6.1.1: cellular control Flashcards
what is a mutation?
change in the sequence of bases in dna
how does substitution and insertion/deletion cause a gene mutation?
substitution
- changes codon (one base switched with a different one)
- if the new codon codes for a different amino acid = change in primary structure of the protein
- degenerate nature = could cause no mutations
insertion/deletion
- causes a frameshift mutation = move to either the left (deletion) or right (insertion)
what are the effects of different mutations?
- no effect: normally functioning proteins are still synthesised
- damaging: proteins are no longer synthesised or proteins are non-functional = interfere with one or more essential processes
- beneficial: new and useful characteristic in the phenotype
what are the 4 different ways genes can be regulated?
- trancriptional = genes can be turned on or off
- post-transcriptional = mrna can be modified which regulates translation and the types of protein produced
- translational = translation can be stopped or started
- post-translational = proteins can be modified after synthesis which changes their functions
what are transcription factors?
- proteins that bind to specific dna sequences to initiate the transcription of genes into mrna
- when a genes is “switched off, transcription factors cannot bind to dna = prevents transcription
what are the 2 forms that chromatin can exist in?
- heterochromatin: densely packed = difficult for rna polymerase to access genes, preventing transcription
- euchromatin: lossely packed = easy access for rna polymerase, enabling transcription
why does histone modification occur?
dna coils around histones as they are positively charged while dna is negatively charged
what are the histone modifications that promote transcription?
- acetylation: adding acetyl groups to histones = decreasing their positive charged = looser dna coil
- phosphorylation: adding phosphate groups to histones = reduces their positive charge = looker dna coil
= increased transcription!
what is a histone modification that inhibits transcription?
methylation: adding methyl groups to histones = increasinf hydropjobic interactions = tightening coil = reduces transcription
how is mrna “edited” after transcription (post transcriptional control of gene expression)?
1) introns = don’t code for an amino acid vs exons = do code for amino acids
2) during transcription, they are both copied into mrna (called pre-mrna)
3) introns are removed from pre-mrna via splicing and exons joined = mature mrna
4) mature mrna leaves nucleus for translation
what happens during post-translational control of genes?
- adding of non-protein groups
- folding and shortening of protein
- activation of cyclic amp (messenger molecule in cells as is often in the activation of enzymes)
what are lac operon?
- group of 3 genes (lacz, lacy and laca) involved in the metabolism of lactose
- structural genes
- code forenzymes beta-galactosidase, lactose permease and transacetylase
-transcribed onto a single long molecule of mrna
what does the lac operon consist of?
- a promoter region (where rna polymerase binds)
- an operator region (where the repressor protein binds to)
- structural genes lac yza
- regulatory gene lac l a short distance away
what happens in lac operon when there is an absence of lactose?
- repressor protein binds to operator region
- prevents rna polymerase from binding to the promoter
- blocks transcription, meaning genes xyz cannot be expressed, resources not waster
what happens in the presence of lactose?
- lactose binds to repressor protein
- changes it shape, so can no longer bind to operator region
- means that rna polymerase can bind to the promoter region and begin transcription
