Cell Bio Ch 7

Ribonucleic acid (RNA)

Molecule produced by the transcription of DNA; usually single-stranded, it is a polynucleotide composed of covalently linked ribonucleotide subunits. Serves a variety of informational, structural,
catalytic, and regulatory functions in cells

gene

a segment of DNA that directs the
production of a particular protein or
functional RNA molecule

Gene expression

the process by which a gene makes a product that is useful to a cell or
organism by directing the synthesis of a
protein or an RNA molecule with a
characteristic activity

genes can be expressed at different

levels

RNA is a linear polymer made of

four different nucleotide subunits linked together by phosphodiester bonds

Chemical differences between RNA and DNA

RNA uses the sugar ribose, RNA uses the base Uracil

Structural differences between DNA and RNA

• RNA is largely single stranded (but not always)
• RNA can fold into a variety of shapes

Functions of RNA

• Conveys information between DNA and
protein
• Forms the core of ribosomes
• Shuttles amino acids to the ribosomes
• Some act as enzymes
• Others have more specialized roles

Transcription begins with

opening of a small portion of DNA to expose the bases on the strands

RNA polymerase

The enzyme responsible for adding
ribonucleotides to the growing chain

transcription produces RNA that is complementary to

one strand of DNA

messenger RNAs (mRNA)

code for proteins

ribosomal RNAs (rRNA)

form the core of the ribosome’s structure and catalyze protein synthesis

MicroRNAs (miRNA)

regulate gene expression

transfer RNAs (tRNA)

serve as adaptors between mRNA and amino acids during proteins synthesis

small interfering RNAs (siRNA)

provide protection from viruses and proliferating transposable elements

long non coding RNAs (lncRNA)

act as scaffolds and serve other diverse functions, many of which are still being discovered

other noncoding RNAs

used in RNA splicing, gene regulation, telomere maintenance, and many other processes

Why is RNA allowed to not proofread

its temporary, can produce de novo

promoter

DNA sequence that indicates where RNA polymerase should bind to initiate
transcription

sigma factor

subunit of RNA polymerase in bacteria that recognizes the promoter