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RNA and Protein Synthesis
RNA
• RNA is a molecule that helps makes proteins.
• It’s similar to DNA and is used to make a
temporary copy of DNA.
Components of RNA
• RNA is single stranded and it consists of :
a. Sugar: Ribose
b. Phosphate
c. 4 nitrogen bases
Adenine and uracil (base pairs)
Cytosine and guanine (base pairs)
Compare RNA to DNA
Sugar
# strands
DNA
Deoxyribose
Double stranded
nitrogen bases Adenine, Thymine
Cytosine, Guanine
RNA
Ribose
Single Stranded
Adenine, Uracil
Cytosine, Guanine
Types of RNA
• There are 3 types of RNA
1. mRNA (messenger RNA)
RNA that carries genetic information from
the cell nucleus to the ribosomes in the
cytoplasm
Types of RNA
2. tRNA (Transfer RNA)
RNA that delivers the amino acids necessary
for protein synthesis to the ribosomes.
AMINO ACID: Compounds that contain carbon,
oxygen, hydrogen and nitrogen. They join
together to form proteins. There are 20
essentail amino acids.
Types of RNA
3. rRNA (ribosomal RNA)
RNA that forms part of the ribosomes where
proteins are built
Proteins
• Proteins are made of amino acids
• Amino acids are made of three nitrogen bases
bonded together
Steps in Protein Synthesis
• Protein Synthesis is the making of proteins
1. DNA unwinds and separates.
2. Each side becomes a pattern on which a new
side forms.
3. Because DNA can not leave the nucleus,
mRNA mades a copy of the instructions in
the DNA for making a particular protein. This
takes place in the nucleus.
Steps in Protein Synthesis
• EXAMPLE:
• If the DNA strand were as follows:
CATAGCGGAACTTTCAGC
the mRNA strand would be:
GUAUCGCCUUGAAAGUCG
There is no thymine in RNA. Uracil takes it place so
everywhere you have adenine on the DNA strand,
uracil will bond to it on the RNA strand.
Steps in Protein Synthesis
4. Once mRNA makes a copy of the instructions
in the DNA for a particlar protein, it leaves
the nucleus and carries these instructions to
the ribosomes in the cytoplasm.
5. tRNA translates the instructions from mRNA.
Steps in Protein Synthesis
• Example:
If the instructions from mRNA are as follows:
GUAUCGCCUUGAAAGUCG
The tRNA translates this to be
CAUAGCGGAACUUUCAGC
(Remember, when there is adenine, the complimentary
base is uracil. If the base is uracil, the complemenatry
base would be adenine.
Steps in Protein Synthesis
Each set of 3 mRNAs is referred to as a “codon” for a specific amino
acid.
tRNA encodes “anticodons” to recognize the codons from mRNA.
Each set of 3 tRNAs is an anticodon.
Anticodons enable tRNA to bring the correct amino acid to the
ribosome, where they bond together in a long chain called a
polypeptide.
The polypeptide will eventually become the protein.
Steps in Protein Synthesis
6. As the tRNA translates the mRNA codons for
a particular amino acid, its anticodons circle
around in the cytoplasm and pick up the
correct amino acid .
It takes the amino acids over to the ribosome
where the acids bond together in a long
polypetide chain. The tRNA is then released
back to the cytoplasm.
Steps in Protein Synthesis
7. When the mRNA has been comletely
translated, the polypeptide chain becomes the
protein.
EXAMPLE
DNA C A T A G C
mRNA G U A U C G
tRNA C A U A G C
Review Questions
1. Which base is in RNA but not DNA?
2. What are the components of RNA?
3. List 3 ways in which RNA is different from
DNA.
4. What are the three types of RNA and what is
the function of each?
5. What is an amino acid?
6. Where are proteins assembled in the cell?
Review Questions
7. What are amino acids made of?
8. What are proteins made of?
9. Why is it necessary for RNA to make a copy of
the DNA?
10. What is the difference between a codon and
an anitcodon?
11. What is a polypeptide chain?
Review Questions
12.Suppose you have the following DNA strand.
CTGAC
What would be the complimentary mRNA
strand that would be synthesized from it?
13. What would be the tRNA strand that would
be created from the mRNA strand in #12?
Review Questions
13.Suppose you had the tRNA strand
CAUGCAUGC
What would the mRNA strand have looked
like?
What would the DNA strand have looked like?