BIO 143 Chapter Notes - Chapter 12: Operon, Methionine, Intron

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8 Jun 2018
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BIO 143 STUDY GUIDE: Chapter 12
Chapter 12: Gene Expression and Regulation
I. How is the information in DNA used in a cell?
A. Most genes contain the information for the synthesis of a single protein
1. Genes provide information to make proteins
2. Proteins are the cell’s “molecular workers”
B. DNA provides instructions for protein synthesis via RNA intermediaries
1. Ribonucleic acid (RNA) carries the information in DNA necessary for making proteins
a. There are structural differences between DNA and RNA
i. RNA is single stranded
ii. RNA has the sugar ribose instead of deoxyribose
iii. RNA has the base uracil (U) instead of thymine (T)
2. DNA codes for the synthesis of the three kinds of RNA
a. mRNA
b. rRNA
c. tRNA
3. Messenger RNA carries the code for protein synthesis from DNA to ribosomes
a. RNA takes genetic information from the nucleus to the cytoplasm
4. Ribosomal RNA and proteins form ribosomes
a. The small subunit of the ribosome has binding sites for mRNA
b. The large subunit of the ribosome has binding sites for tRNA
5. Transfer RNA carries amino acids to the ribosomes
a. Every cell synthesizes at least one tRNA for each amino acid
b. Complementary base pairs between the tRNA anticodon and the mRNA codon ensure
that the correct amino acid is used to synthesize a protein
C. Overview: Genetic information is transcribed into RNA and then translated into protein
1. In transcription, the information contained in the DNA of a specific gene is copied into
mRNA, tRNA, or rRNA (This process occurs in the nucleus)
2. During translation, the mRNA base sequence is decoded into an amino acid sequence
a. tRNA molecules bring amino acids to the ribosome for assembly into proteins
3. Transcription is the process of copying DNA to RNA using the nucleotide “language”
4. Translation is the process of translating the nucleotide “language” into the “language”
of amino acids
D. The genetic code uses three bases to specify an amino acid
1. The genetic code translates the sequence of bases in nucleotides into a sequence of
amino acids in a protein
2. Codons are sequences of three bases that code for specific amino acids
3. Stop and start codons act as the “punctuation” for a mRNA sequence
a. The start codon (AUG) signifies the start of the mRNA message
b. The three stop codons (UAG, UAA, and UGA) signify the end of the mRNA message
4. Anticodons in the tRNA are complementary to the codons in the mRNA
a. The anticodons ensure that the correct amino acid is placed in the proper sequence in
the protein
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