Chapter 8

• Nucleotides

  Consist of a pentose sugar, a phosphate group, and an organic base
• DNA structure

  Made up of a deoxyribose sugar, a phosphate group, and one of four organic bases (A,C,G,T). It is double-stranded, and hydrogen bonds between the bases form a helix shape.
• Role of DNA

  Carries genetic information, determines our inherited characteristics
• RNA structure

  Made up of a ribose sugar, a phosphate group, and one of four organic bases (A,C,G,U). It is single stranded.
• Role of RNA

  Transfers genetic information from DNA to ribosomes for protein synthesis
• Bases

  • Purine (double ring) = adenine, guanine
  • Pyrimidine (single ring) = cytosine, thymine, uracil
• DNA in eukaryotic cells

  • Found in nucleus, long and linear, associated with histone proteins to form chromosomes. Mitochondria and chloroplasts contain prokaryotic-like DNA.
• DNA in prokaryotic cells

  • Short and circular, not associated with proteins
• Genetic code


  The order of bases on DNA. Consists of codons (triplets of bases that code for a particular amino acid).
• Features of the genetic code

  • Non-overlapping= each triplet is only read once
  • Degenerate= more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
  • Universal= same bases and sequences used by all species
• Gene


  A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide. Can also code for functional RNA.
• Locus


  The fixed position on a DNA molecule occupied by a gene
• Allele


  Different versions of the same gene, found at the same locus on a chromosome
• Exons


  Regions of DNA that code for amino acid sequences. Separated by one or more introns.
• Introns


  Regions of DNA that do not code for anything.
• Introns are found between exons and within genes
• Genome


  The complete set of genetic information contained in the cells of an organism
• Proteome


  The complete set of proteins that can be produced by a cell
• Messenger RNA (mRNA)


  • A long, single strand
  • Its base sequence is complementary to the DNA it was transcribed from
• Transfer RNA (tRNA)


  • A single strand of around 80 nucleotides that is folded over into a clover leaf shape
  • On one end is an anti-codon, on the opposite end is an amino acid binding site
• Transcription


  1. DNA uncoils into two strands with exposed bases. One used as a template

  2. Free nucleotides line up next to their complementary bases, and are joined together by RNA polymerase
• What happens to mRNA after transcription?

  1. In eukaryotic cells, pre-mRNA must be spliced to remove introns, leaving only the coding regions

  2. Then it moves out of the nucleus and attaches to a ribosome
• Translation


  1. The anti-codon of tRNA attaches to complementary bases on the mRNA

  2. Amino acids bonded to tRNA form peptide bonds, continuing to form a polypeptide chain until a stop codon is reached

  3. This process requires ATP