Download 8.4 Transcription

8.4
12.3
Transcription
KEY CONCEPT
Transcription converts DNA into a single-stranded
RNA molecule. DNA can not leave nucleus..RNA CAN!
8.4
12.3
Transcription
The Central Dogma includes three processes.
– Replication
– Transcription
replication
– Translation
• RNA is the link between
2.
1.
DNA and making the
proteins.
3.
transcription
4. translation
5.
8.4 Transcription
DNA
 DNA has a deoxyribose sugar.
 DNA has A, T, C and G as bases.
 DNA is a double-stranded structure.
8.4
12.3
Transcription
• RNA differs from DNA in three major ways.
 RNA has a ribose sugar.
 RNA has uracil instead of thymine.
 RNA is a single-stranded structure.
8.4
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Transcription
Job of Transcription is to copy DNA to make a strand of
RNA.
• It does this in 3 major steps
8.4
12.3
Transcription
1. RNA polymerase unzips a specific gene in the
segment of DNA needed.
start site
RNA Polymerase
nucleotides
8.4
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Transcription
2. RNA polymerase bonds complementary
nucleotides with one strand of DNA
5. nucleotides
DNA
4. DNA
strand
RNA polymerase
moves along the DNA
6. mrna
7. RNA polymerase
8.4
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Transcription
3. – The mRNA strand detaches from the DNA once the
gene is transcribed and travels out of nucleus to ribosome
(rRNA).
–The DNA helix winds back up again.
RNA
8.4
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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 part of ribosomes where
proteins are made.
– Transfer RNA (tRNA) brings amino acids from the
cytoplasm to a ribosome.
Remember:
Amino acids are
building blocks of a
protein
8.4
12.3
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 in cell;
transcription copies
a specific gene on a strand of DNA.
one
gene
growing RNA strands
– Replication makes
one copy of DNA;
transcription can
DNA
make many copies.