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Gene expression

Discover the fascinating world of gene expression and how it impacts the growth and development of organisms. Learn about the role of DNA, genetic material, and the process of transcription and translation. Explore topics such as genetic codes, gene mutations, and the influence of genes on traits and diseases.

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Gene expression

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  1. Gene expression

  2. Have you ever wondered how a frog grows? http://www.teara.govt.nz/en/frogs

  3. Native male frogs sit on the eggs and the young froglets hatch almost fully formed. http://www.erodent.co.uk/GardenPond/PondPhotos/Tadpole3w.jpg

  4. Why are their parts where they are?

  5. The answers lie in their cells.

  6. In particular – the answer can be found in their genetic material. A right handed helix

  7. Let’s revisit how we know that DNA is important. Streptococcus pneumoniae S: smooth (virulent) R: rough (avirulent)

  8. DNA is the genetic material - Griffith 1928

  9. Avery, MacLeod & McCarty 1944 • Chemically characterised the ‘transforming extract’ from virulent cells observed by Griffith • Removed the protein from ‘transforming extract’ • and it still transformed • Removed RNA • extract still transformed • Removed DNA • prevented transformation • Therefore transforming substance was DNA • Biochemically characterised the transforming extract, all its properties were consistent with DNA: • High Mw (centrifugation) • High charge (electrophoresis) • Characteristic UV absorbance • Chemical analysis, ratio of nitrogen to phosphorus

  10. Hershey-Chase 1952 • Left, T2 virus protein radioactively labelled 35S • Radioactivity outside • Right: T2 virus DNA radioactively labelled 32P • Radioactivity inside • THEREFORE genetic material infecting E.coli was DNA and not protein • Genes are made from DNA (except some RNA viruses)

  11. Genes are encoded within DNA

  12. What is a gene? Classical molecular gene: “A stretch of DNA sequence that codes for a particular protein that has a particular function”.(10,11) This can be an interrupted sequence within a chromosome.

  13. Other definitions of a gene Evolutionary gene: “any portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection”.(39) As such a gene is an inherited unit which is somewhere between a nucleotide and a chromosome. Systemic Concept: The gene is a combination of (one or more) nucleic acid (DNA or RNA) sequences, defined by the system (the whole cell, interacting with the environment, or the environment alone, in sub-cellular or pre-cellular systems), that gives origin to a product (RNA or polypeptide).(57)

  14. DNA DNA Precursors (deoxyribonucleotides) Replication RNA RNA Precursors (ribonucleotides) Transcription Protein Precursors (amino-acids) Protein Translation The central dogma (Genotype) (Phenotype)

  15. Transcription is the first step in the process. http://vcell.ndsu.nodak.edu/animations/transcription/advanced.htm

  16. How many genes does it take to make a person? 20,000-25,000 26,000 19,000 13,000 6,000 4,000

  17. DSCAM: one gene 38,016 mRNAs An immunoglobulin (Ig) superfamily member an axon guidance receptor Drosophila melanogaster Dscam gene contains 115 exons spanning ~60,000 bp 20 exons are constitutively spliced (open boxes) and 95 exons are alternatively spliced (shaded boxes). Alternatively spliced exons are orgnized into 4 clusters (exons 4,6, 9, 17) that contain 12, 48, 33 and 2 alternative exons each. Exons in each cluster are spliced in a mutually exclusive manner. Celotto & Graveley 2001 Genetics 159:599-608

  18. Immunoglobulin genes recombine within the DNA.

  19. So what if nuclei are the wrong shape? 249250621 bp 85 mm 48129895 bp 16 mm

  20. More or less matters! Patau Klinefelters (XXY) Turners (X) Edwards Down

  21. Albert Einstein (1955)

  22. 30-35% of cells are aneuploid ~4% aneusomy for chr 21 Affects survival, proliferation potential, and protein imbalances

  23. Copy number affects your weight Falchi et al. (2014) Nat Genetics 46:492-498

  24. How big is a vertebrate cell? ~6 µm http://medicalpicturesinfo.com/human-cell/

  25. Progeria (Hutchinson-Gilford progeria) Children with this disease typically have a stroke or heart attack caused by severe atherosclerosis at an average age of 13 years.

  26. Nuclei in Progeria are the wrong shape. Treating progeria cells with remodelin results in the nuclei reverting to the ‘normal’ shape.

  27. Shape directly affects the genes that are turned on. 31 of the altered genes affect vasculature and atherosclerosis 22 of the altered genes affect skeletal, limb and cartilage

  28. Defects in transcription can cause problems. Who amongst us is lactose intolerant?

  29. Lactase is encoded by a single gene LCT gene 17 exons Chr 2q21 -24 Kb G-A -14 Kb C-T A single mutation (C changes to T) causes lactase persistence

  30. The frequency of lactase persistence varies dramatically in different populations. Swallow; Annu Rev Genet 2003:37197-219

  31. Pastoralists and milk drinkers tend to have higher frequencies of lactase persistence than nonpastoralists Swallow; Annu Rev Genet 2003:37197-219

  32. Translation is important too.

  33. tRNA: the adapter

  34. What is the genetic code? Redundant codons are all synonyms for the same protein building block. Degenerate codons differ in their third positions; e.g. both GAA and GAG code for the amino acid glutamic acid.

  35. The genetic code is not always the same Cys Euplotes Trp Mycoplasma Spiroplasma Gln: Ciliates & Acetabularia Ser Candida Nons. Mycoplasma Nons. Micrococcus Nons. Micrococcus

  36. Some people can’t use Glucose.Typically they have mutations in GLUT1 These mutations occur because the codons are changed.

  37. GLUT1 mutations are often in helix 4 R126H R126L R153L

  38. Mitochondria in a mouse myoblast cell Mitochondria are red Actin filaments are green Nucleus is blue Image taken by James Markworth (Liggins Institute)

  39. Differences in the human nuclear and mitochondrial genetic codes Trp Met Stop

  40. Protein structure is important as well.

  41. Prions and Alzheimer’s disease are examples of pathological protein misfolding

  42. What’s different between these bears?

  43. Polar bears and Brown Bears Divereged ~479-343 kya

  44. Polar bears are adapted to high fat diets • Lipids are the predominant energy source • The polar bear has a lipid-rich diet (i.e. seals) throughout life. • Extreme cholesterol levels • Humans <5.2 mmol/l • Polar bear female: 8.58±1.31 (n=20) • Male: 6.61 2.06 (n=20) • Polar bear milk contains 27% fat • Up to 50% of individual’s body weight is adipose (subcutaneous and around organs) Modified from Liu et al. Population genomics reveal recent speciation and rapid evolutionary adaptation in Polar bears. Cell (2014): 157, 785-794 and Ombostad, I. (2012) Relationships between persistent organic pollutants (POPs) and plasma clinical-chemical parameters in polar bears (Ursus maritimus) from Svalbard, Norway. Student thesis (Trondheim, Norway: Norwegian University of Science and Technology).

  45. The environment is affecting the genes that Polar bears have. Basic unit of muscle

  46. Polar bears have seven missense substitutions in the LYST gene These mutations occur in the same region as ones in human disease

  47. Chediak-Higashi syndrome Autosomal recessive Mutation of lysosomal trafficking regulator (LYST)

  48. What do Chimo and a Polar bear have in common?

  49. Lyst affects melanosome maturation The organelle that is involved in synthesis, storage and transport of melanin

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