Download Transcription and Translation

Przeworski
Protein Synthesis
Instructions for proteins are stored as DNA in the
nucleus (one gene = one protein)
The ribosomes that actually make the proteins are
outside in the cytoplasm
DNA is too large to
exit through nuclear
pores… it requires a
messenger to send
the instructions
Ribosome
Transcription
In transcription, a copy of a protein recipe called
messenger RNA (mRNA) is made from DNA
mRNA is half the width of DNA and can leave the
nucleus
DNA
vs
RNA
Deoxyribonucleic acid
Ribonucleic acid
Contains the sugar
Contains the sugar
deoxyribose
Double-stranded
Bases are G, C, A, T
ribose
Single-stranded
Bases are G, C, A, U
U = Uracil, replaces
Thymine
T
P
D
Thymine
Nucleotide
(DNA)
U
P
R
Uracil
Nucleotide
(RNA)
 G still pairs with C
 A pairs with U
D
T
D
P
P
P
R
• The RNA bases are slightly
different.
D
P
P
C
D still pairs with G
• C
P
P
T
(instead of T)
D
• A now pairs with U
P
R
R
D
D
C
D
C
P
P
P
U
P
R
STEP ONE: INITIATION
RNA polymerase locates the section of DNA
(gene) that it wants to transcribe.
It attaches to the promoter region, causing DNA to
unzip with the help of a Helicase.
Polymerase and Helicase are enzymes (special
proteins!)
STEP TWO: ELONGATION
Once DNA is unzipped, the Polymerase
transcribes the DNA section
Free-floating RNA nucleotides attach
This is just like Replication, but with the base
uracil instead of thymine. (A-U and C-G)
STEP TWO: ELONGATION
 For example, if the DNA strand read ACGT, then the RNA
would be UGCA.
 This continues until the entire gene is transcribed, ending
with the Stop sequence.
STEP THREE: TERMINATION
 Once the stop sequence is reached, the RNA strand
detaches
 It is then processed into mRNA by adding a 5’ cap
and a poly-A tail (for protection)
 Finally, the mRNA leaves the nucleus! (DNA rezips)
Ribosome
TRANSCRIPTION CLIP (REAL TIME)
 https://www.youtube.com/watch?v=5MfSYnItYvg
GROUP POSTER PROJECT
 In your groups of four (each table should work with the one behind
them, and turn your chairs around)
 You will be given a step of transcription or DNA vs RNA
 For your assigned topic, make sure there is:
A legible title
Large writing describing what occurs in the step (or large
writing that explains the differences between DNA and
RNA)
A large picture, colored. (All writing should be in marker)
Translation - Overview
In translation, a ribosome uses an mRNA recipe to
select and put together a sequence of amino acids
 mRNA is read 3 bases at a time (3 bases = 1 codon)
 Each codon = 1 amino acid
DNA template: A T A G A T C C A
mRNA: U A U C U A G G U
Amino
Acid 1
Amino
Acid 2
Amino
Acid 3
DNA: A T A G A T C C A
mRNA: U A U C U A G G U
Tyrosine
Leucine
Glycine
Special Codons
 As a ribosome reads an mRNA transcript, special
codons tell it where to start and stop making a protein
 START codon: A U G (must memorize!)
mRNA:
Amino Acid:
A A G G U C A U G C C A C G U U A A
Methionine
Proline
Arginine
STOP
STEP ONE
The mRNA from the nucleus makes its way
through the cell to a free-floating ribosome and
attaches to it.
STEP TWO:
Each set of three RNA bases is called a codon.
For this sequence: AUGCUA, AUG is a codon
and CUA is another codon.
Each codon codes for a single amino acid, which
is the building block of proteins.
STEP TWO:
At the ribosome, the codon of mRNA pairs
with its anti-codon (correct base pairs)
For our earlier codons, AUG would pair with
UAC and the anticodon for CUA is GAU.
STEP TWO:
tRNA (transfer
RNA) translates
each codon into
one amino acid.
Amino Acids are
linked with
peptide bonds to
form a chain
STEP THREE:
Once the amino
acids are linked
with a PEPTIDE
BOND, the mRNA
strand moves like
an assembly line,
releasing the first
codon and
anticodon.
STEP FOUR
The chain of amino acids
(polypeptide chain) will
then form a protein.
There are 20 different
amino acids, which are
the codes for all living
things!
WHEEL OF CODONS!!
Input the mRNA
codon, get out the
amino acid!
Special amino
acids:
AUG= start
UGA=stop
Types of RNA
Structure
mRNA Single strand
(messenger)
Function
Takes copied DNA recipe
to ribosome
tRNA Has anticodon on one
Delivers amino acids to
(transfer) end, carries amino acid on ribosomes
the other
rRNA Folded into ribosome
(ribosomal) shape
The ribosome itself is
made of this
Given the mRNA codon GCU, what is the amino
acid?
PRACTICE TIME!
Given mRNA codon of AUG, what is the amino
acid?