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biology module 6.1 - cellular control - Coggle Diagram
biology module 6.1 - cellular control
gene mutations
define a mutation = a change in dna nucleotide sequence
3 types of mutation : substitution = substituting a nucleotide in the same place
insertion = addition of another nucletide
deletion = removal of a nucleotide
insertion and deletion cause a frame shift - all future codons will be different
effect of mutations : silent = no effect on the amino acid produced
nonsense = produce a stop codon
missense = different amino acid is coded for
mutation effect on organism = can be neutral, harmful or beneficial (create genetic variation)
transcriptional control - eukaryotes
heterochromatin = tightly wound dna (present in cell division)
euchromatin = loosely wound dna (present in interphase)
transcription would not occur if dna was tightly wound because RNA polymerase would not be able to reach required gene
DNA is associated with histones : dna is negatively charged and histones are positively charged
acetylation = add acetyl group to histone to make it less positively charged
phosphorylation = add phosphate group to histone to make it less positively charged
methylation = add methyl to histone to make it more hydrophobic (this makes dna more closely wound to histones)
what are transcription factors?
= proteins that bind to promotor region on dna and aid/inhibit attachment of RNA polymerase to DNA - therefore aid or inhibit transcription of gene
activators start transcription
repressors stop transcription
transcriptional control - prokaryotes
what is an operon?
= a set of genes that are under control of the same regulatory mechanism and are expressed at the same time
structural gene
= gene that codes for a protein (not involved in dna regulation)
lac Z - beta galactoside, hydrolyse lactose into glucose and galactose
lac Y - lactose perMEase - facilitate lactose crossing cell MEmbrane
REgulatory gene = code for a transcription factor
lac I - codes for REpressor protein
repressOR protein binds to the opORator region
rna Polymerase binds to the Promotor region
in the presence of glucose
:
1) lac I codes for a repressor protein
2) repressor protein binds to operator region
3) this blocks RNA polymerase from binding to the promotor region and transcribing structural genes lac Z and lac Y
in the presence of lactose
:
1) lactose binds to repressor protein, changing its shape
2) repressor protein cannot bind to operator region, allowing RNA polymerase to bing to promotor region
3) RNA polymerase can now transcribe structural genes lac Z and lac Y
post-transcriptional regulation
edit of primary mRNA and the removal of introns to produce mature mRNA
intron = section of a gene that doesn't; t code for a protein
extron = section of a gene that does code for a protein
process of slicing removes introns and joins extrons together - uses a spliceosome
spliceosome is formed from combo of snRNPS
cAMP and CAP can bind together and then bind to RNA polymerase - they make transcription of genes more efficient
body plans
homeobox gene = contain a highly conserved region of DNA called the homeobox sequence
homeobox sequence = involved in controlling the development of the body plan
homeodomain protein = transcription factor coded for by the homeobox sequence
a homeodomain protein binds to DNA and switches it on/off
it either promotes/prevents the transcription of developmental genes
highly conserved = have not mutated over a long period of time - these genes must be vital for survival
hox genes are a type of homeobox genes that are involved in the formation of anatomical features of animals in the correct loci - code for homeodomain proteins
3 types of symmatry : bilateral, radial and asymetrical
apoptosis
apoptosis = programmed cell death
homeobox genes regulate mitosis and apoptosis - stop mitosis when body feature is correct
what can trigger apoptosis ?
internal stimuli such as hormones and stress
external stimuli such as lack of nutrients and drugs
apoptosis process :
enzymes break cell cytoskeleton
*cytoplasm becomes densely backed with organelles
blebs form in cell surface membrane
nuclear envelope breaks down and dna breaks into fragments
vesicles form and are ingested by phagocytes
the importance of apoptosis is to form fingers and toes, prevent tumour formation, remove ineffective cells
