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GENE EXPRESSION

GENE EXPRESSION. Gene Expression Our phenotype is the result of the expression of proteins Different alleles encode for slightly different proteins Protein variation is the basis for normal phenotypic variation - blue or brown eyes It is also the basis for abnormal phenotypes

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GENE EXPRESSION

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  1. GENE EXPRESSION

  2. Gene Expression Our phenotype is the result of the expression of proteins Different alleles encode for slightly different proteins Protein variation is the basis for normal phenotypic variation - blue or brown eyes It is also the basis for abnormal phenotypes - cystic fibrosis

  3. In the late 1930s, early 40s, Beadle and Tatum - working with a mold – Neurospora - observed that a mutation in a single gene caused the loss of a single enzyme, and that this resulted in a mutant phenotype This established that genes produce phenotypes through the action of proteins Awarded the Nobel Prize in Medicine in 1958

  4. Replication DNA Transcription RNA Nucleus Translation Protein . Cytoplasm Central Dogma

  5. Gene Expression Together transcription and translation are called gene expression. The genetic information encoded in the DNA of an embryo includes all of the genes needed to develop and maintain the organism. Different cell types express different subsets of genes.

  6. Transcription DNA is used as a template for creation of RNA using the enzyme RNA polymerase. DNA 5’ G T C A T T C G G 3’ 3’ C A G T A A G C C 5’

  7. Transcription RNA polymerase reads the nucleotides on the template strand from 3’ to 5’ and creates an RNA molecule that looks like the coding strand. DNA DNA coding strand 5’ G T C A T T C G G 3’ 3’ C A G T A A G C C 5’ • DNA template strand

  8. 3’ G U C A U U C G G 5’ RNA Transcription The new RNA molecule is formed by incorporating nucleotides that are complementary to the template strand. DNA DNA coding strand 5’ G T C A T T C G G 3’ 3’ C A G T A A G C C 5’ • DNA template strand

  9. RNA Usually single-stranded Has uracil as a base Ribose as the sugar Carries protein-encoding information Can be catalytic DNA Usually double-stranded Has thymine as a base Deoxyribose as the sugar Carries RNA-encoding information Not catalytic Two types of nucleic acids

  10. # of strands kind of sugar bases used

  11. Types of RNA Abbrev.Function mRNA Messenger RNA - encodes protein rRNA Ribosomal RNA - part of ribosome - used to translate mRNA into protein tRNA Transfer RNA - couples the region which binds the mRNAcodon and its amino acid

  12. rRNA is part of ribosome, used to translate mRNA into protein

  13. tRNA is a connection between anticodon and amino acid

  14. Transcription Initiation Occurs in three steps: Elongation Termination

  15. RNA processing mRNA transcripts are modified before use as a template for translation: • - Addition of capping nucleotide at the 5’ end • - Addition of polyA tail to 3’ end • Important for moving transcript out of nucleus • And for regulating when translation occurs Splicing - the removing internal sequences - introns are sequences removed - exons are sequences remaining

  16. RNA processing

  17. DNA template strand DNA C A G C A G T T T Transcription A A G U C A G U C Messenger RNA mRNA Codon Codon Codon Translation Polypeptide (amino acid sequence) Protein Lysine Serine Valine Translation • The process of reading the RNA sequence of an mRNA and creating the amino acid sequence of a protein is called translation.

  18. The genetic code There is a 3 to 1 correspondence between RNA nucleotides and amino acids. The three nucleotides used to encode one amino acid is called a codon. The genetic code refers to the codons that encode each amino acids.

  19. Codons of one nucleotide: A G C U Codons of two nucleotides: AA GA CA UA AG GG CG UG AC GC CC UC AU GU CU UU Can only encode 4 amino acids Can only encode 16 amino acids What is the correspondence between the mRNA nucleotides and the amino acids of the protein? Proteins are formed from 20 amino acids in humans.

  20. Codons of three nucleotides: AAA AGA ACA AUA AAG AGG ACG AUG AAC AGC ACC AUC AAU AGU ACU AUU GAA GGA GCA GUA GAG GGG GCG GUG GAC GGC GCC GUC GAU GGU GCU GUU CAA CGA CCA CUA CAG CGG CCG CUG CAC CGC CCC CUC CAU CGU CCU CUU UAA UGA UCA UUA UAG UGG UCG UUG UAC UGC UCC UUC UAU UGU UCU UUU Allows for 64 potential codons => sufficient!

  21. A codon of three nucleotides determines choice of amino acid

  22. The genetic code is non-overlapping

  23. The genetic code is universal The genetic code is degenerate - All known organisms use the same genetic code. (Rare organisms use one codon for an additional amino acid.) Some codons encode the same amino acid. e.g. GGU, GGC, GGA, and GGG all encode glycine Degeneracy is mostly at the third base of the codon. Some codons have additional functions • AUG encodes methionine. • Methionine can be used within a protein sequence and is often the first amino acid cueing the beginning of translation. • UAA, UAG, and UGA do not encode an amino acid. • These codons signal termination of the protein.

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