bio 6

• Central Dogma


  The process by which the information in genes is used to synthesize proteins

  
• Transcription


  1. DNA mRNA

  2. Occurs in the nucleus

  3. Performed by RNA polymerase

  
• Translation


  1. mRNA polypeptide

  2. Occurs in cytoplasm

  3. Performed by ribosome

  
• Gene


  Distinct segment of DNA that contains the code or instructions to make proteins

  
• Genes are made of DNA

  
• Hundreds of genes can be found on a single human chromosome (46 chromosomes total)
• Each gene is made of a specific sequence of nucleotides
• Each gene has information for one specific type of protein
• There are 20,000 human genes and 20,000 different human proteins
• Different cells express different genes and have different roles in your body
• DNA


  Acts as template for the synthesis of mRNA through the process of transcription

  
• Ribosomal RNA (rRNA)


  • Made in the nucleolus
  • Associates with ribosomal proteins to form ribosomes
  • Ribosome is the site of protein synthesis (translation)

  
• Transfer RNA (tRNA)


  Transports specific amino acids to the ribosomes during protein synthesis

  
• Messenger RNA (mRNA)


  Serves as the template for protein synthesis through the process of translation

  
• Transcription occurs in the nucleus, translation occurs in the cytoplasm

  
• Transcription


  1. DNA strands separate

  2. Messenger RNA (mRNA) copied from DNA template

  3. Transcription executed by enzyme called RNA polymerase

  
• DNA is used as a template for mRNA, mRNA uses complementary base pairing to make a copy of the gene

  
• mRNA uses uracil instead of thymine
• Template strand


  The DNA strand complementary to the newly made RNA (RNA polymerase is reading this strand and adding nucleotides through complementary base pairing)

  
• Coding strand


  The other DNA strand (also called the non-template strand)

  
• The newly made RNA will have the same sequence as the template strand, not the coding strand

  
• Protein synthesis: Translation


  The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule

  
• Protein synthesis occurs in the cytoplasm, executed by a ribosome

  
• Codon


  Triplets of nucleotides on the mRNA that specify a specific amino acid

  
• The genetic code has 64 possible codons (4 nucleotides x 4 nucleotides x 4 nucleotides)
• The genetic code has 20 amino acids, so there is some degeneracy (redundancy) in the code
• The genetic code has start and stop codons
• The third codon position exhibits wobble, allowing for some flexibility in the genetic code
• The genetic code is highly conserved throughout all life on Earth
• Mutations are changes to the sequence of bases (A, C, G, T) in DNA


  Some mutations have no effect, some have mild effects, some are incompatible with life
• Not every mutation in a gene causes a change to the amino acid sequence of the polypeptide due to the redundancy in the genetic code

  
• Some mutations are more severe than others due to the redundancy and flexibility in the genetic code