YIJC [H2] CI2.5 Gene Expression and Regulation II (N)(S)(wo checkpoint answers)

2024 JC1 BIOLOGY LECTURE NOTES CORE IDEA 2: GENETICS AND INHERITANCE TOPIC 2.5: GENE EXPRESSION AND REGULATION (PART 2) (TRANSLATION & TRANSLATIONAL + POST-TRANSLATIONAL CONTROL) Learning Outcomes: (c) Describe how the information on DNA is used to synthesize polypeptides in prokaryotes and eukaryotes (description of the processes of transcription, formation of mRNA from pre-mRNA and translation is required) (j) explain how differential (i.e. spatial and temporal) gene expression in eukaryotes can be regulated at different levels: (iv) translational level (half-life of RNA and initiation of translation) (v) post-translational level (biochemical modification and protein degradation) Use the knowledge gained in this section in new situations or to solve related problems. Textbooks and References Campbell, Urry, Cain, Wasserman, Minorsky, Reece (2018) Biology – A Global Approach (11th Edition)(Global Edition) Chapter 17: Expression of Genes pg. 397 – 406, Chapter 18: Control of Gene Expression pg. 427 - 429 (Pearson Publication) ISBN-10 1-292-17043-3 Note: This textbook is available in our library. You may wish to borrow them to supplement your reading when necessary. H2

2 Contents 1 The Genetic Code: A Blueprint for Life .................................................................................... 3 1.1 Codons: The Language of the Genetic Code ................................................................. 3 1.2 Amino Acids: The Building Blocks of Proteins................................................................ 4 1.3 How the Genetic Code Works ........................................................................................... 4 1.3.1 Transcription: Copying the Code from DNA to RNA .................................. 4 1.3.2 Translation: Reading the Code to Build Proteins ....................................... 5 1.4 Main features of the Genetic Code .................................................................................. 5 2 TRANSLATION ............................................................................................................................. 7 2.1 Amino acid activation.......................................................................................................... 8 2.2 Structure and Function of Ribosomes ........................................................................... 10 2.3 Steps in Translation .......................................................................................................... 11 2.4 Polyribosomes ............................................................................................................... 14 3 Regulation at Translational Level ........................................................................................... 16 3.1 Half-life of mRNA (mRNA Stability) ................................................................................ 17 3.1.1 Length of poly (A) tail ................................................................................. 17 3.1.2 RNA-binding Proteins (RBPs) .................................................................... 17 3.1.3 AU-rich Elements (AREs) ........................................................................... 17 3.1.4 MicroRNAs (miRNAs) ................................................................................. 18 3.2 Control of Translation Initiation ....................................................................................... 19 3.2.1 Initiation Factors ......................................................................................... 19 3.2.2 Internal Ribosome ....................................................................................... 19 3.2.3 Translational Repressors ........................................................................... 20 3.2.4 Secondary Structures in the 5' UTR .......................................................... 20 4 Regulation at Post-translational Level ................................................................................... 21 4.1 Biochemical Modification ................................................................................................. 21 4.1.1 Phosphorylation ............................................................................................... 21 4.1.2 Glycosylation .................................................................................................... 21 4.1.3 Ubiquitination ................................................................................................... 22 4.1.4 Acetylation and Methylation ............................................................................ 22 4.2 Protein Degradation .......................................................................................................... 23 4.2.1 Ubiquitin-Proteasome System (UPS) .............................................................. 23 4.2.2 Autophagy ......................................................................................................... 23 4.2.3 Lysosomal Degradation ................................................................................... 23

3 1 The Genetic Code: A Blueprint for Life  The genetic code is a set of rules that determines how the information in DNA and RNA is translated into proteins, which are the building blocks of all living organisms. It’s like a language that cells use to understand the instructions in their genetic material. Retrivel Practice: Recall that from Topic 2.1 Structure and Function of Nucleic Acids DNA and RNA: The Carriers of Genetic Information  DNA (Deoxyribonucleic Acid): Contains the instructions for building proteins. It’s made up of four nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).  RNA (Ribonucleic Acid): Acts as the messenger that carries instructions from DNA to the ribosomes of the cell. In RNA, thymine (T) is replaced by uracil (U). 1.1 Codons: The Language of the Genetic Code  A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal for translation. For example, the mRNA sequence AUG codes for the amino acid methionine and also serves as the start codon to initiate translation.  There are a total of 64 possible codons. (Fig. 1.1.1) Fig. 1.1.1: Genetic code table Learning Outcome 2(c) modified: Describe how the information on DNA is used to synthesise polypeptides in prokaryotes and eukaryotes. (Description of the processes of translation)

4 The Logic Behind 64 Possible Codons  The logic behind having 64 possible codons in the genetic code is based on the structure of DNA and RNA molecules, and the way the genetic information is encoded. Number of Nucleotides:  There are four different nucleotides (A, U, C, G) in RNA. Combination Logic:  If we consider combinations of these nucleotides in sets of one, two, and three:  Single Nucleotide (1-letter combinations):  Only 4 possible codons (A, U, C, G). This is not enough to code for 20 amino acids.  Two Nucleotides (2-letter combinations):  The number of possible combinations is 4 × 4 = 16. Still not enough for 20 amino acids.  Three Nucleotides (3-letter combinations):  The number of possible combinations is 4 × 4 × 4 = 64. This is more than enough to code for 20 amino acids.  Using three nucleotides per codon gives us 64 possible combinations, which are more than sufficient to code for all 20 amino acids as well as start and stop signals in the genetic code.  Here's how these 64 codons are used:  Amino Acid Coding:  There are 20 different amino acids, and each one is coded by one or more codons. This redundancy helps protect against mutations.  Start Codon:  One codon (AUG) acts as the start codon, signaling the beginning of protein synthesis. It also codes for the amino acid methionine.  S