Genetics of Living Systems

• What is a gene mutation?


  A change in the sequence of DNA bases, which can disrupt protein synthesis, and cause a different protein to be coded for.
• What is a codon?


  A sequence of three nucleotides in DNA or RNA that codes for a specific amino acid during protein synthesis, whereby the bases do not overlap with one another.
• What is a degenerate?


  This is when there is more than one way to create and code for a given amino acid.
• What is the structure of a nucleotide?


  It consists of a sugar molecule, a phosphate group, and a nitrogenous base.
• What are the bases?


  Adenine, thymine, guanine, cytosine, uracil.
• What are the different types of mutation?


  Substitutions (point mutation), insertions, and deletions.
• What is a substitution (point mutation)?

  This is when one nucleotide (base) is swapped for another nucleotide, and changes the codon, causing a potential alteration to the amino acid; however the degenerate nature of the genetic code means the same amino acid could be coded for.
• What occurs if a different amino acid is coded for?

  A change is made to the primary structure of a protein that is coded for, and subsequently a different protein is synthesised with a different function.
• Why is it called a point mutation?


  If only one nucleotide is affected it is called a point mutation.
• What dictates the impact of the new amino acid on the protein synthesised?


  The position and involvement of the amino acid in R group interactions with the protein.
• What is an insertion?


  This is when an extra nucleotide is added, causing a frameshift mutation, due to every successive amino acid coded for after the insertion changing, and a different protein being made, as the sequences of bases are transcribed consecutively.
• What is a deletion?


  This is when a nucleotide is removed, causing this same frameshift mutation, as every successive amino acid coded for after the deletion is changed.
• What are the effects of a mutation?


  Neutral, harmful, beneficial.
• What is a neutral effect?


  This is when normal functioning proteins are still synthesised, and the phenotype of the organism is unchanged.
• What is a harmful effect?


  This is when proteins aren't synthesised or are non functional, and the phenotype of the organism are negatively impacted.
• What is a beneficial effect?


  This is when proteins are synthesised with a new and useful characteristic in the phenotype.
• What is an example of a beneficial effect of a mutation?


  A mutation in the protein present in the cell surface membrane of a human cell means that human immunodeficiency virus (HIV) cannot bind and enter these cells, making individuals immune to infection from HIV.
• What is an example of a harmful effect of a mutation?


  The majority of cystic fibrosis sufferers, have the condition due to a deletion of a triplet of base pairs; and huntington disease is caused by a stutter, caused by repeating sections of CAG sequences.
• Why do mutations cause an issue for the proteins coded for?

  Many proteins coded for by genes are enzymes which regulate metabolic pathways, and mutation can cause the primary structure to change, causing the active site to change and enzyme activity to slow or stop, causing protein denaturation.
• What are mutagens?


  These are chemical, physical, or biological agents which cause mutation; and while mutations occur naturally, mutagens can increase the liklehood.
• What are the categories of mutagens?


  Physical, chemical, and biological.
• What is an example of a physical mutagen?


  Ionising radiation (x-rays), which has the potential to break one or both DNA strands, some of which can be repaired but mutations may occur in the process.
• What is an example of a chemical mutagen?


  Deaminating agents which remove amine groups, and chemically alter DNA bases, changing the base sequence; chemicals in cigarette smoke and caffeine.
• What are examples of biological mutagens?


  Alkylating agents which are compounds that add an alkyl group, such as methyl or ethyl, to bases, resulting in incorrect pairing of bases during replication; bases analogs that are incorporated into DNA in replacement of the normal base; viruses which change base sequencing, as viral DNA is inserted into a genome.
• What is depurination and depyrimidination and what role do these processes have in mutation?


  The loss of a purine or pyrimidine base, which often occurs spontaneously, and often results in the insertion of an incorrect bases through complementary base pairing during DNA replication, due to the absence of a base.
• Which bases are purine bases and which are pyrimidine bases?

  PURINE - AG

  PYRIMIDINE - CT (U)
• What are free radical?


  These are unstable atoms that damage cells, and are oxidising agents that can affect the structures of nucleotides and disrupt base pairing during DNA replication.
• What are anticarcinogens?


  Antioxidants that have the ability to deem the effects of free radical ineffective, such as vitamin A, C, and E.
• What are housekeeping genes?


  The genes that code for the enzymes constantly required in the reactions of metabolic pathways.
• What is gene regulation?


  The control of gene expression.
• Why is gene regulation required?


  The entire genome of an organism is present prokaryote and eukaryote cells with a nucleus, including genes that aren't required by that cell.
• What role does gene expression have in growth and development?


  Protein based hormones required for growth and development are only required at certain times to carry out short lived responses, and are coded for by tissue specific genes, and the fluctuating demand of the synthesis of protein products can be met by the turning on or off genes.
• How do bacteria use gene regulation?


  They respond to internal and external change through gene regulation, expressing genes only when the product is needed and preventing resource waste.
• How do multicellular organisms use gene regulation?

  They respond to internal and external change through gene regulation, allowing coordination throughout the organism.
• How are genes regulated?


  Transcriptional, post transcriptional, translational, post translational.
• What are the forms of transcriptional control?


  Chromatin remodelling, histone modification, and lac operon.
• What is chromatin remodelling?


  The process of altering the structure of chromatin to allow access to DNA for gene expression.
• What do chromatins consist of?


  DNA is a long molecule that is wound around histone proteins in eukaryote cells in order to be packed into the cells nucleus, resulting in the formation of the DNA protein complex chromatin.
• Why does how tightly wound the DNA is around histones effect gene expression?


  If the DNA is tightly wound around the histones, the transcription of genes isn't possible as RNA polymerase can't access the genes, but if it is loosely wound they can be accessed, allowing them to be freely transcribed.
• What is tightly wound DNA around a histone called?


  Heterochromatin.