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8.4 Transcription
KEY CONCEPT
Transcription converts a gene into a single-stranded
RNA molecule.
8.4 Transcription
The transcription process is similar to replication.
• Transcription and replication both involve complex
enzymes and complementary base pairing.
• The two processes have different end results.
– Replication copies
all the DNA;
transcription copies
one
gene
growing RNA strands
a gene.
– Replication makes
one copy;
DNA
transcription can
make many copies.
8.4 Transcription
• The central dogma states that information flows in one
direction from DNA to RNA to proteins.
•
The central dogma includes three processes.
– Replication
– Transcription
– Translation
• RNA carries DNA’s
instructions to make
proteins
replication
transcription
translation
8.4 Transcription
• RNA differs from DNA in three major ways.
– RNA has a ribose sugar.
-DNA uses deoxyribose
– RNA has uracil instead of thymine. -DNA uses Thymine
– RNA is a single-stranded structure.-DNA is double stranded
8.4 Transcription
• Transcription is catalyzed by RNA polymerase.
1. The transcription complex (made of RNA
polymerase and other proteins) recognizes the
start site of a gene and begins to unwind the
DNA.
start site
7. transcription complex
5. nucleotides
8.4 Transcription
2. a. RNA polymerase reads one side of the DNA
template
b. It strings together a complementary strand of RNA
nucleotides.
c. The DNA helix winds again as the gene is transcribed.
d. RNA polymerase bonds the nucleotides together.
4. Original DNA Strand
DNA
RNA polymerase
moves along the DNA
6. New RNA Strand
8.4 Transcription
3. The growing RNA strand hangs freely as it is
transcribed and detaches from the DNA once the entire
gene is transcribed.
RNA
8.4 Transcription
• Transcription makes three types of RNA.
– Messenger RNA (mRNA) carries the message that will
be translated to form a protein.
– Ribosomal RNA (rRNA) forms the part of ribosomes
where proteins are made.
– Transfer RNA (tRNA) brings amino acids (protein “parts”)
from the cytoplasm to a ribosome to help make a
growing protein.