Which of the following is not true of RNA processing?
a. Exons are cut out before mRNA leaves the nucleus.
b. Nucleotides may be added at both ends of the RNA.
c. Ribozymes may function in RNA splicing.
d. RNA splicing can be catalyzed by spliceosomes.

Verified step by step guidance

1. Understand the concept of RNA processing, which involves modifications to the pre-mRNA before it becomes mature mRNA and exits the nucleus.
2. Recall that exons are the coding regions of RNA that are retained in the final mRNA, while introns are non-coding regions that are removed during RNA splicing.
3. Recognize that during RNA processing, nucleotides can be added to both ends of the RNA: a 5' cap is added to the beginning, and a poly-A tail is added to the end.
4. Learn that ribozymes, which are RNA molecules with enzymatic activity, can play a role in catalyzing RNA splicing, although spliceosomes are the primary complexes responsible for this process.
5. Evaluate each statement: a) Exons are not cut out; they are retained. b) Nucleotides are indeed added at both ends. c) Ribozymes can function in splicing. d) Spliceosomes catalyze splicing. Identify the incorrect statement based on these facts.

Key Concepts

RNA Processing

RNA processing is a crucial step in gene expression where precursor mRNA (pre-mRNA) is modified to become mature mRNA. This involves splicing, where introns are removed and exons are joined together, as well as the addition of a 5' cap and a poly-A tail to protect the mRNA and aid in its export from the nucleus.

Exons and Introns

Exons are sequences within a gene that are retained in the mature mRNA and code for proteins, while introns are non-coding sequences that are removed during RNA splicing. The statement 'Exons are cut out before mRNA leaves the nucleus' is incorrect, as exons are retained and introns are removed during RNA processing.

Spliceosomes and Ribozymes

Spliceosomes are complex molecular machines composed of proteins and RNA that facilitate the removal of introns from pre-mRNA. Ribozymes are RNA molecules with enzymatic activity that can also catalyze RNA splicing. Both spliceosomes and ribozymes play roles in RNA processing, highlighting the versatility of RNA in biological functions.