Skip to content
Quick Guides

Microbiology - Microbial Genetics

Preview 4 of 13 pages

See the first 4 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Study Guide Microbiology – Microbial Genetics 1. Bacterial Recombination Bacterial recombination is the process by which bacteria change their genetic material. When DNA changes, bacteria may gain new abilities, such as resistance to antibiotics or the ability to cause disease. These changes happen when new genes enter a bacter ial cell and are expressed as proteins. There are three main types of bacterial recombination : 1. Conjugation 2. Transformation 3. Transduction

  2. Page 2
    Read page 2 as text

    Study Guide 1. 1 Bacterial Conjugation Bacterial conjugation is a process in which DNA is transferred directly from one bacterial cell to another through physical contact. This process was first described in the 1940s by Joshua Lederberg and Edward Tatum . How conjugation works • One bacterium acts as the donor (F ⁺ cell) and the other as the recipient (F ⁻ cell) . • The donor cell contains a small circular piece of DNA called the F factor (fertility factor) . • A special structure called the sex pilus forms a connection between the two cells. • Through this connection, a copy of the F factor DNA is transferred to the recipient cell. • After transfer, the recipient becomes an F ⁺ cell . This DNA transfer is one - way (nonreciprocal) — only the donor gives DNA. High - Frequency Recombination (Hfr) Sometimes, the F factor becomes part of the bacterial chromosome. When this happens: • The bacterium is called an Hfr (high - frequency recombination) cell . • During conjugation, chromosomal genes (not just the F factor) are transferred to the recipient. • Usually, the entire chromosome is not transferred, so the recipient remains F ⁻ . • Only if the entire chromosome is transferred (a rare event) does the recipient become F ⁺ . F′ Plasmids and Sexduction • Occasionally, when the F factor leaves the chromosome, it carries extra bacterial genes with it. • This modified plasmid is called an F′ plasmid . • When transferred, it gives the recipient extra genes. • This process is called sexduction and helps spread useful traits in bacterial populations.

  3. Page 3
    Read page 3 as text

    Study Guide 1. 2 Bacterial Transformation Bacterial transformation occurs when a bacterium takes up free DNA from its surroundings . Discovery • First discovered in 1928 by Frederick Griffith while studying pneumonia - causing bacteria. • He found that harmless bacteria could become harmful after taking DNA from dead pathogenic bacteria. How transformation works • When bacteria die, they release DNA into the environment. • Some bacteria are competent , meaning they can take up this DNA. • Competence usually occurs during the logarithmic (log) growth phase . • The bacterium takes in the DNA, destroys one strand, and integrates the other strand into its chromosome. • The new DNA replaces a similar section of the original DNA. Transformation has been studied in bacteria such as: • Streptococcus pneumoniae • Haemophilus influenzae In laboratories, transformation can be encouraged using heat and calcium chloride , which increase membrane permeability. 1. 3 Bacterial Transduction Transduction is the transfer of bacterial DNA from one cell to another using bacterial viruses , called bacteriophages (or phages). What is a bacteriophage? • A virus that infects bacteria • Contains DNA surrounded by a protein coat

  4. Page 4
    Read page 4 as text

    Study Guide The Lytic and Lysogenic Cycles Once a phage enters a bacterium, two outcomes are possible: Lytic cycle • Phage DNA takes over the bacterial machinery • New phages are produced • The bacterial cell bursts (lysis) and releases phages Lysogenic cycle • Phage DNA integrates into the bacterial chromosome • The virus becomes a prophage • The bacterium survives and reproduces normally • The phage may later exit and enter the lytic cycle Generalized Transduction In generalized transduction : • During phage assembly, random pieces of bacterial DNA are mistakenly packaged into phages. • These phages infect another bacterium. • The donor bacterial DNA becomes integrated into the new host’s chromosome. • The recipient bacterium now expresses new genetic traits .

9 more pages in the full document

Unlock it once and it stays in your library, ready to chat with or turn into flashcards.

Unlock the full document

More Microbiology study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.