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Review of the Genetic Material Gene Expression

Review of the Genetic Material Gene Expression. Dr Maha Al- Sulaimani Department of Biochemistry. The Genetic Material/Definition . What is the genetic material?

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Review of the Genetic Material Gene Expression

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  1. Review of the Genetic MaterialGene Expression Dr Maha Al-Sulaimani Department of Biochemistry

  2. The Genetic Material/Definition • What is the genetic material? • The genetic material of a cell or an organism refers to those materials found in the nucleus, mitochondria and cytoplasm (DNA, proteins and RNA (in some viruses), which play a fundamental role in determining the structure and nature of cell substances, and capable of self-propagating and variation.

  3. The Genetic Material

  4. Genetic Material • Our bodies are made up of millions of cells. Each cell contains a complete copy of a person’s genetic plan or blueprint. • This genetic plan is packaged in the cells in the form of genes. • Chromosomes can be thought of as being made up of strings of genes. • The chromosomes, and therefore the genes, are made up of DNA.

  5. Genetic Material

  6. Genetic Material • Chromosomes consist of DNA chains twisted into the shape of a double helix and are located in the nucleus. • Since chromosomes come in pairs, so do genes. • Genes are also located in mitochondria that are randomly scattered in the cytoplasm of the cell.

  7. Genetic Material • In each of the approximate 20,000 genes, there is a piece of genetic information which guides our growth, development and health and is in the form of a chemical code, called the genetic code. • The genetic code in the DNA, is like a recipe book for the body to make proteins

  8. What is the Genetic Code? • DNA code is made up of Adenine (A), Guanine (G), Thymine (T) and Cytosine (C). • How many combinations? • The code needs to be complex enough to represent 20 different amino acids used to build proteins.

  9. How many combinations? • If one baserepresented one amino acid this would only be able to produce 4 different combinations: (A, C, G and U). • If pairs of bases represented each amino acid this would only be able to produce 4 x 4 = 16 combinations: (AA, AC, AG, AU, CA, CC, CG, CU etc).

  10. How many combinations? • If triplets of pairs represented each amino acid, this would be able to produce 4 x 4 x 4 = 64 combinations. • This is enough combinations to code for the 20 amino acids. • But is the code actually made of triplets?

  11. Yes, it is!! • Over 10 years biochemists synthesised bits of mRNA with different combinations. • Then they used them to synthesise polypeptides. • The results proved the logical answer was correct: the genetic code is made of triplets of bases called Codons.

  12. The Genetic Code • Each three-letter word (triplet) tells the cell to produce a particular amino acid that form proteins. • The sequence of three-letter words in the gene enables the cells to assemble the amino acids in the correct order to makeup a protein.

  13. The Genetic Code • The genetic code consists of the sequence of bases found along the mRNA molecule. • There are only four letters to this code (A, G, C and U).

  14. The Genetic Code

  15. The Genetic Code

  16. The Central Dogma • Proposed by Francis Crick in 1958. • The genetic code is expressed at the ribosome during protein synthesis in the cytoplasm. • The protein produced by the genetic information is what is influenced by natural selection.

  17. The Central Dogma • If a protein is modified, it cannot influence the gene that codes for it. • Therefore there is one way of flow of information: DNARNAProtein

  18. An important discovery • Retro viruses (e.g. HIV) carry RNA as their genetic information. • When they invade their host cell they convert their RNA into a DNA copy using reverse transcriptase. • Thus the central dogma is modified: • DNA↔RNAProtein

  19. Genetic Material • Different genes are active in different cell types, tissues and organs, producing the necessary specific proteins; some genes are ‘switched off’ and others are ‘switched on’.

  20. Genetic Material • Changes to the genetic code can mean that a particular protein is not produced properly, produced in the wrong amounts or not produced at all. • In some cases, the change in the genetic code can result in a genetic condition, affecting our growth, development and how our bodies work.

  21. Gene Expression/Definition • Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. • These products are often proteins, but in non-protein coding genes such as rRNA genes or tRNA genes, the product is a functional RNA.

  22. Ribozymes: Both genetic and catalytic • Certain forms of RNA have catalytic properties. • Ribozymes: • Ribosomes and snRNPs are ribozymes. • snRNPs: (small nuclear ribo-nucleoproteins), are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing pre-mRNA occurs.

  23. Ribosome: a ribozyme

  24. Ribozymes • The action of snRNPs is essential to the removal of introns from pre-mRNA, a critical aspect of post-transcriptional modification of RNA, occurring only in the nucleus of eukaryotic cells. • RNA could have been the first genetic information synthesizing proteins… • …and at the same time a biocatalyst. • Reverse transcriptase provides the possibility of producing DNA copies from RNA.

  25. snRNPs

  26. Gene Expression • The process of gene expression is used by all known life - eukaryotes (including multi-cellular organisms), prokaryotes (bacteria) and viruses- to generate the macromolecular machinery for life.

  27. Gene Expression

  28. Gene Expression: 2 Steps • Transcription:The synthesis of mRNA uses the gene on the DNA molecule as a template.This happens in the nucleus of eukaryotes. • Translation:The synthesis of a polypeptide chain using the genetic code on the mRNA molecule as its guide.

  29. Differences between RNA and DNA • Single v. Double strand. • Ribose v. deoxy ribose. • Uracil v. thymine. • 1 type v. 3.

  30. RNA/DNA

  31. Types of RNA • mRNA: Provides the plan for the polypeptide chain. • tRNA: “Translates” the message on the mRNA into a polypeptide chain. • rRNA: Provides the platform for protein synthesis.

  32. Types of RNA

  33. The paradox of DNA • It is a good medium for storing genetic material but… • DNA can do nothing for itself. • It requires enzymes for replication. • It requires enzymes for gene expression. • The information in DNA is required to synthesise enzymes (proteins) but enzymes are required to make DNA function!! • DNA is a very stable molecule when compared to RNA, why?

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