Unit 4: Molecular Genetics
Content Outline: Protein Synthesis (4. 2) Part 1
I. George Beadle and Edward Tatum (1934) A. They developed the one gene-one enzyme hypothesis. This hypothesis proposed that a single gene has the genetic information for making one enzyme. This is later changed to become the one gene - one polypeptide (protein) hypothesis, as enzymes are a type of polypeptide (protein).
II. Transcription (Means " the process of making a working copy of an original". ) A. This process is the making of a recyclable, workable copy of DNA in the form of RNA. (The recyclable copy will become known as mRNA messenger RNA. It is a recyclable copy of the "Million Dollar DNA Blueprint." ) 1. mRNA is synthesized (made) by an enzyme called RNA Polymerase.
2. The message (mRNA) will be sent to the construction site (ribosomes) for building the protein.
3. RNA nucleotides use Ribose instead of Deoxyribose as the five-carbon sugar.
4. In RNA, Uracil replaces Thymine. (Thymine can't exit nuclear pores. Remember, ribosomes are out in the cytoplasm, so Thymine needs to be substituted by Uracil. ) 5. mRNA is a single-stranded molecule; therefore, it is less stable than DNA.
B. DNA serves as a template (guide) for making the mRNA. A = U and C = G. (Still can use Chargaff's Rule. ) C. Transcription is considered the first part of Protein Synthesis.
III. Translation (Means "The process of taking from one language and changing to another language". ) A. In this process, the cell is turning nucleotide language (DNA/RNA) into the amino acid language to make proteins. Remember, amino acids are the building blocks of proteins.
B. This process occurs at the ribosome. The ribosome has a nickname, "the Translator." It is also considered a "construction site" since the cell is building a protein using the copied "blueprint" that was provided.
C. Translation is considered the second part of Protein Synthesis.
IV. Codon ("A. K. A Triplet Code") - This is the RNA language that will be translated into polypeptides.
A. Codons are a "three letter" or three-nucleotide sequence of RNA. (It is determined by the template strand of DNA/ Important Blueprint Information, but is read on the RNA! The mRNA is being translated, not the DNA. ) 1. The codons must be read 5' 3'on the mRNA! (Because this is how the mRNA was made. You do not write a sentence and then read it backward, do you? It would make no sense. ) B. RNA Codon Chart for Amino Acids (Contains the 20 known amino acids for living organisms. ) 1. There are four essential things you need to know about the genetic code (RNA Codon Chart) a. The RNA referred to is mRNA, and it must be read in a 5' 3 orientation.
b. Each 3-letter codon (e.g., GCU) codes for one, and only one, amino acid.
c. Most amino acids have more than one codon.
d. Therefore, the genetic code is redundant, but it is not ambiguous.
2. 61of the 64 possible codons (4 = 64) codes for an Amino Acid.
a. 4 refers to the four nucleoti...
