chapter 19 - genetics of living systems Flashcards
what is a mutation
a change in the sequence of bases in DNA
what is a mutation caused by
substitution, deleting or insertion of one or more nucleotides within a gene
what does the substitution of a nucleotide cause
codon changes so a different amino acid is produced which changes primary structure of protein or different position of R group affecting function
what does insertion or deletion of a nucleotide cause
leads to a frameshift mutation
what are the effects of different mutations
no effect on phenotype as normal proteins are synthesised
damaging phenotype because proteins are non functional
beneficial as a new useful characteristic is produced
what are the causes of mutations
occurs randomly during DNA replicationbut rate of mutation is sped up by mutagens
depurination or depyrimidination leading to insertion of incorrect base
free radicals
what is a mutagen
chemical, physical or biological agent which causes mutations
what are silent mutations
mutations that do not change protein function but may still affect primary structure
what are nonsense mutation
results in codon becoming a stop coding which results in shortened non-functional protein
what are missense mutations
results in the incorporation of an incorrect amino acid into the primary structure. can be harmless ( conservative) or dangerous ( non-conservative ) or beneficial
what is an example of a beneficial mutation
ability to digest lactose preventing diseases such as osteoporosis
what is sickle-cell anaemia
blood disorder where erythrocytes develop abnormally causesd by mutation in gene coding for haemoglobin.
what base is substituted in sickle-cell anaemia
adenine replaced by thymine making 6th amino acid, valine instead of glutamic acid on beta haemoglobic chain
what are changes in chromosome structure
deletion
duplication
translocation - section of one chromosome breaks off and joins another non-homologous chromosome
inversion - section of chromosome breaks off , is reversed, and then joins back onto the chromosome
what genes form enzymes in metabolic pathways
house keeping genes
what genes form protein based hormones
tissue -specific genes
how are genes regulated
transcriptional - genes turned on or off
post-transcriptional - mRNA modified which regulates translation and types of protein produced
translational - translation stopped or started
post-translational - proteins modified after synthesis to change their function
what is heterochromatin
tightly wound DNA causing chromosomes to be visible during cell division
what is euchromatin
loosely wound DNA present during interphase
how are transcription of genes prevented
DNA is tightly wound ( heterochromatin) so RNA polymerase cannot access the gene
why does DNA coil around histones
DNA is negatively charged and histones are positively charged
how does acetylation and phosphorylation allow genes to be transcribed
reduces positive charge on histones so DNA coils less tightly so genes can be transcribed
how does methylation prevent transcription of genes
makes histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly
what are epigenetics
control of gene expression by modification of DNA
