control of gene expression Flashcards
how many genes does the human genome contain and how many of these are actually expressed?
50,000 and only 10,000 are expressed.
what is differential gene expression?
the different interpretation of the genome in each cell
explain how gene expression is regulated with respect to time and space?
time - embryos express different genes to adults
space - brain expresses different genes to muscle cells
what is an example of a congenital disorder?
bithorax gene mutation in drosophila
where are totipotent cells found?
in zygotes
what tissue can pluripotent stem cells not differentiate into?
placental tissue
how are iPS formed?
introducing new genes and transcription factors to turn on genes that were off
what does the primary transcript consist of?
both exons and introns
what is beta thalassemia caused by?
insufficient expression of beta globin
why donβt zygotes need to transcribe genes?
they have pre existing maternal RNAs
how do cells respond to viral infections?
they transcribe genes that code for antiviral proteins
explain how the ribosome finds the start sequence?
it binds to and recognizes the cap and will keep going until it recognizes the start sequence which is the first AUG near the kozak sequence.
what two proteins recognize the cap?
EFI3 and EFI4
how does ferritin work?
βFerritin binds to iron and retains it in the cytoplasm as a store for excess.
βferritin is needed when there is excess iron.
βWhen there are low levels of iron, an inhibitor blocks the ribosomal subunit from interacting with the ferritin mRNA.
β no translation of the ferritin mRNA takes place.
βin an excess of iron, the iron binds to the inhibitor, taking it away from the ferritin mRNA.
βThis allows the ribosomal subunit access to the mRNA, so translation occurs.
what is the function of the UTRs?
they stabilize the mRNA and regulate their life span.
what does the 3β UTR sequence do?
causes proteins to bind which protects the RNA from degradation
what is the promoter region in eukaryotes and prokaryotes
TATA box and pribnow box
What is Ξ²-thalassaemia and what kind of mutations cause this disease?
βblood disorder that reduces the production of haemoglobin.
βthe Ξ²-globin protein is structurally normal (unlike sickle cell disease).
βMutations that cause this disease are usually single base changes
Give examples of translational control
EARLY EMBRYOGENESIS:
βDuring the first 4-8 weeks of cell division, there is no gene expression.
βAt the end of blastocyst formation, genes are expressed due to the up-regulation of translation from maternally-derived preformed mRNAs.
ENVIRONMENTAL STRESS:
βexposure to heat shock or pathogens can cause global changes in translation.
There are many specific examples, such as ferritin.
What is the function of the 5β UTR?
βdetermining how efficiently the ribosome initiates translation.
What are miRNAs, and what is their function and how many are encoded in the human genome?
βThe human genome encodes over 500 small, noncoding RNAs that are transcribed by RNA Polymerase II.
βThese RNAs are referred to as microRNAs or miRNAs.
βmiRNAs act to control the post-transcriptional regulation of as many as one-third of all human genes.
Describe the synthesis of miRNAs and explain how they work
βEach precursor miRNA transcript is processed to form a double-stranded intermediate
β further processed to form a mature, single-stranded miRNA.
β This miRNA assembles with a set of proteins into a complex called RISC, which then searches for mRNAs that have a nucleotide sequence complementary to its bound miRNA.
βDepending on how extensive the region of complementarity is, the target mRNA is either rapidly degraded by a nuclease within the RISC (this happens when there is an extensive match)
βor transferred to an area of the cytoplasm where other cellular nucleases destroy it (this happens when there is a less extensive match).
