Transcript RNA
From gene to protein Premedical biology RNA chemically similar to DNA, except it contains ribose instead of deoxyribose and has uracil instead of thymin RNA molecule genes (eukaryotic) are thousands nucleotides long almost always consist of a single strand less stable RNA some molecules are able to self-replicate mistakes in replication – variability = differentiation of RNA family of closely related RNA sequencies some molecules are able to self-catalysate First genes were RNA molecules that polymerized abiotically and replicated themselves autocatalytically Ribosyms auto-replicating activity RNA molecules with enzymatic activity (ribosome, spliceosome) Coenzymes non-protein components in enzymes many of them are derived from nucleotides some coenzymes are ribonucleotids, rRNA, mRNA Transcription • Synthesis of RNA under the direction of DNA • Information is simply copied from one to another according to complementarity of bases • enzyme RNA polymerase • the beginning = promotor and initial code • transcription factors, terminator Promotor Typical promoter region for a protein-coding eukaryotic gene. RNA processing • the template strand is used as a template for RNA synthesis • The transcript is pre-mRNA primary transcript (eukaryotic cells) • 7methyl Guanosin cap is added immediately to 5‘ end • for protection from degradation by hydrolytic enzymes and „attach“ sign for ribosomes • poly(A) tail - polyadenylation of 3‘ end • inhibit degradation of the RNA RNA processing • exons = encoding parts • introns = non-encoding parts cutted out • cut and paste job = splicing • during the RNA processing is created messenger RNA – mRNA • snRNPs = spliceosome • Regulation Genetic code nucleotide triplets specify amino acids • 4 nucleotides specify 20 amino acids • triplet code – three nucleotide • according to base-pairing rules the mRNA base triplets are called codons • shared by the simplest bacteria after the most complex plants and animals • genetic code is almost universal • the genetic code must have evolved very early in the history of life • In bacteria is transcription and translation coupled at the same time • translation of eukarytes occurs in cytoplazm • Each codon along mRNA specifies which one of the 20 amino acids will be incorporated • AUG for methionin and it is Initial codon termination codons: UAG, UGA, UAA (stop signals) • 61 of 64 triplets code for 20 amino acids • There is redundancy, and it is not random • codon of the same amino acids differ in third base of triplet • one tRNA exist for each mRNA codon, but number of tRNA is 45, some tRNA have anticodons, that can recognize two or more different codons. • correct a reading frame tRNA • mRNA – series of codons • Interpreter is transfer RNA – tRNA • transfer amino acid to a ribosome • nucleotide triplet called anticodon (in tRNA) links a particular mRNA codon • amino acid is added to the growing end of a polypeptide chain in ribosome • amino acid is joined to tRNA by specific enzyme aminoacyltRNA synthetase - 20 these enzymes • L-shape of tRNA three-dimensional structure Aminoacyl tRNAsynthetase joins a specific amino acids to a tRNA - covalent attachment of amino acids to its tRNA - hydrolysis of ATP Ribosomes • facilitate specific coupling of tRNA anticodons with mRNA codons • subunits: proteins and ribosomal RNA • made in nucleolus (eu) Translation Initiation, elongation, termination specific fators, GTP Peptide bond – new amino acid and carboxyl end Iniciation factors, Elongation factors Termination Polyribosomes Polyribosomes (or polysomes) are a cluster of ribosomes, bound to a mRNA molecule, read one strand of mRNA simultaneously. Coupled transciption and translation in bacteria Comparing protein synthesis in prokaryotes and eukaryotes • very similar but with certain differencies • different polymerases, euk. depends on transcription factors • ribosomes are different – simultaneously transcribe and translate the same gene and protein can quickly diffuse • nuclear envelope segregates transcription and translation • processing stages provides ways to regulate and coordinate proteosynthesis and gene expression in the eukaryotic cells From polypeptide to functional protein • Coiling and folding are spontaneous actions • Genes determines the primary structure, the primary structure determines conformation • Chaperones • Posttranslational modifications: certain amino acid are modified by attachment of sugars, lipids, phosphate groups…………….. • Two or more polypeptides may join to become the subunits of a protein Protein structures Primary structure: the amino acid sequence Secondary structure: local structures stabilized by hydrogen bonds. The most common examples are the alpha helix, beta sheet and turns. Tertiary structure: the overall shape of a single protein molecule; most commonly the formation of a hydrophobic core, but also through salt bridges, hydrogen bonds, disulfide bonds. The tertiary structure is what controls the basic function of the protein. - as synonymous with the term fold Quaternary structure: the structure formed by several protein molecules (polypeptide chains), usually called protein subunits in this context, which function as a single protein complex. 3-dimensional structures of protein Thank you for your attention Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.