Cell Morphology, Size, Cytoplasmic Membrane, and Transport Mechanisms

Flashcards reviewing bacterial morphology, size advantages, cell membrane structures, archaeal adaptations, and active/passive transport mechanisms.

What term is defined as the shape and structural appearance of a cell in microbiology?

Morphology

What four common bacterial cell arrangements result from incomplete separation following cell division?

Diplococci (cells in pairs), staphylococci (cells in clusters), streptococci (cells in chains), and sarcina (cells in cuboidal packets).

Why does cell morphology alone fail to reveal the precise identity or lifestyle of an organism?

Organisms with identical microscopic shapes may possess completely different metabolic pathways, environmental preferences, genetic compositions, and ecological lifestyles.

What is the equivalent measurement of one micrometer ($1\,\mu m$) in millimeters?

$$0.001\,mm$$

How do environmental nutrient conditions affect bacterial cell dimensions?

Under nutrient-rich conditions, bacterial cells may grow larger to reach optimum size, whereas under nutrient stress, cells may become smaller.

What are two examples of giant bacteria mentioned in the lecture, and what are their dimensions?

Epulopiscium fishelsoni (about $600\,\mu m$ long by $75\,\mu m$ wide) and Thiomargarita namibiensis (diameter of approximately $400\text{–}750\,\mu m$).

What evolutionary and physiological advantages are associated with a small cell size in microorganisms?

A higher surface-area-to-volume ratio allows for easier nutrient uptake, faster metabolism, rapid reproduction, and efficient adaptation to environmental changes.

What are the three primary functions of the prokaryotic cytoplasmic membrane?

1. Serving as a selectively permeable barrier
2. Providing an anchor for transport, bioenergetic, and signaling proteins
3. Participating in energy conservation and generating the proton motive force

How do the functional roles of the cell wall and the cytoplasmic membrane differ?

The cell wall primarily provides structural strength and protection against osmotic pressure, whereas the cytoplasmic membrane regulates molecular traffic and transport.

According to the fluid mosaic model, what do the terms 'fluid' and 'mosaic' describe?

'Fluid' refers to the dynamic, flexible movement of lipids and proteins within the layer, while 'mosaic' refers to the diverse mixture of proteins embedded throughout the membrane.

What type of chemical linkage connects glycerol to hydrocarbons in Bacteria and Eukarya versus Archaea?

Bacteria and Eukarya possess ester linkages ($O-C=O$), whereas Archaea possess chemically stable ether linkages ($C-O-C$).

What repeating hydrocarbon unit forms the hydrophobic region of archaeal membrane lipids?

Isoprene units, which form phytanyl ($C_{20}$) or biphytanyl ($C_{40}$) chains.

What archaeal membrane lipid organization provides extreme structural stability in hot environments?

Lipid monolayers composed of diglycerol tetraethers or crenarchaeol.

What membrane-strengthening molecules are present in many bacterial cell membranes to serve a function similar to eukaryotic sterols?

Hopanoids

What is the saturation effect in carrier-mediated transport?

A state where increasing external substrate concentration no longer increases the rate of solute entry because all available carrier proteins are fully occupied.

How do channel proteins and carrier proteins differ in their transport mechanisms during facilitated diffusion?

Channel proteins form open hydrophilic transmembrane pores through which solutes pass without shape changes, while carrier proteins physically bind a solute and undergo conformational changes to release it on the other side.

What specialized channel proteins facilitate high-speed water transport across the cytoplasmic membrane?

Aquaporins

What is the definition of osmolarity?

The total concentration of dissolved solute particles in a solution.

What organelle allows Paramecium to survive in a hypotonic freshwater environment by expelling excess water?

Contractile vacuole

What two components establish the electrochemical gradient across the plasma membrane?

1. Concentration gradient (difference in solute concentration)
2. Electrical gradient (difference in electrical charge across the membrane)

Based on the provided illustration, what are the three major classes of transport systems categorized by direction and number of moved molecules?

Uniporter (transports a single molecule in one direction), Symporter (transports two molecules in the same direction), and Antiporter (transports two molecules in opposite directions).

What is the ion transport ratio and stoichiometry of the primary active sodium-potassium pump per ATP molecule hydrolyzed?

$3\,Na^+$ ions are pumped out of the cell and $2\,K^+$ ions are pumped into the cell.

What energy source powers simple transport systems like lactose permease in Escherichia coli?

The proton motive force

What chemical modification happens to glucose during transport via the phosphotransferase system in Escherichia coli?

Glucose is phosphorylated using energy from phosphoenolpyruvate (PEP) to produce glucose-6-phosphate.

What three essential components make up an ATP-Binding Cassette (ABC) transport system?

1. Periplasmic binding protein
2. Membrane-spanning transport protein
3. ATP-hydrolyzing protein

What are two translocase systems involved in exporting proteins across prokaryotic membranes?

The Sec translocase system (exports proteins and inserts integral membrane proteins) and the Type III secretion system (translocates proteins directly into host cells).