Download Protein Synthesis

Protein Synthesis:
Part 1 (Transcription)
Ch 11
Protein Synthesis means
Synthesizing Proteins
or
“MAKING” PROTEINS
The GOAL is to:
learn how proteins
are made.
Protein Synthesis
can be broken down
into two stages:
• Transcription
• Translation
1st PROCESS
2nd PROCESS
TRANSCRIPTION
TRANSLATION
DNA
1
mRNA
2
Proteins
3
Transcription
Reads and copies
a section of DNA
(AKA gene) and
converts it into
mRNA
(A gene codes for a protein)
Let’s compare
DNA and RNA
DNA
RNA
Sugar =
deoxyribose
Sugar =
ribose
Double helix
(2 strands)
Single strand
DNA
Location:
nucleus
Bases:
A, C, G, T
RNA
Location:
Nucleus &
cytoplasm
Bases:
A, C, G, U
(Uracil)
DNA
Function:
simply stores
genetic info
(instructions
to make
proteins)
RNA
Function:
many
functions, all
used to
assemble
proteins
Three types of RNA
• MESSENGER RNA
(mRNA)
• TRANSFER RNA (tRNA)
• RIBOSOMAL RNA
(rRNA)
MESSENGER RNA
• “mRNA”
• single strand
• contains genetic info
• is transported out of
nucleus
TRANSFER RNA
• “tRNA”
• single strand
• folded like a hairpin
• binds specific amino acids
RIBOSOMAL RNA
• “rRNA”
• single strand
• found in ribosomes
• ribosomes are made up
two pieces of rRNA
Let’s look at
TRANSCRIPTION
“The first process”
DOUBLE HELIX
SPREADS
APART
The product is
called mRNA
mRNA
RNA POLYMERASE
copies the gene by
attaching RNA
nucleotides
Here the DNA is
split open and a
mRNA
strand is
being made
Here the DNA is
split open and a
mRNA
strand is
being made
NOTICE:
RNA
POLYMERASE
ADDS ON RNA
NUCLEOTIDES
TO MAKE mRNA
mRNA
Then the newly constructed
mRNA undergoes “processing”
mRNA
The mRNA then leaves the
nucleus to enter the next
process “translation”
DNA
“start”
sequence
3’
(Signals where
to begin)
“terminator”
sequence
(where to end)
5’
RNA
DNA
T
A
A
A
U
T
C
G
G
T
A
A
G
C
C
A
U
T
T
A
A
A
U
T
T
A
A
C
G
G
5’
3’
RNA processing includes
• cutting out meaningless
DNA (aka introns)
• Adding a cap on the tip
(aka GTP cap)
• Adding on A-A-A-A on the
end (aka Poly-A tail)
Intron
Intron
Intron
+
Introns contain
meaningless
DNA
=
Only the important,
USEFUL DNA
GTP
mRNA
Add on a
GTP cap
A-A-A
Tack on a
poly-A tail
You are finished processing
the mRNA. It can now leave
the nucleus.
Describe
what is
happening
here and
who is
involved
Translation
• The process of converting the mRNA
codons into a sequence of amino acids
to build a protein.
• A codon is a group of three
nucleotides. Each codon codes for
one amino acid.
Translation – using mRNA to bring the
correct tRNA anticodon, with an amino
.acid attached. Occurs at the ribosome.
Translation Sequence
• A ribosome attaches to the “start” of the
mRNA. The codon “AUG” signals the start.
• The tRNA having the anticodon “UAC” will
bring the first amino acid to the ribosome
to begin the formation of the protein.
• The ribosome slides to the next codon on
the mRNA. The complementary tRNA
anticodon brings the second amino acid to
the protein strand.
• This process continues until the
ribosome reaches a “stop” signal.
• Stop codons on mRNA are
– UAA
– UAG
– UGA
A Protein has been made!
Mistakes Happen – Mutations!
A point mutation occurs when a single
base pair is mismatched.
Ex. THE DOG BIT THE CAT
THE DOG BIT THE CAR
A frameshift mutation occurs when a
single base is added or deleted.
Ex. THE DOG BIT THE CAT
THE OGB ITT HEC AT
(the D was deleted)
• Which do you think would be more
harmful? Why?