Chapter 13

• RNA is a polymer consisting of nucleotides joined together by phosphodiester bonds.
• Each RNA nucleotide consists of a ribose sugar, a phosphate group, and a nitrogenous base.
• In contrast to DNA, RNA contains the base uracil and is usually single stranded, which allows it to form secondary structures.
• Cells possess several different classes of RNA. Ribosomal RNA is a component of the ribosome, messenger RNA carries coding instructions for proteins, and transfer RNA helps incorporate amino acids into a polypeptide chain.
• The template for RNA synthesis is single-stranded DNA. RNA synthesis is complementary and antiparallel to the DNA template strand in transcription. A transcription unit consists of a promoter, an RNA-coding region, and a terminator.
• 1. RNA polymerase in bacterial cells consists of a core enzyme, which catalyzes the addition of nucleotides to an RNA molecule and other subunits. The sigma factor controls the binding of the core enzyme to the promoter.
• Eukaryotic cells contain multiple types of RNA polymerases
• The process of transcription consists of three stages: initiation, elongation, and termination.
• Transcription begins at the start site, determined by a promoter's consensus sequences. A short stretch of DNA is unwound near the start site, RNA is synthesized from a single template strand of DNA, and the DNA is rewound at the lagging end of the transcription bubble.
• RNA polymerases are capable of proofreading. There are frequent pauses in the process of transcription.
• RNA synthesis ceases after a terminator sequence has been transcribed.
• 1. Bacterial cells have two types of terminators: rho-independent terminators and rho-dependent terminators.