NOTES: Chapter 13 - RNA & Protein
Synthesis
Vocabulary:
• Messenger RNA
(mRNA)
• Ribosomal RNA
(rRNA)
• Transfer RNA
(tRNA)
• Transcription
• RNA Polymerase
• Codon
• Translation
• Anticodon
Key Concepts:
•What are the 3 main types of
RNA?
What is transcription?
•What is translation?
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Genes and Proteins:
• RECALL: the sequences of
nucleotides in DNA contain
INFORMATION!
• This information is put to
work through the production
of PROTEINS.
2
What do proteins do for the body?
• Proteins are diverse:
 control chemical messages in cell;
 direct the synthesis of carbo’s, lipids,
and nucleotides;
 enzymes;
 give the cell structure and
movement
• Goal of protein synthesis:
MAKE A PROTEIN
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Protein Structure:
• RECALL: proteins are polymers of AMINO
ACIDS
• The sequence of nucleotides in each GENE
contains the information for the sequence of
AMINO ACIDS in a single protein
• Each human cell contains
about +/- 35,000 genes
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•
•
•
•
Like DNA= made of nucleotides
copy of DNA segment
3 main types: mRNA, rRNA, tRNA
3 differences
1) sugar = ribose
2) single stranded
3) instead of the base thymine (T), RNA uses
URACIL (U)
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Job of RNA: Function in
Protein Synthesis
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Role of RNA – an analogy
•
Imagine what goes into a new car
being built on an automobile assembly
line:
1) Engineers make the design and tell
the workers how to make the cars;
2) Workers follow the directions to build
the cars;
3) Suppliers bring parts to the assembly
line so they can be installed in the car
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Role of RNA – an analogy
•
Now imagine what goes into
PROTEIN SYNTHESIS:
1) DNA provides the “workers” with the
instructions for making proteins;
2) The workers (RNA molecules!) follow
the instructions from DNA and build
the proteins;
3) Other workers (other RNA molecules)
bring parts (AMINO ACIDS) over to
the assembly line
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3 Types of RNA:
1) Messenger RNA (mRNA): brings
information from the DNA in the nucleus
out to the ribosomes;
2) Ribosomal RNA (rRNA): clamp on to the
mRNA and use its information to assemble
amino acids into a protein;
3) Transfer RNA (tRNA): the “supplier”;
transports amino acids to the ribosome
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DNA  RNA
• How does the information in DNA ,
which is found in the nucleus, get out
to the ribosomes in the cytoplasm…it
needs a “MESSENGER”!
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• Step #1 (of 2) of protein synthesis
• Transcribe: to make a copy
• transcribing DNA information (gene instructions)
into mRNA
– mRNA can leave the nucleus  ribosomes in the
cytoplasm
• special base sequences in DNA are recognized by
RNA as “start” and “stop” signals
– “Start” sequence called PROMOTER region of DNA
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Details of the Process
• 1. RNA polymerase attaches to DNA at
the site where instructions for the needed
protein begins & it separates the 2 DNA
strands
13
2. RNA polymerase synthesizes the
mRNA strand using complementary
base-pairing
14
• Remember…there aren’t “T” bases in
RNA
• “C” binds with “G”
• DNA “A” binds with RNA “U”
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Which strand was copied? A or B
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3. when RNA polymerase reaches the end or
"STOP" part of the genetic code for that
protein, it releases
4. DNA re-zips
5. finished mRNA (message) leaves the
nucleus and goes to a ribosome in the
cytoplasm
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• Bases are grouped by 3
• Called a CODON (“code”)
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• Transcription ends with mRNA which
will exit the nucleus to the cytoplasm
• So… if transcription is the first step of
Protein Synthesis, what happens next in
the cytoplasm?
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• Making a protein (string of amino acids):
translating from the language of nucleic
acids into a polypeptide
• How does it go from mRNA (copy of DNA) to
amino acids (building blocks of proteins)?
 A group of 3 mRNA bases makes up a
“codon” (think of as a “code word”)
 each codon specifies a particular amino
acid
 there are “start” and “stop” codons
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1) mRNA attaches onto the ribosome
 3 nucleotides of mRNA = codon
• 2nd kind of RNA= ribosomal RNA (rRNA)
 makes up the majority of the ribosome
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• 3rd kind of RNA= transfer RNA (tRNA)
 carries amino acids to the ribosomes (amino
acids join together)
 3 nucleotides of tRNA that “match” or
complement the mRNA = anticodon
 there are 64 different tRNA molecules
(more than 1 for each amino acid)
 REDUNDANCY of the CODE!!
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Amino acid
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amino acid
tRNA
anticodon
codon (mRNA)
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2) By matching the codon of mRNA to the
anticodon of tRNA, the correct amino
acid is put into place
Next tRNA goes here!!!!
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3) a peptide bond is formed between the
2 amino acids
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4) protein chain continues to grow until a
“stop” codon is reached on the mRNA
 no tRNA exists for “stop” codons
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Amino acid
· Molecules of tRNA are specific for
only 1 amino acid
-one end of tRNA attaches to
a
specific amino acid
-the other end attaches to mRNA
codon by base pairing
(anticodon = a sequence of 3 bases
on tRNA)
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● tRNA’s decode the genetic
message codon by codon
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This table shows
the “dictionary”
for the codons
and their
corresponding
amino acids
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Translation: All At Once
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PROTEIN SYNTHESIS: All At Once
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PROTEIN SYNTHESIS
DNA
Step 1. TRANSCIPTION
(nucleus)
mRNA
Step 2. TRANSLATION
(ribosome)
tRNA
PROTEIN
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Protein Synthesis—video
http://www.sciencenetlinks.com/interactives/protein.html
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PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA:
amino
acids:
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PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA: A U G G C G C C A A A U U G A
amino
acids:
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PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA: A U G G C G C C A A A U U G A
amino
acids: met – ala - pro - asn - STOP
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