Genes may be structural genes that encode polypeptides, or they may be nonstructural genes.

A eukaryotic structural gene contains two introns and three exons: exon 1-intron 1-exon 2-intron 2-exon 3. The 5? splice site at the boundary between exon 2 and intron 2 has been eliminated by a small deletion in the gene. Describe how the pre-mRNA encoded by this mutant gene would be spliced. Indicate which introns and exons would be found in the mRNA after splicing occurs.

What are the three stages of translation? Discuss the main events that occur during these three stages.

An mRNA has the following sequence: 5?-AUG UAC UAUGGG GCG UAA-3?. Describe the amino acid sequence of the polypeptide that would be encoded by this mRNA. Be specific about the amino-terminal and carboxyl-terminal ends.

Chapter 19 describes a blotting method known as Western blotting, which can be used to detect the production of a polypeptide that is translated from a particular mRNA. In this method, a protein is detected with an antibody that specifically recognizes and binds to its amino acid sequence. The antibody acts as a probe to detect the presence of the protein. In a Western blotting experiment, a mixture of cellular proteins is separated using gel electrophoresis according to their molecular masses. After the antibody has bound to the protein of interest within a blot of a gel, the protein is visualized as a dark band. For example, an antibody that recognizes the ?-globin polypeptide could be used to specifically detect the ?-globin polypeptide in a blot. As shown here, the method of Western blotting can be used to determine the amount and relative size of a particular protein that is produced in a given cell type.

Lane 1 is a sample of proteins isolated from normal red blood cells.

Lane 2 is a sample of proteins isolated from kidney cells. Kidney cells do not produce ? globin.

Lane 3 is a sample of proteins isolated from red blood cells from a patient with ?-thalassemia. This patient is homozygous for a mutation that results in the shortening of the ?-globin polypeptide.

Now here is the question. A protein called troponin contains 334 amino acids. Because each amino acid weighs 120 daltons (Da) (on average), the molecular mass of this protein is about 40,000 Da, or 40 kDa. Troponin functions in muscle cells, and it is not expressed in nerve cells. Draw the expected results of a Western blot for the following samples:

Lane 1: Proteins isolated from muscle cells

 Lane 2: Proteins isolated from nerve cells

 Lane 3: Proteins isolated from the muscle cells of an individual who is homozygous for a mutation that introduces a stop codon at codon 177