Transcription Termination and Elongation

Key Enzymes and Processes in Transcription

• RNA polymerase is responsible for synthesizing mRNA during transcription.
• Transcription factors facilitate the binding of RNA polymerase to the promoter region, essential for gene transcription initiation.
• RNA splicing is catalyzed by spliceosomes, which remove non-coding introns from pre-mRNA and join exons together.

Promoter Region and Gene Expression

• The promoter region is crucial for starting transcription, typically located about 25 bases upstream of the transcription start site.
• Exons are the coding sequences in a gene that will be expressed in proteins, while introns are non-coding regions that are removed during RNA processing.

Types of RNA and Their Functions

• Three main types of RNA involved in gene expression are:
  • mRNA (messenger RNA): conveys genetic information from DNA to synthesize proteins.
  • tRNA (transfer RNA): transports amino acids to ribosomes during protein synthesis.
  • rRNA (ribosomal RNA): forms the core of ribosome's structure and catalyzes protein synthesis.

Characteristics of RNA

• RNA is typically single-stranded, contains ribose sugar, and has uracil instead of thymine, distinguishing it from DNA.
• Aberrant gene expression refers to the irregular activation or synthesis of specific genes, often resulting from mutations or environmental factors.

RNA Processing and Modifications

• RNA processing involves several steps, including RNA splicing, capping, and polyadenylation.
• A poly(A) tail is added to the 3' end of the mRNA to enhance its stability and facilitate transport out of the nucleus.
• A methylated guanine cap is added to the 5' end of mRNA for protection from degradation and aid in ribosome binding during translation.

Transcription Steps and Elongation

• Transcription occurs in three main stages: initiation, elongation, and termination.
• Elongation finishes when RNA polymerase reaches a termination signal in the DNA sequence.
• The difference between initiation and elongation lies in the phase of transcription, where initiation involves starting the transcription process, and elongation extends the mRNA strand.

Genetic Implications and Eye Color

• Faulty OCA2 expression in both parents can lead to a reduced potential for normal pigmentation and variation in eye color.
• Genetic potential for eye color is influenced by multiple genes, with OCA2 being significant in determining pigment levels.

Alternative Splicing

• Alternative splicing allows for the generation of multiple protein variants from a single gene by rearranging different combinations of exons.
• This process increases the diversity of proteins and is regulated by specific splicing factors.

Structure of mRNA

• The primary transcript mRNA represents the unprocessed RNA produced right after transcription, containing both introns and exons.
• The size range of mRNA in cells is generally between 500-10,000 nucleotides, varying based on the gene being expressed.

Functional Roles in Cells

• Tropomyosins are proteins that regulate muscle contraction and stabilize actin filaments in the cytoskeleton.
• The sense strand or non-template strand of DNA has the same sequence as mRNA, referred to as the coding strand.

Final Notes

• Polyadenylation is the process of adding a poly(A) tail to mRNA, crucial for mRNA stability and regulation.
• 5' capping serves to protect mRNA from degradation and plays a role in the initiation of translation.

Test your knowledge on transcription termination and elongation in this quiz. Learn about the role of the sense strand and the formation of polyT and polyA tails.