RNA and Protein Synthesis
12-3
Biology
Ms. Haut
Flow of Genetic Information
• Flow of genetic information from DNA to RNA
to protein
• The DNA genetic code (genotype) is
expressed as proteins which provide the
physical traits (phenotype) of an organism
GCTGCTAACGTCAGCTAGCTCGTAGC
GCTAGCGCTTGCGTAGCTAAAGTCGA
GCTCGCTTGCGTAGCTAAAGTCGAGC
TGCTGCTAACGTCAGCTAGCTCGTAG
AGCGCTTGCGTAGCTAAAGTCGAGCT
AGCGCTTGCGTAGCTAAAGTCGAGCT
GCTGCTAACGTCAGCTAGCTCGTAGC
AGCGCTTGCGTAGCTAAAGTCGAGCT
AGCGCTTGCGTAGCTAAAGTCGAGCT
GCTGCTAACGTCAGCTAGCTCGTAGC
AGCGCTTGCGTAGCTAAAGTCGAGCT
AGCGCTTGCGTAGCTAAAGTCGAGCT
GCTGCTAACGTCAGCTAGCTCGTAGC
AGCGCTTGCGTAGCTAAAGTCGAGCT
GCTGCTAACGTCAGCTAGCTCGTAGC
AGCGCTTGCGTAGCTAAAGTCGAGC,
cont.
RNA
Proteins
RNA and Protein Synthesis
• Genes are coded DNA instructions that
control the production of proteins.
• Genetic messages can be decoded by
copying part of the nucleotide sequence
from DNA into RNA.
• RNA contains coded information for
making proteins.
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• RNA consists of a
long chain of
nucleotides.
• Each nucleotide is
made up of a 5carbon sugar, a
phosphate group, and
a nitrogenous base.
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http://www.phschool.com/science/biology_place/biocoach/images/transcription/chembase.gif
The Structure of RNA
The Structure of RNA
• Three main differences between RNA and
DNA:
• The sugar in RNA is ribose instead of deoxyribose.
• RNA is generally single-stranded; DNA is doublestranded.
• RNA contains uracil in place of thymine in DNA.
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Types of RNA
• 3 Types of RNA
– messenger RNA (mRNA)
– ribosomal RNA (rRNA)
– transfer RNA (tRNA)
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Types of RNA
• Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids into
proteins.
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Types of RNA
• Ribosomes are made
up of proteins and
ribosomal RNA
(rRNA).
• Line up mRNA and
tRNA
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Types of RNA
• During protein
construction, transfer
RNA (tRNA) transfers
each amino acid to the
ribosome.
• Each tRNA molecule
carries only one kind of
amino acid.
• Carries the anticodon,
complementary to one
mRNA codon.
Anticodon
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Protein Synthesis
• Transcription
 Process in which a
molecule of DNA is
copied into a
complementary
strand of RNA
• Translation
 Process in which the
message in RNA is
made into a protein
Transcription
• RNA molecules are
produced by copying
part of a nucleotide
sequence of DNA into
a complementary
sequence in RNA.
• Transcription requires
the enzyme RNA
polymerase.
• Takes place in the
cell’s nucleus. Copyright Pearson Prentice Hall
Transcription
• During transcription,
RNA polymerase
binds to DNA and
separates the DNA
strands.
• RNA polymerase
uses one strand of
DNA as a template to
assemble nucleotides
into a strand of RNA.
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Transcription
• RNA polymerase
binds only to regions
of DNA known as
promoters.
• Promoters are signals
in DNA that indicate
to the enzyme where
to bind to make RNA.
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Transcription
1. Initiation:
• RNA polymerase (enzyme)
attaches to DNA at the
promoter and “unzips” the
two strands of DNA
2. Elongation:
• RNA polymerase then
“reads” the bases of DNA
and builds a single strand of
complementary RNA called
messenger RNA (mRNA)
3. Termination:
• When the enzyme reaches
the terminator sequence,
the RNA polymerase
detaches from the RNA
molecule and the gene
RNA Editing in Eukaryotes
• Sequences that are not
involved in coding for
proteins are called
introns.
• The DNA sequences that
code for proteins are
called exons.
• When RNA molecules are
formed, introns and exons
are copied from DNA.
• Introns must be removed
and exons spliced together
Exon Intron
Exon
Intron Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
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Coding sequence
NUCLEUS
CYTOPLASM
The Genetic Code
• The genetic code is the “language” of
mRNA instructions.
• The code is written using four “letters” (the
bases: A, U, C, and G).
DNA: T A C A G T T C C A G T
mRNA: A U G U C A A G G U C A
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The Genetic Code
• A codon consists of three consecutive
nucleotides on mRNA that specify a
particular amino acid.
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The Genetic Code
• Each codon
specifies a
particular amino
acid that is to be
placed on the
polypeptide chain.
• Some amino acids
can be specified by
more than one
codon.
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The Genetic Code
• There is one codon AUG that can either
specify the amino acid methionine or serve
as a “start” codon for protein synthesis.
• There are three “stop” codons that do not
code for any amino acid. These “stop”
codons signify the end of a polypeptide.
– UAA
– UAG
– UGA
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Translation
• Translation is the
decoding of an mRNA
message into a
polypeptide chain
(protein).
• Translation takes place
on ribosomes in the
cytoplasm of the cell.
• During translation, the
cell uses information from
messenger RNA to
produce proteins.
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Translation
• Translation begins when an mRNA molecule attaches
to a ribosome starting at the START codon (AUG).
• As each codon of the mRNA molecule moves through
the ribosome, the proper amino acid is brought into
the ribosome by tRNA.
• In the ribosome, the amino acid is transferred to the
growing polypeptide chain.
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Translation
• The ribosome binds new
tRNA molecules and
amino acids as it moves
along the mRNA.
• The growing protein
strand separates from the
former tRNA and forms a
peptide bond with the
amino acid on the new
tRNA.
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Peptide
bond
Translation
• The process
continues until the
ribosome reaches a
STOP codon.
Reading direction
Ribosome
5’
mRNA U U C
3’
UG G
A U G
U A C
Met
U G G
A C C
Trp
U U C
U GG
Incoming tRNA
charged with
amino acid
Ribosome
Reading direction
5’
3’
mRNA U U C
UG G
A U G
U G G
A C C
Outgoing
“empty” tRNA
Trp
Met
U U C
A A G
Phe
U GG
Ribosome
Reading direction
5’
mRNA U U C
3’
UG G
A U G
U G G
U U C
A A G
U GG
A C C
A C C
Phe
Trp
Met
Trp
Ribosome
Reading direction
5’
3’
mRNA U U C
UG G
A U G
U G G
U U C
U GG
A C C
A C C
Phe
Trp
Met
Trp
Reading direction
Ribosome
5’
3’
mRNA U U C
UG G
A U G
Outgoing
“empty” tRNA
Met
Anticodon
A A G
A C C
Phe
Trp
Amino acid
U G G
A C C
Trp
U U C
U GG
Incoming tRNA
charged with
amino acid
The Roles of RNA and DNA
• The cell uses the DNA “master plan” to
prepare RNA “blueprints.” The DNA stays
in the nucleus.
• The RNA molecules go to the protein
building sites in the cytoplasm—the
ribosomes.
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Genes and Proteins
• Genes contain instructions for assembling
proteins.
• Many proteins are enzymes, which
catalyze and regulate chemical reactions.
• Proteins are each specifically designed to
build or operate a component of a living
cell.
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Genes and Proteins
• The sequence of
bases in DNA is used
as a template for
mRNA.
• The codons of mRNA
specify the sequence
of amino acids in a
protein.
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Transcribe and Translate the following
DNA molecule
DNA: T A C A G T T C C A T T
mRNA: A U G-U C A-A G G-U A A
tRNA: U A C-A G U-U G G-A U U
Amino acids: Met-Ser-Arg-Stop
The role of a master plan in a building is similar
to the role of which molecule?
a)
b)
c)
d)
messenger RNA
DNA
transfer RNA
ribosomal RNA
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A base that is present in RNA but NOT in DNA
is
a)
b)
c)
d)
thymine.
uracil.
cytosine.
adenine.
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The nucleic acid responsible for bringing
individual amino acids to the ribosome is
a)
b)
c)
d)
transfer RNA.
DNA.
messenger RNA.
ribosomal RNA.
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A region of a DNA molecule that indicates to
RNA polymerase where to bind to make RNA is
the
a)
b)
c)
d)
intron.
exon.
promoter.
codon.
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A codon typically carries sufficient information to
specify a(an)
a)
b)
c)
d)
single base pair in RNA.
single amino acid.
entire protein.
single base pair in DNA.
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• Stop