Lecture 3: Genes and Proteins 2024-2025

Lecture 3 Genes and Proteins  Learning objectives Appreciate how the genetic code was deciphered. Develop a basic molecular understanding of how genetic information is transcribed and translated. “Inborn Errors of Metabolism." The first person to suggest that...

Lecture 3 Genes and Proteins  Learning objectives Appreciate how the genetic code was deciphered. Develop a basic molecular understanding of how genetic information is transcribed and translated. “Inborn Errors of Metabolism." The first person to suggest that genes dictate phenotype. Alkaptonuria: urine turns black on air exposure, tyrosine and phenylalanine not broken down 1909 He suggested that genes make enzymes Sir Archibald Garrod (1857-1936)  Prototroph – can synthesise all its amino acids for growth auxotroph – lost the ability to synthesise certain substances required for its growth Minimal medium: agar, inorganic salts, glucose, biotin Complete medium: minimal supplemented with amino acids One Gene One Enzyme hypothesis (Beadle and Tatum) Used bread mould Neurospora crassa Minimal medium: agar, inorganic salts, glucose, biotin Not all proteins are enzymes Not all proteins are monomeric Myoglobin - monomeric Haemoglobin - tetrameric One gene - one polypeptide hypothesis  Central dogma Exception: In RNA viruses, RNA Via the enzyme reverse transcriptase DNA Flow of genetic information in cell  The triplet code 20 aa found in cellular proteins 4 nucleotides give 64 possible 3 letter “words” The Genetic Code Nirenberg and Matthaei 1961 Why shouldn’t this experiment have worked? exon exon Stages of Transcription  1 A eukaryotic promoter includes a TATA box Transcription Promoter Initiation in Non-Template Eukaryotes 5 3 3 5 TATA box Start point Template DNA strand 2 Several transcription factors must Transcription bind to the DNA before RNA factors polymerase II can do so. 5 3 3 5 3 Additional transcription factors bind to the DNA along with RNA polymerase II, forming the transcription initiation complex. RNA polymerase II Transcription factors 5 3 3 5 5 RNA transcript Transcription initiation complex https://youtu.be/WsofH46 RNA Processing and Splicing The Synthesis of Protein Structure of Transfer RNA (tRNA) Aminoacyl-tRNA synthetase Base Pairing Wobble Synthesis of a polypeptide The elongation cycle of translation  The termination of translation Click the link to watch an animation on protein synthesis - https://youtu.be/5bLEDd-PSTQ Just to note, this video is slightly incorrect by not depicting the E site. Polyribosom es  Proteins Proteins perform a wide range of biological functions: As enzymes they catalyse reactions. Carrier proteins transport molecules across membranes. Antibodies defend against disease. Structural proteins support cells and tissues. Hormones transmit information. Transport proteins such as haemoglobin carry oxygen. Contractile proteins enable muscles to contract.