Microbiology

[Matthew]

Since bacteriophages infect only bacteria, their size should be smaller than bacteria. Their are two cycles which we should know: the lytic (think lysis, the phages burst out of the cell) and lysogenic (the longer name, b/c the genome of virus is integrated and can go to lysis at some point, but mostly longer and integrated with bacteria's genome)

BTW the capsid is the head function of the virus and made out of protein. The DNA of virus can be all sorts, RNA, ds, ss, DNA. Within the capsid may be enzymes such as reverse transcriptase (notice the -ase) which takes RNA and reverses back to complementary DNA). HIV is big topic for current passages in the MCAT. In your spare time, read up on AIDs and HIV.

The prokaryotes vs. eukaryotes are HIGH yield. I think it is safe to say you will have at least one question from this on every MCAT. (They have to put something in the microbiology). Also no that virus do not have organelles or machinery (hence they "hijack" others tissues or cells and run their "show")

Prokaryotes (abbr:pro) do not have organelles (keep in mind the mitochondria theory which says basically that mitochondria as well as chloroplasts snuck into other cells through endocytosis and that is why eukaryotes have mitochondria in them as well as plants (chloroplasts). Pros also do not have a nucleus envelope(a big hint that it is not eukaryote). It is just out their in the cytoplasm.

Bacteria (pro) reproduce through binary fission or if conditions are rough conjugation. They have cell walls (not to say Eukaryotes dont (plants) but the bacteria have something special that eu's don't in their cell wall, it is peptidoglycan, which is a big one for whether it is gram neg or pos. Identifying whether pos or neg, enables a better use of which antibiotic (antibiotics are known to break down the cell walls, though there are other mechanisms, such as shutting down the protein synthesis, transcription)

Fungi (think molds, mushrooms and yeast) are eu's and multicellular (except yeast, haploid (think haploid budding). There are fungi that can reproduce asexually (yeast) or sexually (spores).

Also saprophytic just means these fungi are feeding off of organic food (not Whole foods). The asexual (haploid) divides by mitosis and sexual spores (diploid) by meiosis. In the event of mating the products of meiosis, being haploid, fuse together and form the diploid. Process repeats again and again.


Note: Viruses only work if they have a host (poor fella).

[frab83]

I just took a practice test which had two passages on microbiology. It had to do with an epidemiologist investigating an illness due to sewage leak.

Blood tests from affected individuals show unknown infectious agents with four different bacterial strains labeled Microbes Q, R, S, and T.

Four different nuient plates were prepared containing only four amino acids. There is a chart that shows the growth or no growth on the 4 different plates for the four different microbes.

This passage was very difficult for me as this is one of my weakest areas. Is there an easier way to understanding these types of passages without losing your mind? I had a hard time figuring out growth or no growth, which bacterial strain is infectious which isnt...etc. Furthermore, structure was also involved.

Is this a typical MCAT passage?

Another passage like this one (on microbiology) was on HIV and many hypotheses on the depletion of T cells. Whats an easier approach toward this kind of stuff?

I'm already stressed because my MCAT is next week.

MY PS is in the 10s but BS still weak especially due to these types of passages. OCHEM Is good but I take it that MCAT is 40% Ochem and 60% Bio correct?

Thanks.

[mcat_premed3832]

Lately OChem has been even less than 40%.

Never stress out with the MCAT. You have to tell yourself that MOST questions have simple answers even when the passage is challenging. You must be confident with that one point.

When there are many different things happening in one bio passage, take very brief notes on your scratch paper indicating what relates to what, or what makes the concentration or population of what go up or down. Make it clear but use short hand, arrows, things like that.

Go back over those 2 passages. Were all the questions complicated or just 1 or 2. If you get all the straightforward questions right, you will still ace the Bio Sci section. Look over those passages and try to look for patterns. Take super brief notes as I described above. Would that have helped? Did you miss a relationship? Even asking yourself those questions will reduce the chance that it will happen again.

[srraghav1542]

Just wanted to correct a couple items in this thread. First, conjugation is NOT a form of reproduction in bacteria. It is a process where one bacterial cell (F-) becomes an F+ through the trasmission of F-plasmid DNA. This inherently leads to an increase in genetic diversity, which is not a characteristic of bacterial replication. Bacteria replicate solely through binary fission, where daughter cells are identical to the parent. Second, the staining of bacterial cell walls by the gram stain has to do with the presence or absence of a 2nd membrane located outside of the cell wall. Gram (+) bacteria do not have the 2nd membrane, therefore are stained and gram (-) do have the 2nd membrane, therefore, are not stained.