Lab 3: Prokaryotes Flashcards
Compare and contrast prokaryotes and eukaryotes
differences:
Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Differences in cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomal DNA.
Similarities:
both contain vesicles and vacuoles, they both have DNA as their genetic material. Both are membrane bound and contain ribosomes. They are diverse in forms and have a similar pattern of metabolism.
State at least 3 ways in which domain Bacteria and domain Archaea differ
Archaea live in virtually every habitat on Earth. These prokaryotes differ from those in domain Bacteria in the structure of their cell walls, plasma membrane lipids, ribosomal proteins and RNA polymerase.
Distinguish between halophiles, thermophiles, and methanogens
the extreme halophiles (salt lovers) tolerate or require high salt concentrations, and the extreme thermophiles (heat lovers) are found in hot springs and deep ocean vents. The methanogens are obligate anaerobes that obtain energy by using CO2 to oxidize H2, releasing methane as waste product
List the major characteristics that define domain Bacteria.
1) The cells are prokaryotic and thus contain no true nucleus or other membrane bound organelles. Their single circular chromosome is concentrated in an area known as the nucleoid region. Although the cells do not have internal membranes like the eukaryotes, invaginations of the plasma membranes provide surfaces on which metabolic reactionscan occur.
2) The cells are small with diameters in the range of 0.5 - 5 m compared to 10 - 100 m for many eukaryotic cells. Because of their small size, nothing of their internal structure can be detected with the light microscope. There are a few species with exceptionally large cells.
3) About half of all prokaryotes are motile by means of structures such as flagella (note that prokaryotic flagella are very different in molecular composition and propulsion mechanisms from eukaryotic flagella).
4) There is a diversity of shapes among bacterial cells, the most common being the spherical cocci, rod shaped bacilli, and the helical spirilla or spirochaetes.
5) Most are unicellular, but some species tend to adhere together to produce colonies consisting of two-celled to many-celled clusters or filaments.
6) Most have cell walls containing a unique polymer, peptidoglycan. Differences in the amount of peptidoglycan and the complexity of structure of the cell wall (see Figure 1) can be detected by means of the Gram stain. Using this staining procedure, bacteria can be separated into two groups: Gram positive bacteria whose cell walls stain purple and Gram negative whose cell walls stain pink.
7) Bacteria reproduce asexually by means of binary fission. There is no sexual reproduction.
8) Under adverse environmental conditions some soil dwelling bacilli can produce endospores. Endospores are thick walled dormant cells which can withstand extreme temperatures, desiccation, and treatment with chemicals. Upon the return of favourable conditions, they can germinate and resume growth.
9) Prokaryotes show great diversity in modes of nutrition. Most are chemoheterotrophs utilizing organic molecules as sources for energy and carbon. Some are saprobes which absorb their nutrients from dead organic matter, while others are parasites which utilize living organisms. Chemoautotrophs obtain carbon from CO2 and oxidize inorganic molecules to obtain energy, while photoautotrophs obtain carbon from CO2 but utilize light as their energy source. Photoheterotrophs use light as their energy source, but must obtain carbon from organic molecules.
10) Some bacteria are obligate aerobes and cannot grow in the absence of oxygen, while others are obligate anaerobes and cannot survive in the presence of oxygen. Others are facultative anaerobes which can use oxygen if it is available, but can carry out anaerobic respiration or fermentation if it is not.
11) The Cyanobacteria are photoautotrophs, which, like plants utilize chlorophyll a and produce oxygen. Presence of the accessory pigment, phycobilin produces their typical blue-green colour. The cells of some species remain attached to each other, forming long filaments. Some species exhibit a simple multicellular organization with division of labour between two or more types of specialized cells. Examples of specialized cells are akinetes in which reserve materials are stored and heterocytes in which nitrogen fixation occurs.
Differentiate between the following modes of nutrition: photoautotroph, chemoautotroph,
photoheterotroph, and chemoheterotroph
Prokaryotes show great diversity in modes of nutrition. Most are chemoheterotrophs utilizing organic molecules as sources for energy and carbon. Some are saprobes which absorb their nutrients from dead organic matter, while others are parasites which utilize living organisms. Chemoautotrophs obtain carbon from CO2 and oxidize inorganic molecules to obtain energy, while photoautotrophs obtain carbon from CO2 but utilize light as their energy source. Photoheterotrophs use light as their energy source, but must obtain carbon from organic molecules.
Differentiate between obligate aerobes, obligate anaerobes, and facultative anaerobes.
Some bacteria are obligate aerobes and cannot grow in the absence of oxygen, while others are obligate anaerobes and cannot survive in the presence of oxygen. Others are facultative anaerobes which can use oxygen if it is available, but can carry out anaerobic respiration or fermentation if it is not.
Distinguish between the structure of Gram positive and negative bacteria, and explain how these
differences allow the Gram staining procedure to differentiate between these groups.
Gram positive have a thick peptidogylycan wall that is not surrounded by membrane on both sides which exposes the peptidogylycan to the first stain (purple) a lot and holds on to that pigment. The gram negative have a smaller layer of peptidogylcan and is surrounded by membrane and will absorb loose the first stain when washed (alcohol) and will absorb the second stain (pink)
Due to differences in the thickness of a peptidoglycan layer in the cell membrane between Gram positive and Gram negative bacteria, Gram positive bacteria (with a thicker peptidoglycan layer) retain crystal violet stain during the decolorization process, while Gram negative bacteria lose the crystal violet stain and are instead stained by the safranin in the final staining process.
- Gram positive bacteria
- Simpler cell wall with large amount of peptidoglycan
- Thick peptidoglycan layer traps the stain crystal violet within the cytoplasm.
• Gram negative bacteria
• More complex, with less peptidoglycan.
• Cell wall sandwiched between the plasma
membrane and an outer membrane.
• Outer membrane contains lipopolysaccharides.
Given the results of a Gram stain, be able to identify which bacteria are Gram positive and which
are Gram negative.
Gram positive bacteria whose cell walls stain purple and Gram negative whose cell walls stain pink
Define “endospores” and explain how endospores have contributed to the success of some
bacteria.
Under adverse environmental conditions some soil dwelling bacilli can produce endospores. Endospores are thick walled dormant cells which can withstand extreme temperatures, desiccation, and treatment with chemicals. Upon the return of favourable conditions, they can germinate and resume growth.
Given a plate (or an image of a plate) that has been incubated with bacteria and antibiotic discs,
identify which antibiotics the bacterium was sensitive to, which antibiotic was most effective
against the bacterium, and which antibiotics the bacterium was resistant to, and justify your
answer by explaining how/why the zones form and what a larger zone means
To determine which antibiotic is the most effective against each type of bacteria, the size of the zone of inhibition needs to be measured. The zone of inhibition is the area in which none of the bacteria are able to grow due to the effect of the antibiotic diffusing out of the disk into the medium. At distances further away from the disk, the antibiotic is present in smaller and smaller concentrations. A large zone of inhibition means that the antibiotic is effective at a relatively low concentration of antibiotic and thus the bacteria is relatively sensitive to the antibiotic. A small or no zone of inhibition indicates that the bacterium is resistant to the antibiotic
Explain how pathogenic bacteria may acquire antibiotic resistance and how antibiotic resistance
can quickly spread through a bacterial population. Hint: Your answer should refer to mutations,
vertical and lateral gene transfer, and natural selection. This was in your assignment!
How can genetic diversity arise if daughter cells are
exact clones of their parent cells?
1. Mutations
2. Gene transfer
• Genetic material is transferred from one bacterial cell to another.
• Can occur in 1 of 3 ways:
• Conjugation: involves direct contact between bacterial cells (see next slide).
• Transformation: DNA that is released into the environment when a bacterium dies is taken up by another bacterial cell, which incorporates the
DNA into its own chromosome.
• Transduction: a virus infects a bacterial cell and then transfers some of the cell’s DNA to another bacterium.
Briefly explain why antibiotics are effective at killing bacterial cells, but do not seem to impact
human cells. Hint: This was in your assignment.
bacteria cells have peptidigylcan and human cells do not.
example: penicillen attacks peptidoglycan in bacteria cell walls and kills the bacteria where as human cells dont even have cell walls
Explain the significance of cyanobacteria to the evolution of life on Earth and the important roles
cyanobacteria play in ecosystems.
This important subgroup of the Bacteria is widespread in the environment and can exist under extremely harsh conditions. They were the first photosynthetic bacteria to evolve which produced oxygen as a by-product of photosynthesis. Subsequent evolution of the oxygen dependent eukaryotes was able to occur because of accumulation of this oxygen in the atmosphere. Many of the cyanobacteria are also able to fix nitrogen by converting atmospheric nitrogen to ammonia, which can be used to synthesize amino acids.
Identify a specimen of Nostoc, Anabaena, or Oscillatoria as a cyanobacterium
look at link
Explain why it is that people who cannot tolerate milk can often eat yogurt.
Because the yogert is digesting the lactose for you
