A1.2

• DNA


  Deoxyribo nucleic acid, the genetic material of all living organisms
• Some viruses use RNA as their genetic material but viruses are not considered to be living
• Nucleotide


  A single unit of a nucleic acid, consisting of a phosphate, a pentose sugar, and a nitrogenous base
• Components of a nucleotide

  • Phosphate
  • Pentose sugar
  • Nitrogenous base
• Sugar-phosphate bonding


  Makes a continuous chain of covalently bonded atoms in each strand of DNA or RNA nucleotides, forming a strong "backbone"
• Nitrogenous bases in DNA

  • Adenine (A)
  • Guanine (G)
  • Thymine (T)
  • Cytosine (C)
• RNA


  A polymer formed by condensation of nucleotide monomers
• DNA


  • Double helix made of two antiparallel strands of nucleotides
  • Strands linked by hydrogen bonding between complementary base pairs
• Differences between DNA and RNA

  • Number of strands (single vs double)
  • Types of nitrogenous bases (RNA has Uracil instead of Thymine)
  • Type of pentose sugar (ribose vs deoxyribose)
• Complementary base pairing


  Allows genetic information to be replicated and expressed
• Diversity of possible DNA base sequences and the limitless capacity of DNA for storing information
• Conservation of the genetic code across all life forms as evidence of universal common ancestry
• Directionality of RNA and DNA

  • 5' to 3' linkages in the sugar-phosphate backbone and their significance for replication, transcription and translation
• Purine-to-pyrimidine bonding


  A component of DNA helix stability
• Structure of a nucleosome

  • DNA molecule wrapped around a core of eight histone proteins held together by an additional histone protein attached to linker DNA
• Hershey-Chase experiment


  Evidence for DNA as the genetic material
• Chargaff's data


  Relative amounts of pyrimidine and purine bases across diverse life forms, which falsified the tetranucleotide hypothesis
• DNA is an acronym for deoxyribonucleic acid
• DNA is called the blueprint for life because it contains all the information an organism needs to develop, function, and reproduce
• DNA stores and transmits genetic information
• DNA is found in every cell of all living organisms
• DNA has a double-helix structure
• If the DNA in a single human cell was unwound, it would be more than two meters long
• DNA is found in every cell of all living organisms: animals, plants, fungi, protists, and bacteria
• A nucleotide is a single unit of a nucleic acid
• There are two types of nucleic acid: DNA and RNA
• Nucleic acids are very large molecules that are constructed by linking together nucleotides to form a polymer
• The base always attaches to the first carbon
• Covalent bond


  Bonds formed between the phosphate of one nucleotide and the pentose sugar of the next, resulting in a phosphodiester bond
• Condensation reaction


  Forms bonds between nucleotides, releasing water
• Successive condensation reactions between nucleotides results in the formation of a long single strand
• RNA shares the same bases as DNA except that Uracil (U) replaces Thymine (T)
• Adenine pairs with thymine (A=T) via two hydrogen bonds, and guanine pairs with cytosine (G=C) via three hydrogen bonds
• The two polynucleotide chains of DNA run in opposite directions (antiparallel)
• The atoms in DNA arrange themselves in an optimal energy configuration, resulting in the double-stranded DNA twisting to form a double helix
• Ribonucleic Acid (RNA) nucleotides consist of a base, a sugar (ribose), and a phosphate group covalently bonded together
• Single RNA nucleotides are monomers, and multiple joined RNA nucleotides are polymers
• Adenosine Triphosphate (ATP) is a single nucleotide with two additional phosphates, used as an energy source
• RNA is often, but not always, single-stranded and linear in shape
• DNA replication is a semi-conservative process, where each new strand contains one original and one new strand