Transcript Transcription and Translation

Transcription and Translation
Building Proteins from DNA
Protein Synthesis
When the cell (or larger organism) requires
proteins, these are created in the cell
– the process is called
*What are some examples of proteins?
Creating proteins happens in two stages:
1. Transcription =
*This occurs in the nucleus of eukaryotic cells
2. Translation = using the
mRNA to create a
*This happens at a
ribosome in the cytoplasm
OR at a ribosome attached
to the rough
endoplasmic reticulum
What is RNA?
• RNA:
• It’s the “working” molecule
• Found all over the cell: nucleus,
mitochondria, chloroplasts, ribosomes,
cytoplasm
Structure of RNA
• Single polynucleotide chain
• Contains the bases cytosine, guanine,
adenine and uracil
• Contains a 5 carbon sugar called ribose
*Is uracil a purine or pyrimidine? How do
you know?
Compare DNA with RNA
DNA
Feature
Sugar
Bases
Structure
Length
RNA
Compare DNA with RNA
DNA
Feature
RNA
Deoxyribose
Sugar
Ribose
Adenine, Guanine,
Thymine, Cytosine
Double stranded, strands
held together with
hydrogen bonds
Bases
Structure
Adenine, Guanine,
URACIL, Cytosine
Single stranded
Long – several million
nucleotides in length
Length
Much shorter – 100 – 1,000
nucleotides
*Has 1 form:
DNA
Forms
*Has 2 forms:
Transfer RNA = tRNA
Messenger RNA =mRNS
mRNA = Messenger RNA
• Messenger RNA = mRNA
– copies the code from DNA during
transcription and carries it out of the
nucleus to the cytoplasm
– Carries the plan for the polypeptide
chain that folds into a protein
– Remains a long and unfolded
molecule
Transcription is the
process of copying one
side of the strand of DNA
to mRNA
1.
DNA is “unzipped”
2.
RNA polymerase
moves along one
side of the DNA
strand matching free
nucleotides to the
exposed bases
3.
Forms a
complimentary
strand of mRNA
Transcription
If the template strand of DNA has the following
bases, what will the mRNA strand look like?
A
T
G
C
A
C
T
A
A
T
A
C
G
T
G
A
T
T
• In order to build a polypeptide, mRNA must
travel outside the nucleus (through a nuclear
pore) to a ribosome
Translation is the second process in protein synthesis:
– uses the sequence of bases in mRNA to build a polypeptide chain that will fold
into a protein
– uses a ribosome as a platform for the construction of the polypeptide
– uses a variety of 20 different amino acids strung together like beads on a
necklace: these are the building blocks of the polypeptide chain
– Uses tRNA to “interpret” the genetic code
Polypeptide Chain
Amino acids
Translation
Protein
tRNA = Transfer
RNA
• RNA folded up
• On one end a specific
attached
• On the other end 3 specific
bases are exposed – called the
• different amino acids will have
different bases exposed
is
Amino Acid
Gly
Ser
Amino Acid
GAA
CGU
• If the anticodon changes, the amino acid that is attached will
also change
• The same amino acids have the same anticodons
Process of Translation
• mRNA will attach to a
ribosome
• Ribosomes match up the
anticodons with the
bases in mRNA
• Every three bases in the
mRNA is called a codon
that matches with the
anticodons in the tRNA
*Put a red box around the codons in
the mRNA, label tRNA
• At the site of the
Translation
ribosome, two tRNA
units will attach to the
mRNA
• their amino acids will
be linked together
with a peptide bond
*Label the peptide bond
*When the amino acids are linked together
is this a condensation reaction or a
hydrolysis reaction?
• Once the bond has been made
one tRNA will detach from the
ribosome
• The ribosome moves down the
mRNA strand ready to attach
another tRNA unit
• When the new tRNA is in place,
another peptide is formed
between the amino acids
• This process continues to happen
which builds a long polypeptide
chain
*What will the anticodons be for
the next tRNA?
• When the polypeptide chain is complete, the
mRNA will have a “stop” codon
• This codon causes the ribosome, mRNA and
polypeptide chain to release
• The polypeptide can then fold into a protein
Translation Animation:
http://www.stolaf.edu/people/giannini/flashani
mat/molgenetics/translation.swf