أسئلة المحاضرة السادسة جينتكس (قبل التعديل)

Post Transcriptional Modification

• Most eukaryotic RNA transcripts (mRNA, rRNA, and tRNA) undergo processing after transcription.
• The primary transcript is the mRNA formed and released from the DNA template.
• This primary transcript undergoes extensive processing to become mature mRNA.
• Processing mainly occurs within the nucleus.

mRNA Processing

• Three main types of mRNA processing:
  • Capping: Addition of a 7-methyl guanosine cap to the 5' end of mRNA
    • Protects the 5' end from exonucleases.
    • Facilitates translation initiation.
  • Tailing: Addition of a poly-adenylate tail (20-250 adenine nucleotides) to the 3' end of mRNA
    • Protects the 3' end from exonucleases.
    • Facilitates translation.
  • Splicing: Removal of introns and joining exons together
    • Primary transcripts are long and contain both coding (exons) and non-coding regions (introns).
    • Splicing removes introns and joins exons to create a mature mRNA molecule.

Spliceosome

• Spliceosome is the molecular complex responsible for splicing.
• Splicing is an energy-requiring process.

tRNA Processing

• tRNA is also processed from a large precursor molecule.
• The processing involves:
  • Removal of sequences at both ends of the precursor molecule.
  • Other modifications to the tRNA molecule.

Post-Transcriptional Modification

• Eukaryotic RNA transcripts undergo extensive processing before they can function.
• Primary transcripts of mRNA, rRNA, and tRNA are modified.
• mRNA processing occurs mainly in the nucleus.
• mRNA processing includes capping, tailing, and splicing.

Capping

• A 7-methyl guanosine cap is added to the 5' end of mRNA.
• The cap is added by mRNA polymerase.
• The cap protects the 5' end from exonucleases.
• The cap is required for efficient translation initiation.

Tailing

• A poly-adenylate (poly-A) tail is added to the 3' end of mRNA.
• The tail consists of 20-250 adenine nucleotides.
• The tail protects the 3' end from exonucleases.
• The tail facilitates translation.

Splicing

• Introns are removed from the primary transcript and exons are joined together.
• The spliceosome is a molecular complex that performs splicing.
• Splicing requires energy.
• The primary transcript is very long and contains coding regions (exons) interrupted by noncoding regions (introns).

tRNA Processing

• tRNA is made from a large precursor molecule that undergoes modifications.
• Sequences at both ends of the tRNA precursor molecule are removed.

Post Transcriptional Modification in Eukaryotic RNA

• Nearly all eukaryotic RNA, including messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA), undergoes significant processing between synthesis and function.
• Primary transcript mRNA is formed and released from the DNA template and requires extensive processing to become mature mRNA.
• Processing primarily occurs within the nucleus.

mRNA Processing

• Capping: Addition of a 7-methyl guanosine cap to the 5' end of mRNA.
  • Protects the 5' end from attack by 5' to 3' exonucleases.
  • Required for efficient translation initiation.
• Tailing (polyadenylation): Addition of a poly-adenylate tail (20-250 adenine nucleotides) to the 3' end of mRNA by poly-A polymerase.
  • Protects the 3' end from attack by 3' to 5' exonucleases.
  • Facilitates translation.
• Splicing: Removal of non-coding regions (introns) and joining the ends of neighboring coding regions (exons).
  • The primary transcript is very long and contains both coding (exons) and non-coding (introns) regions.
  • Performed by a molecular complex called a spliceosome.
  • Splicing requires energy.

tRNA Processing

• tRNA is made from a large precursor molecule that requires modification.
  • Sequences at both ends of the precursor molecule are removed.

Post-Transcriptional Modifications

• Nearly all eukaryotic RNA primary transcripts undergo extensive processing following synthesis.

• Primary transcripts of mRNA, rRNA, and tRNA are processed to become functional RNA.

• Processing occurs primarily in the nucleus.

mRNA Processing

• Capping: Addition of a 7-methyl guanosine cap to the 5' end of the mRNA by mRNA polymerase.

  • Protects the 5' end from attack by 5' to 3' exonucleases.
  • Required for efficient translation initiation.

• Tailing: Addition of a poly-adenylate tail (20-250 adenine nucleotides) to the 3' end of the mRNA.

  • Protects the 3' end from attack by 3' to 5' exonucleases.
  • Facilitates translation.

• Splicing: Removal of introns and joining the ends of neighboring exons.

  • Primary transcripts are long and contain coding regions (exons) interrupted by noncoding regions (introns).
  • The spliceosome performs the splicing process, which requires energy.

tRNA Processing

• tRNA is generated from a large precursor molecule.
• Sequences at both ends of the precursor are removed.