thymine, uracil (C, T, U)
 Purines – adenine, guanine (A,G)
 DNA sugar = deoxyribose & RNA sugar = ribose
o Nucleotide Polymers
 Adjacent nucleotides joined by phosphodiester bonds
 –OH group on 3 carbon of one & phosphate on 5 carbon of next
 Links create a backbone of sugar-phosphate units w/ nitrogenous bases as appendages

DNA Double Helix
o Double helix – 2 polynucleotides spiral around an imaginary axis
 Backbones run in opposite (5 → 3) directions; antiparallel
o DNA bases pair up & form H-bonds
 T w/ A
 G w/ C
 DNA v. RNA
o DNA
 Directs cell processes
 Double stranded
 A, T, G, C
 Deoxyribose sugar
o RNA
 Protein synthesis
 Single stranded
 A, U, G, C (U replaces T)
 Ribose sugar
Evolutionary Tape Measure
 Sequences of nucleotides in DNA are passed from parents to offspring
 Molecular biology is used to assess evolutionary kinship
 2 closely related species’ DNA is more similar than more distantly related species