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Gene Structure and Gene Expression

Gene Structure and Gene Expression. Each chromosome contains one DNA molecule, which consists of roughly 80 million bases. How these extremely long molecules fit in a nucleus?. They are tightly associated with proteins to form nucleoprotein complex.

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Gene Structure and Gene Expression

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  1. Gene Structure and Gene Expression

  2. Each chromosome contains one DNA molecule, which consists of roughly 80 million bases. How these extremely long molecules fit in a nucleus? They are tightly associated with proteins to form nucleoprotein complex Nucleosome is the unit of nucleoprotein complex

  3. Gene 2 Gene 7 Gene 5 Gene 3 Gene 1 Gene 6 Gene 4 Chromosomes contain DNA, which contains genes, which are vital for life

  4. Gene Expression A gene is a unit of inheritance. It is a defined segment of DNA on a chromosome that codes for a specific protein (or RNA), which performs biological functions. DNA mRNA Protein Central dogma

  5. Upstream Downstream ORF 3’ 5’ 3’ 5’ Met-Ile-- ---- Val--------------- Structure of a gene mRNA AUG……CCAGUCAUU……UAG Protein

  6. UUU UUC AGA AGG Phenylalanine Arginine Genetic Code A set of three nucleotides constitute a genetic code AUG= Methionine

  7. ORF is also called coding region because it contains genetic codes Start Codon Stop Codon ATG TAA TAG TGA

  8. Upstream Downstream ORF 3’ 5’ Regulator Regulator Regulatory sequences Where? Leaf, Seed, Root When? seedling, adult, senescing stage Day, night, cold, hot. How much? Abundant, rare, medium

  9. Upstream regulatory sequence Upstream Downstream ORF 3’ 5’ Promoter= facilitates gene expression. Enhancer= enhances or boosts gene expression. Gene expression level minus enhancer plus enhancer

  10. Upstream Downstream ORF 3’ 5’ Downstream regulatory sequences Transcription stop signal

  11. Transcription A U G U A C U U G C A C G U A U G 5’ 3’ mRNA Formation of mRNA from the coding region or ORF is called transcription Sense 5’ 3’ A T G T A C T T G C A C G T A T G T A C A T G A A C G T G C A T A C Anti-sense 3’ 5’

  12. Translation Translation is the process by which the information in the mRNA is decoded into a polypeptide chain • There are 3 steps in the process of translation: • Chain initiation • Chain elongation • Chain termination

  13. 2. The initiation codon of mRNA binds with the respective tRNA Met AUG Chain Initiation 1. First mRNA binds to a ribosome. (Ribosomes are located in the cytoplasm, therefore translation takes place in cytoplasm and not in the nucleus). Nucleus Ribosome

  14. mRNA Ribosome Met

  15. Chain Elongation

  16. Chain Termination When a stop codon such as UAG is encountered, the mRNA and polypetide chain detach from ribosome and the process comes to end.

  17. Gene Expression in a Nutshell First mRNA is generated from the gene. mRNA moves to the ribosome in cytoplasm. The first tRNA loaded with methionine moves to the ribosome complex. The second tRNA loaded with a new amino acid (determined by the nucleotide sequence of mRNA) moves to the ribosome complex. The first amino acid (methionine) is joined to the second amino acid. tRNAs leave. Third tRNA loaded with a new amino acid moves in, and this new amino acid is joined with the elongating chain (peptide chain). The chain keeps elongating till the stop codon of the mRNA is encountered. At this point the peptide chain leaves ribosome complex to become a functional protein.

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