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Chapter 7. Gene Expression and Control Part 1. Ribosomes are THAT important. Ricin is a deadly toxin found in castor-oil seeds. A dose as small as a few grains of salt can kill an adult.
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Chapter 7 Gene Expression and Control Part 1
Ribosomes are THAT important • Ricin is a deadly toxin found in castor-oil seeds. A dose as small as a few grains of salt can kill an adult. • Even though ricin use as a weapon has been banned in most countries as a result of the Geneva Protocol, this poison is easily enough obtained that its use as a poison has been documented many times throughout history. Eating only 8 of these deceivingly beautiful seeds would be enough to kill an adult.
Ribosomes are THAT important • During the Cold War, a Bulgarian writer, Georgi Markov, who had defected to England was killed when an assassin used the tip of a modified umbrella to jam a small, ricin-laced ball into his leg. • Traces of ricin were found in a United States Senate mailroom and State Department building, as well as in an envelope addressed to the White House in 2004. • In 2005, jars of banana baby food laced with ground castor-oil beans made the news.
Ribosomes are THAT important • So how is it that a poison that is so easily obtained could be so deadly? • Ricin is so toxic because it inactivates ribosomes, the organelles upon which amino acids are assembled into proteins in all living cells. • Because proteins are critical to all life processes, cells that cannot make them die very quickly. • Someone who inhales ricin typically dies from low blood pressure and respiratory failure within a few days of exposure.
The Nature of Genetic Information • You already know that DNA contains four letters (which are the nitrogen bases): A, G, T, and C. • The sequence of these four letters, one after the other, carries the information encoded by the DNA, called the genetic code. • The subsets of the information contained within this code are called genes. • A cell uses the base sequence of a gene to build and RNA molecule and eventually a protein product.
The Nature of Genetic Information • The first step in creating a protein product from a gene (DNA) is transcription. • During transcription, enzymes use the DNA sequence of a gene to assemble a strand of RNA.
The Nature of Genetic Information • RNA is similar to DNA in that both are chains containing four kinds of nucleotides. • However, while DNA is a double-stranded molecule, RNA consists of only a single strand. • In addition, the nucleotides that make up RNA differ slightly from those that make up DNA. While DNA contains A, G, T, and C, RNA contains A, G, U, and C. • Finally, while the sugar in DNA is deoxyribose, the sugar in RNA is ribose.
The Nature of Genetic Information • Even though the structural differences in RNA and DNA seem small, the function of these two molecules varies greatly. • DNA’s only role is to store inheritable genetic information. • In contrast, cells make three different kinds of RNA molecules, each of which has a different function. • Even though all three RNA molecules are encoded by information in the DNA, only one of these RNA’s, messenger RNA (mRNA), carries the protein-building message from the DNA. • That message is encoded with the mRNA sequence by sets of three bases. These three letter “genetic words” are called codons.
The Nature of Genetic Information • Like the words of a sentence, a series of the se “genetic words” can form a meaningful package of information, resulting in a specific series of amino acids in a protein after the next, and last, step in the creation of a protein, called translation. • Translation occurs when the protein-building message in the mRNA is translated into a different language, the amino acid language of proteins. • The result is a polypeptide chain that will twist and fold, forming the secondary, tertiary, and quaternary structures of functional proteins.
The Nature of Genetic Information • The processes of transcription and translation together result in gene expression, the process by which genetic information encoded in the DNA is converted to RNA and then to a protein product. • This is called the Central Dogma of biology.
