upload2 - From Gene to Protein The information content of...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
From Gene to Protein The information content of DNA is in the form of specific sequences of nucleotides along the DNA strands. The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. Gene expression, the process by which DNA directs protein synthesis, includes two stages called transcription and translation. Proteins are the links between genotype and phenotype. ° For example, Mendel’s dwarf pea plants lack a functioning copy of the gene that specifies the synthesis of a key protein, gibberellin. ° Gibberellins stimulate the normal elongation of stems. A. The Connection between Genes and Proteins 1. The study of metabolic defects provided evidence that genes specify proteins. In 1909, Archibald Gerrod was the first to suggest that genes dictate phenotype through enzymes that catalyze specific chemical reactions in the cell. ° He suggested that the symptoms of an inherited disease reflect a person’s inability to synthesize a particular enzyme. ° He referred to such diseases as “inborn errors of metabolism.” Gerrod speculated that alkaptonuria, a hereditary disease, was caused by the absence of an enzyme that breaks down a specific substrate, alkapton.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
° Research conducted several decades later supported Gerrod’s hypothesis. Progress in linking genes and enzymes rested on the growing understanding that cells synthesize and degrade most organic molecules in a series of steps, a metabolic pathway. Beadle and Edward Tatum were finally able to establish the link between genes and enzymes in their exploration of the metabolism of a bread mold, Neurospora crassa . ° They bombarded Neurospora with X-rays and screened the survivors for mutants that differed in their nutritional needs. ° Wild-type Neurospora can grow on a minimal medium of agar, inorganic salts, glucose, and the vitamin biotin. Beadle and Tatum identified mutants that could not survive on minimal medium, because they were unable to synthesize certain essential molecules from the minimal ingredients. ° However, most of these nutritional mutants can survive on a complete growth medium that includes all 20 amino acids and a few other nutrients. Not all proteins are enzymes. ° Keratin, the structural protein of hair, and insulin, a hormone, both are proteins and gene products. Later research demonstrated that many proteins are composed of several polypeptides, each of which has its own gene. Therefore, Beadle and Tatum’s idea has been restated as the one gene–one polypeptide hypothesis.
Background image of page 2
Some genes code for RNA molecules that play important roles in cells although they are never translated into protein.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 08/11/2009 for the course SF wedf taught by Professor Adsfs during the Spring '09 term at Collin College.

Page1 / 26

upload2 - From Gene to Protein The information content of...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online