Cellular Control Flashcards
Proteome?
proteins being expressed by a cell
non coding DNA?
- Junk DNA
* found in introns
what is a codon?
a base sequence on mRNA that codes for a single AA
What is an anticodon?
corresponding bse seq on tRNA
What is a mutation?
a change in the sequence of bases in DNA
Point mutation?
only 1 nucleotide is changed
Chromosome mutation?
multiple nucleotides, entire sections of chromosome or entire chromosome changed.
e.g. down syndrome - extra copy of a chromosome
3 types of point mutation?
- Substitution
- deletion
- addition
substitution mutation?
where 1 base is replaced by another
deletion mutation?
where 1 or more bases are removed
addition mutation
where 1 or more bases are added
addition and deletion cause a
frame shift - as the genetic code is read as triplets, the frame shifts meaning the ‘right’ protein is not synthesised
the effec of mutations?
mutations can change the protein that is synthesised from the mutated section of DNA - the gene
Mutations can be:
- neutral
- harmful
- beneficial
Neutral mutation?
- have no effect on the structure and or function of the protein
- (the AA coded for doesn’t change or the AA has very similar properties to the original AA)
Harmful mutations?
- structure and function of the protein is changed so the organism is affected in a negative way
- e.g. sickle cell anaemia, PKU
- causes a selective disadvantage, decreasing chance of survival and decreasing chance of reproduction
beneficial mutations?
structure and function of the protein is changed so the organism is affected in a + way e.g. HIV resistance
sickle cell anaemia?
- most common genetic disorder
- mutation in the gene coding for Hb
- sub of 1 base
- thymine replaces adenine, making valine instead of glutamic acid on the beta chain
- Usually, Hb soluble bc hydrophilic R groups are on the surface
- but valine = hydrophobic so less soluble, causes Hb to stick together in low O2 conc
- changes shape of E to spiky and less flexible
- sickle cells block capillaries, starving tissues of O2
PKU?
- genetic disorder caused by mutation in the gene coding for the enzyme PAH
- PAH needed to convert phenylalanine to tryosine
- when PAH deficient, phenylalanine accumulates
- diet low in phenylalanine and high in tyrosine = treatment but there is no cure
- heel prick test
beneficial mutations: lactose tolerance?
- lactase breaks down lactose
- body stop producing lactase after adolescence
- diary farmers evolved genetic mutations that kept lactase active throughout life
beneficial mutations: HIV resistance?
- CCR5A32 = 32 base pair deletion
- results in non-functioning HIV receptor on T lymphocyte
- HIV can’t bind to T lymphocyte and infect them
mutations occur?
all of the time, randomly in the genome
mutagens?
- inc chance of mutation occuring
* are chemical, physical or biological agents that cause mutations
chemical mutagens?
e.g. deaminating agents - chemically altered bases in DNA
physical mutagens?
e.g. ionising radiation
biological mutagens?
viruses may insert DNA into genome, changing base seq
ways to control gene expression?
- transcriptional control
- post transcriptional control
- post translational control
transcriptional control?
• controlling rate at which gene(s) is transcribed, or whither they are transcribed or not e.g. lac operon, epigenetics
post translational control?
• processing and modification of polypeptide chains formed by translation (Golgi)
post transcriptional control?
processing, modification and editing of mRNA IMMEDIATEDLY AFTER TRANSCRIPTION
What is an operon?
set of genes and regions of DNA that control the transc of structural genes
lac operon occurs in?
bacterial cells, it’s an inducable system
structural genes?
are expressed
control regions?
don’t code for proteins
structural genes are switched on when (lac operon)
in the presence of lactose, off in absence
Components in the lac operon?
- Lac I gene
- Promoter region
- Operator region
- Lac Z
- Lac Y
- Lac A gene
what are the structural genes?
Lac Z, Y and A
What does the lac I gene do?
codes for lac repressor protein which binds to operator region. Is expressed all of the time
what does the lac Z gene do?
codes for lactase (beta galactosidase)
what does the lac Y gene do?
codes for lactose permease, a membrane protein that inc the permeability of the bacterial cell membrane to lactose
lac A gene role?
no direct role, but codes for beta galactosidase transacetylase - no direct role
Control region [lac operon]?
- promoter region
- operator region
- found upstream of structural genes
promoter region?
• where RNAP binds to transcribe the structural genes (every gene has 1)
operator region?
• where the lac repressor protein can bind, locking binding of RNA P to promoter region and transcription of the structural genes
lac operon formed from?
control region and 3 structural genes
non-coding DNA is now called
introns
if a gene is expressed?
it’s transcribed and translated
in the lac operon, lactose acts as a ?
transcription factor bc controls transcription
Epigenetics means
above or on top of the genome
DNA in eukaryotes?
- tightly wound around histone proteins forming chromatin
* the tighter this coiling, the less likely a gene is to be transcribed and vv
how can transcription be increased or decreased?
- histone proteins and DNA can be modified to inc or decrease tightness of coiling and therefore increase or transcription of genes
- e.g. acetylation
- e.g. methylation
acetylation of histones?
causes loosening of coiling
methylation of histones?
coiling becomes tighter, meaning RNAP can’t access gene easily, rate of gene expression = low
acetyl and methyl groups are e.g.s of ?
epigenetic tags
what are epigenetic tags?
chemicals that don’t change the seq of bases in DNA but change the way the genetic code is read
epigenetic tags can be
picked up during an individual’s life and can be passed onto the next gen
Passing of epigenetic tags onto offspring?
- during indiv’s life, envir can cause histone proteins and DNA to become modified by addition/ removal of epigenetic tags and gene expression can change
- e.g. diet, exercise, physical activity, stress
- most tags removed from parental genome after fert but some remain imprinted
- offspring can inherit something learned by parents
- no change in DNA seq, but a change in epigenome - the way in which genes are expressed
post transvriptional modification?
- pre-mRNA is the 1st product of transc
- modified to form mature mRNA, which can then be transl
- modified nucleotide ‘cap’ is added to 5’ end of pre-mRNA
- Tail added to 3’ end
- stabilises molecule, and aids ribosome binding
- then, pre-mRNA spliced
splicing?
- removes non coding sections - introns
* exons remain and expressed
splicing means that
mRNA can produce more than 1 protein from the same gene
Alternate splicing ⭐
exons are always in order, never shuffled
Post translational modification occurs?
after the ribosome has synthesised the polypeptide chain the molecule is modified
How can the polypeptide chain be modified?
- non-protein groups can be added, like CHO chains - often in Golgi
- Structure of indiv AA changed - changes overall folding of the protein
- folding and shortening of proteins
- modification by cAMP
cAMP?
- 2nd messenger, many regulatory effects
- can activate proteins after transl
- e.g. activation of enzyme PKA which starts off the amplification cascade
control of development?
by homeobox genes
homeobox genes?
- control body plan
- same set of genes used by all animals
- set of genes w very similar base seq shared by wide variety of organisms - plants, animals, fungi
what is a hox gene?
1 homeobox gene in an animal
what is the homeodomain?
the seq of AA coded for by homeobox genes
how do homeobox genes provide good evidence for evolution?
v similar, shows that these organisms evolved from a common ancestor
How do homeobox genes work?
- code for transcription factors
* which control gene expression of other genes
what is a homeobox?
the base sequence
proteins containing the homeodomain…
can bind to DNA and act as transcription factors, controlling the expression of whole sets of other genes. These genes control the body plan of the organism.
how do homeobox genes determine the body plan of an organism?
v active during early development, controlling gene expressed of 1000s of other genes which determine the body plan of an organism
if a homeobox gene is mutated?
• the right thing will still develop, because the homeobox gene is still being expressed just in the wrong place
consequences of a mutation in a homeobox gene ?
- usually fatal so mutations rarely passed onto next gen
- means the base sequence of the genes has hardly changed - is highly conserved
- and very similar between diff organisms
Homeobox genes code for transcription factors that?
can bind to the promoter region of sets of genes affecting their expression
proteins coded for by homeobox genes have a wide variety of effects…
- controlling metabolic pathways
- synthesising structural proteins
- setting off cascades of other reaction, eventually determining an aspect of the body plan of an organism e.g development of eyes
Homeobox genes also control?
- mitosis
* apoptosis - programmed cell death
2 ways through which homeobox genes control an organism’s BP?
- controlling gene expression
* controlling mitosis and apoptosis
Stages of apoptosis?
- apoptosis is triggered by external/ internal stimuli
- complex cascades of metabolic reactions cause disintegration of cytoskeleton
- Cell loses its structure and organelles fragment
• blebs form
• cells breaks up into apoptotic bodies which are engulfed by phagocytes and molecules recycled
Factors affecting expression of HG?
- stages of development or age of organism
- abiotic stressed e.g. LI, T
- Psychological stress
- Presence of hormones
- Other chemicals e.g. drugs
Nurturing rats - e.g. of epigenetic tags
ewfw
epigenetics is an e.g. of ?
transcriptional control
E.g. of epigenetics
- nurturing rays
- nurtured = calm adults
- little nurturing = anxious
- when the GR gene is active, it produces a protein that helps body relax
- licking activates GR gene, DNA loosens transcription can occur, so GR protein can be produced
- GR protein binds to cortisol causing cell to send out calming sigal
