Genetics I. DNA, RNA and protein structure

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1 DNA, RNA and protein structure

2 Genetic information is stored in: - nucleus genome - mitochondria mitochondriome - chloroplasts plastome - cellular parasites (viruses) - genomic parasites (transposons)

3 Genetic information must be stored in a long molecule, like music in magnetophone tape. But which macromolecules store that information? - polysachharides? - proteins? - nucleic acids?

4 From 1910s to 1940s most scientists believed that genes were made of protein. Griffith and Avery showed that DNA is the genetic material of bacteria. Transforming principle = mixture from homogenized (broken) virulent bacteria: contains DNA, RNA, protein etc.

5 The structure of DNA (Deoxyribonucleic acid) O Deoxyribose Purines Pirimidines

6 The structure of DNA

7 The structure of DNA The polymerization reaction that results in synthesis of a DNA polynucleotide. Compare it with the sturcture of ATP (adenosine triphosphate):

8 The structure of DNA Erwin Chargaff showed that DNA from even very different organisms contains A and T, G and C in equal proportions. Erwin Chargaff Why???

9 The structure of DNA Rosalind Franklin ( )

10 The structure of DNA Three biologically-active DNA conformations A form - dehydration of B DNA drives it into the A form, - and this apparently protects DNA under conditions - such as the extreme desiccation of bacteria - shape that double-stranded RNA molecules - usually take (RNA-RNA double helix) - shape that RNA-DNA hybrid molecules take B form - normal DNA shape at physiological conditions Z form - may play a role in transcription process

11 The structure of DNA

12 The structure of DNA Hydrogen bonds between DNA bases are resopnsible for complementary base pairing of the opposite DNA strands

13 DNA replication Synthesis of new DNA molecules occures in 5 to 3 direction. It is catalized by an enzyme called DNA polymerase. Each new DNA molecule contains one strand from the old molecule.

14 The structure of RNA (Ribonucleic acid) (C) A deoxyribonucleotide (D) Thymine - RNA molecules are usually single-stranded. - They form secondary structures due to - complementarity to its own nucleotides. - First enzymes on the Earth were not protein - but RNA-enzymes (ribozymes).

15 RNA synthesis = transcription RNA molecules can be synthesised on DNA templates in a process similar to DNA replication (5 to 3 direction). It is catalysed by an enzyme called RNA polymerase. DNA synthesis RNA synthesis

16 Protein structure Peptide bond formation is a typical condensation reaction. It is catalysed by various proteins and RNA in ribosomes.

17 (E) Phe, Trp, and Tyr are so-called aromatic aminoacids

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19 There are four levels of protein organization (structure) Note that one protein can contain one or more polypeptides. Polipeptides within one protein can be coded by the same or by different genes. Quaternary structure One subunit = polypeptide Four subunits = protein

20 β α α Tertiary protein structure is stabilized by four types of interactions (bonds) β hemoglobin

21 Protein synthesis = translation

22 Standard genetic code 20 proteinogenic amino acids - Most amino acids are coded by 2-6 codons each. - Met and Trp are coded by only one codon each. - AUG codes for start (every protein begins with Met); UAA, UAG, UGA code for stop.

23 How many words are there in the genetic language? Turkish language: 29 letters, 1 word = 10 letters theoretically: 4.2 x actually: 7 x 10 5 (700,000) Atoms in the universe: Protein language : 20 letters, 1 word = 1000 letters 1.1 x

24 Non-standard genetic code Genetic code is not universal. trna properties in mitochondria are very different they recognize different codons.

25 Unusual proteinogenic amino acids These two amino acids are coded by UGA and UAG, respectively, which normally code for translational stop. Lysine Pyrrolysine UGA selenocysteine (selenoproteins, all organisms) UAG pyrrolysine (methanobacteria)

26 Thank you for your attention!