Cell Structure, Function, and Membrane Transport

Comprehensive practice flashcards covering cellular organization, prokaryotic and eukaryotic organelles, membrane structure, cell signaling, passive and active transport mechanisms, and cell surface modifications based on Chapters 4 and 5.

Which scientists contributed to the establishment of the Cell Theory, and what were their specific contributions?

Matthias Schleiden (1838) stated that all plants are composed of cells; Theodor Schwann (1839) stated that all animals are composed of cells; and Rudolph Virchow (1821–1902) stated that cells come only from preexisting cells because cells are self-reproducing.

Why is a large surface-area-to-volume ratio advantageous for cells?

Small cells have a larger surface area relative to their volume, which allows them to efficiently exchange materials in and out of the cell across the plasma membrane. As cell size increases, surface area relative to volume decreases, lowering transport efficiency.

Based on the surface-area-to-volume relationship diagram, how does the surface area and ratio change when one $4\text{-cm}$ cube is divided into sixty-four $1\text{-cm}$ cubes?

While the total volume remains constant at $64\text{ cm}^3$, the total surface area increases from $96\text{ cm}^2$ (a $1.5:1$ ratio) for the single $4\text{-cm}$ cube to $384\text{ cm}^2$ (a $6:1$ ratio) for the sixty-four $1\text{-cm}$ cubes.

How do Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM) differ in operation and output?

TEM passes electrons through a specimen focused by magnetic lenses to resolve objects separated by $0.0002\,\mu\text{m}$ ($500,000\times$ human eye resolution) in 2D. SEM scans an electron beam across a metal-coated specimen to detect secondary electrons, producing a 3D image on a screen.

What are the two taxonomic domains of prokaryotes, and what basic shapes do prokaryotic cells exhibit?

Prokaryotes belong to Bacteria and Archaea. Their basic shapes are spherical (coccus), rod-shaped (bacillus), and spiral (rigid spirillum or flexible spirochete).

Identify the key cellular structures labeled in this diagram of a prokaryotic cell.

Key structures include: Ribosomes (site of protein synthesis), Nucleoid (location of circular DNA), Plasma membrane (inner sheath regulating entry/exit), Cell wall (middle sheath providing support and shape), Capsule (outer gel-like coating), Fimbriae (bristlelike adhesion fibers), and Flagellum (rotating propulsion filament).

What are the distinct functions of bacterial flagella, fimbriae, and conjugation pili?

Flagella provide cell motility; fimbriae are small bristlelike fibers that allow adhesion to surfaces; conjugation pili are rigid, tubular structures used to pass DNA from cell to cell.

According to the Endosymbiotic Theory, how did mitochondria and chloroplasts originate in eukaryotic cells?

Energy-related organelles originated when a larger host cell engulfed smaller prokaryotes: mitochondria arose from engulfed aerobic bacteria, and chloroplasts arose from engulfed photosynthetic bacteria.

What structural elements compose the cell nucleus, and what are their functions?

The nucleus consists of the nuclear envelope (double membrane with pores for molecular exchange), nucleoplasm (semifluid matrix), chromatin (diffuse threads of DNA and protein that condense into chromosomes), and the nucleolus (dark region producing ribosomal RNA subunits).

How does the Signal Recognition Particle (SRP) direct ribosomes synthesizing specific proteins to the Endoplasmic Reticulum (ER)?

As a ribosome begins protein synthesis from mRNA, it produces a signal peptide. SRP binds to this signal peptide and temporarily halts synthesis. SRP then binds to an ER membrane receptor, opening a channel. SRP leaves, synthesis resumes, and the polypeptide is simultaneously fed into the ER lumen.

How do rough ER and smooth ER differ structurally and functionally?

Rough ER is studded with ribosomes on its cytoplasmic side and synthesizes, modifies, and processes proteins (such as adding carbohydrates to form glycoproteins). Smooth ER lacks ribosomes and synthesizes lipids (e.g., testosterone in testes), detoxifies drugs (e.g., in liver cells), and forms transport vesicles.

How do the $cis$ and $trans$ faces of the Golgi apparatus process and direct molecular cargo?

The $cis$ (inner) face receives transport vesicles containing proteins and lipids from the ER. After modifying them with signal sequences, the Golgi apparatus packages them into vesicles that depart from the $trans$ (outer) face to destination sites, plasma membrane for exocytosis, or lysosomes.

What is the function of lysosomes, and what clinical condition results from a defect in a lysosomal enzyme?

Lysosomes are acidic, membrane-bound vesicles produced by the Golgi apparatus containing hydrolytic-digestive enzymes that break down macromolecules, worn-out cell parts, and engulfed pathogens. A defect in a lysosomal enzyme causes Tay-Sachs disease.

What metabolic reaction do peroxisomes perform to manage toxic hydrogen peroxide ($H_2O_2$)?

Peroxisomes catalyze reactions that produce toxic hydrogen peroxide ($H_2O_2$) during lipid metabolism, which is subsequently broken down into water ($H_2O$) and oxygen ($O_2$) by the enzyme catalase.

What are the primary functions of the plant cell central vacuole?

The central vacuole stores water, nutrients, pigments, and waste products; maintains turgor pressure; degrades aged organelles using digestive enzymes; and holds toxic substances for protection against herbivores.

Define thylakoids, grana, and stroma within the chloroplast structure.

Thylakoids are disc-like photosynthetic sacs stacked to form column-like grana inside the inner membrane. Chlorophyll is located strictly in the thylakoid membrane. Stroma is the fluid-filled space surrounding the grana that contains enzymes for carbohydrate synthesis.

What structural features characterize the inner environment of a mitochondrion?

Mitochondria are bounded by a double membrane where the inner membrane is folded into convoluted cristae surrounding an inner semifluid matrix, which contains respiratory enzymes that break down carbohydrates to generate ATP.

What are the three macromolecular fibers of the cytoskeleton, listed in order of increasing diameter?

Actin filaments (thinnest, twisted pearl-necklace structure), intermediate filaments (ropelike assembly of fibrous polypeptides), and microtubules (thickest, hollow cylinders).

How are microtubules constructed, and which motor molecules facilitate vesicle movement along them?

Microtubules are hollow cylinders assembled from spontaneous pairings of globular $\alpha$ and $\beta$ tubulin dimers arranged into spirals of 13 dimers around. They interact with the motor molecules kinesin and dynein to transport organelles and vesicles.

What microtubule arrangement is found in eukaryotic cilia and flagella shafts compared to their basal bodies?

The shaft of cilia and flagella features a $9+2$ pattern consisting of a ring of 9 microtubule doublets surrounding a central pair of single microtubules. The basal body consists of a ring of 9 microtubule triplets with no central microtubules.

What structural elements compose the fluid-mosaic model of the plasma membrane?

The model consists of a phospholipid bilayer with hydrophilic polar heads facing outward and hydrophobic fatty-acid tails inside, integral and peripheral proteins embedded or attached, cholesterol regulating fluidity, and carbohydrate chains (glycolipids and glycoproteins) on the exterior surface.

Match the plasma membrane protein defects described in the lecture to their clinical outcomes: faulty $Cl^-$ channels, faulty growth hormone receptors, and cholera toxin interaction.

Faulty chloride ($Cl^-$) channels cause Cystic Fibrosis; faulty growth hormone receptors prevent hormone binding and result in certain forms of dwarfism; cholera bacteria release a toxin that disrupts adenylate cyclase, causing severe sodium ($Na^+$) and water loss resulting in severe diarrhea.

Why do Major Histocompatibility Complex (MHC) glycoproteins present an obstacle during organ transplantation?

MHC glycoproteins are cell recognition proteins unique to each individual. Tissues with foreign MHC glycoproteins are recognized as foreign invaders and attacked by white blood cells responsible for immunity.

Which types of molecules can freely cross the plasma membrane without energy expenditure or carrier assistance?

Small, noncharged molecules such as carbon dioxide ($CO_2$), oxygen ($O_2$), glycerol, and alcohol freely cross the phospholipid bilayer by moving down their concentration gradient.

What role do aquaporins play in plasma membrane transport?

Aquaporins are specialized membrane channel proteins that speed up the transport of water molecules across the selectively permeable plasma membrane.

How does simple diffusion differ from facilitated transport across a plasma membrane?

Simple diffusion moves lipid-soluble molecules and gases directly across the bilayer down their concentration gradient without channel/carrier proteins. Facilitated transport moves molecules (such as glucose and amino acids) down their concentration gradient using specific channels or carrier proteins. Neither requires ATP.

How do animal and plant cells behave when placed in hypotonic versus hypertonic solutions?

In a hypotonic solution, water enters cells: animal cells swell and may undergo lysis (bursting), whereas plant cells gain turgor pressure. In a hypertonic solution, water leaves cells: animal cells shrink (crenation), whereas plant cytoplasm shrinks away from cell walls (plasmolysis).

What are the ion movement numbers and energy requirements for one complete cycle of the sodium-potassium ($Na^+\text{--}K^+$) pump?

The sodium-potassium pump splits one ATP molecule to pump $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell against their respective concentration gradients.

Distinguish between phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Phagocytosis engulfs large solid particles into a vesicle; pinocytosis forms vesicles around liquids or very small particles; receptor-mediated endocytosis uses specific receptor proteins located in a coated pit to import targeted molecules (such as cholesterol).

What functions do collagen, elastin, fibronectin, and integrin serve in the Extracellular Matrix (ECM)?

Collagen resists stretching; elastin provides resilience; fibronectin acts as an adhesive protein binding to integrin; and integrin spans the plasma membrane to play a role in cellular signaling between the ECM and cytoskeleton.

Differentiate between adhesion junctions (desmosomes), tight junctions, and gap junctions in animal tissues.

Adhesion junctions (desmosomes) hold cells together via cytoplasmic plaques and intercellular filaments; tight junctions join plasma membranes to form impermeable barriers; gap junctions consist of joined membrane channels that allow direct communication between adjacent cells.

What are plasmodesmata, and what is their functional role in plant tissues?

Plasmodesmata are membrane-lined channels that penetrate plant cell walls, each containing a strand of cytoplasm that allows direct passage of materials and communication between neighboring plant cells.