Download Protein Synthesis

Protein Synthesis
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Integrated Science 4
Redwood High School
Name:
Per:
Read pages 364-370 in chapter 17 of your Integrated Science textbook and answer the following questions.
 Part 1. RNA and Transcription
1. Compare and contrast RNA and DNA (1 similarity and 3 differences).
similarity – made of nucleotides
differences – ribose sugar, single-stranded (most often), uracil (instead of thymine), location (nucleus,
cytoplasm and ribosome)
2. Name and describe the three main types of RNA.
messenger RNA - mRNA
transfer RNA - tRNA
ribosomal RNA - rRNA
3. What is the purpose of transcription? How does it differ from DNA replication?
The purpose of transcription is to re-write a portion of DNA, a gene,
Transcription constructs an mRNA molecule through complimentary base pairing a portion of DNA.
DNA replication makes an exact copy of the entire DNA molecule, whereas transcription re-writes a
gene by producing an mRNA molecule from only part of the DNA molecule.
4. Why is it necessary for DNA to transfer its genetic information to RNA?
Many genes are being transcribed simultaneously.
DNA cannot leave the nucleus.
5. Summarize transcription. Describe the roles of DNA, messenger RNA and RNA polymerase in your
response.
RNA polymerase locates a gene along DNA. It attaches to, and separates the DNA molecule. It uses
one strand of the DNA as a template to construct mRNA through complimentary base pairing.
6. Use the following sequence of a template strand of DNA to transcribe a segment of messenger RNA.
The letters represent nucleotides.
DNA Template Strand Sequence:
A
G
G
T
T
C
G
T
A
T
Complementary mRNA Strand Sequence:
U
C
C
A
A
G
C
A
U
A
T
A
C
A
A
G
U
U
 Part 2. Translation
7. Summarize the genetic code. Include the connection between codons and amino acids.
There are 20 different amino acids that assemble into polypeptides and eventually proteins.
Three consecutive nucleotides of mRNA that code for a particular amino acid is a codon.
8. Describe the relationship between amino acids, polypeptides, peptide bonds and proteins.
Amino acids form peptide bonds.
Long chains of amino acids are referred to as polypeptides.
Proteins are produced by different sequences amino acids and different arrangements of
polypeptides.
9. In detail, describe the process of translation. In your response, describe the roles of messenger RNA,
transfer RNA, ribosomal RNA, ribosomes and amino acids.
Translation is the process through which mRNA produces proteins.
mRNA travels from the nucleus to the cytoplasm where it binds with a ribosome (rRNA).
As the mRNA codons pass through the ribosome tRNA molecules bring the appropriate amino acids.
Amino acids form peptide bonds with one another and create polypeptide chains.
10. What is a “stop” codon? Describe its role in protein synthesis.
A three nucleotide sequence on mRNA which indicates the end of a polypeptide chain.
11. Describe the importance of proteins. Give several examples of protein functions in living cells.
Proteins are responsible for the structure and function of living things.
 Part 3. Summary and Application DNA  RNA  Protein
12. Put the following steps of protein synthesis in order; (1) happens first to (7) happens last.
__4__ tRNA carries amino acids to the ribosome, matching its anticodon with an mRNA codon
__6__ a stop codon on mRNA is encountered. The ribosome releases the polypeptide.
__1__ messenger RNA is transcribed from DNA in the nucleus.
__2__ messenger RNA leaves nucleus and travels to cytoplasm.
__5__ amino acids are added to a growing chain as mRNA codons are read by the ribosome.
__3__ an initiation codon on messenger RNA binds to a ribosome.
__7__ the polypeptide bends and folds into a 3-dimensional shape, forming a functional protein.
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13.
Step
1. Transcription
2. Translation
Initial Macromolecule
(What do you start with?)
DNA
mRNA
Final Macromolecule
(What is created?)
mRNA
polypeptide chain
Location in Cell
(Where does this occur?)
nucleus
ribosome (in cytoplasm)
Use the codon chart provided to help answer questions #14-#17.
14. If a three nucleotide sequence on a DNA molecule is CTA, what is the messenger RNA codon
sequence?
GAU
What is the amino acid this portion of the DNA molecule codes for?
Aspartic Acid
15. RNA polymerase binds to a portion of the DNA molecule and reads the sequence of bases below.
Transcribe and translate the DNA sequence to determine the amino acid sequence of the polypeptide
chain. Remember that you always translate the messenger RNA codon sequence!
Template DNA Strand Sequence:
Messenger RNA Strand Sequence:
T A C
A U G
T T G
A A C
G G A
C C U
T G C
A C G
C C C
G G G
Transfer RNA anticodon Sequence:
U A C
U U G
G A U
U G C
C
Amino Acid Sequence:
Isoleucine
Asparagine
Proline
Threonine
A C T
U G A
C C A C U
Glycine
Stop
16. RNA polymerase binds to a portion of the DNA molecule and reads the sequence of bases below.
Transcribe and translate the DNA sequence to determine the amino acid sequence of the polypeptide
chain. Remember that you always translate the messenger RNA codon sequence!
Template DNA Strand Sequence:
Messenger RNA Strand Sequence:
T A C
A U G
G C C
C G G
T C T
A G A
G G T
C C A
C T T
G A A
A T C
U A G
Transfer RNA anticodon Sequence:
U A C
G C C
U C U
C G U
C U U
A U C
Proline
Glutamic
Acid
Stop
Amino Acid Sequence:
Isoleucine
Arginine
Arginine
17. UAG is a stop codon. What might happen if the uracil in this codon was changed to cytosine?
Glutamine would have been added to the polypeptide chain.
18. List the four different sets of DNA nucleotide sequences that code for the amino acid Valine. Explain
why this redundancy in the genetic code is significant to life.
GUG, GUA, GUC, GUU
There is repetition to insure random changes (mutations) don’t always result in different proteins.
19. Once a polypeptide chain is formed, it must be arranged into a 3-dimensional conformation before it
is considered a functional protein. List and describe the 4 levels of protein structure.
(Note: this question will be addressed in class as notes)
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