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Transcription and Translation
Required notes (paraphrase!)
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I assume that you all carefully read 12-3 beforehand.
If you didn’t get it all, reread 12-3 and review the presentation at home.
Paraphrase these required notes.
• Review the Paper Model Activity
• Questions 9 and 10?
DNA Basics
• What does DNA hold the instructions to build?
• Proteins
• What can proteins do?
• Build your traits (eye color, height, blood type, etc.)
• Help cells and organisms respond to their environment
• Speed up chemical reactions
• Move materials in/out of cells
• Build muscle/tissue
• And everything else (proteins run cells, organisms, and build traits)
• How does DNA make proteins? (Two steps)
• Transcription and translation...
Types of RNA
• What are the three types of RNA?
• Messenger RNA (mRNA)
• Takes info from DNA (nucleus) to ribosomes (cytoplasm)
• Ribosomal RNA (rRNA)
• Ribosomes are made of rRNA (and proteins)
• Transfer RNA (tRNA)
• Transfers amino acids to the ribosome
• Transcription – how would you define it based on the reading?
Transcription - defined
• Transcription – what is it?
• Process in which the information from a section of double-stranded
DNA is converted into complimentary, single-stranded mRNA.
• What is “complimentary”?
• Opposite base pair. Adenine is complimentary to thymine.
Transcription – 1
Process in which the information from a section of double-stranded DNA
is converted into complimentary, single-stranded mRNA.
DNA
ATATTTAATAATATGGCAACCGGG
TATAAATTATTATACCGTTGGCCC
Promoter
(sequence varies)
RNA polymerase finds promoter (“start here”) region
Separates (“unzips”) two strands. Note – helicase unzips in replication
Transcription can then occur on either/both strands.
What would be the first base on the mRNA created from the bottom DNA?
Transcription - 2
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DNA
ATATTTAATAATATGGCAACCGGG
DNA
TATAAATTATTATACCGTTGGCCC
RNA polymerase next finds the “TATA” box. What bases are in TATA boxes?
(a region of repeating T’s and A’s in most eukaryotes).
Then removes “introns” and transcribes only the “exons”
How many bases would be transcribed (only exons)?
Transcription - 3
DNA
mRNA
DNA
ATATTTAATAATATGGCAACCGGG
AUGACCGGT
ACCGGG
TATAAATTATTATACCGTTGGCCC
• RNA polymerase creates single stranded mRNA using only exons
• (exons = “expressed” DNA, introns are “in between,” edited out)
• Base pair rules; but “uracil” is in place of thymine. What’s wrong here?
• “spell checks” mRNA, sends to ribosome
Cytoplasm
Transcription - 4
DNA
DNA
AUGACCGGG
TATAAATTATTATACCGTTGGCCC
• DNA strands come back together (double-stranded again)
• mRNA is single-stranded and goes to ribosomes
• ***mRNA never attaches to DNA!***
Stays in
nucleus
mRNA
ATATTTAATAATATGGCAACCGGG
Transcription
• http://highered.mheducation.com/sites/0072556781/student_view0/c
hapter12/animation_quiz_1.html
• http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html
• http://www.johnkyrk.com/DNAtranscription.html
Cool current event note!
• New erythropoietin (EPO) test.
• EPO boosts production of red blood cells – Lance Armstrong used it.
• Concern now that athletes may inject genes to make EPO into their cells
• New test can scan for this gene using introns/exons!
• A person’s own EPO gene has introns.
• An inserted gene would likely lack those introns. So their absence
could signal gene doping.
Translation- defined
• Translation– what is it? Discuss, be ready to share
• When mRNA is converted to a chain of amino acids (protein!).
• 20 naturally occurring amino acids
• Order of these a.a. determines shape & function of protein.
• What is the amino acid order called?
• Primary structure! (The “spelling” of the protein)
Translation – 2
When mRNA is converted to a chain of amino acids (protein!).
20 naturally occurring amino acids
Order of these a.a. (primary structure) determines shape & function of protein.
RIBOSOME
mRNA
AUGACCGGG
codon (3 bases)
ACG
anti-codon
tRNA
(LOTS available
in cytoplasm)
UAC
CCC
UGG
Translation - 3
RIBOSOME
mRNA
AUGACCGGG
ACG
tRNA
(attached to
amino acids
See page 303.)
UAC
CCC
UGG
cysteine
methionine
glycine
threonine
Translation - 4
RIBOSOME
mRNA
AUGACCGGG
ACG
tRNA
UAC
(randomly moves
around; binds
with correct codon) methionine
CCC
UGG
cysteine
glycine
threonine
Translation - 5
RIBOSOME
mRNA
AUGACCGGG
ACG
Methionine-
tRNA
(randomly moves
around; binds
with correct codon)
CCC
UGG
cysteine
glycine
threonine
Translation - 6
RIBOSOME
mRNA
AUGACCGGG
Methionine- threonine
tRNA
Only correct tRNA molecules are
used; unlimited amounts of all types
are available.
ACG
CCC
cysteine
glycine
Translation - 7
RIBOSOME
mRNA
AUGACCGGG
Methionine- threonine- glycine
ACG
tRNA
Only correct tRNA molecules are
used; unlimited amounts of all types
are available.
cysteine
Translation - 8
RIBOSOME
mRNA
AUGACCGGG
Methionine- threonine-glycine  goes to ER, Golgi, and beyond!
• This example protein is three amino acids long;
most are hundreds to thousands
• Protein is then finished (ER) and packaged up (Golgi) for use…
• mRNA is used again
• Note: AUG is common “start” codon; can you find a “stop” codon?
• http://www.sciencenetlinks.com/interactives/protein.html
• http://www.wiley.com/college/test/0471787159/biology_basics/an
imations/fromGeneToProtein.swf
Practice
Transcribe the lower strand of DNA into an amino acid sequence. The bases in red
are introns. This sequence of DNA is near the beginning of a gene that codes for a
protein.
ATGGCCGTCCCCAAAATTGACTTA
TATA BOX AND PROMOTER TACCGGCAGGGGTTTTAACTGAAT
Key: Methoinine – Serine – Proline – Aspartic acid – Leucine
Pass out homework (as always, working together on HW is not ok).