BELLRINGER:
Draw the following box and fill in the squares:
REPLICATION
Where in the cell does this take place?
TRANSCRIPTION
Where in the cell does this take place?
What is created in this process?
What is created in this process?
WHY does this take place?
WHY does this take place?
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THE THREE TYPES OF RNA
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
There are three types of RNA that help build proteins.
# 1 Messenger RNA (mRNA)
brings instructions from DNA in the nucleus to the
cytoplasm.
Then mRNA binds to ribosomes.
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#2
Transfer RNA (tRNA) is the supplier.
Transfer RNA delivers amino acids (the building
blocks of proteins) to the ribosome to be assembled
into a protein.
Amino Acid
How it binds with mRNA
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#3
Ribosomes are made of Ribosomal RNA (rRNA).
rRNA uses the instructions from mRNA and the
supplies from tRNA to assemble the amino acids in
the correct order.
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
mRNA brings the instructions.

tRNA supplies the amino acid parts.

rRNA builds the proteins using the
instructions and amino acids.
RIBOSOME
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THE PROCESS OF TRANSLATION
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Protein Synthesis
1.
2.
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Transcription
Translation
Why does mRNA have to be made?
(Why can’t DNA deliver it’s own instructions)
Nucleus
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The Genetic Code

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Every three letters on a mRNA
strand, called a codon, is a code
for a specific amino acid (a
building block to make protein)
Every three letters on an mRNA
strand is a codon.
Each codon codes for a specific
amino acid.
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CODON CHART
Things to notice:
There are 64 possible codon combinations
There are only 20 different amino acids
Most amino acids correspond to more than one codon
Translation
changing
nucleic acid language
to
amino acid language
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Step 1:

As translation begins, the “capped” end of mRNA
strand attaches to a ribosome.
mRNA strand
Ribosome
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tRNA’s role

tRNAs bring amino acids to the ribosomes.
mRNA
Coming from
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Nucleus
RIBOSOME
Each tRNA only
carries one amino
acid.

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Amino
acid

There are also three nucleotides on the bottom of the
tRNA called an anti-codon.

Anti-codons complementary base pair with the codons
on mRNA.
(this is to make sure they are bringing the correct amino acidIf the anti-codon doesn’t base pair with the codon, then the wrong
amino acid was brought)
Anti-codon
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Step 2: Initiation

AUG is usually the first codon on the mRNA strand.

This signals the ribosome to START making a protein.
Methionine
The initiator tRNA with anticodon UAC comes and
binds with this codon and drops off it’s amino acid
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“Methionine”.

After the first tRNA binds with its codon, the
mRNA slides down so that the ribosome can read the
next codon.

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
A new tRNA molecule carrying an amino acid pairs
with the second mRNA codon.
Alanine
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

The amino acids then bond together.
What kind of bond is it? PEPTIDE BOND
Once the first tRNA lets go of it’s amino acid, it is
released from the ribosome.
Methionine
Alanine
bond
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Step 3: Elongation

Refers to the time that the amino acid chain
(poly-peptide) is being built or “elongated”.
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Step 4: Termination

A chain of amino acids is formed until the
stop codon is reached on the mRNA strand.
The end result
is a protein
Stop
codon
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Ribosomes

A site (aminoacyl-tRNA site)


P site (peptidyl-tRNA site)


holds tRNA carrying next amino acid to
be added to chain
holds tRNA carrying growing
polypeptide chain
Met
E site (exit site)

empty tRNA leaves
ribosome from exit site
U A C
A U G
5'
E
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P
A
3'
Look at your codon chart and find an example of different
codons that code for the same amino acid.
For codon-anticodon interactions, the third base of the
codon isn’t read as “strictly” in the DNA/mRNA sequence
during transcription or DNA replication.
This is called the wobble effect.
CUU; CUC; CUA
As long as the first two bases are the same, the last base
doesn’t matter all that much. Each of these mRNA codon
sequences will bond with a single type of tRNA that carries
leucine.
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Prokaryote vs. Eukaryote genes

Prokaryotes

Eukaryotes


DNA in cytoplasm
circular
chromosome
naked DNA

no introns





DNA in nucleus
linear
chromosomes
DNA wound on
histone proteins
introns vs. exons
intron = noncoding (inbetween) sequence
eukaryotic
DNA
exon = coding (expressed) sequence
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