Genes in Action<br />
Gene Function<br />Structural genes<br />Become part of the structure & functioning of an organism<br />Regulatory genes<b...
Two types of gene regulation<br />Regulatory genes may code for a DNA-binding protein<br />These have a positively charged...
Homeotic Genes<br />“Master genes” that control embryonic development in  insects and vertebrates.<br />A malfunctioning h...
Homeotic Genes<br />In humans, homeotic genes fall in to 4 groups (Hox A,B,C & D).<br />These encompas 39 genes spread ove...
Gene Structure<br />The arrangement of base pairs (c) in a piece of double stranded DNA (d) will determine many things, su...
Gene Structure<br />Enzymes need to know when to start and stop reading a section of DNA.<br />If the base pairs were a se...
Gene Expression<br />Our DNA is like the master plan for building an organism<br />Genes are specific instructions on how ...
Gene Expression<br />In order to be expressed, DNA must be transcribed in to mRNA.<br />A<br />C<br />A<br />T<br />A<br /...
Transcription<br />After the complimentary strand is unzipped, the RNA is written against the template strand of DNA<br />...
Transcription: step-by-step<br />The enzyme RNA polymerase attaches to the DNA in the upstream (3’) region of the template...
Transcription: continued<br />Once RNA polymerase reaches the terminator sequence a hairpin loop forms in the mRNA, causin...
Post-transcription modification<br />The DNA in Eukaryotic genes is made up of ...<br />Introns (non-coding sequences)<br ...
Post-transcription modification<br />Introns are removed by a spliceosome, which is made up of a bundle of protein factors...
One gene, multiple products<br />Research reveals that a single gene is able to make a different product at different stag...
Alternative splicing of pre-mRNA<br />A) Intron retention<br />The final product can look quite different if not all intro...
Translation<br />The mature mRNA moves out of the nucleus, through a nuclear pore, in to the cytoplasm<br />Ribosome assem...
What is tRNA?<br />tRNA is a molecule consisting of a single strand of 76 RNA nucleotides<br />The 3 nucleotides at one en...
Codons with corres-ponding amino acids<br />The genetic code is universal<br />99.9% of species use the same triplet code ...
Prokaryotes vs Eukaryotes<br />Where transcription / translation occurs<br />Eukaryotes: nucleus then cyctoplasm<br />Prok...
Gene regulation in Prokaryotes<br />CASE  STUDY: THE LAC OPERON<br />Bacteria have groups of genes that are controlled tog...
The LAC Operon<br />Usually a repressor protein (produced by LAC regulatory gene) sits on the controlling region<br />When...
Not all genes produce proteins<br />Instead of mRNA, genes can also be transcribed as:<br />tRNA: then move out in to the ...
Mitochondrial DNA<br />In Eukaryotes, mitochondrial DNA (mtDNA) is a double-stranded circular molecule<br />In humans, it ...
Genes in Action
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Genes in Action

  1. 1. Genes in Action<br />
  2. 2. Gene Function<br />Structural genes<br />Become part of the structure & functioning of an organism<br />Regulatory genes<br />Control the action of other genes<br />ie. “switch genes on or off”<br />Or control rate of production of proteins<br />Can switch genes on or off in one of two ways<br />
  3. 3. Two types of gene regulation<br />Regulatory genes may code for a DNA-binding protein<br />These have a positively charged binding site that will enable it to bind to DNA<br />They will bind to a region near a gene and directly turn it on or off<br />Regulatory genes may code for a signalling protein<br />This will bind to a receptor on the cell membrane<br />Genes will be turned on or off via signal transduction<br />
  4. 4. Homeotic Genes<br />“Master genes” that control embryonic development in insects and vertebrates.<br />A malfunctioning homeotic gene in flies may result in wings, legs, antennae and halteres being absent, or appearing in places that they should not.<br />
  5. 5. Homeotic Genes<br />In humans, homeotic genes fall in to 4 groups (Hox A,B,C & D).<br />These encompas 39 genes spread over 4 chromosomes<br />Malfunction of HOXC8 results in an extra pair of ribs<br />Malfunction of HOXD13 results in an extra digit between digits 3 & 4 (often fused)<br />
  6. 6. Gene Structure<br />The arrangement of base pairs (c) in a piece of double stranded DNA (d) will determine many things, such as the coding and non-coding portions of DNA (a), and the length of a gene (b). Thus many representations of the same strand required.<br />
  7. 7. Gene Structure<br />Enzymes need to know when to start and stop reading a section of DNA.<br />If the base pairs were a sentence, regulatory genes may be likened to capital letters and full stops.<br />5’<br />3’<br />3’<br />5’<br />Regulatory <br />gene<br />START<br />STOP<br />Promoter<br />region<br />Terminator <br />region<br />
  8. 8. Gene Expression<br />Our DNA is like the master plan for building an organism<br />Genes are specific instructions on how to build one tiny part of the entire organism.<br />Genes are located on the DNA, in the nucleus of our cells<br />The mechanisms for making the products for which these genes code are in the cytoplasm<br />How does the message get out of the nucleus and in to the cytoplasm?<br />
  9. 9. Gene Expression<br />In order to be expressed, DNA must be transcribed in to mRNA.<br />A<br />C<br />A<br />T<br />A<br />G<br />G<br />C<br />T<br />T<br />G<br />T<br />A<br />T<br />C<br />C<br />G<br />A<br />
  10. 10. Transcription<br />After the complimentary strand is unzipped, the RNA is written against the template strand of DNA<br />A<br />C<br />A<br />T<br />A<br />G<br />G<br />C<br />T<br />U<br />G<br />U<br />A<br />U<br />C<br />C<br />G<br />A<br />1<br />2<br />
  11. 11. Transcription: step-by-step<br />The enzyme RNA polymerase attaches to the DNA in the upstream (3’) region of the template strand on the promoter sequence.<br />The double-stranded DNA helix unwinds<br />As RNA polymerase moves down the strand, complimentary RNA bases are put down in a 5’ to 3’ direction.<br />A methylated cap is added to the 5’ end of the mRNA<br />The transcribed portion of the helix recoils once it has provided a template for the mRNA bases<br />
  12. 12. Transcription: continued<br />Once RNA polymerase reaches the terminator sequence a hairpin loop forms in the mRNA, causing it to be released<br />Poly-A polymerase cleaves the end of the mRNA and synthesises a poly-A tail (adenine bases and proteins).<br />A single stranded molecule called pre-messenger RNA (pre-mRNA) is produced<br />
  13. 13. Post-transcription modification<br />The DNA in Eukaryotic genes is made up of ...<br />Introns (non-coding sequences)<br />Exons (coding sequences)<br />Prokaryotic DNA does not contain introns<br />The entire gene is copied during transcription, so it is necessary to the spice out the introns<br />Exon<br />Exon<br />Exon<br />Intron<br />Intron<br />
  14. 14. Post-transcription modification<br />Introns are removed by a spliceosome, which is made up of a bundle of protein factors called snerps (snRNP)<br />The introns are coiled in to a shape called a lariat and released<br />The remaining exons are then joined together. <br />
  15. 15. One gene, multiple products<br />Research reveals that a single gene is able to make a different product at different stages of development<br />Also, a single gene can make one type of product in one type of tissue and a different product in another type of tissue tissue<br />How is this possible?<br />The human genome contains approx. 25,000 genes<br />Yet there are approx. 120,000 recognised protein-coding mRNA sequences.<br />How is this possible?<br />
  16. 16. Alternative splicing of pre-mRNA<br />A) Intron retention<br />The final product can look quite different if not all introns are spliced out<br />B) Exon juggling<br />Exons can be recombined in a anumber of different combinations<br />
  17. 17. Translation<br />The mature mRNA moves out of the nucleus, through a nuclear pore, in to the cytoplasm<br />Ribosome assembles around mRNA and sequence of bases is read in blocks of 3 bases known as triplets ( = 1 codon)<br />A transfer RNA (tRNA) molecule with the complementary anticodon is brought in and attaches to the mRNA<br />The AUG triplet is the “start” codon<br />
  18. 18. What is tRNA?<br />tRNA is a molecule consisting of a single strand of 76 RNA nucleotides<br />The 3 nucleotides at one end form the anticodon<br />The other end forms a binding site for a specific amino acid molecule<br /><ul><li>Amino acyltRNAsynthase catalyses the linking of each amino acid to its carrier tRNA molecule</li></li></ul><li>Translation (continued)<br />Each carrier molecule adds its attached amino acid to the base of the growing chain<br />Not all codons code for a different amino acid<br />There are 64 different codons, that code for 20 amino acids<br />Translation continues until a “stop” codon is reached<br />
  19. 19. Codons with corres-ponding amino acids<br />The genetic code is universal<br />99.9% of species use the same triplet code for the same amino acid<br />
  20. 20.
  21. 21. Prokaryotes vs Eukaryotes<br />Where transcription / translation occurs<br />Eukaryotes: nucleus then cyctoplasm<br />Prokaryotes: cytoplasm<br />Speed at which it occurs<br />Slower in Eukaryotes due to necessity to move out to cytoplasm as well as time required to splice mRNA<br />Life span of mRNA<br />Prokaryotes: a few minutes<br />Eukaryotes: hours/days to allow time for p/t modification<br />Ribosomes<br />Eukaryotic ribosomes are larger and have a different rRNA to protein ratio<br />
  22. 22.
  23. 23. Gene regulation in Prokaryotes<br />CASE STUDY: THE LAC OPERON<br />Bacteria have groups of genes that are controlled together and are turned on/off as required<br />The LAC operon is a group of genes that produce the enzymes required to preak down lactose to glucose and galactose<br />The bacterium only wants to produce these enzymes when lactose is present.<br />
  24. 24. The LAC Operon<br />Usually a repressor protein (produced by LAC regulatory gene) sits on the controlling region<br />When lactose enters the cell it binds to the repressor, and the repressor releases from the DNA<br />The LAC genes will now start transcribing mRNA, which will enter a ribosome and produce the 3 enzymes required for lactose metabolism<br />When concentration of lactose in the cell decreases, the lactose is released from the repressor and it returns to inhibiting the operon<br />
  25. 25. Not all genes produce proteins<br />Instead of mRNA, genes can also be transcribed as:<br />tRNA: then move out in to the cytoplasm as a transfer molecule<br />rRNA: then move in to the cytoplasm to form part of a ribosome<br />The nucleolus is a region in the nucleus where rRNA is transcribed and stored until required<br />
  26. 26. Mitochondrial DNA<br />In Eukaryotes, mitochondrial DNA (mtDNA) is a double-stranded circular molecule<br />In humans, it encompasses only 16,568 base pairs and 37 genes in total.<br />Apart from the genes coding for tRNA and rRNA, the rest are involved in cellular respiration.<br />Mitochondrial DNA is inherited entirely along maternal lines.<br />
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