Section 4

Sequences at the ends of eukaryotic chromosomes critical for replication and maintenance Telomeres prevent broken chromosomes from being unstable and are essential for normal chromosomal termini.

TTAGGG This sequence is repeated hundreds or thousands of times and includes a 3′ overhang of single-stranded DNA.

Replicates telomeric DNA sequences using reverse transcriptase activity Telomerase is crucial for maintaining telomeres, impacting cell lifespan and reproductive capacity.

Movement of a transposable element via reverse transcription of an RNA intermediate This process can lead to gene duplication and the formation of pseudogenes.

A pseudogene that has arisen by reverse transcription of mRNA Processed pseudogenes lack introns and normal transcription sequences.

Generation of different mRNAs by varying the pattern of pre-mRNA splicing This process allows multiple proteins to be encoded by a single gene.

90% This results in the potential for nearly 80,000 different proteins from about 20,000 protein-coding genes.

• Drosha: Cleaves primary miRNA into precursor miRNA • Dicer: Processes precursor miRNA into double-stranded miRNA • RISC: Incorporates one strand of miRNA to target mRNAs This process regulates mRNA translation and degradation.

TRUE This means that a significant portion of protein-coding genes may be regulated by miRNAs.

Binds to the inactive X chromosome, blocking its transcription Xist is a long noncoding RNA that plays a key role in dosage compensation in females.

• Transcription of exons and introns • Splicing to remove introns • Formation of mature mRNA This process ensures that only coding sequences (exons) are included in the final mRNA.