Macromolecules II PDF

Nucleic Acids  Nucleic acids are of paramount importance to the cells because they store, transmit, and express genetic information  They are linear polymers of nucleotides  DNA is deoxyribonucleic acid, and RNA is ribonucleic acid Which component of DNA and RNA is responsible for the “ac...

Nucleic Acids  Nucleic acids are of paramount importance to the cells because they store, transmit, and express genetic information  They are linear polymers of nucleotides  DNA is deoxyribonucleic acid, and RNA is ribonucleic acid Which component of DNA and RNA is responsible for the “acidic” part of nucleic acid? A) the phosphate group B) the 5-carbon sugar C) the nitrogenous base D) there is actually nothing acidic about DNA and RNA Nucleic Acid Components Nomenclature  Nucleotides with one phosphate group can be thought of as nucleoside monophosphates (example: adenosine monophosphate, AMP)  Adenosine diphosphate (ADP) has two phosphate groups, and adenosine triphosphate (ATP) has three The Polymers Are DNA and RNA  Nucleic acids are linear polymers of nucleotides linked by a 3ʹ,5ʹ phosphodiester bridge, a phosphate group linked to two adjacent nucleotides via two phosphoester bonds  The polynucleotide formed by this process has a directionality with a 5ʹ phosphate group at one end and a 3ʹ hydroxyl group at the other  Nucleotide sequences are conventionally written in the 5ʹ to 3ʹ direction Nucleic Acid Synthesis  A preexisting molecule is used to ensure that new nucleotides (NTPs for RNA, dNTPs for DNA) are added in the correct order  This molecule is called a template, and correct base pairing between the template and the incoming nucleotide is required to specify correct order  A complementary relationship exists between certain purines and pyrimidines Complementary relationships between purines and pyrimidines A) allow adenine to form two hydrogen bonds with thymine (or uracil) and guanine to form three hydrogen bonds with cytosine to form double-stranded nucleic acids. B) allow the interaction of the oppositely charged amino acids to form the tertiary structure of proteins. C) allow adjacent bases in a nucleotide chain to stack tightly, stabilizing the DNA double helix. D) provide highly ordered, repetitive bonding to form α helices and β sheets within proteins. E) Both A and C are correct. Complementary Base Pairing A–T G–C anti-parallel The DNA Molecule Is a Double-Stranded Helix Base Pairing and RNA  RNA is normally single stranded  RNA structure is still influenced by complementary base pairing  However, the pairing is usually between bases in different areas of the same molecule and is less extensive than that of DNA Macromolecules II  Polysaccharides and Lipids Polysaccharides  Polysaccharides are long chain polymers of sugars and sugar derivatives  They serve primarily in structure and storage  They usually consist of a single kind of repeating unit or sometimes an alternating pattern of two kinds  Short polymers, oligosaccharides, are sometimes attached to cell surface proteins A sugar may be an aldehyde, aldosugars with a terminal carbonyl group; or ketone, ketosugars with an internal carbonyl group Sugars within these groups are named generically based on how many carbon atoms they contain  Most sugars have between three and seven carbons and are classified as  Trioses (three carbons) Ribose  Tetroses (four carbons) Deoxyribose  Pentoses (five carbons)  Hexoses (six carbons) Glucose  Heptoses (seven carbons) Galactose Fructose The Structure of Glucose Two Ring Forms of D-glucose Polysaccharides  The linkage of disaccharides is a glycosidic bond, formed between two monosaccharides by the elimination of water  Glycosidic bonds involving the α form of glucose are called α glycosidic bonds (e.g., maltose); those involving the β form are called β glycosidic bonds (e.g., lactose) Storage Polysaccharides  The most familiar storage polysaccharides are starch in plant cells and glycogen in animal cells and bacteria  Both consist of α-D-glucose units linked by α glycosidic bonds, involving carbons 1 and 4 (1→4)  Occasionally α(1→6) bonds may form, allowing for the formation of side chains (branching) Storage Polysaccharides Consist of α-D- glucose units linked by α glycosidic bonds, involving carbons 1 and 4 (1→4) Occasionally α(1→6) bonds may form, allowing for the formation of side chains Storage Polysaccharides Plants: Amylose – unbranched Amylopectin – branched (both starches) Animals: Glycogen - branched α glucose polysaccharides form helices Structural Polysaccharides  The best-known structural polysaccharide is the cellulose found in plant cell walls Cellulose, composed of repeating monomers of β-D-glucose, is very abundant in plants β glucose polysaccharides form strands You are investigating the structure of the seeds of a newly discovered tropical plant. There is storage material inside the seed. You treat the seed with peptidase (an enzyme that breaks peptide bonds), glycoside hydrolases (an enzyme that breaks β glycosidic bonds), and amylase (an enzyme that breaks α glycosidic bonds). Only the amylase appears to dissolve the storage material in the seed. What does this tell you about the identity of the storage material? A) The seed contains fibrous proteins to store carbon and energy. B) The seed contains lipids to store carbon and energy. C) The seed contains starch to store carbon and energy. D) The seed contains cellulose to store carbon and energy. E) The seed contains globular proteins to store carbon and energy. Other Monomers for Structural Polysaccharides  Bacterial Polysaccharide The “PS” part of the LPS component of gram negative bacterial cell walls Chitin: Insect exoskeletons Crustacean shells Polysaccharide Structure Depends on the Type of Glycosidic Bonds Involved  α and β glycosidic bonds are associated with marked structural differences  Starch and glycogen (α polysaccharides) form loose helices that are not highly ordered because of the side chains  Cellulose (that forms β linkages) exists as rigid linear rods that aggregate into microfibrils, about 5–20 nm in diameter  Plant and fungal cells walls contain these rigid microfibrils in a noncellulose matrix containing other polymers (hemicellulose, pectin) and a protein called extensin Lipids  Lipids are not formed by the same type of linear polymerization that forms proteins, nucleic acids, and polysaccharides  All have a hydrophobic nature and thus little affinity for water  They have relatively few polar groups, but some are amphipathic, having polar and nonpolar regions  Functions include energy storage, membrane structure, or specific biological functions such as signal transmission Fatty acids are ________; they function in the cell as ________. A) short chains of double-bonded carbon molecules; storage lipids B) short chains of double-bonded carbon molecules; vitamins and cofactors C) four-ringed hydrocarbon molecules; key components of membranes D) long, unbranched hydrocarbon chains with a carboxyl group at one end; building blocks for other lipids E) short chains of double-bonded carbon molecules; vitamins, cofactors, and storage lipids Fatty Acids Are the Building Blocks of Several Classes of Lipids  Fatty acids are components of several other kinds of lipids  A fatty acid is a long amphipathic, unbranched hydrocarbon chain with a carboxyl group at one end Trans Fats Triacylglycerols Are Storage Lipids Triacylglycerols containing Triacylglycerols in plants are mostly saturated fats are liquid at room temperature usually solid or semisolid at (e.g., vegetable oil) and are room temperature and are predominantly unsaturated called fats The term amphipathic describes the characteristic of some molecules that have A) two polar regions. B) only a single polar region. C) both a polar and a nonpolar region. D) no polar regions. E) two nonpolar regions. Phospholipids Are Important in Membrane Structure  Phospholipids are important to membrane structure because of their amphipathic nature Glycolipids Are Specialized Membrane Components  Glycolipids are lipids containing a carbohydrate instead of a phospholipid and are often derivatives of sphingosine and glycerol (glycosphingolipids)  Carbohydrate groups attached to a glycolipid may be one to six sugar units (D-glucose, D-galactose, or N-acetyl-D-galactosamine)  Glycolipids occur largely on the outer monolayer of the plasma membrane Steroids Are Lipids with a Variety of Functions Steroids are derivatives of a four-ringed hydrocarbon skeleton, which distinguishes them from other lipids Mostly non-polar Cholesterol is the common building block for the rest of the steriods Steroid Hormones Act as signaling molecules femininization masculinization gluconeogenesis ion reabsorption A general trend in the structure of biological polymers is A) that the order and bonding of monomers form the basis for the three-dimensional structure and therefore function of the polymer B) that they are all insoluble in water independent of the size of the polymer. C) that each class of polymer forms one type of secondary structure independent of the order of the monomers in the polymer. D) that each class of polymer can form either fibrous or globular conformations depending on the chemical conditions inside the cell. E) that four different monomers form the basis for the functional and structural properties of each polymer.