Question

1. What is a gene? Describe the function, structure, and location within the cell.
2. What are the three stop codons? What is the start codon?
3. Compare and contrast bacterial and eukaryotic ribosomes.
4. Do a web search to find another example of a disease caused by a mutation in a single gene. Do the resulting symptoms (new trait) make sense considering the role of the affected protein? Why or why not?
5. Transformation, conjugation, and transduction were discovered in the laboratory. How important are these mechanisms of genetic recombination in nature?
6. Use the internet to investigate DNA fingerprinting. What is this process, and how is it used in criminal forensics?
7. How can plasmids be used to manufacture proteins such as insulin for diabetic patients, or antibiotics for bacterial infections?

Answer 1

1. Gene:

• Genes are sequences of nucleotides or fragment of nucleic acid (DNA, sometimes RNA),which forms the hereditary unit of life.
• Genes are located within DNA, (or RNA, such as some viruses).
• DNA may be in nucleiod form in prokaryotes.
• In eukaryotes DNA form chromosomes and packed within nucleus.
•    Location of a gene in a chromosome is called its locus. The location of the gene determines its traits, evolutionary variations, mutations, recombination, linkages, and several other important aspects.
• The genetic information in the fragment of DNA or a gene, may be expressed by its ability to encode a specific RNA or protein. The product thus generated typically “expresses” the genetic information of the gene.
• As described by the hypothesis of George Wells Beadle and Edward Lawrie Tatum, “One gene one enzyme”; the product of each genetic expression influences the activity of the cell.

• Gene expression mainly occurs in two steps:

1. Transcription- genetic code is transcribed to form mRNA. 2. Translation- mRNA is translated to proteins.

• Thus the process of transcription to produce mRNA and translation to produce protein is defined as the central dogma.
• DNA-> mRNA-> Protein

2. Codons:

• Codons are represented as three nucleotides (triplet codon) codes for a single amino acid.
• Translation starts from the start codon sequence and ends at Stop codons.
• Stop codons:

1. UAG – Amber
2. UAA- Ochre
3. UGA- Opal

• In eukaryotes, the AUG codon is the start codon for the process of translation.
• In prokaryotic cells, GUG and UUG codons also function as start codons.
• Messenger RNA or m RNA carries the genetic code received from the DNA, in 5’to 3 ‘direction reading frame. The initiator t-RNA (with anticodon (UAC) recognizes the start codon, which is essential for initiation of translation.

3. Prokaryotic and Eukaryotic Ribosome:

Features	Prokaryotes	Eukaryotes
Ribosomes	Molecular weight- 27000kD Sedimentation co-efficient-70s Subunits: larger subunit- 50s Smaller subunit- 30s rRNA (in larger subunit)- 23s and 5s	Molecular weight- 42000kD Sedimentation co-efficient-80s Subunits: larger subunit- 60s Smaller subunit- 40s rRNA (in larger subunit)-28s, 5.3s, 5s