Nucleotide and Nucleic Acid Structure Lecture Note - Transcription

University:
Boston University
Course:
CAS BI 108 | Biology 2
Academic year:

2023
Views:

422

Pages:

21
Author:

Christine Knapp

Transcription Central Dogma The central dogma of molecular biology Replication Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA) • What is the relationship between a DNA sequence and an amino acid sequence? Central Dogma RNA is key to this process: • Messenger RNA (mRNA)—carries copy of a DNA sequence to site of protein synthesis at the ribosome • Transfer RNA (tRNA)—carries amino acids for polypeptide assembly • Ribosomal RNA (rRNA)—catalyzes peptide bond formation and provides structure for the ribosome Transcription Transcription components: • A DNA template for base pairings—one of the two strands of DNA • Nucleoside triphosphates (ATP,GTP,CTP,UTP) as substrates • An RNA polymerase enzyme Transcription process: • RNA polymerase unwinds DNA about ten base pairs at a time; reads template in 3’ to 5’ direction, synthesizes RNA in the 5’ to 3’ direction. • The RNA transcript is antiparallel to the DNA template strand, and adds nucleotides to its 3’ end. • NTPs incorporate NMP and PPi is a product! Transcription • Production of mRNA transcript by RNA polymerase Transcription: Where to start? 5' Flanking Coding Region 3'-flanking prokaryotes Promoter eukaryotes The consensus sequence for each element in human genes (N is any nucleotide) Transcription Translation Central Dogma The central dogma of molecular biology Replication Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA) • What is the relationship between a DNA sequence and an amino acid sequence? • The Code • The Adaptors (tRNA) • The Ribosome (rRNA + rProteins) Translation: The Genetic Code The genetic code: Specifies which amino acids will be used to build a protein Codon: A sequence of three bases—each codon specifies a particular amino acid. Start codon: AUG—initiation signal for translation. Stop codons: UAA, UAG, UGA—stop translation and polypeptide is released. Translation: The Genetic Code The genetic code is redundant. The genetic code is universal. Translation: tRNA tRNAs must deliver amino acids corresponding to each codon The conformation (three-dimensional shape) of tRNA results from base pairing (hydrogen bonding) within the molecule. 3‘-end is the amino-acid attachment site—binds covalently. At the other end (middle of the tRNA sequence) is the Anticodon—site of base pairing with mRNA. Unique for each species of tRNA. Translation: tRNA Translation: tRNA Template for mRNA – read 3’5’ tRNA anticodon N C Translation: Ribosome Ribosome: the workbench—holds mRNA and charged tRNAs in the correct positions to allow assembly of polypeptide chain. Ribosomes are not specific, they can make any type of protein. Translation: Protein Biosynthesis: Ribosome Structure Ribosomes have two subunits, large and small. When not active in translation, the subunits exist separately. • The small subunit (40S) has one ribosomal RNA (rRNA) (18S) and 33 proteins. • The large subunit (60S) has three molecules of rRNA (28S, 5.8S, 5S) and 49 different proteins. • Ribosomal subunits are held together by ionic and hydrophobic forces (not covalent bonds) (80S). Translation: Ribosome Translation: Protein Biosynthesis; Elongation EF-Tu GTP Decoding (GTP hydrolysis) Peptidyltransferase Translation: Protein Biosynthesis; Elongation ELONGATION Translocation (GTP hydrolysis) Central Dogma The central dogma of molecular biology Replication