Lecture 15: Genetic Recombination 2024 PDF

BABS1202: Applied Biomolecular Sciences Genetics reviewed – and then some! Dr Michael Janitz School of Biotechnology and Biomolecular Sciences [email protected] DNA = Deoxyribonucleic acid RNA = Ribonucleic acid  Purines Structure of the four bases that...

BABS1202: Applied Biomolecular Sciences Genetics reviewed – and then some! Dr Michael Janitz School of Biotechnology and Biomolecular Sciences [email protected] DNA = Deoxyribonucleic acid RNA = Ribonucleic acid  Purines Structure of the four bases that comprise DNA Pyrimidines Hydrogen bonding between the bases directs base pairing A always pairs with __ G always pairs with __ Structure of double-stranded DNA  Gene Expression Ø DNA contains the instructions for how a cell will function Ø Proteins perform these functions Ø How are the instructions translated from the nucleotide language of DNA into the amino acid language of proteins? Ø Via an intermediary - RNA Ø Central dogma: DNA --> RNA --> protein Gene Expression DNA is transcribed into messenger RNA (mRNA), using base pairing. This mRNA is translated into protein. The code is a triplet code - 3 nucleotides code for each amino acid.  The Genetic Code What do the following code for? AGC ______ GGG ______ UAG ______ AUG ______ How is the mRNA translated into amino acids? There is a “go- between”. The go-between is transfer RNA (tRNA) There is a separate tRNA for every amino acid The amino acid is attached to one end of the tRNA The other end has a triplet code that will base-pair with the mRNA  Translation: RNA -> protein § The protein synthesis factory is called the ribosome § tRNAs carrying their amino acids move to the ribosome § They base-pair with the mRNA § This places their amino acids in the correct sequence to form the protein that was coded in the mRNA (and hence in the DNA sequence) What makes us what we are???? Control of Gene Expression Control of gene expression at the transcription level in Drosophila Control of gene expression § In prokaryotes, control of gene expression occurs at the level of transcription, i.e. whether a gene is transcribed or not. § Once the mRNA is formed it is translated immediately Control of gene expression - transcript level An example of transcriptional regulation in E.coli The usual energy and carbon source for E.coli is glucose. When glucose is scarce, lactose can be used. Lactose is a disaccharide which must be hydrolised before it can be utilised. The enzyme that catalysizes this reaction is b-galactosidase. b-galactosidase is only produced when lactose is present  Regulatory elements control the level of expression of genes that code for proteins repressor operator genes coding for the enzymes promoter site needed to metabolise lactose What would happen if the DNA sequence for a human protein replaced these bacterial genes? Insulin gene Insulin protein? Eukaryotic cells The mRNA is formed as pre-mRNA in the nucleus (where the DNA is!) The pre-mRNA is extensively modified It is then exported to the cytoplasm, where protein synthesis occurs § In eukaryotes, the control of gene expression occurs at many levels. §Other levels include the processing, transport and degradation of the mRNA. § At the protein level, proteins can be modified, transported and degraded. Initiation of transcription in eukaryotes § Proteins called transcription factors mediate the initiation of transcription § This is an additional control mechanism for gene expression in eukaryotes Activators are also required for eukaryotic gene transcription Exons can be spliced in different ways to produce different proteins from the same gene sequence Muscle a-tropomyosin has 12 exons which are spliced to produce different mRNAs in different tissues. Summary of transcriptional regulation in eukaryotes Post-translational modifications of proteins in eukaryotes Protein degradation