Transcript Transcription & Protein Synthesis

Transcription, Translation &
Protein Synthesis
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Do you remember what proteins
are made of ?







Hundreds of Amino Acids link
together to make one Protein
􀂄 There are 20 types of amino acids, some
we can make, and some we can’t
􀂄 There are infinite combinations of amino
acids
􀂄 Can be hundreds or thousands monomers
Long
These long chains are called polypeptide chains
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Protein Synthesis
 Protein synthesis is the process in which a
cell makes protein based on the message
contained within its DNA.
 However:
– DNA is only found in the nucleus
– Proteins are only made outside the nucleus – in
the cytoplasm.
 Houston, we have a problem.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Protein Synthesis
 How do the many different messages within
the DNA molecule get to the many
ribosomes outside the nucleus?
 A molecular cousin of DNA – RNA – is
used to carry these messages.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Ribonucleic Acids (RNA)

The job of RNA (ribonucleic acid) is to carry
messages from the DNA (in the nucleus) to the
ribosomes (in the cytoplasm).
There are three types of RNA:

1. mRNA – carries a message from the DNA to the
cytoplasm
2. tRNA – transports amino acids to the mRNA to
make a protein
3. rRNA – make up ribosomes, which make protein.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Ribonucleic Acids (RNA)
 RNA is almost exactly like DNA, except:
– Contains a ribose sugar, instead of a
deoxyribose sugar (hence the name…)
– Contains uracil instead of thymine.
– RNA is single-stranded, not double-stranded
(usually…)
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Ribonucleic Acids (RNA)
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Protein Synthesis
 Occurs in TWO steps:
1. Transcription – the genetic information from a
strand of DNA is copied into a strand of mRNA
2. Translation – the mRNA, with the help of the
ribosome, forms a chain of amino acids
(eventually forming a protein) based on the
information contained on the mRNA.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
The Central Dogma
 This order of events is called the central
dogma of molecular biology:
DNA
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
RNA
P
R
O
T
E
I
N
Step One: Transcription
1.
2.
3.
DNA unzips: enzymes split apart base pairs and
unwind the DNA double helix.
Bases pair up: Free nucleotides in the cell find
their complementary bases along the new
strands with the help of RNA polymerase. What
will be different??
New backbone formed: The sugar-phosphate
backbone is assembled to complete the RNA
strand, and separates from the DNA strand.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step One: Transcription
 Watch this simplified animation:
http://www.stolaf.edu/people/giannini/flashani
mat/molgenetics/transcription.swf
 Watch the more complex animation!
 http://www-
class.unl.edu/biochem/gp2/m_biology/anim
ation/gene/gene_a2.html
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step One: Transcription
 Try it! What RNA strand will be made
from the following DNA sequence?
TACGCATGACTAGCAAGTCTAACT
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step One: Transcription
 Try it! What RNA strand will be made
from the following DNA sequence?
TACGCATGACTAGCAAGTCTAACT
AUGCGUACUGAUCGUUCAGAUUGA
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step 1½: RNA Editing


An mRNA molecule has to be “edited” in
order to be useful. There’s a lot of
unnecessary information that needs to be
removed.
An mRNA sequence that does NOT code
for protein is called an interon. A
sequence that is useful in making a protein
is called an exon.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step 1½: RNA Editing
DNA
transcription
pre-RNA (in nucleus)
exon 1
interon
RNA editing
exon 2
interon
interon
interon
RNA (in cytoplasm)
exon 1
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
exon 2
exon 3
exon 3
Step Two: Translation “to decode or
decipher the meaning of”


Now that our mRNA molecule has been
made, it’s time for its message to be made
into a protein sequence.
How does the mRNA sequence translate
into an amino acid sequence?
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
 Problem:
– There are 20 different amino acids.
– There are 4 RNA bases.
A T C G
phe
ile
leu
val
met
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
pro
ser
ala
thr
his
tyr
asn
gln
asp
lys
cys
glu
arg
trp
gly
Step Two: Translation
 Watch this simplified animation:
http://www.stolaf.edu/people/giannini/flashani
mat/molgenetics/translation.swf
 Watch the more complex animation!
 http://www-
class.unl.edu/biochem/gp2/m_biology/anim
ation/gene/gene_a3.html
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
1. So how do you exactly go about
determining what protein your cells are
going to make?
2. FIRST, Divide the mRNA sequence into
codons. As you just saw and heard,
codons are three-base sections of mRNA:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
2. Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
?
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
The Genetic Code
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
2. Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
?
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
The Genetic Code
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
2. Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
arg
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
thr
asp
arg
ser
asp
???
The Genetic Code
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
Step Two: Translation
2. Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
met
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL
thr
asp
arg
ser
asp
STOP
RECAP:
1.
2.
3.
DNA is transcribed into
mRNA in the nucleus.
The mRNA leaves the
nucleus and enters the
cytoplasm.
The protein is translated
from the mRNA
sequence using tRNA
and amino acids.
Mr. Armfield – Level II Biology 1,2
Science Department
Deerfield High School, Deerfield IL