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RNA 1
Biology 9
Sumner High School
So far...
• DNA codes for genes which are the
instructions for proteins.
• All living things use the same code.
• We know ribosomes are where proteins
are made.
Today’s question...
• How do we get from gene to ribosome?
• We need a messenger from the nucleus
to the cytoplasm
• We need a way to transfer the code into
protein.
RNA
• RNA = ribonucleic acid
• DNA = deoxyribonucleic acid
• The RNA chain is also a polymer, with similarities
to DNA.
• But only a single strand (in most cases)
• RNA has:
• a sugar portion (plain ribose)
• a phosphate group
• a nitrogen base (3 same as DNA, but 1 different).
Deoxyribose vs Ribose
DNA vs. RNA
Part
DNA
RNA
Sugar
deoxyribose
ribose
Phosphate
Yes
Yes
Nitrogen
bases
ATGC
AUGC
double helix
single
strand
Shape
The four RNA bases
are...
• Adenine
• Uracil
• Guanine
• Cytosine
• The pairing is different between RNA
and DNA
Base pairing
DNA Double Helix
DNA to RNA
Template
Complement
DNA
Template
A
T
A
U
T
A
T
A
G
C
G
C
C
G
C
G
RNA
Lecture Question
•
•
What is the relationship among DNA, a gene, and
a chromosome?
a)
A chromosome contains hundreds of genes, which are
composed of protein.
b)
A chromosome contains hundreds of genes, which are
composed of DNA.
c)
A gene contains hundreds of chromosomes, which are
composed of protein.
d)
A gene is composed of DNA, but there is no relationship to
a chromosome.
e)
A gene contains hundreds of chromosomes, which are
composed of DNA.
Correct answer is b
What job is the woman in the
front of the picture doing?
Preparing the
message
• What does it mean to “transcribe”
something?
• What does a “transcriptionist” do?
• Keys about transcription
• The “language” is the same (English)
• The format of the message is different
(spoken to written).
Message in a Bottle
• To start the process, an RNA copy of
the DNA strand is made
• This is called transcription
• Transcription = creation of the message
from nucleus to cytoplasm.
• The form of RNA made is messenger
RNA or mRNA.
mRNA
• A single strand of RNA
• Formed from the template of one DNA
strand
• Process is governed by the enzyme
RNA polymerase.
mRNA Synthesis
mRNA Synthesis
• DNA template strand (the side of the
DNA with the code) is read from the
phosphate end.
• mRNA strand made from the phosphate
end as well.
• DNA complement strand (DNA across
from the template strand) is not used in
making the mRNA.
At the start codon...
• Enzyme
(RNA
polymerase)
attaches to
DNA and
“unzips” a
short length.
Moving along...
• Enzyme moves
down the DNA
• New area
“unzips”
• mRNA bases
added using the
“rules.”
• DNA “re-zips”
when the
enzyme moves
past.
mRNA Synthesis
At the end...
• Enzyme reaches
a stop codon
• New mRNA set
free.
• Enzyme leaves
the DNA strand.
Key Ideas
• Transcription uses the same “language”
• DNA codons copied to mRNA codons
• Transcription makes a copy of the
genetic info in another form.
• DNA codons to mRNA codons
• Same order, same meaning for which
amino acid is added to the protein.
Practice
• Write the following DNA template strand
on your paper:
• [leave a line space]
• TACATACACGGGAAATTCCCCTAGATT
• [leave a line space]
• Above this strand, make the opposite
side of the DNA (complement strand).
• Below, make the mRNA strand.
Practice Answers
•Complement
DNA:
ATGTATGTGCCCTTTAAGGGGATCTAA
•Template
DNA:
TACATACACGGGAAATTCCCCTAGATT
•Messager
RNA:
AUGUAUGUGCCCUUUAAGGGGAUCUAA