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MCB 2050 W21 Final exam with 100- correct answers 2025
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MCB 2050 W21 Final exam with 100- correct answers 2025
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MCB 2050 W21 Final exam with100% correct answers 2025
Below you see the TATA box of a promoters and the general RNApol II
transcription factor TFIID. Please describe in bullet format the 5 key steps
leading to the building of the closed PIC - answer 1. TFIID binds to the
promoter (start of process)
2. Next, TFIIB and TFIIA bind to the TFIID-promoter complex
3. RNAPII is recruited
4. the TFIIF/RNAPII joins the complex by binding to the TFIIB
5. Once bound to the TFIIB, TFIIE and TFIIH enter the complex in
succession
post-translational modification of which domain of a particular protein is
the key event during the transition from initiation to elongation? What is
the purpose of this event? - answer The carboxy terminal domain of
RNAPII is phosphorylated (by TFIIH Kinase).
Purpose = release RNAP from the promoter, allowing RNAPII to transcribe
RNA
Genes that are not highly transcribed do not contain TATA. Which element
in the promoter of these genes would be critical for gene expression? -
answer CpG islands
How do CpG promoters differ from TATA-containing promoters? - answer
TATA-containing promoters initiate and proceed in one direction. At CpG -
both directions
List and Explain in point form the process of RNA interference, starting
with the formation of the dsRNA shown below. Name the complexes
involved in each step - answer 1. RNAPII transcribes DNA
2. Drosha cleaves hairpin structure in dsDNA
, 3. Exportin transports processed dsRNA to cytoplasm
4. dsRNA is cleaved into small RNA fragments by DICER - siRNA complex
formed
5. small ds-siRNAs bind to RISC and form inactive complex
6.Argonaut in RISC unwinds ds-siRNA, active RISC formed
7. Active RISC, guided by ss-siRNA cleaves target mRNA (siRNA/mRNA
complex)
Describe in point format the three key steps of the molecular mechanisms
governing the initiation of DNA replication. Start with the loading of the
Origin Recognition Process (ORC) on DNA. 1 mark for each complete step.
- answer STEP 1: Exit from mitosis and early G1
STEP 2: Late G1 MCM helicase subunits phosphorylated
STEP 3: DNA polymerases recruited to origins to initiate DNA replication
During DNA replication, which proteins form rings around the new
chromatids? When is this protein degraded? - answer In S Phase,
duplicated chromatids are tethered together by Cohesin rings
Degraded in mitosis (Polo + Aurora phosphorylate cohesins causing their
dissociation and degradation by APC)
Describe in point format the key steps in the intrinsic death pathway
starting with the arrival of Bad to the mitochondria and its binding to Bcl-
2, as shown on the picture on the right. Clearly outline what precisely is
the consequence of binding of Bad to Bcl-2. - answer - Bad is activated by
cell stress and DNA damage
- Bad inhibits Bcl-2 (green in the image) from binding to Bak or Bax (blue
in image), which are therefore released from Bcl-2
- Bak or Bax oligomerize, forming pores in the outer mitochondrial
membrane
- Cytochrome C escapes Bak/Bax pores from intermembrane space into the
cytosol
- Cytochrome C then binds to adapter protein Apaf-1 creating a complex
that oligomerizes to form an apoptosome
- Apoptosome dimerizes which activates initiator Caspase-9
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