Transcript Document

Protein Synthesis and
Gene Expression
Why does a cell need proteins to
function properly?
Time to make the
proteins...
SO…how does a cell make proteins
anyway?
There are two important nucleic acids
involved in making proteins...
1. DNA
2. RNA
Where are proteins made?
B. Ribosomes
Let’s Review DNA & RNA
DNA: deoxyribonucleic
acid
DNA is double
stranded.
Contains sugar
deoxyribose.
DNA contains bases
adenine, thymine,
guanine, cytosine.
DNA never leaves the
nucleus.
RNA: ribonucleic acid
RNA is single stranded.
Contains sugar ribose.
RNA contains bases
adenine, guanine,
cytosine and URACIL.
RNA can leave the
nucleus.
Remember there are three types
of RNA
mRNA: messenger RNA
DNA
mRNA
tRNA: transfer RNA.
Transcription
tRNA
towing
rRNA: ribosomal RNA
Translation
Overall process of protein
synthesis
transcription
DNA
translation
mRNA
Protein
Summary of Protein Synthesis
 DNA  mRNA  tRNA  protein
1. The process of going from DNA to mRNA
is transcription.
2. The process of going from mRNA to
protein is translation.
Let’s explore this in a little more detail...
First, let’s see how the message
in DNA gets to the ribosomes…
DNA’s tragedy
If I could only
get out there…
I’d show them
a thing or two!
DNA contains
volumes of
information about
making protein.
Unfortunately,
DNA is too huge
to leave the
ribosomes
nucleus.
nucleus
How does the cell solve this
problem….transcription
That’s where
mRNA comes in.
mRNA helps get
DNA’s message
out to the
ribosomes...
How do I tell
those guys what
I want them
to do?
I can help!
First, DNA unzips itself...
DNA unzips
itself, exposing
free nitrogen
bases.
First, DNA unzips itself...
DNA unzips
itself, exposing
free nitrogen
bases.
First, DNA unzips itself...
DNA unzips
itself, exposing
free nitrogen
bases.
First, DNA unzips itself...
DNA unzips
itself, exposing
free nitrogen
bases.
First, DNA unzips itself...
DNA unzips
itself, exposing
free nitrogen
bases.
IV. Transcription
a. The process of going DNA to mRNA
IV. Transcription
b. The steps of transcription:
1. First DNA unzips itself along the
segment of code needed for a certain
protein.
2. mRNA is made by forming
complementary bases on the
unzipped portion of DNA.
IV. Transcription DNA→RNA
DNA
A-T
T-A
G-C
C-G
RNA
A
U
G
C
IV. Transcription
b. The steps of transcription:
3. DNA’s code is copied into groups of
3 bases at a time called a codon.
4. Each codon codes for 1 amino acid.
5. Once the mRNA strand is
transcribed, it can leave the nucleus
to find a ribosome to carry out the
next step.
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complimentary
fashion
Next, mRNA is made...
mRNA is made
from the DNA
template
mRNA matches
with free DNA
nitrogen bases in
a complementary
fashion
Some additional notes about making
mRNA…
DNA contains two kinds of
sequences: Coding and Noncoding
regions
Some additional notes about making
mRNA…
One kind of noncoding is used to start
transcription
Another kind is call Introns and is old, unused
sequences of bases
The coding regions are called Exons
Final Processed mRNA is made from Exons
mRNA leaves the nucleus...
I hope he can
tell them what
to do!
DNA’s code is copied
to mRNA in three letter
groups called codons.
After mRNA is made
from the DNA
template, it is ready to
leave the nucleus.
The next step... Translation
Translation
Translation
mRNA meets the
Ribosomes!
(No, it’s not a new sitcom on FOX…)
mRNA tries to talk to the
ribosomes…
I have a message
mRNA leaves the
for you! It’s
nucleus and travels
from DNA!
to the cytoplasm,
where the ribosomes
are located.
Once there, mRNA
meets up with the
ribosomes
What does
he want now?
It’s always
something!
mRNA tries to talk to the
ribosomes…but is unsuccessful.
Why don’t they
get it???
@%$!!
Why can’t we tell
what he’s saying?
However, the ribosomes
cannot understand the
message mRNA is
carrying.
We need a
translator!
tRNA Saves the Day!
Tyrosine
The boss will NOT
be happy about
this...
We won’t work until
we know what to do!
Where is that
translator?
Looks like trouble
for this cell…
I’d better help!
Now the cell
can make a
protein!
tRNA: Transfer RNA
Tyrosine
1. Chemically, tRNA is
clover-leaf shaped.
2. At one end, it carries
an amino acid (like a
tow truck).
3. At the other end, it
has a three letter
code known as an
anticodon.
Anticodon? What’s that?
This anticodon is the
complement to the
codons contained within
mRNA.
Can you find the mRNA
complement to the
anticodon on tRNA?
Tyrosine
Some notes about Amino Acids
There are 20 known amino acids present
in living things.
How is it possible to get a group of four
letters to code for 20 things?
Put them into groups of three…
43 = 64 codes
Number of members in a group of nitrogen bases
Number of nitrogen bases
What’s a codon, anyway?
Here is what a codon looks
like. It is a sequence of 3
bases.
How we determine what
amino acid each codon
codes for must be read off
of a codon chart.
This is also known as the
genetic code.
Codon chart
Second Base
U
A
G
Phenylalanine
Phenylalanine
Leucine
Leucine
Serine
Serine
Serine
Serine
Tyrosine
Tyrosine
Stop
Stop
Cysteine
Cysteine
Stop
Tryptophan
U
C
A
G
C
Leucine
Leucine
Leucine
Leucine
Proline
Proline
Proline
Proline
Histidine
Histidine
Glutamine
Glutamine
Arginine
Arginine
Arginine
Arginine
U
C
A
G
A
Isoleucine
Isoleucine
Isoleucine
Methionine
Threonine
Threonine
Threonine
Threonine
Asparagine
Asparagine
Lysine
Lysine
Serine
Serine
Arginine
Arginine
U
C
A
G
Valine
Valine
Valine
Valine
Alanine
Alanine
Alanine
Alanine
Aspartic Acid
Aspartic Acid
Glutamic Acid
Glutamic Acid
Glycine
Glycine
Glycine
Glycine
U
C
A
G
U
First
Base
C
G
Third
Base
Other Codon Charts
Reading a Codon Chart
It is possible for some amino acids to
have more than one codon.
There are three stop codons…they are
UAA, UGA and UAG.
There is also one START codon…AUG.
How a Translator works…
First, the anticodons on
tRNA meet up with the
mRNA start codon (AUG)
at the ribosome.
Next, another tRNA meets
up with it’s corresponding
mRNA.
Each tRNA carries an
amino acid.
Methionine
How a Translator works…
Once two amino acids
are made, a bond forms
between them.
This process continues
until a stop codon on
mRNA is reached.
Methionine
Animation of translation
Click to automatically start
animation.
This is a
ribosome.
Single Messenger RNA Strand
Met
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Single Messenger RNA Strand
Met
Ala
Pro
Single Messenger RNA Strand
Met
Ala
Pro
Single Messenger RNA Strand
Met
Ala
Pro
Single Messenger RNA Strand
Met
Arg
Pro
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Single Messenger RNA Strand
Met
Pro
Ala
Phe
Single Messenger RNA Strand
Met
Pro
Ala
Phe
Single Messenger RNA Strand
Met
Pro
Ala
Phe
Single Messenger RNA Strand
Met
Ala
Pro Phe
Single Messenger RNA Strand
Met
Ala
Gly
Phe
Single Messenger RNA Strand
Met
PhePro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Single Messenger RNA Strand
Met
Phe Pro
Ala
Met
Phe Pro
Ala
Ala Met
Pro
Phe
Stop
Ala Met
Pro
Phe
Stop
Ala Met
Pro
Phe
Stop
Ala Met
Pro
Phe
Stop
Ala Met
Pro
Phe
Stop
Pro
Phe
Stop
Phe
Stop
Stop
Stop
Stop
Stop
Stop
Stop
Stop
Stop
Stop
Stop
How Does it Know When to Quit?
This process continues
until a stop or a
termination codon (found
on mRNA) is reached.
There are three stop
codons: UGA, UAA and
UAG.
STOP
Regulation of Transcription and
Translation
 Think about your house, do you keep all
the lights on ALL the time in every room??
 Gene expression is a regulated process
where genes can be turned on and off as
needed due to environmental factors.
In summary…
 DNA contains the information needed to
make proteins.
 However, DNA is too large to leave the
nucleus.
 RNA acts as a set of working instructions
for ribosomes to make proteins.
 This process is also known as gene
expression.
 Gene expression is a regulated process.
The Central Dogma is Universal