The Genetic Code and 3 types of RNA Notes 11/19/15

The Genetic Code  Cracking the genetic code, the language of DNA, required determining how the 4 letters (A, T, G, C) could encode more than 20 different amino acids.  Francis Crick and Sydney Brenner determined that the DNA is read in sets of 3 nitrogen bases called a triplet. In RNA it is called a codon.  Scientists identified that the triplet codes for a specific amino acid and that a specific amino acids codes for a certain protein.

 Their are 64 possible codons that will code for 20 different amino acids. - stop codons: 3 codons (UUA, UGA, UAG) in the genetic code used to terminate translation - start codon: the codon (AUG) used to signify the start of translation The Genetic Code

Codon Chart: (mRNA) 3 Stop Start

MUTATION  Changes in sequence of nitrogen bases (DNA) that results in a change in the amino acid sequence of a protein.  This can result in a different protein being made.

Significance of Mutations Some are harmful Sickle Cell Anemia Down Syndrome Some are beneficial Sickle Cell Anemia to Malaria Immunity to HIV Most are neutral Eye color Birth marks

3 types of RNA  DNA.  DNA is often called the blueprint of life.  In simple terms, the genetic code of DNA contains the instructions for making proteins within the cell called gene expression or protein synthesis.  The code for DNA must be first transcribed into a RNA molecule in order for the correct amino acid to be made.

Their are 3 main difference between DNA and RNA:  1. Number of Nucleotide strands  2. Type of Sugar Present in Nucleotide  3. Type of Nitrogen Bases used in Nucleotide

Number of Nucleotide strands  DNA is a double helix.  The DNA double helix has two strands twisted together.  RNA consist of a single strand of nucleotides.  Plays a key role in the production of proteins.

 Ribose  a 5-carbon sugar  Deoxyribose  a 5-carbon sugar Both molecules may be represented by the symbol below: Type of Sugar Present: DNAcontains the sugar:RNA contains the sugar:

12 Nitrogen bases Used  Adenine A  Cytosine C  Guanine G  Thymine T DNA has four different bases: RNA has four different bases:  Adenine A  Cytosine C  Guanine G  Uracil U adenine 5 carbon sugar Phosphate PO 4 Nitrogen base

3 Types of RNA:  1. Messenger RNA (mRNA) It carries the instructions for making a proteins from a gene (the DNA in the nucleus) and delivers it to the site of translation a ribosome. It is complementary copy of a segment of DNA. It is read in triplets called a codons.  2. Transfer RNA (tRNA) It carries amino acids to the ribosome where they are assembled into proteins. They have a 3-nitrogen base sequence that is complementary to the mRNA codon calledan anticodon.  3. Ribosomal RNA (rRNA) This part of the structure of a ribosome.

Gene Expression/ Protein Synthesis

Numbers 5 and 6: 5. Show how the following sequence of nitrogen bases is “read” by placing lines between the codons. T-T-T-T-G-C-G-C-G-A-C-A-T-G-C-C-G-T 6. Use the key provided to determine what amino acid is coded for by each codon shown above. Codon 1 = ? = ? Codon 2 = ? = ? Codon 3 = ? = ? Codon 4 = ? = ? Codon 5 = ? = ? Codon 6 = ? = ?

Genetic Code Notes 1.The genetic code is the language of DNA. 2.What are the letters of the genetic code language? A C G T 3.The letters are read in triplets, which are sequences of 3 nitrogen bases. 4.Each triplet codes for a specific amino acid, or start or stop codon. 5.A specific sequence of amino acids codes for a certain protein. 6.A mutation is a change in the sequence of nitrogen bases in a strand of nucleotides that results in a change in the amino acid sequence of a protein. This can result in a different protein being made which might be harmful, helpful, or neutral.

Three types of RNA 1.The genetic code of DNA includes the instructions for making proteins. This process for making proteins is called gene expression or protein synthesis. 2.In gene expression, the code on a DNA molecule must first be transcribed onto an RNA or ribonucleic acid molecule in order for the correct amino acid to be made. 3. Complete the chart below to compare/contrast a DNA molecule and a RNA molecule: DNARNA Number of nucleotide strands 21 Type of sugar presentdeoxyriboseribose Nitrogen base usedA,T,G,CA, U, G, C

3 types of RNA Notes 1.Messenger RNA (abbreviated) mRNA It carries the instructions for making proteins from the DNA in the nucleus to the ribosome. It is a complementary copy of a segment of DNA. It is read in triplets called codons. 2.Transfer RNA (abbreviated) tRNA It carries amino acids to the ribosome where they are assembled into proteins. They have a 3-nitrogen base sequence that is complementary to the mRNA codon called an anticodon. 3. Ribosomal RNA (abbreviated) rRNA This part of the structure of a ribosome.

5. Show the following sequence of nitrogen bases is “read” by placing lines between the codons. T-T-T-] T-G-C-] G-C-G]-A-C-A]-T-G-C]-C-G-T 6. Use the key provided to determine what amino acid is coded for by each codon shown above. Codon 1 = A A A = Lysine Codon 2 = A C G = Threonine Codon 3 = C G C = Arginine Codon 4 = U G U = Cysteine Codon 5 = A C G = Threonine Codon 6 = G C A = Alanine 7. The sequence of amino acids shown above is the beginning of a chain of amino acids that will eventually make a specific protein.

Mutation Examples

Gene Mutations  Point Mutations – changes in one or a few nucleotides 1.Substitution  THE FAT CAT ATE THE RAT  THE FAT HAT ATE THE RAT

Gene Mutations  Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function. 1.Insertion  THE FAT CAT ATE THE RAT  THE FAT HCA TAT ETH ERA T 2.Deletion  THE FAT CAT ATE THE RAT  TEF ATC ATA TET GER AT

Chromosome Mutations  Changes in number and structure of entire chromosomes Original Chromosome ABC * DEF 1.Deletion AC * DEF 2.Duplication ABBC * DEF 3.Inversion AED * CBF 4. Translocation ABC *JKL*GHI * DEF