FROM DNA TO
PROTEIN
Transcription – Translation
We will use: http://prezi.com/rjwxngctmqlp/ap-bio-molecular-genetics-2-the-central-dogma/
I. Overview
Although DNA and the genes on it are
responsible for inheritance, the day to day
operations of the cell are done by proteins.
 The information from DNA has to be
converted into a functioning protein.
 The molecule that carries, edits and
regulates this information to make proteins
are various forms of RNA
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Central Dogma of Molecular
Biology
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The flow of information in the cell
starts at DNA, which replicates to
form more DNA. Information is then
‘transcribed” into RNA, and then it is
“translated” into protein. The proteins
do most of the work in the cell.
Information flows in the other
direction only in cases of some
viruses and prions.
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Points to review:
 Difference
between DNA and RNA
 Cell organelles – nucleus, ribosomes
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RNA molecules are smaller polynucleotide
chains that are formed from ribose, nitrogencontaining bases (A, C, G and U) and
phosphate. They are usually single stranded
Some types of RNA:
 Messenger RNA (mRNA) – carries
information
 Transfer RNA (tRNA) – carries amino acids
 Ribosomal RNA (rRNA) – forms ribosomes
II. Transcription
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Transcription – the copying of a part of
a DNA molecule to make an mRNA
(messenger RNA) molecule.
Active transcription occurs in specific
parts of the nucleus
The process of transcription:
1.
Initiation – Transcription protein factors
bind to the promoter region of the DNA
molecule. This region is recognized by the
presence of a “TATA box”
2. The transcription factors help RNA
polymerase enzyme to find the proper
region to be copied.
3. After binding, RNA polymerase begins to
unwind the DNA double helix – the template
chain of the DNA molecule will be copied.
4. Elongation – RNA polymerase assembles
the RNA nucleotides that complement the
template DNA nucleotides. This enzyme also
reads from the 3’ – 5’ direction and builds the
new RNA strand in the 5’-3’ direction.
5. As the RNA polymerase continues to copy
the new strand, the copied section of the DNA
molecule joins back because the RNA chain
separates from the template.
6. Termination – The transcription
continues until the enzyme encounters a
terminator signal – a sequence of
nucleotides that signals the end of
transcription.
7. After the terminator nucleotides are
transcribed the pre-mRNA molecule is
released.
8. When the pre-mRNA is released the
DNA reforms its original double helix
structure.
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http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
http://www.youtube.com/watch?v=WsofH466lqk
Game: http://learn.genetics.utah.edu/content/begin/dna/transcribe/
III. mRNA Processing
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Process that protects and allows the mRNA to
leave the nucleus.
Before the mRNA leaves the nucleus, its ends
are modified with a 5’cap and a polyA tail to
protect it from damage in the cytoplasm.
The introns are also removed from the premRNA by splicosomes. Introns are part of the
primary transcript but do not provide useful
information for protein coding.
Exons are segments that will code amino acids
for proteins.
After introns are removed the exons join
together to form the final mRNA molecule
 Some organisms use the mRNA editing to
mix up and form new types of mRNA and
new proteins.
 Only eukaryotes perform mRNA
processing.

IV. The Genetic Code
The genetic code – triplets of mRNA
nucleotides that determine an amino acid
 These triplets are called codons
 There are 64 variations of codons
 The genetic code is

 Universal
 Continuous
 Redundant
(wobble)
Start codon – AUG (also determines
methionine) – start translation
 Stop codons – UAA, UGA, UAG – stops
translation
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V. Transfer RNA (tRNA)

Clover leaf” structure
on “clover leaf” end
 amino acid attached on 3 end
 anticodon
VI. Ribosomes
Small organelles that are made up of
rRNA and proteins.
 Composed of two subunits (small and
large)
 Located on the rough ER or in the
cytoplasm. There are also a few
ribosomes in mitochondria and chloroplast
 Function: makes proteins by reading the
code on the mRNA molecule
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Binding sites:
 A-site
binds to the tRNA anticodon that
carries the proper amino acid
 P-site binds to the last entering tRNA that
holds the growing polypeptide chain
 E-site allows the exit of the empty tRNA
VII. Translation
Review: protein structure and function
 Translation – The process of converting
the information from the “language” of
nucleic acids to the “language” of proteins.
 It takes place in ribosomes in the
cytoplasm or on the surface of the
endoplasmic reticulum
 The product of this process is a
polypeptide chain (primary protein
structure)

The actual process is composed of an
initiation, elongation, and termination
stage.
 During initiation all participants of
translation come together: mRNA (for
genetic information) bind to the small
subunit of the ribosome. The tRNA
molecule that carries Met (start codon)
also attaches to the small subunit (on the
A-site). Finally, the large subunit binds to
the small subunit. The copying starts at
the 5’ end of the mRNA
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This process requires energy (GTP
provides it)
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During elongation: The ribosome moves
over and reads the next codon on the
mRNA. The matching tRNA enters to the
A-site, the previous tRNA moves over to
the P-site. The amino acids on the two
tRNA molecules bind by peptide bond.
This process keeps repeating until a stop
signal on the mRNA is reached.
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Termination starts when the stop codon on
the mRNA is reached. Instead of the
tRNA, a release factor comes in, reads the
triplet and makes the entire complex of
mRNA, tRNA, polypeptide fall apart.
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Related animations:
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http://vcell.ndsu.edu/animations/translation/movie.htm
http://wwwclass.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.
html
http://highered.mcgraw-hill.com/olc/dl/120077/micro06.swf
VIII. Mutations
This section is done as a concept map and a
lab activity.