DNA Structure and Function Lab Report3 14

BioLab3
DNA Structure and Function Lab Report

Student Name:

I. DNA Structure

Define the following terms:
Purines
A colorless crystalline compound with basic properties, forming uric acid on oxidation.
Pyrimidines
A colorless crystalline compound with basic properties; a substituted derivative of this, especially the bases thymine and cytosine present in DNA.
Nucleotides
A compound consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit of nucleic acids such as DNA.
Complementary
bases
Guanine is the complementary base of cytosine, and adenine is the complementary base of thymine in DNA and of uracil in RNA.
Double helix A pair of parallel helices intertwined about a common axis, especially that in the structure of the DNA molecule.

EXERCISE 1 –DNA structure

Which carbon atom (position) in the sugar forms a covalent bond with the nitrogen base?
The 1’ carbon Which carbon atoms of deoxyribose bond with the phosphate molecule?
4’ carbon and 5’ carbon

Which bases will pair with one another?

Adenine will pair only with
Thymine
Cytosine will pair only with
Guanine

In the figure below, write the letters that stand for the complementary bases in the double-stranded DNA puzzle. Indicate the number of hydrogen bonds between the complementary base pairs by dotted lines.

Complementary DNA nucleotide strands

The phosphate group at the top on the left strand is attached to which carbon atom (position) in the sugar? Which carbon atom of ribose would be attached to the next phosphate group added to the bottom of the left strand?
It is attached to the OH group on the 5-carbon. Bottom left –OH is attached to 3 carbon.

Which carbon atom of ribose would be attached to the next phosphate group that will be added to the top of the right strand? Which carbon atom of ribose is attached to the bottom right phosphate group?
3 carbon on top, 5 on bottom.

What do you notice about the direction in which each strand is oriented?
The left strand is from 5’ to 3’ and the right strand runs from 3’ to 5’; they go in opposite directions. II. DNA Replication

Define the following terms:
DNA replication
During the S stage of interphase, each molecule of DNA makes an exact copy of itself.
Origin.
The place where the enzymes open up the double helix strand of DNA.
Semi-conservative replication
Saving a half of the old strand and constructing a new one alongside.

EXERCISE 2 – DNA replication

How much of the newly formed DNA molecule is new and how much is the original strand? What term is used for this type of replication?
8 original and 8 new. How often in the life of a cell does replication occur?
Only once. Explain the purpose of replication.
The purpose is for each cell to make exactly one copy of itself.

In the figures below, write the letters A, T, C, G representing the nitrogen base compounds on the two replicated DNA molecules. Label the old and the new strands.

Complementary DNA nucleotide strands

Did the nitrogen base sequence change in DNA replication?
No, it remained the same. III. RNA Structure

Define the following terms:
RNA
A type of nucleic acid.

EXERCISE 3 – Comparison of DNA and RNA

How are ribose and deoxyribose sugar molecules similar and different?

Similar
Both are sugar molecules.
Different
Ribose is a compound of RNA and deoxyribose is a component of DNA.

Why is the sugar molecule in DNA called deoxyribose and the sugar in RNA called ribose? Note the number of oxygen atoms.
Ribose has more oxygen.
Which bases are included in the DNA molecule? C A T G Which bases are included in the RNA molecule? A U G C What do you notice about the number of strands making up each molecule? RNA had 1 and DNA had 2

Record your findings comparing DNA and RNA.

DNA
RNA
Sugar
8
4
Bases
8
4
Strands
2
1

IV. RNA Synthesis

Define the following terms:
Genetic code
Contained in the DNA molecule, the genetic code consists of three bases in a sequence along one strand of the DNA.
Transcription
The process of assembling RNA using a DNA molecule as a template. mRNA Messenger RNA tRNA Transfer RNA rRNA Ribosomal RNA
Triplet
A series of three bases on the DNA molecule
Codon
Each three base sequence on a strand of mRNA

EXERCISE 4 – RNA synthesis (transcription)

Write in the DNA strand according to the instructions given. Next, write the letters for the base sequence of mRNA in the spaces below DNA.

DNA
C
G
T
C
G
T
C
C
A
A
T
T
5’
mRNA
G
C
A
G
C
A
G
G
U
U
A
A
3’

Considering the structure of the nuclear envelope, how does the mRNA exit the nucleus?
It travels out of the nucleus through the nuclear pores.

To transcribe means to copy. Is the RNA transcribed from DNA an exact copy? If not, what are the differences?
The transcribed RNA is not an exact copy. RNA is single and Uracil replaces the thymine base.

What happens to the original DNA section after RNA is transcribed from it?
The DNA will re-bond with its complementary bases.

Distinguish between replication and transcription.
Replication is the exact copy while transcription uses DNA as a template but the structures are different.

V. Protein Synthesis

Define the following terms:
Translation
An mRNA sequence is read using the genetic code, which is a set of rules that defines how an mRNA sequence is to be translated into the 20-letter code of amino acids, which are the building blocks of proteins.

EXERCISE 5 – Translation

mRNA
5’
G
C
A
G
C
A
G
G
U
U
A
A
3’
Amino acids
3’
Alanine
Alanine
Glycine
Terminate
5’

What does the final mRNA codon (UAA) in the sequence above specify on the polypeptide chain?

The UAA codon is a chain terminating codon.

Summarize the process of transcription to translation.

mRNA containing the code from the DNA in the nucleus proceeds to the cytoplasm and the ribosome. The ribosome reads the codon on the messenger RNA and the tRNA lines up according to the anticodon on the rRNA molecule. The amino acids brought by the tRNA are attached in the specified sequence.

DNA
3’
C
G
T
C
G
T
C
C
A
A
T
T
5’
DNA Template Strand

mRNA
5’
G
C
A
G
C
A
G
G
U
U
A
A
3’
Codon

tRNA
5
G
C
A
G
C
A
G
G
U
U
A
A

Anticocon

Amino acids 5
Alenine
Alenine
Glyane
Terminate

Polypeptide Chain

VI. Genes
Define the following terms:
Gene
Unit of inheritance that codes polypeptide.
One gene, one polypeptide hypothesis.
Unit that codes 1 polypeptide.
Sickle-cell anemia
Genetically inherited disordered sequence of amino acids on the polypeptide chain.

Does a gene consist of one, several or many deoxyribonucleotides?
It varies from one gene to another.

In the table in section V, locate the base pair in the HbS that differs from the normal gene for HbA. What are they and how do they differ? Glycine, GGU and terminate, UAA. They contain Uracil.

What change occurs in the amino acid sequence?
The last mRNA code is UAA.

VII. Gene Cloning

Define the following terms:
Plasmid
A small circle of DNA in addition to the larger loop of DNA fond in many bacteria.
Clone
Exact copies of foreign DNA.

Summary Questions

1. Describe the three-dimensional structure of DNA.
DNA is double helical in structure and each spiral strand is composed of a sugar phosphate backbone and attached bases are connected to a complementary strand by hydrogen bonding. These non-covalent bonds
2. What is the ratio of guanine to cytosine in a double-stranded DNA molecule? Of adenine to thymine?
G to C and A to T.
3. Define:

Replication
Process of duplication.
Transcription
The process by which the information in a strand of DNA is copied into a new molecule of messenger RNA.
Translation
The process of using the message encoded on the mRNA to link up amino acid in a specific sequence to form a polypeptide.
Codon
A triplet of adjacent nucleotides in the messenger RNA chain that codes for a specific amino acid in the synthesis of a protein molecule.
Anticodon
A sequence of three nucleotides in a region of transfer RNA that recognizes a complementary coding triplet of nucleotides in messenger.

4. List three differences between DNA & RNA.

DNA
RNA
AT and CG
AU and CG
OH
H
One less oxygen than ribose.
Ribose has one more oxygen than deoxyribose.

5. If the base sequence on one DNA strand is 3’ ATAACCTAG 5’, what will the sequence be on the other strand of the helix?

DNA
3’
A
T
A
A
C
C
T
A
G
5’
DNA
5’
T
A
T
T
G
G
A
T
c
3’

From this double strand, write out the result of replication.

6. If 3’ GCATAGATC 5’ serves as the template for transcription, what will be the sequence of nitrogen bases on the newly formed RNA strand?

DNA
3’
G
C
A
T
A
G
A
T
C
5’
mRNA
5’
C
G
T
A
T
C
T
A
G
3’

How many codons are present? 3
Determine which amino acid is coded for. Arginine, Isoleucine and Tyrosine.
7. If a DNA sequence is 3’ TAG 5’, give the following:

mRNA sequence (codon)
5’ CGUAAUCUAG 3’ tRNA sequence (anticodon)
3’ GCAUUAGAUC 5’
Amino acid
Alanine, tyrosine and isoleucine.

8. What are plasmids and how do they function in genetic engineering?
Plasmids are a genetic structure in a cell that can replace independently of the chromosomes. Their function in genetic engineering is that they become manipulation genes.

9. Suggest two advantages and two disadvantages of genetic engineering.

Advantages
Plants and animals can be made to have desired characteristics.

Diseases could be prevented.
Disadvantages
Genetic engineering can be morally incorrect.

Nature is complex and all changes may not be good.

10. The dinosaurs in Jurassic Park were developed from DNA found in the stomach of mosquitoes preserved in amber. The mosquitoes had ingested the blood of dinosaurs. Starting with the DNA in the dinosaur white blood cells, explain how transcription and translation were involved in the process. White blood cells have a nucleus containing DNA.
The DNA would be transcribed to RNA via RNA polymerase. The RNA sequence would then leave the nucleus and go into the cytoplasm to be translated into protein using ribosomes and amino acids.