✓ Board-verified
Biology · 2023 · 3 marks
CBSE 2023 · Region 3 · Set 1 · Q22
(a) (i) How many types of RNA polymerases are there in a eukaryote cell? Mention which one of them transcribes hnRNA. (ii) Write the changes that…
(a)(i)
How many types of RNA polymerases are there in a eukaryote cell ? Mention which one of them transcribes hnRNA.
(ii)
Write the changes that hnRNA undergoes before it leaves the nucleus as mRNA.
OR
(b)
The length of DNA in any cell is far greater than the dimension of its nucleus. Explain how this enormous DNA is packaged in a eukaryotic cell.
Marking-scheme solution
(i)
$\displaystyle 3$ types
RNA Polymerase -II
(ii)
Splicing /Introns are removed and exons are joined in a definite order, undergoes capping /at $\displaystyle 5$' end where unusual nucleotide (methyl guanosine triphosphate) is added , tailing/ at $\displaystyle 3$' end where ($\displaystyle 200$-$\displaystyle 300$) adenylate residues are added.
A set of positively charged proteins called histones, due to presence of lysine and arginine( basic amino acids), holds the negatively charged DNA around it in a coiled manner, histones are organised to form a unit of eight molecules (histone octamer), a typical nucleosome contains $\displaystyle 200$ bp of DNA helix, Nucleosomes constitute repeating units of a structure in nucleus called chromatin thread ( like bodies as "beads on string" structure in a nucleus).
All Molecular Basis of Inheritance questions2023 question paperNCERT solutions: Molecular Basis of InheritancePractice Molecular Basis of Inheritance →
More from Molecular Basis of Inheritance
- A bacterium having radioactive thymidine in its DNA is allowed to multiply in a medium having non-radioactive thymidine for two generations. What…2026
- Assertion: Repetitive sequences are stretches of DNA sequences that are thought to have no direct coding functions. Reason (R): They shed light on…2026
- Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.2025
- In a human, the average gene consists of (i) bases and the largest known human gene contains (ii) bases. Select the correct option to fill in the…2026
- In a translational unit UTRs are present at:2025
- The simplest definition of a gene in eukaryotes is - A unit of DNA that has information to mainly specify the synthesis of:2025
- Explain the processing of heterogeneous nuclear RNA (hnRNA) into a fully functional mRNA in eukaryotes. Where does this processing occur in the cell?2024
- The type of bond represented by the dotted line '-----' in a schematic polynucleotide chain is:2024
CBSE Class 12 Biology past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.