Transcript Slide 1

RNA and Protein
Synthesis
From Genes to PRoteins
All of the 100 trillion cells in your body came from one
original cell: the fertilized egg that grew into YOU!
And all of those 100 trillion cells have exactly the
same DNA in them.
So how come there are so many different kinds of
cells in your body? How did they get so specialized?
The answer is… Different genes are
turned on in different types of cells.
Each gene carries the instructions for
making a protein, which does the work of
the cell. Different cells make different
proteins. For example, liver cells make
different proteins than nerve cells, or eye
cells, or stomach cells.
DNA is the “boss” or manager of each
cell. It’s the DNA that has the instructions
for making the proteins.
So what are the “workers” of the cells?
The answer: RNA
Here’s what happens…
DNA
RNA
Protein
transcription
translation
Trait
RNA
RNA is very similar in structure to DNA with 3
main differences.
 RNA contains the sugar ribose instead of
deoxyribose
 RNA has the base uracil (U) instead of
thymine (T).
 RNA Is Single-Stranded instead
of Double-Stranded like DNA
There are Different RNAs with Different Functions
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Recently, a new class of RNA, microRNA, has been
shown to regulate gene expression.
name
sugar
shape
DNA
RNA
deoxyribonucleic
acid
ribonucleic acid
deoxyribose
ribose
double-helix
(twisted ladder)
one-sided ladder
nitrogen • adenine
• cytosine
bases
DNA/RNA
• guanine
• thymine
location
# types
function
stays in
nucleus
1 type
forms genetic
code that
specifies what
proteins are
produced by a
cell
• adenine
• cytosine
• guanine
• uracil
travels between
nucleus &
cytoplasm
3 types: mRNA
tRNA, rRNA
carries genetic
code from nucleus
to the ribosomes;
directs production
of the proteins
Transcription
makes an RNA copy of DNA
RNA polymerase acts here
The enzyme RNA polymerase opens the DNA strands and
makes an RNA copy of one of the DNA strands.
The Genetic Language Uses 4 Letters Written
Into 3-Letter Words
Amino Acids – What the
Genetic Code Specifies
There are 20 different amino acids
Two examples
Amino acids are the building blocks of
proteins. A protein is made up of many
amino acids bonded together. It’s the
proteins that carry out every function in
all your cells. It’s the proteins that give
an organism its traits.
 The 4 nitrogen bases (A, C, G, T) are read in
groups of three.
 Each group of 3 bases is called a codon.
 Each codon stands for 1
of the 20 amino acids.
 Since there are 64
possible combinations of 3
and only 20 amino acids,
some amino acids have
more than one codon. For
example, AAA and AAG
both code for lysine.
 There are also codes for
“Start” and “Stop”.
Ribosomes are
Complicated
ProteinSynthesizing
Machines
Ribosomes are located in
two places:
 attached to the ER
(Endoplasmic Reticulum), or
 floating in the
cytoplasm.
Protein Synthesis
1. DNA molecule
unzips and makes a
single-stranded copy
of itself (mRNA)
1
2. mRNA leaves the
nucleus and attaches
to a ribosome.
3. Ribosome moves
along the mRNA
and “reads” it.
2
4. tRNA brings amino
acids to ribosome
and attaches them to
the protein chain.
4
3
5. The ribosome
releases the protein.
5
Protein Synthesis
Protein Synthesis
QuickTime™ and a
decompressor
are needed to see this picture.
Protein Synthesis
Protein Synthesis
(tRNA)
(mRNA)
Protein synthesis
Protein Synthesis
Protein Synthesis
QuickTime™ and a
decompressor
are needed to see this picture.
This is a molecule of messenger RNA.
It was made in the nucleus by
transcription from a DNA molecule.
codon
A U G G G C U U AAA G C A G U G C A C G U U
mRNA molecule
A ribosome on the rough E.R.
attaches to the mRNA molecule.
ribosome
A U G G G C U U AAA G C A G U G C A C G U U
Amino acid
tRNA molecule
•A transfer RNA molecule arrives.
•It brings an amino acid to the first
three bases (codon) on the mRNA.
anticodon •The three unpaired bases
(anticodon) on the tRNA link up
with the codon.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
•Another tRNA molecule comes into
place, bringing a second amino
acid.
•Its anticodon links up with the
second codon on the mRNA.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Peptide bond
•A peptide bond (chemical
bond) forms between the two
amino acids.
A U G G G C U U AAA G C A G U G C A C G U U
•The first tRNA molecule releases
its amino acid and moves off into
the cytoplasm.
A U G G G C U U AAA G C A G U G C A C G U U
•The ribosome moves along the
mRNA to the next codon.
A U G G G C U U AAA G C A G U G C A C G U U
•Another tRNA molecule
brings the next amino
acid into place.
A U G G G C U U AAA G C A G U G C A C G U U
•A peptide bond joins the
second and third amino acids
to form a polypeptide
(protein) chain.
A U G G G C U U AAA G C A G U G C A C G U U
•The process continues.
•The polypeptide (protein)
chain gets longer.
•This continues until a
termination (stop) codon is
reached.
A U G G G C U U AAA G C A G U G C A C G U U
•The process continues.
•The polypeptide (protein)
chain gets longer.
•This continues until a
termination (stop) codon is
reached.
A U G G G C U U AAA G C A G U G C A C G U U
•The polypeptide (protein) is
then complete, and is released
from the ribosome.
A U G G G C U U AAA G C A G U G C A C G U U