Genetics of living systems Flashcards
Mutation
Change in the sequence of bases within the DNA
Gene mutations occur due to
Deletion
Substitution
Insertion
Type of mutations
Frameshift (caused by insertion or deletion)
Damaging
Silent (mutation doesn’t cause any change)
Beneficial (rare)
Chromosome mutations occur due to
Deletion (section of chromosome breaks off and is lost within the cell)
Duplication (sections get duplicated on a chromosome)
Translocation (a section breaks off and joins another non-homologous chromosome)
Inversion (section breaks off, is reversed, and then joins back onto the chromosome)
Regulation of genes
Transcriptional (chromatin remodelling, histone modification, lac operon, cAMP)
Post-transcriptional (RNA processing, RNA editing)
Translational
Post-translational
Chromatin remodelling
- DNA has to be wound around histones in order to be packed into the nucleus of a cell in eukaryotic cells
- heterochromatin is tightly wound DNA, making chromosomes visible during cell division, not allowing RNA polymerase to access the genes, therefore transcription is not possible
- euchromatin is loosely wound DNA present during interphase, which allows transcription during interphase
Histone modification
- DNA is negatively charged, while histones are positively charged => DNA coils around histones
- Histones can be modified to increase or decrease the degree of packing of DNA
- acetyl groups or phosphate groups addition to histones reduces the positive charge, so DNA coils less tightly
- methyl group addition causes the DNA to coils more tightly as it makes it even more negative
Epigenetics
Control of gene expression by the modification of DNA
Lac operon in the presence of lactose/absence of glucose
- Lactose binds to repressor protein
- This prevents the repressor protein from binding to the operator as it changes its tertiary structure
- RNA polymerase is able to bind to the promoter
- structural genes are transcribed => mRNA is produced, enzymes are produced
Lac operon in the absence of lactose/presence of glucose
- Repressor protein binds to the operator
- The binding prevents RNA polymerase from binding to the promoter and starting transcription
Role of cyclic AMP
cAMP has to bind to CRP (cAMP receptor protein) in order to increase the rate of transcription as this activates proteins by altering their 3D structure.
Glucose presence reduces transcription and action of cAMP
RNA processing
- pre-mRNA is formed, which is modified to form mature mRNA before it can bind to ribosomes
- cap is added to the 5’ end and a tail to the 3’ end in order to stabilise mRNA and prevent its degradation in the cytoplasm, and help it attach to ribosomes
- splicing of introns
RNA editing
base addition, deletion, substitution
Translational control
- mRNA degradation
- binding to inhibitory proteins
- activation of initiation factors to help mRNA bind to ribosomes
- protein kinases catalyse phosphorylation
Post-translational control
- addition of non-protein groups
- modifying amino acids and formation of disulphide bridges
- folding or shortening proteins
