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CMB2001 Questions and Answer | Latest Update 2024/2025

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Describe how H3Lys9me heterochromatin is formed ~~> H3Lys9me heterochromatin formation: Lys9 deacetylated by HDAC. Suvar39 then methylates lys9. Methylated lys9 is recognised by HP1 and then HP1 binds. HP1 has chromodomain - chromodomains often recognise and bind to methylated lys residu...

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  • September 15, 2024
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CMB2001 Questions and Answer |
Latest Update 2024/2025
Describe how H3Lys9me heterochromatin is formed


✓ ~~> H3Lys9me heterochromatin formation: Lys9 deacetylated by

HDAC. Suvar39 then methylates lys9. Methylated lys9 is recognised by

HP1 and then HP1 binds. HP1 has chromodomain - chromodomains

often recognise and bind to methylated lys residues. Chromodomain

on HP1 is specific for H3Lys9me (with di or tri methylated lys 9). Binding

of HP1 is thought to compact nucleosome arrays as HP1s join together.




What is gene expression?


✓ ~~> Process by which DNA is decoded to proteins

Causes protein synthesis (DNA to RNA by transcription, RNA to protein by

translation)




It is highly regulated




What is transcription?


✓ ~~> ds DNA to ss mRNA

Template strand copied 5' to 3'



Master01 | September, 2024/2025 | Latest update

, 2 | P a g e | © copyright 2024/2025 | Grade A+




Describe transcription in prokaryotes


✓ ~~> RNA polymerase with sigma factor 70 (holoenzyme) makes

contact with -35 and -10 promoter region (upstream from transcription

start site). This forms closed complex.




The DNA is opened (open complex) over transcription start site and RNA pol

uses template strand to begin making copy (initiation). Sigma factor 70 is

released and the mRNA strand is elongated 5' to 3'.




What does a promoter do?


✓ ~~> Initiate and control transcription when RNA pol binds




What are +1, -10 and -35 sequences on prokaryote promoter?


✓ ~~> + 1 is the first base that is used as template

-10 and -35 are consensus sequences which are strongest promoters and are

upstream. Both hexamers




Sequences are very defined in prokaryotes




Master01 | September, 2024/2025 | Latest update

, 3 | P a g e | © copyright 2024/2025 | Grade A+


Describe eukaryotic promoters (go into detail on core and regulatory regions)


✓ ~~> There is a core (basal region) around transcription start site, and a

regulatory region upstream.




TATA box at -30 and initiator at +1 are found on the core region. There is also

DPE at +30 and BRE at -35. Often core regions will not have all of these

elements




Regulatory region has proximal elements (UAS and URS) and distal (enhancer

and silencer). UAS and enhancer and activator binding sites which increases

transcription. URS and silencer are repressor binding sites which decrease

transcription.




Sequences are less defined than they are in prokaryotes




What are CpG islands?


✓ ~~> Regions with high frequency of CG sequences (CpG islands).

These CG sequences have C residues that are hypomethylated which

causes decreased transcription (due to less initiation)




Master01 | September, 2024/2025 | Latest update

, 4 | P a g e | © copyright 2024/2025 | Grade A+


What do reporter genes do?


✓ ~~> Encode proteins whose levels can be easily measured eg GFP

and LacZ




Amount of reporter protein is proportional to gene expression (activity)




Reporter genes can be added to plasmids which cause recipient cells to

have reporter gene expression




Contrast types of RNA pol in prokaryotes and eukaryotes


✓ ~~> In prokaryotes there's only one

In eukaryotes there are at least 3 main ones




Similar structure but bacterial has 2 alpha, 1 beta, 1 beta prime and one

omega subunit. Yeast RNA pol II has 12 subunits.




What are types of RNA pol in eukaryotes?


✓ ~~> RNA pol I - transcribe rRNA (28S, 18S and 5.8S). Found in nucleolus




Master01 | September, 2024/2025 | Latest update

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