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Chapter 8: From DNA to Protein
Section 8.4 - Transcription
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What do we know so far?
 DNA



DNA is the genetic information
Located in Nucleus (protected in vault)
So the DNA molecule
Proteins
is the instructions
making proteins!!!
 all living things made offor
proteins


Proteins made by ribosomes in cytoplasm
I get it!!!
proteins run living organisms
 example – enzymes
DNA is like
a blueprint!!
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But there is a problem……….
 Need to get the blueprint information (DNA
message) from nucleus to cytoplasm
We need
a messenger
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We need
mRNA!!!!
Who is the mRNA messenger?

messenger RNA
DNA
build proteins
nucleus
RNA
mRNA
cytoplasm
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The “Central Dogma” – information
flows in one direction
transcription
DNA
protein
mRNA
translation
trait
cell nucleus
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cell cytoplasm
(phenotype)
You have to know differences between
DNA and RNA for my test and EOC!!!!
RNA
 ribose sugar
 nitrogen bases

G, C, A, U
DNA
 deoxyribose sugar
 nitrogen bases

 U = uracil


U:A
C:G
 single stranded
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G, C, A, T
 T = thymine


T:A
C:G
 double stranded
Transcription is making mRNA from DNA
 Double stranded DNA unzips by
helicase enzyme
T G G T A C A G C T A G T C A T CG T A C CG T
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Transcription is making mRNA from DNA
 Now that DNA is unzipped; enzyme
RNA polymerase attaches base pairs
T G G T A C A G C T A G T C A T CG T A C CG T
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Transcription is making mRNA from DNA
A
 RNA polymerase will match
RNA bases to DNA bases
on one of the DNA strands
 Notice NO THYMINE!!!!!!!
G
U
A
G
G
U
U
C
A
AG
C
C
G
A
U
A
C
RNA
A C C polymerase G
A
U
T G G T A C A G C T A G T C A T CG T A C CG T
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U
C
Transcription is making mRNA from DNA
 U instead of T is matched to A in mRNA
DNA
TACGCACATTTACGTACGCGG
mRNA
AUGCGUGUAAAUGCAUGCGCC
 Once mRNA molecule is completed it
leaves nucleus and goes to cell cytoplasm
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Chapter 8: From DNA to Protein
Section 8.5 - Translation
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 DNA

instructions remain in nucleus
and we have to send message
out
nucleus
 mRNA

has the instructions for building
proteins from DNA
A C C A U G U C G A U C A G U A G C A U G GC A
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 Proteins are built as chains
of amino acids
 What reads RNA?

need a mRNA reader!
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RNA to protein




mRNA leaves nucleus
mRNA goes to ribosomes in cytoplasm
amino acids are linked bc of mRNA message
proteins built from sequence of amino acids
Now lets look at bigger picture!!!
mRNA
A C C A U G U C G A U C A GU A GC A U G GC A
aa
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aa
aa
aa
aa
aa
aa
aa
RNA to protein bigger picture
Cell cytoplasm
transcription
DNA
translation
mRNA
Cell nucleus
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a
a
protein
a
a
mRNA leaves
nucleus through
nuclear pores
a
a
a
a
a
a
a
a
a
ribosome
a
A C C A U G U C G A U C A GU A GC A U GGC A
proteins synthesized
by ribosomes using
instructions on mRNA
trait
How does mRNA code for proteins?
DNA
mRNA
TACGCACATTTACGTACGCGG
AUGCGUGUAAAUGCAUGCGCC
?
protein
How can you code for 20 amino acids with only
4 nucleotide bases (A,U,G,C)?
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mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
codons
AUGCGUGUAAAUGCAUGCGCC
ribosome
mRNA
protein
Met
Arg
Val Asn
Cys Ala
 Ribosomes read mRNA in blocks of 3
nucleotides called a “Codon”
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Ala
How are the codons matched to amino acids?
DNA
mRNA
tRNA
amino
acid
TACGCACATTTACGTACGCGG
AUGCGUGUAAAUGCAUGCGCC
UAC GCA CAU
anti-codon
Met Arg Val
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The mRNA code
 Start codon

AUG
 Stop codons

UGA, UAA, UAG
codon for
methionine (Met)
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codon for
leucine (Leu)
Summarize whole process of “DNA to
Proteins”
transcription
DNA
translation
a
a
a
a
a
a
protein
mRNA
a
a
a
a
a
a
a
ribosome
a
A C C A U G U C G A U C A GU A GC A U GGC A
tRNA
Cell nucleus
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a
a
Cell cytoplasm
trait
Different view of “DNA to Proteins”
aa
aa
aa
Cell cytoplasm
transcription
translation
aa
aa
aa
aa
aa
protein
aa
aa
aa
Cell nucleus
trait
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DNA
transcription
amino
acids
mRNA
ribosome
protein
tRNA
translation
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Section 8.6:
Gene Expression and
Gene Regulation
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The BIG Questions…
 How are our traits turned “on”
or “off”?
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How do cells control Gene Expression?
 Cells turn genes “on” & “off” by controlling
transcription

Remember what RNA Polymerase did?
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How do cells control Gene Expression?
 For RNA Polymerase to do its job it has to
attach to the DNA molecule


Promoter - area of DNA where RNA polymerase binds.
Also area where the “Gene” sequence begins.
Operator – area of DNA that turns gene “on” or “off”. It’s
the switch
Lets take a closer
look at how this
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works!
Gene regulation using “lac Operon Model”
 The lac Operon uses a repressor protein as a
stop sign until gene is ready to be made
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Do you want all your genes turned on if you
just need to make one trait? NO!!!!!
 Eukaryotic RNA is processed before
leaving nucleus. “RNA Splicing”
Introns – gene segments
that are cut out before
mRNA leaves nucleus
Exons – gene segments
that attach to each other
that will code for mRNA
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http://www.pbslearningmedia.or
g/resource/tdc02.sci.life.gen.pro
teinsynth/from-dna-to-protein/
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