Lecture DetailsEdit

Rod Devenish; Week 3 MED1011; Biochemistry

Lecture ContentEdit

One cell can transform another; dead bacterial cells can genetically transform living bacterial cells. To test for 'transforming substance' treat different samples with DNAase, RNAase and protease, whatever one doesn't transform is the substance. Viruses transfer their genome by inserting DNA into a host cell. Viral genes take over the host's machinery which synthesises new viruses. The bacterium bursts, releasing 200 viruses.

DNA is composed of nucleotides, which contain a nitrogenous base (adenine, cytosine, guanine, thymine), a sugar and a phosphate. GC and AT have equal amounts as they are paired. dd prefix indicates modification of DNA, often to add flourescent markers. AG are purines (large), CT are pyrimidines.

X ray crystallography provided a sense of the structure of DNA, determined by the diffraction of X rays passed through DNA. Watson and Crick interpreted the crystallography. DNA is double stranded helix, diameter is uniform, twist is right handed, two strands are antiparallel. The sugar/phosphate backbones of each strand coil around the outside of the double helix. H bonds hold the two strands together; AT has 2 bonds and GC has 3. Phosphate groups link 3' ends of one molecule to 5' of the other. 5' end has phosphate group at one end, 3' has free hydroxyl group.

DNA is 3m long but nucleus is 5um in diameter. The DNA is segmented into chromosomes. Chromosomes also contain proteins called histones which regulate transcription. Chromatin is DNA/protein complex. It condenses during mitosis and meiosis. DNA in chromatin is wound around histones to create nucleosomes; which each have a core of 8 histone molecules (2 H2A, H2B, H3 and H4) with 146 base pairs of DNA wrapped around it. H1 clamps the DNA to the core and facilitates the next level of packaging. DNA folds repeatedly, packing within the nucleus. Histones have tails that allow them to interact with other molecules.

RNA is single stranded, uses ribose and base uracil rather than thymine.

Central dogma is DNA > RNA > polypeptide- DNA is transcribed to RNA and translated to proteins. Some viruses go against this by transcribing RNA to DNA before genetic material can be expressed. Other RNA viruses exclude DNA altogether and go from RNA to protein.

Coding sequences are exons and quiescent internal sequences are introns. Noncoding flanking sequences also exist that interfere with transcription (promotors, start and end codons).

Almost 2/3 of eukaryotic genes are related that are similar and code for similar proteins. Pseudogenes are almost identical to some expressed genes, but are rarely transcribed.

Globin genes have 3 alpha genes on chromosome 16 and 5 beta genes on chromosome 11. There are also alpha and beta pseudogenes. Fetal haemoglobin is alpha/gamma, infant/adult is alpha/beta.


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