Protein Synthesis

• single-gene mutations/point mutations


  a mutation resulting in the change of a nucleotide sequence in a gene
• frameshift mutations


  mutations that cause a shift in the reading frame of the gene, therefore different amino acids are coded instead

  
• insertion point mutation


  when an extra base is added, causing a shift in the reading frame

  
• deletion point mutation


  one nucleotide is removed, shifts reading frame

  
• types of point mutations

  silent, missense, nonsense

  
• silent mutation


  a single nucleotide is changed, but the same amino acid is still coded

  
• missense mutation


  a single nucleotide is changed and the codon codes for a different amino acid

  
• nonsense mutation


  a nucleotide is changed and accidentally codes for a stop codon, so no protein is made

  
• chromosome mutations


  changes in chromosome structure involving many genes

  
• types of chromosome mutations

  deletion, duplication, inversion, translocation

  
• deletion in chromosome

  entire coding regions of a gene are removed, leading to a loss of a part of a chromosome, so that certain protein cannot be coded

  
• duplication chromosomal mutation

  when a segment of genes in a chromosome is copied again, can lead to an overproduction of proteins, which can be toxic to the body

  
• inversion chromosomal mutation


  a certain section of a gene or chromosome is flipped around, can cause problems depending on which codon should be read first

  
• translocation chromosomal mutation


  when one section of a chromosome breaks off and attaches to another chromosome

  
• spontaneous causes of mutations


  when an error during DNA replication occurs and a mutation happens

  
• induced cause of mutation


  a mutation caused by an environmental agent (mutagen)

  
• mutagen


  chemical or physical agents in the environment that interact with DNA and may cause a mutation

  
• chemical mutagen


  substance that causes genetic changes, or mutations, in the DNA of an organism

  
• examples of chemical mutagens

  CO, HNO2, ethidium bromide

  
• examples of radiation mutagens

  UVB rays, X-Rays

  
• gene regulation


  the control of the level of gene expression

  
• constitutive genes


  genes that are always transcribed (e.g. amylase)

  
• Why are some genes regulated?

  so the body doesn't waste time producing molecules when they are not needed, and an overproduction of molecules can be toxic to the body
• 4 types of control mechanisms

  transcriptional control, post-transcriptional control, translational control, post-translational control
• transcriptional control

  controls the rate of transcription so not too many mRNA molecules are transcribed, mRNA stays inside the nucleus without any modifications
• examples of transcriptional control

  - access to promoters is provided by loosening DNA from histones

  - activator and repressor proteins bind to the promotor and impact the rate of transcription

  - methyl groups are added to cytosine bases so RNA cannot bind and transcribe
• post-transcriptional control

  controls modifications of mRNA while in the nucleus (does not allow it to be translated)
• examples of post-transcriptional control

  - Alternative Splicing of mRNAs (different combinations of introns are removed and remaining exons join together)

  - masking proteins bind to mRNA and inhibit further processing

  - rate of degradation of mRNA is dependent on the need of the cell for the gene product
• translational control


  controls how often mRNA is translated
• example of translational control


  variation of poly-a tail is related to the rate of translation
• post-translational control


  controls which proteins should become active
• example of post-translational control


  - processing occurs and the polypeptide is chemically modified to render an active protein

  - the presence of hormones may lengthen or shorten the length of time that a protein is functional

  - ubiquitin-tagged-proteins are degraded
• operon


  cluster of genes under the control of a single promoter

  
• inducer


  a signal molecule that triggers the expression of an operon's genes

  
• lac operon


  a gene system whose operator gene and three structural genes code for lactase production

  
• What is a repressor protein?


  a regulatory protein that binds to the operator of the operon and blocks transcription
• repressor protein for lac operon

  Lacl protein

  
• what happens if lactose is present?

  the Lacl protein binds to the lactose molecule to break it down into its monomers, changing the shape of the Lacl protein, so it cannot bind to the operator anymore. therefore, the RNA polymerase can transcribe mRNA since it is not blocked

  
• what happens when there is no lactose present?

  the repressor protein (Lacl protein) binds to the operator of the operon, blocking RNA polymerase from transcribing RNA, so the gene cannot operate

  
• what controls transcription speed?

  activator proteins