Cellular Control

• Define mutation

  A change in the genetic material which may affect the phenotype of the organism.
• Define point mutation

  a mutation affecting only one or very few nucleotides in a gene sequence.
• Define substitution

  a mutation where one or more nucleotides are substituted for another in a DNA strand
• Define deletion

  a mutations where one or more nucleotides are deleted and lost from the DNA strand.
• Define insertion

  a mutation where one or more extra nucleotides are inserted into a DNA strand
• Define frame shift

  The deletion or insertion of a nucleotide or nucleotides leads to a frame-shift mutationIt shifts the reading frame of the sequence of bases as it will change every successive codon from the point of mutation
• Define silent mutation

  when the change of a single DNA nucleotide within a protein-coding portion of a gene does not affect the sequence of amino acids that make up the gene's protein.
• Define nonsense mutation

  the substitution of a single base pair that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid.
• Define missense mutation

  Change in nucleotide sequence which changes the amino acid and alters the properties of the protein, two types: loss of function, gain of function
• Define gene mutation


  occur in single genes or sections of DNA
• Define chromosome mutation

  Chromosome mutations affect the whole chromosome or number of chromosomes within a cell
• Explain why a change in the sequence of nucleotides of a gene can affect the function of the protein produced from that gene.

  The sequence of nucleotides could be mutated to a new sequence that codes for a different amino acid triplet and therefore a different protein meaning the new protein won't carry out the same functions.
• Describe how a mutation can have a neutral effect, a harmful effect or a beneficial effect, and give an example of each.

  Mutations can be silent, causing no change to proteins for example a mutation of a sequence of nucleotides could lead to no change in sequence of amino acids as the genetic code is degenerate. They can have a harmful effect when the phenotypoe of an organism is affected in a negative way as proteins are no longer synthesised or they are synthesised but are non-functional. For example, nonsense mutations.They can have a beneficial effect when a protein is synthesised that results in a new and useful characteristic. For example, a mutation in a protein present in the cell surface membranes of human cells means HIV cannot bind and enter.
• State the 3 types of mutagen and give an example of each.

  Physical- X-raysChemical- Deaminating acidsBiological- Viruses
• Name and describe the 4 types of chromosome mutation.

  Deletion- a section of chromosome breaks off and is lost within the cellDuplication- sections get duplicated on a chromosomeTranslocation- a section of one chromosome breaks off and joins another non-homologous chromosomeInversion- a section of chromosome breaks off, is reversed, and then joins back onto the chromosome
• Describe and explain the possible effects of a substitution mutation.

  No effect- no effect on the phenotype as normally functioning proteins are still synthesised Damaging- the pehnotype is affected in a negative way because proteins are no longer synthesised or the proteins that are are non-functional. Beneficial- the protein that is synthesised results in a new and useful characteristic in the phenotype
• Describe and explain the possible effects of insertion or deletion mutations.

  Move or shifts the the reading frame of a sequence of nucleotides. This will change every successive codon from the point of mutation
• Define the terms "gene expression", and "epigenetics"

  Gene expression- When the genetic information in DNA is converted into instructions for making proteins Epigenetics- the control of gene expression by the modification of DNA
• Name and describe the four levels at which genes (or proteins) are regulated and give examples for each

  Transcriptional- genes can be turned off or on eg. chromatin remodellingPost-transcriptional- mRNA can be modified which regulates translation and the types of proteins produced eg. RNA processingTranslational- translation can be stopped or started eg. degradation of mRNAPost-translational- proteins can be modified after synthesis which changes their functions eg. folding or shortening of proteins
• Define the terms "chromatin", "heterochromatin" and "euchromatin"

  chromatin- uncondensed DNA in a complex with histonesheterochromatin- tightly wound DNA causing chromosomes to be visible during cell divisionEuchromatin- loosely wound DNA
• Describe how chromatin remodelling allows the expression of some genes but not others.

  Transcription is not possible when DNA is tightly wound so genes in Euchromatin can be easily transcribed whereas genes in Heterochromatin cannot.
• Describe how histone modification can affect gene expression.

  Histones can be modified to increase or decrease the degree of packing. Therefore the DNA less tightly packed can be transcribed whereas the DNA tightly packed cannot be transcribed
• Define the term "operon"


  A group of genes that are under control of the same regulatory mechanism and are expressed at the same time
• Draw and label a diagram to show the lac operon and its associated regulatory gene.

  
• Define the term "structural gene" and name the proteins produced from the structural genes in the lac operon

  Structural genes code for 3 enzymes and they are transcribed onto a single long molecule of mRNA. The enzymes are b-galactosidase, lactose permease and transacetylase
• Describe the roles of the regulatory gene, the structural genes, the operator region and the promotor region of the lac operon for the metabolism of lactose.


  The regulator gene codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose. The repressor protein binds to the operator and stops RNA polymerase binding to DNA and beginning transcription. RNA polymerase binds to the promoter region which releases the lactose/repressor protein complex from the operator region allowing transcription to begin.
• Explain how the lac operon works when lactose is absent from the growth medium.

  No lactose present to attach to the repressor protein so RNA polymerase cannot bind to the promoter region. Therefore no structural genes produced. This causes regulation.
• Explain how the lac operon works when lactose is present in the growth medium.

  Lactose binds to the repressor protein causing it to change shape so it can no longer bind to the operator. As a result RNA polymerase can bind to the promoter and start transcription of the structural genes.
• Describe the role of cAMP in control of the lac operon

  It speeds up the rate of transcription.
• Define intron

  regions of non-coding DNA
• Define exon

  regions of coding DNA
• Define pre-mRNA

  product of transcription
• Define mature mRNA

  Modified pre-mRNA that can bind to a ribosome and code for proteins.
• Define RNA processing

  preparing RNA to leave nucleus
• Define RNA editing

  The nucleotide sequence of mRNA molecules is changed through base addition, deletion or substitution
• Describe how pre-mRNA is modified to produce mature mRNA, where this occurs and the benefit of this modification process

  A cap is added to the 5' end and a tail is added to the 3' end. These both help to stabilise mRNA and delay degradation in the cytoplasm. The cap also aids binding of mRNA to ribosomes. Splicing occurs where the RNA is cut at specific points. Occurs in the nucleus
• Describe 3 mechanisms that can regulate protein synthesis at the translational level.

  Degradation of mRNA- the more resistant the molecule the longer it will last in the cytoplasm, a greater quantity of protein synthesised Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins. Activation of inhibitory factors which aid the binding of mRNA to ribosomes
• Describe the role of protein kinases in regulation of gene expression or protein activity.

  Catalyses the addition of a phosphate group to proteins, this changes the tertiary structure and so the function of the protein.
• Describe 4 ways in which proteins can be modified to provide post-translational control.

  Addition of non-protein groups such as carbohydrate chainsmodifying amino acids and the formation bonds folding or shortening of proteinsmodification by cAMP
• Define body plan

  relative positions of body parts