© Amy Brown Science
Protein Synthesis:
DNA and RNA
Lesson 3.03
© Amy Brown Science
Objectives
After completing this lesson, you will be able to:
© Amy Brown Science
What you need to know for Biology EOC
DNA vs. RNA
Wednesday, we talked about DNA…
DNA vs. RNA
Now, let’s talk about RNA
(uracil instead of thymine)
.
DNA is a double strand.
RNA – Ribonucleic Acid
Differences Between DNA and RNA
RNA – Ribonucleic Acid
Differences Between DNA and RNA
2. The sugar in RNA is ribose.
The sugar in DNA is deoxyribose.
Double
strand
Single
strand
Deoxyribose
Ribose
3. In RNA, uracil pairs with adenine.
In DNA, thymine pairs with adenine.
RNA – Ribonucleic Acid
Differences Between DNA and RNA
U
Function of RNA
Protein synthesis is the primary function of rRNA. Proteins are made by the ribosomes in the cytoplasm.
DNA determines which proteins need to be made.
Function of RNA
A gene on the DNA molecule is copied.
This copy is called RNA.
The copy of the instructions is then sent out to the ribosomes in the cytoplasm.
RNA carries the message from the DNA.
RNA tells the ribosomes which proteins to make and how to make them.
Three Types of RNA
Ribosomal RNA (rRNA)
Messenger
RNA (mRNA)
Transfer
RNA (tRNA)
Messenger RNA (mRNA)
1. Messenger RNA travels from the nucleus to the cytoplasm (ribosomes) with the instructions for making proteins.
2. Messenger RNA (mRNA) is the “messenger” between the DNA in the nucleus and the ribosomes in the cytoplasm.
4. The rest of the molecule is a sequence of nucleotides that dictates the sequence of amino acids for the particular protein
that is being made.
5. The last codon is called the “stop” codon.
This tells the ribosome to stop the production of the protein.
Messenger RNA (mRNA)
3. The instructions are carried in the form of codons.
The first codon is called the “start” codon.
This is the point at which mRNA will attach to the ribosome.
This tells the ribosome where the protein-building instructions begin.
Transfer RNA (tRNA)
2. Transfer RNA reads the message carried by mRNA and gathers the amino acids for making the protein.
anticodon
transfer
RNA
amino acid
The bases composing the anticodon are complementary to mRNA
4. One end of the tRNA attaches to one amino acid and carries it to the ribosome.
Transfer RNA (tRNA)
3. Transfer RNA transfers amino acids from the cytoplasmic pool of amino acids to a ribosome.
Ribosomal RNA - rRNA
Ribosomal RNA is found in the ribosome.
These are used to bind the mRNA and the tRNA to the ribosome. This allows all components required for the synthesis of the proteins to be held together.
transfer RNA
ribosomal RNA
ribosomal RNA
messenger RNA
3 types of RNA– An Overview
1. Messenger RNA (mRNA) is the RNA molecule that carries copies of the instructions (from the DNA) to other parts of the cell. (Blueprint)
2. Ribosomal RNA (rRNA) Ribosomes are where proteins are made. Each of the ribosomes’ subunits is made
of both rRNA and protein molecules. (factory)
3. Transfer RNA (tRNA) molecules transfer a specific amino acid to the ribosomes according to the coded instructions provided in the mRNA to build the protein chain. (delivery truck to the construction site)
Let’s check… DNA or RNA
Found in the nucleus
Single strand
Sugar-phosphate backbone
Adenine (A) bonds with Thymine (T)
Adenine (A) bonds with Uracil (U)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand
Sugar-phosphate backbone
Adenine (A) bonds with Thymine (T)
Adenine (A) bonds with Uracil (U)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand (RNA)
Sugar-phosphate backbone
Adenine (A) bonds with Thymine (T)
Adenine (A) bonds with Uracil (U)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand (RNA)
Sugar-phosphate backbone (Both)
Adenine (A) bonds with Thymine (T)
Adenine (A) bonds with Uracil (U)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand (RNA)
Sugar-phosphate backbone (Both)
Adenine (A) bonds with Thymine (T) (DNA)
Adenine (A) bonds with Uracil (U)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand (RNA)
Sugar-phosphate backbone (Both)
Adenine (A) bonds with Thymine (T) (DNA)
Adenine (A) bonds with Uracil (U) (RNA)
Cytosine (C) binds with Guanine (G)
Let’s check… DNA or RNA
Found in the nucleus (DNA)
Single strand (RNA)
Sugar-phosphate backbone (Both)
Adenine (A) bonds with Thymine (T) (DNA)
Adenine (A) bonds with Uracil (U) (RNA)
Cytosine (C) binds with Guanine (G) (Both)
Transcription of RNA – Copying
1. Transcription is the process of forming a strand of RNA from a strand of DNA.
4. The RNA molecule is a faithful copy of a gene’s protein building instructions. This type of RNA is called messenger RNA (mRNA).
2. This process occurs in the nucleus.
3. The cell must make RNA to send to the cytoplasm to tell the ribosomes how and which proteins to make.
5. An enzyme called RNA polymerase catalyzes this reaction.
Transcription of RNA – An Overview
6. The purpose of transcription is to copy one gene from the DNA molecule.
Now, let's take a closer look……
Steps of Transcription
RNA polymerase binds to a site on the DNA molecule called the promoter.
RNA polymerase
RNA polymerase separates the DNA strands.
One strand of DNA is used as a template.
Template strand of DNA
Inactive DNA strand
New nucleotides are inserted according to the base pairing rules. When transcribing RNA, adenine pairs with uracil. Cytosine pairs with guanine.
Steps of Transcription
RNA polymerase
Template strand of DNA
Inactive DNA strand
This continues until the terminator is reached.
As the RNA polymerase moves along the DNA molecule, hydrogen
bonds between the two strands of DNA are reformed.
A single stranded RNA molecule has been transcribed.
mRNA transcript
Let’s Practice!
DNA Strand: T-T-C-G-C-T-G-A-A
mRNA Strand:
The gene for a large single eyeball is coded by the gene sequence TTCGCTGAA. Let’s go through transcription…
Let’s Practice!
DNA Strand: T-T-C-G-C-T-G-A-A
mRNA Strand: A-A-G-C-G-A-C-U-U
The gene for a large single eyeball is coded by the gene sequence TTCGCTGAA. Let’s go through transcription…
Let’s Practice!
DNA Strand: G-G-A-C-T-C-T-A-G
mRNA Strand:
Now, let’s look at the gene for green body color, which is GGACTCTAG.
Let’s Practice!
DNA Strand: G-G-A-C-T-C-T-A-G
mRNA Strand: C-C-U-G-A-G-A-U-C
Now, let’s look at the gene for green body color, which is GGACTCTAG.
Our mRNA strand will now carry the message from the nucleus out to the ribosome to begin building the protein that will give Mike his green body and one big eye.
Remember: The purpose of transcription is not to copy the entire length of the DNA molecule, but to copy only a single gene.
The mRNA transcript will be sent to the ribosome as the instructions for protein synthesis.
The “language” of mRNA instructions is called the genetic code.
The genetic code is read three nitrogen bases at a time. Each group of three nitrogen bases is called a codon.
A codon is a group of three nitrogen bases that specifies one amino acid.
Consider the following mRNA sequence, for example:
AGA CUG GCA
The sequence would be read three bases at a time:
AGA - CUG - GCA
These three codons represent three different amino acids.
The three amino acids coded for by these codons:
Arginine
Leucine
A
A
A
G
G
G
C
C
U
mRNA
Alanine
There is one codon, AUG, which specifies the amino acid, methionine, and serves as the “start” codon for protein synthesis.
This codon is found at the beginning of every set of mRNA instructions.
This codon “tells” the ribosome where the instructions will start.
A
U
G
START
There are three “stop” codons.
These do not code for any amino acid.
Stop codons act like the period at the end of the sentence. Stop codons signify the end of the protein.
U
U
U
A
A
A
A
G
G
STOP
STOP
STOP
Protein Synthesis – Translation
The synthesis of proteins is called translation.
The cell must translate the base sequence of an mRNA molecule into the amino acid sequence of a protein.
Steps in Protein Synthesis
3. The mRNA attaches to a ribosome.
4. As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA. The amino acids are lined up in the right order on the ribosome.
1. In the nucleus, DNA transcribes RNA.
2. The RNA is sent to the cytoplasm in the form of mRNA.
Steps in Protein Synthesis
5. The ribosome hitches the amino acids together with peptide bonds and polypeptides are made.
Remember, a polypeptide is a long chain of amino acids but is not a functioning protein.
Polypeptides are sent to the endoplasmic reticulum and the Golgi apparatus where they are modified and shaped into functioning proteins.
Transfer RNA
The function of tRNA is to transfer amino acids from the cytoplasm’s amino acid pool to a ribosome.
Transfer RNA molecules are not all the same.
Each type of tRNA molecule links a particular mRNA codon with a particular amino acid.
The ribosome adds each amino acid brought to it by tRNA to the growing end of a polypeptide chain.
As a tRNA arrives at a ribosome, it carries a specific amino acid
at one end.
At the other end is a nucleotide triplet
called an anticodon.
Transfer RNA
anticodon
tRNA
amino acid
*Read carefully to determine if a test question is giving you the codon or the anticodon... Only look up codons in the amino acid chart!*
The tRNA that delivers the amino acid aspartic acid has as its anticodon CUG.
It carries aspartic acid at its other end
mRNA codons
tRNA anticodon
amino acid
Each tRNA is used repeatedly to locate a particular amino acid and deposit it at the ribosome. It then leaves the ribosome to go and find another amino acid.
For example: If an mRNA codon is GAC
Codon Wheel vrs Codon Chart
3rd position
1st position
2nd position
= Trp
U | G | G |
1 | 2 | 3 |
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Translation- Let's Practice!
Anticodon examples:
If a tRNA molecule has an anticodon which reads AUG, what was the codon of the mRNA molecule?
If a tRNA molecule has an anticodon which reads CAG, what was the codon on the mRNA molecule?
If a tRNA molecule has an anticodon which reads GCU, what was the codon of the mRNA molecule?
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Translation- Let's Practice!
Anticodon examples:
If a tRNA molecule has an anticodon which reads AUG, what was the codon of the mRNA molecule?
If a tRNA molecule has an anticodon which reads CAG, what was the codon on the mRNA molecule?
If a tRNA molecule has an anticodon which reads GCU, what was the codon of the mRNA molecule?
© Amy Brown Science
Translation- Let’s Practice!
Anticodon examples:
If a tRNA molecule has an anticodon which reads AUG, what was the codon of the mRNA molecule?
If a tRNA molecule has an anticodon which reads CAG, what was the codon on the mRNA molecule?
GUC- Vol
If a tRNA molecule has an anticodon which reads GCU, what was the codon of the mRNA molecule?
© Amy Brown Science
Translation- Let’s Practice!
Anticodon examples:
If a tRNA molecule has an anticodon which reads AUG, what was the codon of the mRNA molecule?
If a tRNA molecule has an anticodon which reads CAG, what was the codon on the mRNA molecule?
GUC- Vol
If a tRNA molecule has an anticodon which reads GCU, what was the codon of the mRNA molecule?
CGA - Arg
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The codons must be read correctly and in the correct order.
Consider the statement:
The red dog ate the cat.
What happens if the reading of the code starts at the wrong place? Consider the same sentence. Read the letters in groups of three, but omit the “T” at the beginning of the sentence
her edd oga tet hec at.
The codons must be read correctly and in the correct order.
The red dog ate the cat.
her edd oga tet hec at.
The result will be gibberish.
A polypeptide will be made by putting the wrong amino acids in order.
It is unlikely that this protein will be able to function.
Let’s Practice A Bit More!
Transcription:
Translation:
Codons:
A-A-G C-G-A C-U-U
Amino Acids:
______ _______ ______
The gene for large single eye is TTCGCTGAA.
Let’s Practice!
Transcription:
Translation:
Codons:
A-A-G C-G-A C-U-U
Amino Acids:
______ _______ ______
The gene for large single eye is TTCGCTGAA.
Let’s Practice!
Transcription:
Translation:
Codons:
A-A-G C-G-A C-U-U
Amino Acids:
______ _______ ______
The gene for large single eye is TTCGCTGAA.
Let’s Practice!
Transcription:
Translation:
Codons:
A-A-G C-G-A C-U-U
Amino Acids:
______ _______ ______
The gene for large single eye is TTCGCTGAA.
Lys Arg Leu
The protein Lys-Arg-Leu creates a large single eye.
What Do I Do Now?
DNA sequence | TAC | TTA | CAA | ACC | ATA | ATT |
mRNA codons | | | | | | |
tRNA anticodons | | | | | | |
Amino acids | | | | | | |
Putting It All together!
If the sequence on the DNA molecule calls for a protein with the following DNA codons:
(1) What would be the sequence of the mRNA codons?
(2) What would be the sequence of the tRNA anticodons?
(3) What would be the amino acid sequence of the protein being made?
AUG
UAA
UAU
UGG
GUU
AAU
UAC
AUU
AUA
ACC
CAA
UUA
Methionine
(Start)
Asparagine
Valine
Tryptophan
Tyrosine
STOP
1 2 3 4 5 6
Complete the 3.03 Quiz in your gradebook.
Questions?