topic 4

• RNA


  A polymer made up of nucleotides
• Nucleotide


  The monomer that RNA is made up of
• Nucleotide


  • Contains a ribose sugar
  • Contains a phosphate group
  • Contains one of four nitrogenous bases: adenine, guanine, cytosine, or uracil
• Ribose is a pentose sugar (5 carbons)
• RNA


  Similar in structure to DNA, but with ribose instead of deoxyribose, and uracil instead of thymine
• Function of RNA


  • To copy and transfer genetic information
  • Combines with proteins to create ribosomes
• Types of RNA


  • mRNA
  • tRNA
  • rRNA
• mRNA


  A copy of one gene in DNA, used to code for one protein
• mRNA


  • Much shorter than DNA
  • Single-stranded
  • Short-lived (quickly degraded)
• tRNA


  Transfers amino acids to the ribosome
• tRNA


  • Single-stranded
  • Folds into a cloverleaf shape held by hydrogen bonds
  • Has an amino acid attachment site
• rRNA


  Combines with proteins to form ribosomes
• Differences between DNA and RNA monomers

  • DNA contains thymine, RNA contains uracil
  • DNA contains deoxyribose, RNA contains ribose
• Differences between DNA and RNA polymers

  • DNA is much longer (contains all genes)
  • RNA is much shorter (only a copy of one gene)
  • DNA is double-stranded, RNA is single-stranded
• DNA is stored in the nucleus of eukaryotic cells
• Chromosome


  Tightly coiled DNA
• Histone proteins


  Proteins that DNA is wrapped around to prevent tangling
• Nucleosome


  Complex of DNA wrapped around histone proteins
• In prokaryotic cells, DNA is circular and not wrapped around histones
• Mitochondria and chloroplasts contain their own circular, histone-free DNA</b>
• Mitochondrial and chloroplast DNA is similar to prokaryotic DNA
• Gene


  Short section of DNA that codes for a polypeptide and functional RNA
• Allele


  Different form/version of the same gene
• Locus


  Location of a gene on a chromosome
• Homologous pair


  Pair of chromosomes with the same genes
• Humans have 23 pairs of chromosomes
• The 23rd chromosome pair are the sex chromosomes (X and Y)
• Compacting DNA into chromosomes

  DNA is tightly coiled around histone proteins
• Function of histone proteins is to assist in the tight coiling of DNA
• Protein synthesis


  The process where proteins are made
• Protein synthesis


  1. Transcription

  2. Translation
• Transcription


  The first step of protein synthesis, happening inside the nucleus, where a copy of a gene is made as mRNA
• Transcription


  • DNA is too big to leave the nucleus, so a copy is made as mRNA
  • DNA is protected from enzymes in the cytoplasm by staying in the nucleus
• Transcription


  1. Unwind DNA double helix

  2. One DNA strand acts as template

  3. RNA nucleotides align complementarily

  4. RNA polymerase joins nucleotides

  5. Pre-mRNA is formed

  6. Introns are spliced out by spliceosome
• Translation


  The second step of protein synthesis, happening in the cytoplasm, where the mRNA attaches to a ribosome and tRNA molecules bring specific amino acids to build the polypeptide chain
• Translation


  1. mRNA attaches to ribosome at start codon

  2. tRNA anticodons align to mRNA codons

  3. Ribosome holds tRNA in place

  4. Peptide bonds form between amino acids

  5. Ribosome moves along mRNA

  6. Process continues until stop codon reached
• Protein synthesis requires energy (ATP) to form peptide bonds between amino acids
• The polypeptide chain formed in translation is the primary structure of a protein, which then undergoes further modifications in the Golgi body to form the final 3D shape
• Meiosis


  A type of cell division that produces daughter cells which are genetically different
• Meiosis


  1. Parent cell divides once

  2. Parent cell divides twice

  3. Results in four haploid daughter cells