life11e_ch14

Three types of RNA have roles in the information flow from DNA to protein

There are numerous types of RNA. Three of them have vital roles in gene expression.

MESSENGER RNA AND TRANSCRIPTION When a protein-coding gene is expressed, one of the two DNA strands in the gene is transcribed to produce a complementary RNA strand, which is then processed to produce messenger RNA (mRNA). In eukaryotic cells, the mRNA travels from the nucleus to the cytoplasm, where it is translated into a polypeptide (Focus: Key Figure 14.2). The nucleotide sequence of the mRNA determines the ordered sequence of amino acids in the polypeptide chain, which is built by a ribosome.

focus: key figure

Figure 14.2 From Gene to Protein This diagram summarizes the processes of gene expression in eukaryotes. Note that the nucleus is typically about ¼ the size shown here.

Question

Q: In general, how would this diagram be different for a prokaryotic cell?

Prokaryotic cells lack a nucleus, so transcription and translation are not spatially separated.

Activity 14.1 Eukaryotic Gene Expression

www.life11e.com/ac14.1

RIBOSOMAL RNA AND TRANSLATION The ribosome is essentially a protein synthesis factory composed of multiple proteins and several ribosomal RNAs (rRNAs). One of the rRNAs catalyzes peptide bond formation between amino acids, to form a polypeptide.

TRANSFER RNA MEDIATES BETWEEN mRNA AND PROTEIN Another type of RNA called transfer RNA (tRNA) can both bind a specific amino acid and recognize specific sequences of nucleotides in mRNA. It is the tRNA that recognizes which amino acid should be added next to a growing polypeptide chain.

Media Clip 14.1 Protein Synthesis: An Epic on a Cellular Level