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MOLECULAR GENETICS ASSIGNMENT
After reading the Introduction answer the following questions:
- Complete the following table comparing chromosomal DNA and mRNA:
| Comparison | Chromosomal DNA | mRNA |
| Five Carbon Sugar: | Deoxyribose | Ribose |
| Nitrogenous Bases: | Adenine | Adenine |
| Cytosine | Cytosine | |
| Guanine | Guanine | |
| Thymine | Uracil | |
| Number of Strands | Two | One |
| Typical Location in Cell | Nucleus | Cytoplasm |
- Below you are given one half of a DNA molecule. Show the nucleotide sequence of the complementary strand of DNA using the letters of the nucleotides. The first nucleotide on Strand B is already done for you.
Strand A of the DNA
____________________________________________________________
| | | | | | | | | | | |
- T A G A C T C T A A G
G A U C U G A G A U U C
| | | | | | | | | | | | .
Stand B (complementary to Strand A)
- Suppose that strand A from above is transcribed to mRNA. Show the mRNA portion that would result. Remember uracil replaces thymine in RNA.
Strand A of the DNA
____________________________________________________________
| | | | | | | | | | | |
- T A G A C T C T A A G
G A U C U G A G A U U C
| | | | | | | | | | | | .
mRNA transcript of Strand A
- Now circle each codon in the mRNA strand (already done for you).
- Please indicate the corresponding mRNA nucleotides from the DNA strand below, circle the codons, and identify the amino acids coded for by the mRNA using the table below for the genetic code. The first one is done for you.
Strand of the DNA
____________________________________________________________
| | | | | | | | | | | |
A C A C T T T A A C G C
U G U G A A A U U G C G
| | | | | | | | | | | | .
mRNA from DNA
UGU codes for Cys GAA code for Glu AUU code for ile GCG code for ala
_________________ _______________ _______________ _______________
Amino Acids Coded for by the mRNA
- After reading your Introduction, complete the following table:
| Codon | Anticodon |
| UUU | AAA |
| ACG | UGC |
| GAC | CUG |
| UGA | ACU |
| AGG | UCC |
- Use the amino acid table from above complete the following table and #8 and #9:
| Amino Acid | Possible Codons |
| Leucine (Leu) | CUU, CUC, CUA, CUG |
| Phenylalanine (Phe) | UUU, UUC |
| Isoleucine (Ile) | AUU, AUC, AUA |
| Glycine (Gly) | GGU, GGC, GGA, GGG |
- What codon is the start codon?
The start codon is AUG, and it marks the site at which translation of protein sequence commences.
- What codons are the stop codons?
The stop codons are UAA, UGA, and UAG, and they mark the site at which translation of protein sequence ends (they encode no amino acid).
- What is the difference between the DNA that codes for normal red blood cell haemoglobin and the DNA that codes for sickle cell anaemia haemoglobin?
The sickle cell haemoglobin varies from normal haemoglobin by a single amino acid; valine replaces glutamate at position six on the surface of the beta chain, thus creating a new hydrophobic spot.
- Where does transcription occur in the cell?
Nucleus.
- What is the function of the transcription?
The function of transcription is to yield an mRNA copy of the gene which permits information in the nucleus to pass out through pores to be used to make a protein.
- Where does translation occur in the cell?
The cytoplasm of the cell
- What is the function of translation?
The function of translation is taking information from DNA as a messenger RNA and turning it into a sequence of amino acids bound together with peptide bonds.
- What are purines in DNA?
They are two-carbon nitrogen bases, adenine and guanine, which are constituents of DNA and RNA formation.
- What are pyrimidines in DNA?
They one of the two categories of heterocyclic nitrogenous bases in nucleic acids DNA and RNA.
- What is a double helix?
This refers to the structure of two strands of DNA molecule that are wound around each other like a twisted ladder.
- What were the contributions of the following scientists?
- Gregor Mendel – he discovered the fundamental laws of inheritance through his work on pea plants. He construed that genes arise in pairs and inbred as discrete pieces from every parent.
- Friedrich Meischer – he identified DNA as a discrete molecule; thus, the DNA with associated proteins from cell nuclei.
- A. Levene – he categorized various forms of nucleic acid and concluded that DNA contained Adenine, Guanine, Thymine, Cytosine, Deoxyribose, and Phosphate group.
- Erwin Chargaff – he came up with two rules; one- the number of guanine units is equal to the number of cytosine units in DNA, and the number of adenine units is same to the number of thymine units. Second, the relative quantity of guanine, cytosine, adenine, and thymine bases vary with species.
- Rosalind Franklin – she worked on the X-ray diffraction images of DNA, her contribution, especially with photo 51, led to the discovery of the DNA double helix.
- James Watson – together with the other two, he discovered the double helix structure of the DNA molecule.
- Francis Crick – he found that DNA is made up of two chains of nucleotide pairs which encode the genetic information for all species.