Download Part 4 Transcription

Part 4
Transcription
24-1
Learning Targets
8. Compare and Contrast DNA and RNA
9. Understand transcription and the role that RNA
polymerase plays in it.
10. Know how eukaryotic RNAs are modified before
leaving the nucleus.
24-2
RNA Structure & Function
• RNA
• Single-strand
• found in both nucleus & cytoplasm
• Composed of nucleotides
• Each nucleotide has 3 parts
• Phosphate
• 5-C sugar--Ribose
• 4 possible nitrogen bases
• Adenine and guanine
• Cytosine and uracil (uracil replaces thymine)
• Gene Expression
• Segment of DNA  codes for a polypeptide
24-3
Types of RNA
(Overview)
• mRNA- carries genetic information from the
DNA out to ribosomes
• rRNA- composes ribosomes, site of protein
assembly
• tRNA- brings in amino acids to the
ribosomes
24-4
Transcription
• Transcription
• Makes RNA from a DNA
template
• 3 phases-initiation, elongation,
termination
• Process
• RNA polymerase binds
to a promoter region
• DNA helix unzips
• RNA polymerase adds
complementary RNA
nucleotides
• Terminator
24-5
Processing
• Primary mRNA becomes mature
mRNA
• Contains bases complementary
to both intron and exon
segments of DNA
• Intron sequences are removed,
• Ribozyme (RNA enzyme) splices
exon segments together
24-6