Chapter 7 Gene Expression and Control Part 1

Ribosomes are THAT important o Ricin is a deadly toxin found in castor-oil seeds. A dose as small as a few grains of salt can kill an adult. o 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 o 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. o 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 o In 2005, jars of banana baby food laced with ground castor-oil beans made the news.

Ribosomes are THAT important o So how is it that a poison that is so easily obtained could be so deadly? o Ricin is so toxic because it inactivates ribosomes, the organelles upon which amino acids are assembled into proteins in all living cells. o Because proteins are critical to all life processes, cells that cannot make them die very quickly. o Someone who inhales ricin typically dies from low blood pressure and respiratory failure within a few days of exposure.

The Nature of Genetic Information o You already know that DNA contains four letters (which are the nitrogen bases): A, G, T, and C. o The sequence of these four letters, one after the other, carries the information encoded by the DNA, called the genetic code. o The subsets of the information contained within this code are called genes. o A cell uses the base sequence of a gene to build and RNA molecule and eventually a protein product.

The Nature of Genetic Information o The first step in creating a protein product from a gene (DNA) is transcription. o During transcription, enzymes use the DNA sequence of a gene to assemble a strand of RNA.

The Nature of Genetic Information o RNA is similar to DNA in that both are chains containing four kinds of nucleotides. o However, while DNA is a double-stranded molecule, RNA consists of only a single strand. o 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. o Finally, while the sugar in DNA is deoxyribose, the sugar in RNA is ribose.

DNA vs. RNA

DNA vs. RNA: Homework 1  Complete a Venn Diagram to compare and contrast the structure and function of DNA and RNA.

The Nature of Genetic Information o Even though the structural differences in RNA and DNA seem small, the function of these two molecules varies greatly. o DNA’s only role is to store inheritable genetic information. o In contrast, cells make three different kinds of RNA molecules, each of which has a different function. o 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. o That message is encoded with the mRNA sequence by sets of three bases. These three letter “genetic words” are called codons.

Types of RNA

The Nature of Genetic Information o Like the words of a sentence, a series of these “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. o Translation occurs when the protein-building message in the mRNA is translated into a different language, the amino acid language of proteins. o The result is a polypeptide chain that will twist and fold, forming the secondary, tertiary, and quaternary structures of functional proteins.

Translation

The Nature of Genetic Information o 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. o This is called the Central Dogma of biology.

Gene Expression: Homework 2  List and describe the function of each of the 3 types of RNA.  What is the Central Dogma?  Briefly describe the processes of transcription and translation.