M6 C19: genetics of living systems Flashcards
What is the structure of DNA?
phosphate
pentose sugar
nitrogenous base
what is a mutation?
change in the sequence of bases
what is different between purine and pyrimidines
purines- have a double ring
pyrimidines- single ring
what are purines?
adenine
guanine
what are pyrimidines?
cytosine
thymine
why is dna degenerate?
more codons than amino acids so there is multiple combinations for same amino acids
why is dna non overlapping?
3 bases are read at a time so no codons overlap
why is the dna code universal?
everyone has the same ammino acids and codon combinations
what is insertion?
extra nucleotide may be added which messes up the codons after it changes the protein
what is deletion?
nucleotide is removed. this moves all the nucleotides up 1 space so the wanted AA aren’t coded for
what is frame shift?
shifts codons back or forwards witch causes further AA to be changed including start and stop codons
eg insertion or deletion
what is substitution?
a nucleotide is substituted for another. it can change the AA made or the tertiary strucuture. could also change the shape/ function
what is a nonsense change?
when a change leads to a stop codon/AA being coded for shortening the protein. this can lead to loss of function
what is a missense change?
changes amino acid may lead to a big or a minimal change. this could lead to a loss of function/ shape or improved function
what is a silent change?
when change has no affect on the amino acid that is produced
what is the difference between a conservative and non conservative mutation?
conservative- aa change leads to an aa with similar properties to original being synthesized
non conservative- aa coded for has different properties than orginial
what are the effects of mutations?
neutral
harmful
beneficial
what is a neutral effect?
also known as no effect!
caused by a silent mutation where normal proteins are still synthesised. phenotype isnt changed
what is a harmful effect?
also known as damaging
proteins synthesised are non functional and the phenotype is negatively impacted. can interfere with bodily processes
what is a beneficial effect?
protein synthesised means it may work better or carry out something new more useful
has a useful characteristic
what are some causes of mutations?
radiation eg- x rays, gamma
smoking, drugs and alchohol
chemicals in caffine
UV light
virus
alkylying agents
what are some diseases caused by mutations?
cystic fibrosis
huntingtons disease
protooncogenes change to oncogenes which can cause uncontrolled cell division which causes cancer
how can mutations lead to difference in shape?
new bases= new amino acids which could have different bonds, changes the shape as bonds may be different
how can chromosomes be changed due to mutations?
deletion- part of chromosome breaks off
duplication-sections get duplicated
translocation- section of one chromosome breaks of and joins with aother non- hmologous chromosome
inversion- section of chromosome breaks off, is reversed them joins back on
what are housekeeping genes?
genes that code for enzymes that are constantly required for reactions such as respiration.
why is gene regulation needed?
some products of gene expressions are needed not all of the time. e.g. hormones for growth or not needed in that certain cell
how can genes be regulated?
transcriptional- genes can be turned on/ off
post transcriptional- mRNA can be modified to regulate translation
translational- translocation can be stopped/ started
post translational- protiens modified after synthesis
how does chromatin control transcription?
part of transcriptional control
heterochromatin- tightly wound DNA, no transcription as RNA polymerase cant access genes, in cell division
euchromatin- loosely wound DNA, interphase,
how can histone proteins be modified to regulate gene expression?
acetylation/ phosphorylation- reduces the +ve charge of histone proteins, causes DNA to coil less tightly, allowing genes to be transcribed
methylation- makes histones hydrophobic so they coil more tightly to each other/ DNA coils more tightly, prevents transcription
what is a operon?
genes that are under control of same regulatory mechanisms and are expressed at the same time
what is the lac operon responsible for?
group of 3 genes involved in metabolism of lactose
what are lacZ lacY and lacA?
structual genes as they code for 3 enzymes
lactose permease
b-galactosidase
transacetylase
what is the regulatory gene responsible for?
codes for repressor proteins
is lacI in the lac operon
what do repressor proteins do in the case of lac operon?
prevents the transcription of the structural genes in absence of lactose
what does the repressor protein do to prevent transcription?
prevents RNA polymerase binding to DNA to begin transcription by binding to the operator
where does rna polymerase bind to to start translation?
the promoter
what does lactose do to the receptor when oresent?
binds to repressor protein causing it to change shape so it cant bind to the operator. therefore RNA polymerase can bind and transcription can begin
what are transcription factors?
proteins which move in from cytoplasm to DNA. they attach rna polymerase to dna. proteins that bind to specific regions of DNA to control the transcription of genes
what do trancription factors do?
bind to the promoter region of a gene (i.e. the region of DNA ‘upstream’ of the gene that controls the expression of the gene)
binding can either allow or prevent the transcription of the gene from taking place
what is a promoter?
controls where the gene is trancribed
what does a transcription inhibitor do?
won’t attach to the promoter
what is special about oestrogen?
steroid therefore lipid soluble so can pass through the bilayer/membrane
what does oestrogen do?
binds to an oestrogen receptor
which causes a change in the shape of the receptor
As a result, the receptor moves away from the protein complex it is normally attached to and binds to the promoter region of one of its target genes
This allows RNA polymerase to bind and to begin transcribing that gene
what does the operator do?
allows repressor to bind blocking the promoter
what does beta galactosidase do?
hydrolyses glycosidic bonds in lactose. converts lactose to glucose and galactose
what does lactose permease do?
increases membrane permeability to lactose so it can get into cell easily
how is transcription sped up?
the binding of camp receptor protein which is when CRP binds to CAMP
what is a intron?
section of a gene that doesnt code for an amino acid
what is a exon?
section of a gene that does code for an amino acid
what happens to introns and exons once the dna is transcribed?
introns are cut out and exons stay and are joined together
how are exons joined together?
By a spliceosome that cause the introns to form a loop shape and be removed while splicing the exons together
what are spliceosomes made up of?
snRPS which are small nuclear ribonucleoprotiens that are usually free floating in the nucleus
what are some forms of post transcriptional control?
the mrna being modified by the introns being removed
rna editing where the nucleotide sequence can be changed by base addition
how is degradtion of mrna a form of translational control?
degradtion of mrna- longer it can last in cytoplasm, greater quantity of proteins made
what is another form of translational control?
initiation factors- aid binding of mrna to ribosomes to be transcribed
binding of inhibitory proteins to mrna to prevent it binding to ribsomes to be synthesised
what are protein kinases?
enzymes that catalyse the addition of phosphate groups to proteins which changes the tertiary structure
aka phosphorylation
what is the role of protein kinases?
carry out phosphorylation which can activate enzymes therefore have a role in regulation cell activity
what are some forms of post translational control?
addition of non protein groups
modifying amino acids and formation of binds eg disulfide bridges
folding/shortening of proteins
modification by cAMP
morphogenesis
regulation of the pattern of anatomical development
whya re fruit flies commonly used in genetic studies?
small
easy to keep
short life cycle
what are homeobox genes
group of genes that all contain a homebox
what is a homeobox
section of DNA 180 base pairs long coding for a part of the protein 60 ammino acids long that is highly conserved
froms a homeodomain
what does highly-conserved mean?
(amino acid) very similar in plants animals and fungi
what does the homeodomain produced by the homeobox genes do?
binds to dna and switches other genes on and off
are regulatory genes
what homeobox gene shows that it is universal along most organisms?
Pax6- which can cause blindness when mutated
found in humans, mice and fruit flies
what are hox genes?
a group of homeobox genes that are ONLY present in animals
what are hox genes responsible for?
correct positioning of body parts
where are hox genes found?
in gene clusters
mammals have 4 clusters on different chromosomes
how is the order in which the homeobox genes are along the chromosome significant?
they are in order in which their effects are expressed in the organisms
what is radial symettry?
no left or right side only top and a bottom
what is bilateral symmetry?
have both left and right sides and a head and tail
what is assymetry?
no lines of symmetry
what is apoptosis?
programmed cell death
what genes regulate mitosis and apoptosis?
hox genes
what happens in apoptosis?
cell and nucleus starts shrinking/ condensing
membrane starts to bleb, forms a funny shape
cell frgaments are fromed from the bleb which are then engulfed by a phaogcyte which digest the cell due to lysosomes
what are some factors that can affect the expression of regulatory genes?
internal and external stressor such as:
temperature
light intensity
hormones
psychological stress
drugs
