6.1.1 Cellular control Flashcards
substitution mutation features
also known as point mutation
one base pair replaces another
same number of amino acids results
types of mutation and effects
silent mutations (no effect on protein) missense mutations (usually has effect on protein) nonsense mutations (usually had a large effect on protein)
silent mutations
change in base pair will still code for same amino acid = same protein = no effect
(most AA coded for by more than one DNA codon)
why genetic code is non-overlapping
makes sure genes are read “in-frame” by start and stop codons
no codon codes for more than one amino acid
why genetic code is redundant / degenerate
more than one codon codes for the same amino acid
missense mutation features
change in base pair causes change in amino acid
= change in primary and tertiary structure of protein
= change in shape and function
e.g. sickle cell anaemia
nonsense mutation features
change in base pair causes it to become a stop codon
= early termination of polypeptide chain
= change in shape/function of protein
e.g. cystic fibrosis
insertion and deletion mutation features
indel mutations
extra base pairs inserted / some deleted
results in number of base pairs not being in multiples of 3
causes frameshift
alters all subsequent DNA codons
= large change in primary and tertiary structure of protein
= large change in shape and function
if 3 bases are inserted/deleted no frame shift occurs (only 1 less/more amino acid)
lac operon in prokaryotes
lacI transcripted and translated to synthesise lacI repressor protein
lacI repressor protein binds to operator region on bacterial DNA, preventing expression of lacZ and lacY genes
when all glucose used up and lactose present
lactose binds to repressor protein
alters its shape and prevents it binding to operator
allows RNA polymerase to bind to promoter region
lacZ and lacY genes undergo transcription
beta-galactosidase and lactose permease are synthesised
thus, lactose induces the enzymes needed to break it down
what gene expresses beta-galactosidase
lacZ
what gene expresses lactose permease
lacY
lactose permease function
embedded into plasma membrane
acts as channel protein for lactose
greater rate of lactose entering the cell
beta-galactosidase function
breaks down lactose into glucose and galactose
control of gene expression at transcriptional level in eukaryotes method
certain genes only expressed in certain cells
transcription factors (proteins) control which genes are switched on or off
transcription factors bind to specific promoter regions of DNA for gene they control
helps or prevents RNA polymerase from binding and transcribing gene
how primary mRNA is spliced method
both intron and exons are transcribed to produce primary mRNA
primary mRNA binds to endonuclease enzyme (forms spliceosome)
primary mRNA spliced by endonuclease enzyme to remove introns
exons join together to produce mature mRNA, leaves cell and translated
why introns exist
some primary mRNA spliced in different ways - allows it to code for more than 1 protein
do prokaryotes have introns
no
control of gene expression at post-transcriptional level method
protein has been made
signalling molecule (first messenger) binds to receptor on cell surface membrane
causes G-protein to activate adenyl cyclase
converts ATP to cAMP (secondary messenger) which activates the protein
can then involve adding functional groups e.g. phosphorylation of many proteins
modified proteins enters nucleus and acts as transcription factor to regulate transcription
spliceosome definition
structure formed when primary mRNA binds to endonuclease enzyme
regulatory gene definition
codes for repressor protein/transcription factor that switches (structural/another) gene on/off
structural gene definiton
codes for protein/polypeptide
relationship between regulatory gene and structural gene
regulatory gene controls expression of structural gene
homeobox gene definition
homeotic gene containing 180 base-pair sequence that codes for a 60-amino acid sequence called homeodomain sequence (transcription factors)
homeotic genes function
control morphogenesis (anatomical development) of organisms
homeodomain sequence function
shape specific to part of enhancer region on DNA so it binds to DNA to initiate/stop transcription to switch genes on/off
controls development of body plan
60 amino acids long
master gene definition
control expression (switch on/off) of many other genes
why homeobox genes are highly conserved
found in all plant, animal and fungi species from a common ancestor
very similar in all organisms
very few mutations in genes as they would largely affect body plans of organisms
mutations selected against as they would have killed organisms
Hox genes function
homoebox genes found only in animals
control formation of anatomical features in correct locations of body plan
expressed in embyronic development one by one along anterior-posterior axis
causes development of particular body parts in this particular order
why different classes of animals develop in similarly as segments
Hox genes similar across different classes of animals
Hox genes switched on in segments, causing development in segments
Hox genes between different animals
number and arrangement of Hox genes varies among different animals
due to evolution, Hox clusters have duplicated, leading to greater complexity in body structure
tetrapods (e.g. humans) have 4 similar Hox genes
characteristics scientists want for animals to use in experiments
cheap to buy and keep reproduce quickly small large cells readily available
what information can be learnt from model organisms applied to humans
all in same kingdom shared ancestors similar cells shared genes similar embryonic development/ homeobox/Hox genes
apoptosis definition
programmed cell death
necrosis definition
cell death due to trauma/disease
apoptosis method
triggered by transcription factors made by Hox genes causing:
cytoskeleton broken down by enzymes
cell shinks, plasma membrane forms blebs (small protrusions), chromatin condenses
DNA breaks up, nuclear envelope breaks down into fragments
blebs form vesicles containing organelles
vesicles engulfed and digested by phagocytes, preventing damage to other cells by dead cells’ contents
controlling apoptosis
genes that regulate cell cycle and apoptosis able to respond to internal and external cell stimuli e.g. stress
cell-signalling molecules released (e.g. cytokines, hormones, nitric oxide)
how nitric oxide causes apoptosis
makes inner membrane of mitochondria more permeable to hydrogen ions, dissipating proton gradient (reduces ATP production)
proteins released into cytoplasm, bind to apoptosis inhibitor proteins, causing apoptosis
how mitosis and apoptosis control body development
mitosis causes growth in zygote
cells destroyed by apoptosis when cells reach Hayflick limit (divide ~50 times)
rate of mitosis and apoptosis should be equal otherwise tumours would form or tissues would degenerate (e.g. Alzheimers)
apoptosis vital in body development (e.g. separation of digits, loss of vestigial tail in humans)
Hayflick limit
cells should only divide around 50 times
why cells are broken down by apoptosis instead of hydrolytic enzymes
hydrolytic enzymes could destroy neighbouring cells
