Cycle 2: The Central Dogma of Molecular Biology

• Gene expression


  When a gene is turned into a function, different genes are expressed in different cells
• What is a gene?


  A DNA sequence that codes for an RNA strand
• Not all genes code for mRNA

  Some code for rRna, tRNA and these are not transcribed into proteins
• mRNA makes up


  The smallest portion of RNA in the cell
• Information transfer


  Info in DNA is transcribed into RNA and then mRNA is translated into proteins, enzymes are involved in each step
• DNA uses hydrogen bonds to


  Form its double helix shape
• RNA can use hydrogen bonding to

  Bond with itself and form different shapes
• Proteins can form


  A variety of different shapes related to their function
• Which evolved first? (DNA, RNA, or Proteins)

  RNA
• Ribosome


  A class of catalytic RNA molecules and a key organelle that plays a role in the synthesis of proteins (2/3 rRNA and 1/3 protein)
• Spliceosomes are involved in


  Removing introns
• Transcript Abundance


  How much mRNA corresponds to a specific gene is in the cell, measured using Northern Blots (RNA blot hybridization), transcription rate and rate of mRNA breakdown
• Protein Abundance


  How much of a protein is in the cell, measured using Western Blots, translation rate and rate of protein breakdown
• SNOW DROP


  Southern -DNA, Northern -RNA, OOOO -OOOO, Western -Protein
• DNA and RNA similarities


  Polymers of nucleotides (nucleotide = 5 C sugar + phosphate + nitrogenous base), both carriers of information
• DNA and RNA differences

  Contain different sugars (DNA = deoxyribose sugar, RNA = ribose sugar), DNA does not have OH at carbon 2 (has an H), RNA is less stable/ more reactive, RNA is attacked by enzymes called ribonucleases
• The OH on carbon 2 of RNA reacts with the phosphate group and


  Can cause the RNA to be degraded more easily
• Why is it good that RNA degrades more quickly than DNA?


  Temporal regulation, we don't need mRNA present all the time if unnecessary because this is a waste of cellular resources
• 3 types of expression


  Induced (up-regulation in gene expression), constitutive (expression of the protein or transcript will always be the same), repressed (down-regulation in gene expression)
• What is half-life


  It is the time for 1/2 of the mRNA to be degraded
• When opsin binds retinal


  Opsin has now been modified, functional rhodopsin protein is formed
• The conversion of beta-carotene to retinal requires enzymes


  Retinal is not a protein, there are no beta-carotene or retinal genes
• Forward genetics


  We start with a phenotype and identify the underlying gene
• Reverse genetics


  We start with a specific gene which is altered, and identify the phenotype
• Insertional Mutagenesis (forward genetics)


  To generate a population of mutants, we can insert a gene randomly into the genomes of organisms