the first lecture of microbio introduced some basic ideas about microbes: general structural characteristics, methods of identification, and some bacterial genetics. the first topic was the difference between prokaryotes (the focus in microbio) and eukaryotes. prokaryotes have cell walls, "70s" (a name related to the centrifuge strength required to isolate) ribosomes, 1 circular chromosome, and relatively abundant flagella. eukaryotes don't have cell walls, and have "80s" ribosomes, 46 linear chromosomes, and no flagella (except on male sperm cells). some different shapes that are found with bacteria: cocci (round), rods, spiral, streptococci. different arrangements of these shapes include streptococci (chains of cocci), diplococci, staphylococci (grape like clusters), sarcina, tetrads.
one of the main methods of identifying bacteria is the gram staining method. the method is based on structural differences between the gram+ and gram- bacteria. gram+ bacteria has a thick pepsidoglycan layer outside of its cell membrane which is made up of a net like structure: repeating NAM-NAG sugar backbone strands with amino acid chains that crosslink with each other. gram- bacteria have a thin pepsidoglycan layer outside of the cell membrane, which is then covered by an additional lipid bilayer. the outer layer of this second membrane has the endotoxin lipopolysaccharide embedded within: LPS is made of a fatty acid, a core sugar, and a polysaccharide chain. the fatty acid and core sugar is known as "lipid A" and is the pathogenic portion. during the gram staining procedure, gram+ bacteria show up as purple and gram- bacteria show up as pink.
there are many other methods of identifying bacteria, such as the acid fast test, endospore stain, flagellar stain (these tests are "differential tests"), flourescent antibody stain, growing bacterial colonies on differential/selective media, enzyme tests (such as catalase tests), coagulase tests, PCR tests, and presence of certain antibody/antigens.
bacterial replication is an asexual process and is called binary fission, in which the bacterial chromosome replicates itself and the cell divides into two identical daughter cells. there are 4 "phases" of bacterial growth which correlate to general principles of population growth. the lag phase is first, where the population of bacteria is acclimating to the environment and relatively stable. the log phase is an explosive, exponential growth of bacteria where resources are plenty as compared to the population. the stationary phase is a period in which the population begins to cannibalize itself due to limited resources, thereby halting growth. the death phase is the exponential decrease of the population due to the lack of resources.
there are 4 different ways in which bacteria can acquire new DNA: mutation, transformation, conjugation, and transduction. mutation is the random addition, deletion, or substitution of a random base pair within the genome of the bacteria. transformation is the transfer of soluble, "naked" DNA which enters a host cell's genome and changes its phenotype. (see question 24 for a schematic experiment describing the discovery of transformation). conjugation is the direct transfer of DNA in the form of a plasmid, from cell to cell mediated by pili attachment. finally, transduction is DNA transfer via bacteriophages, which are viruses that infect bacteria. bacteriophages can undergo the lytic cycle, in which transcription of viral DNA within the host cell produces enough viral elements to kill and lyse the cell, or the lysogenic cycle, in which the viral DNA is incorporated into the host cell genome and replicated during normal host cell replication without necessarily killing the bacteria.
questions
prokaryotes and eukaryotes differences in...
1. cell membrane
2. ribosomes
3. cell wall
4. DNA
5. flagella
shapes and arrangements...
6. what are some features that are unique to prokaryotic cells?
7. what are the different types of shapes found in bacteria?
8. what are the different arrangements of shapes that bacteria form?
9. what does the streptococci arrangement look like?
10. what does the staphylocci arrangement look like?
gram staining...
11. what are the characteristics of a gram positive cell?
12. describe the peptidoglycan layer.
13. what are the characteristics of a gram negative cell?
14. describe the structure of LPS. what part of LPS is pathogenic?
15. briefly describe the procedure for gram staining.
16. what colors do gram+ and gram- bacteria show up as after the gram staining procedure?
binary fission...
17. describe the process of binary fission.
18. what are the 4 phases of bacterial population growth for bacteria that undergo binary fission?
identifying bacteria...
19. what are some different methods for identifying bacteria?
20. what is a dichotamous key?
21. what is the difference between selective media and differential media?
bacterial genetics...
22. what are the four different methods of acquiring new DNA?
23. describe the process of transformation.
24. describe the mice experiment involving rough and smooth streptococcus pneumonia which demonstrates the principle of translation.
25. describe the process of conjugation.
26. describe the process of transduction.
27. what is the difference between the lytic cycle and the lysogenic cycle for bacteriophages?
answers
1. both have cell membranes, but prokaryotes have different membrane phospholipids.
2. both have ribosomes, but prokaryote ribosomes are "70S" whereas eukaryote ribosomes are "80S" (except inside mitochondria)
3. only prokaryotes have cell walls (except mycoplasma)
4. prokaryotes have DNA in cytoplasm in the form of one circular chromosome, eukaryotes have DNA in the nucleus in the form of 46 chromosomes in a linear shape.
5. some prokaryotes have flagella, which contribute to pathogenicity. in eukaryotes, only male sperm cells have flagella.
6. flagella, capsules that surround the cell membrane, endospores which preserve DNA, and pili which are used for attachment.
7. rods, cocci, spiral shape.
8. random, diplococci, streptococci, staphylocci, sarcina, tetrads.
9. chains of cocci bacteria -- not to be confused with streptococcus pneumonia, which is not in the streptococci arrangement.
10. grape-like clusters
11. cell membrane is surrounded by a thick peptidoglycan layer.
12. the peptidoglycan layer is a net like structure that is composed of a repeating NAM-NAG sugar backbone from which amino acid chains branch off, which then crosslink which each other via the transpeptidase enzyme.
13. a thin peptidoglycan layer surrounding the cell membrane, which is surrounded by an additional lipid bilayer which contains LPS on its outer layer.
14. LPS is an endotoxin which is composed of a fatty acid, a core sugar, (this is the relatively constant portion) and a long chain of sugars (which varies from organism to organism). the constant portion is called the "lipid A" portion and is the toxic part.
15. gram staining involves flooding a bacteria containing slide with crystal violet, rinsing, flooding with iodine, rinsing, decolorizing with ethanol, and counterstaining with saffrinin.
16. gram+: purple, gram-: pink.
17. the process by which a bacterial cell duplicates its DNA and splits into two identical daughter cells.
18. the lag phase, in which the bacteria is getting acclimated to the environment. the log phase, in which bacteria is dividing and population is expanding exponentially. the stationary phase, when resources become limited and bacteria start to cannibalize each other. the death phase, when resources run out and bacteria begin to die at an exponential rate.
19. gram stain, acid-fast, endospore stain, flagellar stain, flourescent antibody stain, selective media, differential media, biochemical tests, enzyme tests, coagulase test, antigen/antibody test, PCR test.
20. a way of charting the results of different differential tests to hone in on the identify of an unknown bacteria.
21.
22. translation, transduction, conjugation, mutation.
23. the process by which a bacterial cell takes up "naked DNA" from another cell and incorporates it into its own genome.
24. two distinct bacterial species were injected into different mice: smooth streptococcus pneumonia (SP-S) and rough (SP-R). the mouse injected with rough SP survives, and no presence of rough SP is detected in the serum. the mouse injected with smooth SP dies and the smooth SP shows up in the dead mouse's serum. a third mouse is injected with live rough SP and dead smooth SP, which results in a dead mouse with live smooth SP. the implication is that the DNA from the dead smooth SP was translated into the live rough SP, conferring pathogenicity to it.
25. direct transfer of DNA by cell to cell contact by way of pili: a one way transfer of DNA in the form of a plasmid which allows the bacteria to make pili.
26. the transfer of DNA from bacteria to bacteria via a virus (bacteriophage).
27. in the lytic cycle, phage DNA is inserted into the bacterial cell and viral components are transcribed, eventually producing enough viral units to cause lysis and death of the host cell. in the lysogenic cycle, phage DNA is incorporated into the host genome and replicated during normal bacterial division but not necessarily causing cell death or lysis.
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