Download Chapter 12:

RNA & Protein Synthesis
Quick Review
A. What are some proteins you are made of?
Ex: keratin, hemoglobin, enzymes, antibodies
B. What are the building blocks of proteins?
Amino acids
C. What organelle makes proteins?
Ribosomes
D. Where are the instructions for
making a protein?
DNA!
E. Where is this molecule located
in cell?
Nucleus
Central Dogma
So, if DNA has the instructions for genes,
which build proteins, but DNA never leaves
the nucleus, then how can these proteins
get made at the ribosomes??
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DNA “master plan”
RNA “blueprints”
DNA stays in the
nucleus
RNA goes to
ribosomes to build
proteins
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Photo source:
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ans_(Blueprints).pdf/page1-1280pxHouse_Plans_(Blueprints).pdf.jpg
What is RNA?
RNA is a class of molecules
RNA vs. DNA
1. Ribose is the sugar in RNA
2. Single-stranded
3. Uracil, not Thymine
Structure of RNA
1. Phosphate group
2. 5-carbon sugar- ribose
3. Bases
i. Adenine
ii. Uracil
iii. Cytosine
iv. Guanine
Three Main Types of RNA
1. Messenger RNA (mRNA)
2. Ribosomal RNA (rRNA)
3. Transfer RNA (tRNA)
1. Messenger RNA
- Made in nucleus
- Transcribes a single gene in DNA
- Contains instructions for making
amino acids
--> EXITS the nucleus
2. Ribosomal RNA
- Actual site where mRNA codons
are translated into amino acids
- Like the “workbench”
 Ribosome attaches to mRNA strand
 As mRNA strand slides through
subunits, the codons are ‘read’
mRNA
3. Transfer RNA
- RNA with amino acid
attached
- Carries complementary
anti-codon that matches
the codon using base
pairing
About Codons
mRNA transcripts are read 3-letters at a time.
These are called ‘CODONS’. They are like the
words that make up the sentences of a gene.
D.START codon: AUG – stimulates beginning of
translation
D.STOP codons:
UGA, UAA, UAG
III. Steps for Protein Synthesis
A. Transcription
• During transcription, RNA polymerase binds to
DNA and separates the DNA strands
• RNA Polymerase then uses one strand of
DNA as a template to assemble nucleotides
into RNA
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3. Promoters are regions on DNA that show
where RNA Polymerase must bind to begin
the Transcription of RNA
4. Called the TATA box
5. Specific base sequences act as signals to
stop and are called the termination signal
Transcription- nucleus
B. mRNA Processing
1. After the DNA is
transcribed into RNA,
editing must be done to
the nucleotide chain to
make the RNA
functional
2. Introns, nonfunctional segments of
DNA are snipped out of
the chain
3. Exons, segments of DNA that code
for proteins, are then rejoined by the
enzyme ligase
4. A cap is added to the 5’ end of the
newly copied mRNA
5. A poly-A tail is added to the 3’ end
of the RNA
Exons
Introns
21
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mRNA Transcript
mRNA leaves the nucleus through
its pores and goes to the ribosomes
22
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C. Translation
1. Translation is the process of decoding the
mRNA into a polypeptide chain
2. Ribosomes read mRNA three bases or 1
codon at a time and construct the proteins
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3. mRNA transcript start codon AUG
attaches to the ribosome
Process continues until a stop codon.
End Product –The Protein!
4. The end products of protein synthesis is
a primary structure of a protein
5. A sequence of amino acid bonded
together by peptide bonds
aa2
aa1
aa3
aa4
aa5
aa199
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27
aa200
One gene,
one
polypeptide
Translation
Second base in codon
So how can you
tell what amino
acid will be
carried on the
tRNA? Use this
chart!
Try AUG codonwhat amino
acid? (use codon!)
First base in codon
Third
base
in
codon
Name the Amino Acids
•
•
•
•
•
GGG?
UCA?
CAU?
GCA?
AAA?
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• Translation guided animation
• All of DNA Translation
Mutations
M
u
t
a
t
i
o
n
s
Ryan Clark of Pittsburgh Steelers
Photo source: http://www.dnalc.org/resources/3d/17-sickle-cell.html
438-base sequence.
Can’t Carry Oxygen
Tay Sachs
http://www.pbs.org/wgbh/nova/body/cracking
-the-code-of-life.html
Time- 17:00-20:00

Inherited genetic mutation
HEXA codes for an enzyme that
breaks down fatty acids


Build up of fatty acids in the brain
IV. Mistakes Happen!
Gene mutations
A. Mutation is any change in the DNA sequence
 Ex: Lactase mutation for lactose digestion
 Ex: Sickle cell- no hemoglobin
 Some mutations are helpful
 Sickle cell anemia & malaria
B. A mutagen is any agent that causes a change in
DNA
Mutagens can be chemical or physical
• Ex: UV rays, nuclear radiation, chemicals (benzene,
formaldehyde)
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C. Point Mutations
Diseases Caused by Point Mutations
Colorblindness
 Hemophilia
 Cystic Fibrosis
 Tay Sachs
 PKU



Occur at ONE point in the DNA sequence.
It is a change on one nucleotide
Cat ate the rat.
Car ate the rat.
The protein might still be functional.
Types of Point Mutations
Original Strand RNA:
AUG CCA ACA GAU CAG UAG CGC GUA
1. Substitution
AUG CCA ACA GAU CAG UAC CGC GUA
2. Insertion into original
ACU GCC AAC AGA UCA GUA GCG CGU A
3. Deletion from original
AGC CAA CAG AUC AGU AGC GCG UA
The cat ate the rat.

Substitution
The car ate the
rat.

Insertion
The caa tat eth era
t.

Deletion
Tec ata tet her at.
D. Frameshift Mutations
• Effects of insertions or deletions are
more dramatic
• Addition or deletion of a nucleotide
causes a shift in grouping of codons
• Changes like these are called
frameshift mutations
Some substitutions don’t cause
changes in the amino acids
GCC, GCA = alanine
CGG, AGG = arginine
Remember: there are extra amino acid
“words”: 20 A.A.’s, 64 codons!
BUT, both insertion and deletion cause
frameshifts
E. Chromosomal Mutations
• Change in shape, size, or structure of
chromosome
• Now you are affecting 1000s of
proteins
• System deformities can occur
Chromosomal Mutations