Introduction to Transcription and Translation Flow of Information

Introduction to Transcription and Translation

Flow of Information �How does a gene’s encoded message become a trait? �DNA (genotype) proteins phenotype �DNA directs “protein synthesis” – also known as… “gene expression” �Each gene specifies a certain protein.

Basic Principles of Transcription and Translation �RNA (ribonucleic acid) is the link between DNA and protein synthesis. DNA –> RNA –> Protein �Key differences: � 1. single strand � 2. uses the base U (uracil) instead of T (thymine)… so U pairs with A � 3. has a ribose sugar

Basic Principles of Transcription and Translation �DNA is made of nucleotides. �Proteins are made of amino acids. �To transition from one language to the other, 2 major steps are required: transcription and translation.

Basic Principles of Transcription and Translation �Transcription = the synthesis of RNA under the direction of DNA An RNA copy (m. RNA) of the DNA carries the gene’s instructions to the protein-synthesizing machinery (ribosomes) �Translation = the synthesis of a polypeptide, under the direction of RNA Ribosomes facilitate the orderly linking of amino acids into peptide (protein) chains

Basic Principles of Transcription and Translation �Why an intermediate (RNA)? 1. Protection – original DNA copy stays inside the nucleus 2. Efficiency – many copies of a protein can be made simultaneously, and RNA transcripts can be used repeatedly �After the initial transcription of RNA, it must also go through RNA processing.

The Genetic Code �How do 4 nucleotide bases specify 20 amino acids? �Triplicate code: The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words. Each set of 3 bases specifies a certain amino acid. ▪ “Codons” = m. RNA base triplicates ▪ Genetic code was decoded by Marshall Nirenberg (1961)

The Genetic Code � Only one strand of DNA is used as the template for a given gene. � The m. RNA strand is complementary to the DNA. � For a given codon, it is generally understood to be written in the 5’ 3’ direction, but may be specified � Example: if a DNA strand is 3’-ACC-5’ then the RNA strand would read 5’-UGG-3’. � During translation, the sequence of m. RNA codons is decoded, “translated, ” into a sequence of amino acids making up a polypeptide chain.

The Genetic Code �Start and Stop codons begin and end translation. AUG = Start �There is redundancy but not ambiguity in the genetic code. �Multiple codons result in the addition of the same amino acid, but a given codon will always result in the addition of the same amino acid. �Cells read codons as three-letter words Reading frame is important

The Genetic Code �The genetic code is nearly universal! �Genes from one organism can be transplanted into another…

The Genetic Code �https: //www. youtube. com/watch? v=n. HM 4 U UVHPQM