1. Gene Expression and Control Part 1
Chapter 7
Gene Expression and Control Part 1

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. DNA vs. RNA

9. 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.

10. Types of RNA

11. 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.

12. Translation

13. 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.