Genetics Of Living Systems 2 Flashcards
Transcription factors
Proteins that bind to dna at specific sites
This way they regulate transcription turn genes on and off
Homeobox genes
Encode transcription factors
Contain a homeobox
Control the growth and development of organisms
Switch on head develop genes thorax genes etc in foetus
Homeobox
Section of DNA 180 base pairs
Codes for a region of transcription factor called the homeodomain (60AA)
Homeodomain
Allows transcription factor bind to dna
Homeobox genes common ancestors
Homeobox genes in mice and humans have identical nucleotide sequences
Eg Pax6 eye development if genes not turned on blindness
Body plans
Morphogenisis
Regulation of the pattern of anatomical development
Evolution effect on Homeobox genes
Homeobox sequence is highly conserved has changed very little during evolution
Naturally selected against
Discovery and fruit flies
Studied flies w mutations legs on head
Mutations found in genes in a section of dna 180bp in length similar for all flies except mutated
Homeodomain function
Allows transcription factor to bind to dna
Conserved region of protein
When mutate certain genes weren’t turned on or off result in defects
Hox genes
Group of Homeobox genes only present in animals
Correct positioning from head to tail
Vertebrates development
Develop from segments in embryo called somites
Directed by hox genes to develop particular way depending on sequence
Human development
humans have 39 hox genes organised into 4 clusters each on different chromosomes - expressed in different body segments
Order of genes
= order in which effects are expressed in the organism
Sequence / gene structure
Promoter - trans start site - 5’ untranslated region - start codon - coding region- stop codon - 3’ untranslated region
Stages of gene expression control
Transcriptional
Post transcriptional level
Translation level
Post translational level
Transcriptional level control
Increased trans more mRNA make more proteins
Chromatin varieties
Heterochromatin tightly wound DNA causing chromosomes to be visible during cell division
Euchromatin is loosely wound- present in interphase
Transcription of chromatin
Transcription not possible when tightly wound RNA polymerase cannot access genes
Euchromatin can be freely transcribed interphase replication
Histone
Dna is wrapped round it
DNA negatively charge Histone positively charged because made of lysine AA
Histone modification
Addition of acetyl groups or phosphate groups
Addition of methyl groups
Addition of acetyl/phosphate groups
reduces positive charge of histones causing dna to coil less tightly - allow certain genes to be transcribed
Addition of methyl groups
makes histones more hydrophobic so they bind more tightly to each other preventing DNA transcription
Epigenetics
Study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence
Using transcriptional factors
Trans factors help or block the binding of rna polymerase to dna
Start= activators
Stop= repressors
Shape determines whether it binds to dna or not - altered by binding w certain molecules
Environment on transcription factors
Amount of some mol in an environment control synthesis of proteins by affecting transcription factor binding
Lac operon in E.coli
Operon is a cluster of genes that are transcribed together
Ecoli can respire lactose if glucos not present control via operon
Lac operon group of genes
•Regulatory gene codes for a repressor protein prevent trans when no lactose
•Structural genes :Lac Z Lac Y Lac A
Code for 3 enzymes in the breakdown of lactose
Repressor protein
Constantly produces and bonds to operator
•Prevents RNA polymerase binding to DNA and beginning trans - regulation
•When lactose present repressor protein binds changing its shape allowing RNA to bind to promoter - enzymes transcribed
Role of cAMP
Binding of RNA polymerase is slow rate of transcription
Up regulated by cAMP receptor protein CRP
Transport of glucose into cell decreases levels of cAMP reducing transcription of genes responsible for metabolism of lactose
Post transcriptional pre translation control
•RNA processing - modifies pre mRNA to mature mRNA before translating
Cap added to 3’ & 5’ end stabilise mRNA prevent degradation
•RNA editing sequence can be changed through base addition deletion or sub - range of proteins prod
Translation control
•degradation of mRNA more resistant molecule longer it will last more protein
•bind of inhibitory proteins prevent synthesis of proteins
• activation of initiation factors which aid binding of mRNA to ribosomes
Mutation
Change in the sequence of bases in dna
Mutation types
Substitution deletion insertion
If only one nucleotide change called one point mutation
Substitution mutation
Changes the codon in which may code for a different amino acid changing primary structure
May not affect due to degenerate code
Insertion/deletion
Frameshift mutation shifts the reading frame of the sequences of bases read in 3 change every successive codon from mutation point
Effects of mutations
None- normally func still synthesised
Damaging- phenotype is affected as protein synthesised non func
Beneficial- new beneficial phenotype eg immunity to HIV
Causes of mutation
Increased by mutagens - loss of a purine or pyrimidines base lead to insertion of the wrong base in DNA rep
Chemical physical or biological agent
Physical mutagens
Ionising radiation x rays
Break dna strands some breaks repaired mutations occur
Chemical mutagens
Deamination agents
Chemically alter bases in DNA changing base sequences
Biological mutagens
Alkylating agents- methyl groups attach to bases incorrect pairing
Base analogs- change base sequence
Viruses - viral dna insert changing base sequence
Chromosome mutations
Deletion- a section chrom breaks off and lost
Duplication- section duplicated
Translocation break off and join to another non homologous chromosome
Inversion- a section of chromosomes break off and reversed and join back
