Basic Principles of Transcription and Translation - Computer ...

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5′ Protein snRNA RNA transcript (pre-mRNA) Exon 1 Intron Exon 2 5′ snRNPs Spliceosome components 5′ Spliceosome mRNA Exon 1 Exon 2 Other proteins Cut-out intron The roles of snRNPS and spliceosomes in pre mRNA splicing. The diagram shows only a portion of the pre mRNA transcript, additional introns and exons lie downstream from the pictured ones here. 1) Small nuclear ribonucleoprotein (snRNPs) and other proteins form a molecular complex called a spliceosome on a pre mRNA molecules containing exons and introns. 2) Within the spliceosome snRNA base pairs with nucleotides at specific sites along the intron. 3) The spliceosome cuts the pre mRNA releasing the intron and at the same time splices the exons together. The spliceosome then comes apart releasing mRNA which now contains only exons. Ribozymes Ribozymes are catalytic RNA molecules that function as enzymes and can splice RNA The discovery of ribozymes rendered obsolete the belief that all biological catalysts were proteins Three properties of RNA enable it to function as an enzyme It can form a three-dimensional structure because of its ability to base pair with itself Some bases in RNA contain functional groups RNA may hydrogen-bond with other nucleic acid molecules
The Functional and Evolutionary Importance of Introns Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing Such variations are called alternative RNA splicing Because of alternative splicing, the number of different proteins an organism can produce is much greater than its number of genes Proteins often have a modular architecture consisting of discrete regions called domains In many cases, different exons code for the different domains in a protein Exon shuffling may result in the evolution of new proteins
Page 1 and 2: The Flow of Genetic Information Th
Page 3 and 4: TRANSCRIPTION DNA mRNA (a) Bacteria
Page 5 and 6: The Genetic Code How are the instr
Page 7 and 8: Cracking the Code All 64 codons we
Page 9 and 10: Molecular Components of Transcripti
Page 11 and 12: RNA Polymerase Binding and Initiati
Page 13 and 14: Eukaryotic cells modify RNA after t
Page 15: 5′ Exon Intron Exon Intron Pre-mR
Page 19 and 20: Polypeptide Trp Phe Ribosome Amino
Page 21 and 22: Amino acid P P P ATP Adenosine Amin
Page 23 and 24: Building a Polypeptide The three s
Page 25 and 26: The elongation cycle of translation
Page 27 and 28: Growing polypeptides Completed poly
Page 29 and 30: Polypeptide synthesis always begins
Page 31 and 32: Type of RNA Small nucleolar RNA (sn
Page 33 and 34: RNA polymerase RNA polymerase Polyr
Page 35 and 36: Individual bacteria respond to envi
Page 37 and 38: Eukaryotic gene expression can be r
Page 39 and 40: CYTOPLASM mRNA in cytoplasm Degrada
Page 41 and 42: Histone tails DNA double helix Amin
Page 43 and 44: Epigenetic Inheritance Although th
Page 45 and 46: The Roles of Transcription Factors
Page 47 and 48: Mechanisms of Post-Transcriptional
Page 49 and 50: Initiation of Translation The init
Page 51 and 52: Noncoding RNAs play multiple roles
Page 53: Chromatin Remodeling and Silencing

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