Biology  5/e   Raven/Johnson
	Student   Online Learning Center

Structure of DNA: DNA is a double helix formed from two strands of nucleotides. Each strand is made up of deoxyribose sugar molecules linked by phosphodiester bonds and bases attached to each sugar molecule. The strands are linked, ladder fashion, by hydrogen bonds between the bases of each strand. The base cytosine pairs with guanine while the base thymine, pairs with adenine. The resulting "ladder" is twisted into a helix.

Genes: A gene is a DNA segment containing a nucleotide sequence that specifies one enzyme.

Transcription: Transcription is a process in which an RNA polymerase enzyme assembles an mRNA molecule complementary to the nucleotide sequence of the gene.

Primary transcripts and mRNA processing: A primary transcript is an mRNA molecule transcribed as a faithful complement to a gene. It contains introns that do not code for amino acids and exons that do code for amino acids. mRNA processing removes the introns and splices the exons together.

Translation: Translation is a process in which a ribosome assembles a polypeptide whose amino acid sequence is specified by the nucleotide sequence in the mRNA.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.