DNA, RNA, and Proteins

• nucleic acids: polymers of nucleotides (polynucleotides)

  two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
• information flow in biology: DNA -> RNA -> protein
• nucleotides: the building blocks of nucleic acids
• three components of every nucleotide

  sugar: either ribose or deoxyribose

  base (a.k.a. nucleobase): one of four molecules that act as a ”letter” of code

  phosphate group: holds sugars of adjacent nucleotides together in a chain
• if sugar has a hydroxyl group (OH) on the 2’ carbon, it is a ribose,and that nucleotide is a building block of RNA; if it only has a hydrogen on the 2’ carbon of the sugar it is a deoxyribose, and it is a building block of DNA.
• nitrogenous bases are the bases that code for amino acids in DNA and RNA
• nitrogenous bases are planar (flat) and hydrophobic (not soluble in water)
• nitrogenous bases can either be purines (A and G; bigger) or pyrimidines (T, U, and C; smaller)
• uracil replaces thymine in RNA (uracil is "cheaper" for the cell to make, but thymine is more stable)
• n-glycosyl bond or glycosidic bond: a type of bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate
• the bond between the sugar in a nucleotide (either ribose or deoxyribose) and the base is a glycosidic bond
• phosphodiester bond: links nucleotides together in DNA and RNA
• the circled group shows a phosphodiester bond between the nucleotides

  
• a polynucleotide chain consists of many mononucleotides joined by phosphodiester bonds
• DNA has two strands held together by hydrogen bonds between complementary nitrogenous bases on opposite strands
• nucleotide: a molecule made up of a sugar, a phosphate group, and a nitrogenous base

  nucleoside: a molecule made up of a sugar covalently bonded to a nitrogenous base without a phosphate group
• primary structure of DNA: base sequence and directionality (5' to 3')
• phosphate "bridges" connect adjacent nucleotides via the 5' and 3' carbons, creating a "phosphate-sugar backbone" that covalently links the nucleotides together
• the "phosphate-sugar backbone" is hydrophillic (soluble in water)
• phosphate groups each have a -1 charge (acidic)
• the 1' carbon of sugar is bound to the nitrogenous base

  
• DNA is a heteropolymer
• the 5' end of the strand has the unconnected phosphate group and the 3' end has the unconnected hydroxyl of the sugar
• secondary structure of DNA: right-handed double helix
• pentose: a monosaccharide with five carbon atoms
• nucleotides are linked by dehydration synthesis
• the secondary structure of DNA creates major and minor grooves, where proteins can bind to the DNA and alter its expression.

  
• DNA strands are anti-parallel and complementary

  
• the sugar-phosphate backbone is on the outside of the helix and is hydrophillic (has charged and polar molecules)
• the bases are on the inside of the helix and are hydrophobic
• amino acids are the building blocks of proteins and are made up of a central carbon atom (the alpha carbon) bonded to a hydrogen atom, an amino group, a carboxyl group, and a side chain (R group)
• carboxylic acid: an organic compound in which a carbon atom is bonded to an oxygen atom by a double bond and a hydroxyl group (OH) by a single bond; the fourth bond is to a hydrogen atom or some other group
• hydroxyl group: -OH group
• carbonyl group: C=O (double bonded)
• carboxyl group: C double bonded to O and single bonded to a hydroxyl group (OH)
• amino group (in an amino acid): N bonded to two H
• peptide bond: a covalent bond formed when the carboxyl group of one amino acid reacts with the amine group of another amino acid
• There are 20 different amino acids found in proteins (20 different R groups)
• Some R groups (and thus their amino acids) are hydrophobic (they are not polar or charged), whereas others are hydrophilic (they are either polar or charged)
• amino acids are joined by peptide bonds to form a linear chain (a polypeptide or protein)