RVHS 10. Control of Gene Expression - Eukaryotes 9477

River Valley High School 2025 JC1 H2 Biology Lecture Topic 10: Control of Gene Expression - Eukaryotes 1 River Valley High School 2025 JC1 H2 Biology Lecture Topic 10: Control of Gene Expression - Eukaryotes Name: ( ) Class: 25J _____ Date: References Title Authors Biology (8th Edition) Campbell and Reece Biology: An Australian Focus (3rd Edition) Knox, Ladiges, Evans and Saint Molecular Cell Biology (6th Edition) Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh and Matsudaira Molecular Biology of the Cell (5th Edition) Alberts, Johnson, Lewis, Raff, Roberts and Walter Principles of Genetics (3rd Edition) Snustad and Simmons Websites URL Description http://highered.mcgraw- hill.com/sites/9834092339/student_view0/chapter10/chr omatin_remodeling.html transcriptional activation and regulation. https://highered.mheducation.com/sites/9834092339/stu dent_view0/chapter15/processing_of_gene_information __prokaryotes_vs__eukaryotes.html basic differences between prokaryotic and eukaryotic gene expression. https://highered.mheducation.com/sites/9834092339/stu dent_view0/chapter15/rna_splicing.html summary of the splicing process.

River Valley High School 2025 JC1 H2 Biology Lecture Topic 10: Control of Gene Expression - Eukaryotes 2 H2 Biology Syllabus 9477 (2025) Candidates should be able to use the knowledge gained in the following section(s) in new situations or to solve related problems. Related Topics Content Organisation of Genomes Control of Gene Expression - Prokaryotes The structure of eukaryotic chromatin Operons Learning Outcomes 2C. Control of Gene Expression b. Explain how differential (i.e. spatial and temporal) gene expression in eukaryotes can be regulated at different levels: i. Chromatin level (histone modification and DNA methylation); ii. Transcriptional level (control elements, such as promoters, silencers and enhancers, and proteins, such as transcription factors and repressors); iii. Post-transcriptional level (processing of pre -mRNA in terms of splicing, polyadenylation and 5’ capping); iv. Translational level (half-life of RNA, 5’ capping, initiation of translation); and v. Post-translational level (biochemical modification and protein degradation). c. Describe the principles and procedures of these molecular techniques: i. Polymerase chain reaction (including its advantages and limitations); ii. Gel electrophoresis; and iii. Southern blotting and nucleic acid hybridisation. Lecture Outline I. Control of Gene Expression A. Chromatin-level Control A1. Availability of genes for transcription A1.1. Histone modification A1.2. DNA methylation B. Transcriptional Control B1. Initiation of transcription B1.1. Control elements B1.2. Transcription factors C. Post-transcriptional Control via Processing of pre-mRNA C1. Alteration of mRNA ends C2. RNA splicing D. Translational Control D1. mRNA stability D2. Initiation of translation E. Post-translational Control E1. Biochemical modification E2. Protein degradation F. Gene Amplification II. Molecular Techniques A. Polymerase Chain Reaction B. Gel electrophoresis C. Southern blotting and nucleic acid hybridisation

River Valley High School 2025 JC1 H2 Biology Lecture Topic 10: Control of Gene Expression - Eukaryotes 3 I. CONTROL OF EUKARYOTIC GENE EXPRESSION Gene expression, the generation of a protein or RNA product from a particular gene, is regulated by complex mechanisms in eukaryotes. Normally, only a fraction of the genes in a eukaryotic cell are expressed at any one place (tissue specificity) and at any one time (temporal specificity). Gene expression and control in eukaryotes differ from those in prokaryotes for the following reasons: 1. Eukaryotic DNA is organised into nucleosomes. The genes must be in an active structure to be expressed. 2. Eukaryotic genes are not organised into operons. The genes encoding proteins that function together are usually located on different chromosomes. Each gene thus needs its own regulatory sequences (e.g. promoters, silencers and enhancers). 3. The processes of transcription and translation are separated in eukaryotes by the nuclear envelope. Eukaryotic pre-mRNA (which is heterogeneous nuclear RNA) must be processed and translocated out of the nucleus before it is translated. Eukaryotic gene expression can be regulated at variuos levels: A. Chromatin-level control ⬧ Availability of genes for transcription B. Transcriptional control ⬧ Initiation of transcription C. Post-transcriptional control ⬧ Processing of pre-mRNA D. Translational control ⬧ mRNA stability ⬧ Initiation of translation E. Post-translational control ⬧ Biochemical modification ⬧ Protein degradation F. Gene amplification A. Chromatin-level Control The organisation of chromatin discussed earlier in Topic 9 serves a dual purpose. One function is to pack the DNA into a compact form that fits inside the nucleus of a cell. The other main function is regulatory: the physical state of DNA in or near a gene is important in helping control whether the gene is available for transcription. Chemical modifications of the histone proteins and DNA of chromatin play a key role in chromatin structure and gene expression.

River Valley High School 2025 JC1 H2 Biology Lecture Topic 10: Control of Gene Expression - Eukaryotes 4 A1. Availability of Genes for Transcription Once the haploid sperm and egg combine to form a diploid zygote, the number of genes in cells r emains approximately the same. As cells differentiate, different genes are available for transcription. A1.1. Histone modification 1. A typical nucleus contains c hromatin that is diffused ( euchromatin) and chromatin that is condensed (heterochromatin). ⬧ The genes found in euchromatin are active (available for transcription ) whereas those found in heterochromatin are inactive. ⬧ Long-term changes in gene activity occur during development as chromatin goes from a diffused to a condensed state or vice versa. 2. The nuclear genome is packed together with histones into nucleosomes. ⬧ Transcription initiation is prevented if the promoter region is part of a nucleosome. Thus, activation of a gene for transcription requires changes in the state of the chromatin, called chromatin remodelling. ⬧ The N-terminus of a histone molecule in a nucleosome protrudes outward from the nucleosome. These histone tails are accessible to various modifying enzymes, which catalyse the addition or removal of specific chemical groups 3. Histone acetylation ⬧ In acetylation, acetyl groups are attached to lysines in histone tails. The enzyme catalysing the transfer is histone acetyltransferase (HAT). ⬧ When lysines are acetylated, their positive charges are neutralised. As such, histone tails no longer interact with the neighbouring nucleosomes. ⬧ Electrostatic interaction between neighbouring nucleosomes promotes folding of chromatin into more compact structure. When this interaction does not occur in an acetylated region, chromatin has a more diffused structure. Transcription factors have easier access to genes. ⬧ Histone acetylation does not only promote transcription initiation by remodelling the chromatin structure, the enzyme HAT also binds to and aids in the recruitment of the transcription machinery. 4. Methylation ⬧ Histone methylation is the modification of specific amino acids in a histone protein through the addition of methyl groups, cataly sed by histone methyltransferase. ⬧ In most cases, histone methylation i