Lecture 11 CSF DNA Mutations and Cancer 2024 (1).pdf

Recap Lecture 10….. Lecture 11: Mutations and Cancer 1. describe how DNA mutations can alter gene products 2. recall the role of cell cycle checkpoints in mitosis 3. describe how mutations in tumour suppressor genes or protooncogenes can impact cell cycle control 4. appreciate that loss of cell cycl...

Recap Lecture 10….. Lecture 11: Mutations and Cancer 1. describe how DNA mutations can alter gene products 2. recall the role of cell cycle checkpoints in mitosis 3. describe how mutations in tumour suppressor genes or protooncogenes can impact cell cycle control 4. appreciate that loss of cell cycle control can result in cancer Remember Lecture 9? If needed, rewatch the BioFLIX protein synthesis movie, 3:32m - is on CANVAS page (modules/cell structure and function) United by sequence… Objective One DNA changes / mutations Q: which is more likely to impact the final protein? a mutation within a coding region, or a mutation within an intron? Objective One Effect of DNA sequence changes Mutations can affect the structure and function of a protein Q: why “can” why not “always”? Altered DNA sequence can have major effects on resulting protein function (or minor, or none, or positive) - germ line – passed on to future progeny - local/somatic – during cell division, not whole body – local effects (e.g. tumors) Large scale alterations – chromosomal rearrangements Small scale alterations– one or a few nucleotides altered we will focus on small scale (including point) mutations Small scale mutations can be: Substitutions – where one base is replaced by another - can have minimal or major effect Insertions/Deletions –can have major effect if within coding sequence - can cause a frameshift Objective One Substitutions and Indels in protein coding regions Substitutions can be: silent missense nonsense Insertions or Deletions (indels): cause frameshift if 1 or 2 nt can maintain frame if 3 nt Objective One An example of a silent mutation GGC codon becomes GGU codon, but still codes for Glycine – so no effect on protein Objective One An example of a missense mutation GGC codon becomes AGC codon, so Gly becomes Ser– effect depends on residue role Q: what could you do to assess the likelihood of impact? Hint, look at slide 13 Objective One An example of a nonsense mutation AAG codon becomes UAG codon, so Lys becomes a STOP – truncated protein Objective One An example of a frameshift mutation via insertion AAG codon becomes UAA codon, so Lys becomes STOP – truncated protein Objective One An example of a Frameshift mutation via deletion Protein is completely altered from point of frameshift, can have catastrophic effect Q: When is there more chance of disaster? If the frameshift is at the 5’ end or the 3’ end of the mRNA? Campbells, 10th, 17.26 UUU codon becomes UUG, so Phe becomes Leu, plus downstream residues Objective One An example of a 3 nucleotide-pair mutation Did you know? Huntington’s Disease is due to a triplet repeat expansion – lots of extra glutamines (CAG) Campbells, 10th, 17.26 AAG codon is lost (Lys), but downstream residues are intact – frame is maintained Objective One Sickle Cell Anaemia an example of a missense substitution mutation Q: why is red blood cell shape important? Want to know more about sickle cell anaemia? Read more (not examinable) in the Campbells text or https://en.wikipedia.org/wiki/Sickle_cell_disease Objective Two Remember Mitotic cell cycle checkpoints (Lecture 10) Multiple signals required to pass cell cycle checkpoints For example: Is the DNA undamaged? Is cell size and nutrition OK? appropriate signals present? chromosomes attached to spindles? If not - G1 may exit to G0 - G2/M may result in cell death Last lecture looked at G1 and M Let’s look at G2 now Objective Two MPF at the G2 checkpoint Cyclin: a protein that fluctuates throughout the cell cycle Cyclin dependant kinase (Cdk): a kinase that is activated when attached to a cyclin Maturation (or M-phase) promoting factor (MPF): a specific cyclin / Cdk complex – key for G2 checkpoint MPF phosphorylates many other proteins, allows mitosis to commence Objectives 2&3 The checkpoints rely on stop and go cell signals Many gene products associated with the checkpoints Many can be considered STOP and GO molecules: - genes that normally keep proliferation in check - genes that normally stimulate cell proliferation No, you don’t need to know the details in these images!! In this image, cyclin B+cdc2 = MPF Please don’t worry about the specific names (cyclin and cdk is enough) cdc2=cdk1=p34 Illustration reproduced courtesy of Cell Signaling Technology, Inc. Objectives 3&4 Mutations in STOP and GO genes can cause cancer If STOP and GO molecules are not working correctly, the cell cycle could proceed when it shouldn’t - uncontrolled cell growth, can result in tumours DNA mutations can change the function of STOP and GO molecules How do the cancer-causing DNA mutations arise? Genetic predisposition: in all cells of the body inherited from parents (or de-novo) - an issue or deficiency in a gene (typically one copy, eg p53, BRCA). Acquired: locally, in one cell initially eg UV damage, smoking, carcinogens, viruses, drugs and treatments e.g. chemotherapy. In both acquired and inherited DNA changes, altered protein function can result, which may lead to loss of cell cycle control. Objectives 3&4 Proto-oncogenes and Tumor suppressor genes In a car: to keep moving you can either apply accelerator or remove brakes In cancer, the genes affected by DNA changes are often: Proto-oncogenes - genes that normally stimulate cell proliferation Tumor suppressor genes - genes that normally keep proliferation in check over-activation of proto-oncogenes (pressing the “accelerator”) deactivation of tumor suppressor genes (or loss of “brakes”) both alterations can result in uncontrolled cell growth - i.e. a tumor Objectives 3&4 Proto-oncogene to oncogene >> increased function Too much accelerator! Normal DNA Q: Can you relate the image above to what you learned in Lecture 8? Mutated DNA Two examples: Ras – a GTPase Myc – a transcription factor Objectives 3&4 Deactivated tumor suppressor genes >> loss of function Loss of “brakes” Normal DNA Mutated DNA eg. TP53, BRCA1, BRCA2 Objectives 3&4 Multiple DNA changes in the development of cancer cell/tumor level versus systemic Q: Which tissue would you sample for DNA analysis of possible cancer-causing mutations? In summary: Sam Levin Flickr Some useful resources for this lecture only use them if you need them, they are just additional resources https://www.youtube.com/watch?v=cSXFjUpACWE An explanation about oncogenes and tumour suppressors, ~5m long Details not in lecture in either of these videos are not examinable https://www.youtube.com/watch?v=1cVZBV9tD-A A longer video (~12m), but useful if you are confused, as it pulls together DNA packaging, cell division and cancer quite nicely (note, it does not cover tumor supressors or oncogenes specifically) Publisher permission was granted for lecture slide use of images/resources from the 107 texts (Tortora and Campbell). Unless otherwise stated content was sourced from these texts or were lecturers own Next lecture - putting it all together + test tips and questions Lecture 6: Cell Structure & function – Introduction Lecture 7: Harvesting Chemical Energy Lecture 8: How Cells Communicate Lecture 9: From Gene to Protein Lecture 10: Cell Division Lecture 11: Mutations and Cancer