Download DNA Replication lab

REPLICATION, TRANSCRIPTION, TRANSLATION, Oh My!
Purpose: How are DNA replication, transcription, and translated related to one another?
Materials:
Paper
DNA and RNA Templates
Deoxyribonucleic acid, or more simply DNA, is a complex molecule in all-living organisms. It is the
chemical of which genes are composed. Genes, in turn, are found in chromosomes. An understanding of
the organization of this molecule has answered many questions. Scientists now know how
CHROMOSOMES CAN DUPLICATE and TRANSFER THEIR GENETIC INFORMATION TO NEW
CHROMOSOMES. Scientists also understand how chromosomes can direct the formation of specific
proteins outside the nucleus while still in the nucleus.
IN THIS INVESTIGATION, IT IS EXPECTED THAT YOU:
(A) use paper models to construct a portion of a DNA molecule
(B) use paper models to show the replication of a DNA molecule
(C) complete the self-test on this activity
Part A: STRUCTURE OF A DNA MOLECULE
The molecules, which make up DNA are DEOXYRIBOSE, PHOSPHORIC ACID (phosphate), and
NITROGEN BASES. There are FOUR bases in DNA. Each base (guanine, thymine, cytosine, and
adenine) is chemically joined to a molecule of Deoxyribose. These three molecules form a group called a
NUCLEOTIDE. The paper models represent the three molecules that make up the nucleotide.
A DNA molecule is twisted, “ladder-like” shape. Deoxyribose and phosphoric acid molecules join to
form the sides or uprights of the ladder. Base molecules join together to form the rungs of the ladder.
Part A Procedure:
1. Cut out the molecules of Deoxyribose, phosphoric acid (phosphate) and the four bases.
Construct six nucleotides with the following bases:
 cytosine nucleotide
 thymine nucleotide
 guanine nucleotide
 adenine nucleotide
 guanine nucleotide
 cytosine nucleotide
2. Now, connect the six nucleotides together to form a row in the sequence listed above from top
to bottom. Let this represent the left half of a DNA(ladder) molecule. This should consist of
one side or upright plus six half rungs.
3. Connect six more nucleotides with bases that will properly pair (fit) the bases on the left half
of the DNA. This will represent the right half of the DNA (ladder) molecule. Arrange these
two halves to form a complete DNA model. Connect the two halves with tape.
Part A Questions:
1. What are the two molecules that alternate to form the sides of the DNA?
2. To which molecule do the bases attach?
3. Which end represents the 5’ end of the DNA? Which end represents the 3’ end?
4. Which part of the nucleotide forms the rungs of the DNA ladder?
5. What did you have to do to the right half of the DNA molecule to make it fit to the left? WHY?
6. Which bases are purines? Which bases are pyrimadines?
7. Only two combinations of the base pairings are possible for the rungs. Name these molecule
combinations or pairs.
8. If four guanine bases appear in a DNA model, how may cytosine bases should there be?
9. The following are the bases on the left side of a DNA molecule. List the bases that would make up
the right side of a DNA molecule.
Thymine, Adenine, Guanine, Guanine, Cytosine, Thymine, Cytosine, Adenine
10. There is one feature you can’t show with this model. What is that feature?
Part B: CHROMOSOMES AND DNA REPLICATION
Your DNA model represents only a short length of the DNA portion of a chromosome. An entire
chromosome has thousands of rungs rather than only six. Although your model is only a small part of a
chromosome, its replication is the same as that of an entire chromosome during the S phase prior to
mitosis and meiosis.
Part B: Procedure
1. Cut out 12 more deoxyribose molecules. Cut 12 phosphoric acid molecules and the
remaining bases. Assemble 12 nucleotides.
2. Open your DNA model along the point of attachment between base pairs (rungs) and separate
the two ladder halves. (A chromosome un-twists and unzips in a similar way prior to
replication).
3. Using the left half of your model pattern, add new nucleotides to form a right side. Make sure
to add in the 5’ to 3’ direction so the sides are antiparallel. Connect the two sides. Build a
second DNA model by adding new nucleotides to the right half of the original model.
Part B Questions:
1. Do the two molecules contain the same number of rungs?
2. What enzyme is responsible for “unzipping” the original DNA strand?
3. What enzyme is responsible for adding nucleotide to the new complementary strand?
4. What are the other enzymes / proteins involved in DNA replication? What does each do?
5. Describe how the leading and lagging strands are different from one another in real DNA replication.
6. If there is an error in the replication process how is it fixed?
7. Where in the cell does DNA replication occur?
8. When does DNA replication occur?
9. Is the order from top to bottom of base pairs (rungs) different or the same for each new DNA
molecule?
10. Are the “new” DNA strands bonded to each other? If not, what are they bonded to?
11. TEMPLATE means an exact copy of an original. COMPLIMENTARY means something that is not
an exact copy but rather will “fit” in with the original. These two words are used to describe EACH
STRAND of the newly replicated DNA. Using the color of the deoxyribose sugar, describe which
strand is which and explain why?
Glue one of the strands of your replicated DNA as your data AFTER COMPLETING Part C and F and
give the other strand to your partner to glue in their data book.
PART C: TRANSCRIPTION
mRNA copies the information necessary to make a protein from one strand of the DNA molecule. The
SINGLE-STRANDED mRNA then travels from the nucleus to the ribosomes, carrying the genetic
message (thus it is called messenger RNA). At the ribosomes mRNA will DIRECT THE BUILDING OF
PROTEINS. Each group of THREE nucleotides on the mRNA codes for a particular AMINO ACID (The
20 amino acids make up the building blocks of proteins). The table attached shows which CODONS
(three nucleotide bases) code for which amino acid.
Part C: Procedure
1. Using the model of DNA you made from activity 1, carefully “unzip” the DNA. Use only the side
that codes C,T,G,A,G,C. This is the gene coding sequence.
2. The mRNA will now bond to the exposed DNA bases, copying the code in the sequence of bases.
To do this, tape the mRNA nucleotides together as you match them to the exposed bases. DO
NOT BIND THE mRNA DIRECTLY TO THE DNA.
3. Remove the mRNA strand from the DNA. Close the DNA back up.
4. Glue the mRNA strand in your data book next to your DNA strand.
Part C Questions:
1. Write out the sequence of the mRNA strand.
2. What is transcription?
3. Where in the cell does transcription take place?
4. What enzyme is responsible for adding complementary nucleotides to the mRNA strand?
5. What 3 things must happen to the mRNA before it leaves the nucleus? WHY?
6. After mRNA is made it travels from where to where?
7. How many strands of mRNA did you make?
8. How does this differ from DNA?
9. The mRNA base, uracil replaces what DNA base?
10. What base on DNA does the base uracil pair with?
Part D: TRANSLATION
Part D: Procedure
1. Place a sheet of 8.5x11 paper in landscape orientation. Using a pen, divide the paper in half.
This is your ribosome.
2. On the left half of the page, mark the letter P. This is the peptidyl site.
3. On the right half of the page, mark the letter A. This is the aminoacyl site.
4. Remember that three nucleotide bases make up a codon.
5. Use the mRNA strand made in part C and place the first 3 bases so they are in the P site. The
second 3 bases should be in the A site.
6. Move the ribosome one space over so the codons that were in site A are now in site P.
7. If the mRNA strand were longer the ribosome would continue to read the mRNA until a stop
codon was reached.
Part D Questions:
1. Where in the cell does translation occur?
2. What is translation?
3. Write out the amino acids coded for by the short mRNA strand in the model.
4. What are the 3 base groupings on the mRNA called?
5. What do they “pair” with?
6. What does each group of 3 nucleotides code for?
7. What molecule is responsible for bringing the correct amino acid to the ribosome? How
does it know which amino acid is correct?
8. You will notice there are several codons for some of the amino acids. Each codon differs
from the others (for the same amino acid) by how many bases? Which base in the codon is
usually the one which differs?
9. Mutations can be caused by altering a DNA base pair in some way. If a mutation changed
our codons from GAC, UCG, to GAU, UCG what would happen?
10. Codons are “read” at the ribosomes in sets of three bases (one codon at a time). What does
the following mRNA strand which read UUU – GUU - CAA code for?
11. Transcribe and Translate the following DNA strand:
DNA:
TAC AAA AGA ATA ACA ATT
MRNA:
____ _____ ____ ____ ____ _____
AMINO ACID SEQUENCE: ____ _____ ____ ____ ____ _____
ANTICODONS:
____ _____ ____ ____ _____ ____
12. What would happen to the polypeptide in question 10 if the first U was completely
deleted? The resulting amino acids would be? How would this change the overall protein?
13. Give an example of a disease caused by a point mutation.
14. Complete the following table to show the similarities and differences between DNA and
RNA. A checkmark indicates the presence of the characteristic.
DNA
RNA
Ribose present
Deoxyribose present
Phosphoric Acid present
Adenine Present
Thymine present
Uracil present
Guanine present
Cytosine present
Double strand
Single strand
Remains in nucleus
Moves out of nucleus
Codon Chart
Discussion:
Describe the structure of DNA and RNA.
Describe DNA replication.
Describe transcription.
Describe translation.
Be as detailed as possible in your explanations of each, by mentioning specific enzymes, proteins, and
processes for each.
Conclusion: Answer the purpose question.