Transcript 8.4 Transcription

8.4 Transcription
KEY CONCEPT – DNA directs the synthesis of proteins
through three steps (Replication, Transcription, &
Translation)
Transcription is step 2 of Protein Synthesis and
converts a gene into a single-stranded RNA molecule.
8.4 Transcription
DNA directs the synthesis of proteins through three
steps (Replication, Transcription, & Translation)
What was step ONE of protein synthesis?
8.4 Transcription
• Yuuuuuhhhp,…
Replication of new copies of DNA for new daughter cells.
8.4 Transcription
RNA carries DNA’s instructions.
• RNA copies the
DNA’s info (in a
gene) from the
nucleus and takes it
to the cytoplasm.
• The central dogma
states that
information flows in
one direction from
DNA to RNA to
proteins.
8.4 Transcription
•
The central dogma includes three processes.
– Replication
– Transcription
replication
– Translation
transcription
• RNA is a link between
DNA and proteins.
translation
8.4 Transcription
• RNA differs from DNA in three major ways.
– RNA has a ribose sugar (DNA has a deoxy ribose sugar.)
– RNA has uracil (U), (DNA has thymine - T, instead.)
– RNA is a single-stranded structure, (DNA is ?).
RNA
8.4 Transcription
• Transcription is catalyzed (started) by RNA polymerase.
– RNA polymerase and other proteins form a
transcription complex.
Step 1. The transcription complex recognizes the
start of a gene and unwinds a segment of it.
start site
transcription complex
nucleotides
8.4 Transcription
Step 2. Nucleotides pair with one strand of the DNA.
– RNA polymerase bonds the nucleotides together.
– The DNA helix winds again as the gene is transcribed.
DNA
RNA polymerase
moves along the DNA
8.4 Transcription
3. The RNA strand detaches from the DNA once the 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 part of ribosomes where
proteins are made.
– Transfer RNA (tRNA) brings amino acids from the
cytoplasm to a ribosome (to assemble a protein).
8.4 Transcription
TESTIFY!
• What mRNA strand will be transcribed from the following
DNA sequence (gene)?
Gene (DNA) Sequence:
ATTAGATTACAATTTGATTACCA
8.4 Transcription
An-swer:
Gene: A T T A G A T T A C A A T T T G A T T A C C A
(only 1 of the
2 DNA strands
Is copied)
mRNA: U A A U C U A A U G U U A A A C U A A U G G U
8.4 Transcription
Summary: 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;
one
gene
growing RNA strands
transcription copies
a gene.
– Replication makes
DNA
one copy;
transcription can
make many copies.
8.4 Transcription
How is DNA used by your cells?
DNA stores an organism’s genetic information
in sections called “genes”, the info to make one
protein, in a three step process: Replication,
Transcription, and Translation.
There are two categories of proteins:
1)enzymes (proteins that catalyze reactions)
2)structural proteins that form parts – structures
– of your cells and body.