Study guides › B/B › Biology
Prokaryotes, Viruses & Microbiology
Microbes are simple but their experiments fill the MCAT. You will compare bacterial structure and the Gram stain, read a growth curve, sort the three gene-transfer mechanisms, follow viral life cycles including HIV, and match antibiotics to their targets.
Study this chapter in PrepMed (free)
What this chapter covers
- Bacterial Structure & Classification. Gram stain, oxygen requirements, and cell-envelope structures are standard questions. Know what each structure does.
- Bacterial Growth & Genetic Exchange. Learn the four phases of the growth curve, the doubling equation, and how conjugation, transformation, and transduction differ.
- Viruses & Bacteriophage Life Cycles. Viruses are not cells. Know their structure, the lytic versus lysogenic choice, and how RNA virus genomes differ.
- Retroviruses, Prions & Viroids. HIV's enzymes and drug targets, and how prions differ from every other infectious agent, appear again and again.
- Antibiotics, Resistance & Lab Microbiology. Pair each antibiotic class with its target, and understand how resistance arises and spreads. Expect experimental-design questions.
Key points to know
- Bacteria: circular chromosome, 70S ribosomes, no organelles
- Gram +: thick peptidoglycan; Gram −: outer membrane with LPS (endotoxin)
- Growth phases: lag, log, stationary, death
- N = N₀ × 2ⁿ in exponential growth
- Virus = genome + capsid (+ envelope); obligate intracellular parasite
- Lytic kills the host; lysogenic integrates a prophage until induction
- Retroviruses: reverse transcriptase, integrase, provirus
- HIV enters via CD4 and a co-receptor; AIDS is CD4 < 200/µL
Try a practice question
In the Gram stain, what structural feature causes Gram-positive bacteria to keep the crystal violet-iodine complex?
- A thick peptidoglycan layer
- An outer membrane containing lipopolysaccharide
- A polysaccharide capsule
- The presence of endospores
Show the answer
A. A thick peptidoglycan layer traps the crystal violet-iodine complex during the alcohol wash. Gram-negatives have an outer membrane and only a thin wall, so the dye washes out.
Common questions
What does this chapter cover?
Prokaryotes, Viruses & Microbiology covers Bacterial Structure & Classification, Bacterial Growth & Genetic Exchange, Viruses & Bacteriophage Life Cycles, Retroviruses, Prions & Viroids, Antibiotics, Resistance & Lab Microbiology.
What should I know first?
Bacteria: circular chromosome, 70S ribosomes, no organelles Gram +: thick peptidoglycan; Gram −: outer membrane with LPS (endotoxin) Growth phases: lag, log, stationary, death
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.