Download Section 8.4: DNA Transcription

Chapter 8
Section 8.4: DNA Transcription
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Objectives
• SWBAT describe the relationship between
RNA and DNA.
• SWBAT identify the three kinds of RNA and
their functions.
• SWBAT compare transcription to replication.
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Vocabulary
• Central dogma
• RNA
– Messenger RNA (mRNA)
– Ribosomal RNA (rRNA)
– Transfer RNA (tRNA)
• Transcription
• RNA polymerase
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RNA Carries DNA’s Instructions
• Central Dogma
of molecular
biology states
that information
flows in one
direction: from
DNA to RNA to
Proteins.
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RNA Carries DNA’s Instructions
• Replication copies DNA
• Transcription converts a DNA instruction into
an intermediate molecule called RNA
(ribonucleic acid).
• Translation interprets the RNA message and
turns it into a protein.
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RNA Carries DNA’s Instructions
• In prokaryotic cells, DNA replication,
transcription and translation all take place in
the cytoplasm due to no nucleus.
• In eukaryotic cells, DNA replication and
transcription take place in the nucleus while
translation occurs in the cytoplasm.
• In eukaryotic cells, RNA is a link between DNA
in the nucleus and protein synthesis in the
cytoplasm.
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RNA (ribonucleic acid)
• Like DNA, RNA is a chain of nucleotides.
– Also made up of a phosphate group, ribose (a
sugar), and a nitrogen containing base.
– “RNA can be thought of as a temporary copy of
DNA that is used and then destroyed.
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RNA (ribonucleic acid)
RNA differs from DNA in
three different ways:
1. RNA has a different
sugar, ribose.
2. The nucleotide uracil
replaces thymine in
RNA.
3. RNA is a singlestranded molecule
whereas DNA is
double-stranded.
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Transcription Practice
• Transcribe the following “genes.”
– AACGTTCCG
– UUGCAAGGC
– ACGTTAACG
– UGCAAUUGC
– GCCGAATCG
– CGGCUUAGC
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Transcription
• Transcription is the process in which a
sequence of DNA is utilized to produce a
complementary strand of RNA.
• During transcription, a gene or genes are
transcribed into strands of RNA (whole
chromosomes are not transcribed into RNA,
only genes).
– The genes, held in DNA, are instructions and the
RNA (messenger RNA) acts as the courier.
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Transcription
• In the process of transcription, DNA
polymerases are replaced with RNA
polymerases.
– Remember, they are enzymes that catalyze
transcription and replication reactions.
– RNA polymerases bInd nucleotides together to
make RNA chains.
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Transcription
Transcription is
catalyzed by RNA
polymerase.
• RNA polymerase
and other proteins
form a transcription
complex.
• The transcription
complex recognizes
the start of a gene
and unwinds a
segment of it.
start site
transcription complex
nucleotides
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Transcription
• Nucleotides pair
with one strand of
the DNA.
• RNA polymerase
bonds the
nucleotides
together
• The DNA helix
winds again as the
gene is
transcribed.
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Transcription
The RNA strand
detaches from
the DNA strand
once the gene is
transcribed.
RNA
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Types of RNA
• Transcription makes several types of RNA, the three that
concern us are:
– Messenger RNA (mRNA) carries the message that
will be translated to form a protein (made by
transcription of DNA).
– Ribosomal RNA (rRNA) forms part of ribosomes
where proteins are made.
– Transfer RNA (tRNA) brings amino acids from the
cytoplasm to a ribosome.
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Transcription and 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
a gene.
– Replication makes
one copy;
transcription can
make many copies.
one
gene
growing RNA strands
DNA
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