Question

Chapter 8: Microbial Genetics and Genetic Engineering Reading Assignment: Chapter 8 1. Describe the structure and function of DNA in the microbial cell. List the chemical components of DNA including the nitrogen bases and the role of histones. 2. Define the following: genome, chromosome, gene, genotype, phenotype, and palindrome. 3. Describe the process of DNA replication in microbes. Explain the term semi-conservative replication 4. Describe the steps in protein synthesis. Compare and contrast transcription and translation. Describe the roles of rRNA, MRNA, and tRNA. Be able to transcribe and translate a DNA sequence into the appropriate amino acid sequence. 6. Explain the differences between an inducible operon and a repressible operon. Give examples of each. 7. Explain the key parts of the typical bacterial operon and how the operon regulates gene expression. * Explain the differences between the 4 major methods of genetic transfer in bacteria: Conjugation, Transformation, Transduction, Transposition Define the terms mutation, mutant strain, and wild type. 10. Explain the differences between the following types of mutations: induced, random, point, deletion, frame shift, insertion, inversion, substitution, and back-mutation. 11. Explain what the AMES TEST is used for. Explain the difference between a carcinogen, mutagen, and teratogen. 12. Describe the following tools and structures important to Genetic Engineering: plasmids, restriction endonucleases, palindromes, sticky-end and blunt-end endonucleases, ligase. Give some examples and discuss how endonucleases work. 13. Explain how the technique of gel electrophoresis works. What are gels made of? 14. Explain what a RFLP is. Discuss how the size of DNA fragments is determined using gel electrophoresis and a DNA marker (ladder). is Explain how they are

Answer 1

1).

Bacteria are unicellular organisms and they have only one circular chromosome attached to the plasma membrane and it does not contain any nucleus. So, the DNA in microbes (bacteria) is present in the cytoplasm, both the transcription and translation occur in the cytoplasm.

The DNA is a double helical structure in which two nucleotide strands are bonded together by hydrogen bonds. The double helical structure of DNA is formed by the coiling of two polynucleotide chains, similar to a spiral staircase.

Each nucleotide contains three subunits in their structure, i.e. one phosphate, nitrogen-containing base (purines and pyrimidine) and a 5-carbon sugar. It is the polymer chains of nucleotides that make up DNA (deoxyribonucleic acid) strands, which is called as “polynucleotides.”

The four bases in DNA are, adenine (A), thymine (T), guanine (G), and cytosine (C), which are the building blocks of DNA’s double helical structure. Adenine and thymine are pyrimidines, guanine and cytosine are purines. Among these base pairs, adenine binds with thymine and guanine binds with cytosine, this is called a complementary pairing.

The two nucleotide chains run in an antiparallel direction to each other. Means, one strand runs in 5’ to 3’ direction and the other runs in 3’ to 5’ direction. The two nucleotide chains are bonded together by the hydrogen bonds.

The 3’ ends of DNA contain hydroxyl group, whereas the 5’ end contains the phosphate group. During the DNA synthesis, DNA ligase forms phosphodiester bonds between the hydroxyl group of 3' end and the phosphate group of 5' end of adjacent DNA strands.

Histones:

The chromosome is a genetic component of a cell carries inheritance, the genetic material in the form of deoxyribonucleic acid (DNA).

The Chromosomes contain DNA bound proteins called “histones,” which serve to “package” the DNA and thereby controls its functions (transcription process). The interaction between the positively charged histones and negatively charged phosphate groups of DNA and the intra-histone interactions form beadlike structures called “nucleosomes.” Thus, the chromosomes are made of DNA, histones, chromatin (euchromatin or heterochromatin).