Unit 1, Lecture 4

Name three infections that may be transmitted to humans by endospores.

1. Anthrax, caused by Bacillus anthracis; endospores can be inhaled, ingested, or enter wounds where they germinate and the vegetative bacteria subsequently replicate. 2. Tetanus, caused by Clostridium tetani; endospores enter anaerobic wounds where they germinate and the vegetative bacteria subsequently replicate. 3. Botulism, caused by Clostridium botulinum; endospores enter the anaerobic environment of improperly canned food where they germinate and subsequently replicate

Name 2 common genera of bacteria capable of producing endospores and state which is an obligate anaerobe.

1. Clostridium (obligate anaerobe) 2. Bacillus.

Composition of a bacterial chromosome

3. The region of the bacterial cytoplasm where the chromosome is located and visible when viewed with an electron microscope called the nucleoid. 4. The bacterial chromosome is typically a physical and genetic circle, becomes supercoiled,and is not surrounded by a nuclear membrane. 5. Bacteria do not carry out mitosis or meiosis.

Briefly describe the process of DNA replication. In terms of protein synthesis, briefly describe the process of transcription and translation.

7. Like eukaryotic DNA, prokaryotic DNA replicates by sequential unwinding of the two DNA parent strands and the subsequent complementary base pairing of DNA nucleotides with each parent strand. 8. During DNA replication the nitrogenous base adenine forms hydrogen bonds with thymine and guanine forms hydrogen bonds with cytosine. 9. Genes located along the DNA are transcribed into RNA molecules, primarily messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Messenger RNA is then translated into protein at the ribosomes. (Transcription and translation are coupled in bacteria.) 10. During transcription, ribonucleic acid (RNA) is synthesized by complementary base pairing of ribonucleotides with deoxyribonucleotides to match a portion of one strand of DNA called a gene. 11. During translation, specific tRNA molecules pick up specific amino acids, transfer those amino acids to the ribosomes, and insert them in their proper place according to the mRNA "message."

State the function of DNA.

a nucleic acid that contains the genetic instructions for the development and function of living things. All known cellular life and some viruses contain DNA. The main role of DNA in the cell is the long-term storage of information.

State the function of the following: a*. transposons b. integrons c. episome d*. conjugative plasmid

a. Transposons (transposable elements or "jumping genes") are small pieces of DNA that encode enzymes that transpose the transposon, that is, move it from one DNA location to another, either on the same molecule of DNA or on a different molecule. Transposons may be found as part of a bacterium's chromosome (conjugative transposons) or in plasmids and are usually between one and twelve genes long. A transposon contains a number of genes, coding for antibiotic resistance or other traits, flanked at both ends by insertion sequences coding for an enzyme called transpoase. Transpoase is the enzyme that catalyzes the cutting and resealing of the DNA during transposition. Thus, such transposons are able to cut themselves out of a bacterial chromosome or a plasmid and insert themselves into another chromosome or plasmid and contribute in the transmission of antibiotic resistance among a population of bacteria. b. Integrons are transposons that can carry multiple gene clusters called gene cassettes that move as a unit from one piece of DNA to another. An enzyme called integrase enables these gene cassettes to integrate and accumulate within the integron. In this way, a number of different antibiotic resistance genes can be transferred as a unit from one bacterium to another. c. a genetic element inside some bacterial cells, especially the DNA of some bacteriophages, that can replicate independently of the host and also in association with a chromosome with which it becomes integrated. d. A prokaryotic plasmid that carries genes for sex pili and for transfer of the plasmid to another cell.

Define sporulation and germination.

a. Under conditions of starvation, especially the lack of carbon and nitrogen sources, a single endospores form within some of the bacteria b. allowing outgrowth of a single vegetative bacterium (non-dormant for of bacterium)

State the function of the following enzymes in bacterial DNA replication: a. DNA polymerase III b. DNA polymerase II c. DNA helicase d. primase e. DNA ligase

a. replaces the primase and is able to add DNA nucleotides to the RNA primer. b. digests away the RNA primer and replaces the RNA nucleotides of the primer with the proper DNA nucleotides to fill the gap. c. unwinds the two complimentary parent DNA strands during DNA replication d. an enzyme capable of joining RNA nucleotides without requiring a preexisting strand of nucleic acid, first adds several comlementary RNA nucleotides opposite the DNA nucleotides on the parent strand e. enzyme that hooks the final DNA strands together

Briefly discuss the function of a bacterial endospore.

An endospore is a dormant, tough, non-reproductive structure produced by a small number of bacteria from the Firmicute family. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. Bacterial endospores are resistant to antibiotics, most disinfectants, and physical agents such as radiation, boiling, and drying. The impermeability of the spore coat is thought to be responsible for the endospore's resistance to chemicals. The heat resistance of endospores is due to a variety of factors.

State the most common way plasmids are transmitted from one bacterium to another.

Conjugation. Conjugation involves a donor bacterium that contains a conjugative plasmid and a recipient cell that does not. A conjugative plasmid is self-transmissible, in that it possesses all the necessary genes for that plasmid to transmit itself to another bacterium by conjugation.

Name the enzymes that enables bacterial DNA to become circular, supercoiled, and unwind during DNA replication.

DNA topoisomerase enzymes are used to supercoil and relax the bacterial chromosome during DNA replication and transcription.

In terms of protein synthesis, briefly describe the process of transcription and translation.

During translation, specific tRNA molecules pick up specific amino acids, transfer those amino acids to the ribosomes, and insert them in their proper place according to the mRNA "message." In bacteria, transcription and translation are coupled.

Define horizontal gene transfer.

Horizontal gene transfer, also known as lateral gene transfer, is a process in which an organism transfers genetic material to another organism that is not its offspring. The ability of Bacteria and Archaea to adapt to new environments as a part of bacterial evolution most frequently results from the acquisition of new genes through horizontal gene transfer rather than by the alteration of gene functions through mutations.

State, in a general sense, how antibiotics like neomycin, tetracycline, doxycycline, erythromycin, and azithromycin affect bacterial growth.

Many antibiotics alter bacterial ribosomes, interfering with translation and thereby causing faulty protein synthesis. The portion of the ribosome to which the antibiotic binds determines how translation is effected. For example: - The tetracyclines (tetracycline, doxycycline, demeclocycline, minocycline, etc.) bind reversibly to the 30S subunit, distorting it in such a way that the anticodons of charged tRNAs cannot align properly with the codons of the mRNA. - The macrolides (erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.) bind reversibly to the 50S subunit. They appear to inhibit elongation of the protein by preventing the enzyme peptidyltransferase from forming peptide bonds between the amino acids. They may also prevent the transfer of the peptidyl tRNA from the A-site to the P-site.

Describe the structure of a bacterial endospore.

The completed endospore consists of multiple layers of resistant coats (including a cortex, a spore coat, and sometimes an exosporium) surrounding a nucleoid, some ribosomes, RNA molecules, and enzymes.

Describe plasmids and indicate their possible benefit to bacteria.

Plasmids are small molecules of double stranded, helical, non-chromosomal DNA. In most plasmids the two ends of the double-stranded DNA molecule that make up plasmids covalently bond together forming a physical circle. Some plasmids, however, have linear DNA. Plasmids replicate independently of the host chromosome, but some plasmids, called episomes, are able to insert or integrate into the host cell's chromosome where their replication is then regulated by the chromosome. * However, if that bacterium finds itself in the body when the particular antibiotic that the plasmid-coded enzyme is able to degrade is being given to treat an infection, the bacterium containing the plasmid is able to survive and grow.

Describe the structure and chemical composition of bacterial ribosomes and state their function.

Ribosomes are composed of ribosomal RNA (rRNA) and protein. Bacterial ribosomes are composed of two subunits with sedimentation rates of 50S and 30S, as opposed to 60S and 40S in eukaryotic cells. Ribosomes function as a workbench for protein synthesis whereby they receive and translate genetic instructions for the formation of specific proteins.

Briefly state how the following antibacterial chemotherapeutic agents affect bacteria: a. fluoroquinolones (norfloxacin, lomefloxacin, fleroxacin, ciprofloxacin, enoxacin, trovafloxacin, etc.) b. trimethoprim and sulfamethoxazole

Some antibacterial chemotherapeutic affect bacteria by inhibiting normal nucleic acid replication a. work by inhibiting one or more of the topoisomerases, the enzymes needed for bacterial nucleic acid synthesis. b. block enzymes in the bacteria pathway required for the synthesis of tetrahydrofolic acid, a cofactor needed for bacteria to make the nucleotide bases thymine, guanine, uracil, and adenine. Without the tetrahydrofolic acid, the bacteria cannot synthesize DNA or RNA.

Genome

The sum of an organism's genetic material.