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Protein Synthesis and Gene Expression
DNA: deoxyribonucleic acid--contains sugar deoxyribose.
DNA is double stranded.
DNA contains bases adenine, thymine, guanine, cytosine.
DNA never leaves the nucleus.
RNA: ribonucleic acid--contains sugar ribose.
RNA is SINGLE stranded.
RNA contains bases adenine, guanine, cytosine and URACIL.
RNA can leave the nucleus.
Let’s Review DNA & RNA
Remember there are three types of RNA
mRNA: messenger RNAmRNA
tRNA towingAmino acid
rRNA: ribosomal RNA
tRNA: transfer RNA.
Overall process of protein synthesis
transcription translation
DNA RNA Protein
TRANSCRIPTIONTRANSCRIPTION
Takes place in the Takes place in the nucleusnucleus
translationtranslation
Moves out of nucleus Moves out of nucleus into the cytoplasm & into the cytoplasm & attach to ribosomeattach to ribosome
DNA’s tragedy
DNA contains volumes of information about making protein.
Unfortunately, DNA is too huge to leave the nucleus.
If I could onlyget out there…I’d show thema thing or two!
ribosomes
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 tellthose 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.
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 complimentary fashion
mRNA leaves the nucleus...
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.
I hope he can tell them what
to do!
The next step...Translation
mRNA meets the Ribosomes!
(No, it’s not a new sitcom on Fox…)
mRNA tries to talk to the ribosomes…
mRNA leaves the nucleus and travels to the cytoplasm, where the ribosomes are located.
I have a message for you! It’sfrom DNA!
What does he want now?
It’s alwayssomething!Once there, mRNA
meets up with the ribosomes
mRNA tries to talk to the ribosomes…but is unsuccessful.
However, the ribosomes cannot understand the message mRNA is carrying.
Why don’t theyget it???@%$!!
Why can’t we tellwhat he’s saying?
We need a translator!
tRNA Saves the Day!
Now the cell can make a protein!
The boss will NOT be happy about
this...
We won’t work untilwe know what to do!
Where is thattranslator?
Looks like troublefor this cell…I’d better help!
Tyrosine
tRNA: Transfer RNA
Tyrosine Chemically, tRNA is clover-leaf shaped.
At one end, it carries an amino acid.
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 nitrogen bases
Number of members in a group 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
U C A G
UPhenylalaninePhenylalanineLeucineLeucine
SerineSerineSerineSerine
TyrosineTyrosineStopStop
CysteineCysteineStopTryptophan
UCAG
C LeucineLeucineLeucineLeucine
ProlineProlineProlineProline
HistidineHistidineGlutamineGlutamine
ArginineArginineArginineArginine
UCAG
A IsoleucineIsoleucineIsoleucineMethionine
ThreonineThreonineThreonineThreonine
AsparagineAsparagineLysineLysine
SerineSerineArginineArginine
UCAG
GValineValineValineValine
AlanineAlanineAlanineAlanine
Aspartic AcidAspartic AcidGlutamic AcidGlutamic Acid
GlycineGlycineGlycineGlycine
UCAG
First Base
Second Base
ThirdBase
The Wonderful World of Amino Acids
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.
Tyrosine
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.
Tyrosine