Cell Structure and Function

Identify the plasma membrane as the cell’s boundary and skin, and describe its phospholipid bilayer within the fluid mosaic (sandwich) model, with amphipathic heads and hydrophobic tails.

Exhibiting selective permeability, the plasma membrane allows compounds and ions to cross. Embedding transport proteins in the phospholipid bilayer, the membrane regulates traffic into and out of the cell.

Identify how selective permeability of the plasma membrane regulates molecule passage, driven by embedded proteins and the phospholipid bilayer's hydrophilic heads and hydrophobic tails.

Explore the fluid mosaic model of plasma membrane, proposed by Singer and Nicolson in 1972, known as the sandwich model, where embedded proteins form the mosaic and phospholipids move freely.

Explore the six major components of the phospholipid bilayer—phospholipids, proteins (enzymes, receptors, transport), glycolipids, glycoproteins, carbohydrates, and cholesterol—and how they contribute to the plasma membrane.

Learn how membrane proteins act as transporters, anchors, receptors, and enzymes, enabling ions and molecules to cross the cell membrane and move along concentration gradients while mediating specific interactions.

Learn about transport proteins: uniport, symport, and antiport, and how they move solutes across membranes in single, same direction, or opposite direction transport.

Explore cellular transport, including non carrier mediated diffusion and osmosis, carrier mediated facilitated diffusion and active transport, and vesicle mediated exocytosis and endocytosis with pinocytosis and phagocytosis.

Explore diffusion, the passive transport where molecules spread down their concentration gradient from higher to lower concentrations across the lipid bilayer from outside to inside the cell.

Examine factors that affect diffusion rates—lipid solubility, molecular size, temperature, membrane thickness, surface area, and gradients—alongside diffusion through lipid bilayers and protein channels in lungs, digestive system, placenta, and leaves.

Explore osmosis versus diffusion, highlighting how a semi-permeable membrane drives water from low to high solute concentration, with solute and solvent concepts and hypertonic and hypotonic scenarios.

Explains tonicity in cells without walls, showing isotonic solutions with equal solute concentrations and no water movement, and hypertonic solutions driving water movement that can shrink or swell the cell.

Explore the differences between osmosis and diffusion, focusing on solvent versus solute movement, membrane involvement, and examples like potato shrinkage in hypertonic solutions and ink diffusion.

Explain how the plasma membrane is selectively permeable, letting small hydrophobic molecules and small uncharged polar molecules pass, while larger uncharged polar molecules and ions require transport proteins.

Explore facilitated diffusion, a protein-assisted passive transport with ion channels, aquaporins, and glucose transporters, and bicarbonate chloride co-transporters. Compare to energy-driven active transport moving substances against the gradient.

Describe exocytosis and endocytosis, including pinocytosis, phagocytosis, and receptor-mediated endocytosis, with energy requirements and key proteins, then compare passive versus active transport and diffusion with LDL, glucose, and O2 examples.

Explore the nucleus and nucleolus, their double membrane, nuclear envelope, pores, and chromatin, and learn how DNA and RNA drive transcription and protein synthesis in eukaryotic cells and prokaryotic cells.

The nucleus stores genetic material and drives DNA replication, while transcription forms mRNA that travels to the cytoplasm for translation with the endoplasmic reticulum and Golgi and post-translational modifications.

Describe dna and rna as double-stranded and single-stranded, with thymine versus uracil bases and deoxyribose versus ribose backbones.

Explain the basic unit of nucleic acids as nucleotides and map the level of genetic organization from nucleotides to genes, DNA, chromosomes, and the genome.

Describes dna composition with a deoxyribose sugar and phosphate backbone, four bases (adenine, thymine, cytosine, guanine), and the pairing rules a-t and c-g via hydrogen bonds.

DNA forms a double helix where adenine pairs with thymine and guanine with cytosine through hydrogen bonds, creating a ladder-like structure with a sugar-phosphate backbone.

Explore the Watson–Crick model of DNA, a double helix formed by two coiled strands, and how genes code for proteins that determine traits like eye color, height, and complexion.

Explore the RNA structure: a single-stranded ribose backbone with a phosphate group, containing adenine, guanine, cytosine, and uracil, with thymine absent.

Explore key differences between dna and rna, including thymine versus uracil, cytosine in both, single-stranded rna versus double-stranded dna, ribose versus deoxyribose, and their relative size and localization.

Explore mitochondria, a double-membrane powerhouse with intermembrane space and matrix that synthesize ATP via ATP synthase, featuring cristae folds, maternal DNA, and 70S ribosomes involved in oxidative phosphorylation.

Explore chloroplasts, the plant cell organelles that drive photosynthesis with chlorophyll-rich thylakoids forming grana and stroma supporting the Calvin cycle; learn about plastids like amyloplasts and chromoplasts.

Endoplasmic reticulum forms a continuous membrane system with rough and smooth regions, supporting protein synthesis by ribosomes, processing near the nucleus, and delivering products to the Golgi.

Demonstrates the Golgi apparatus structure with cisternae, cis and trans phases, and how ER-derived vesicles are modified, glycosylated, phosphorylated, and packaged for secretion and lipid and lysosome transport.

Encounter lysosomes, membrane-bound organelles housing acid hydrolases that enable intracellular and extracellular digestion. Examine how they drive autophagy, phagocytosis, and the regulated release of enzymes via exocytosis.

Peroxisomes oxidize fats and detoxify hydrogen peroxide with catalase, supporting plant beta-oxidation and glyoxylate cycle, photorespiration, and human liver lipid and purine metabolism.

Discover how the cytoskeleton shapes cells, provides rigidity, and enables movement and transport of organelles. Identify actin filaments (microfilaments), microtubules, and intermediate filaments as the main filament types.

Filaments provide unidirectional movement tracks built from small subunits that assemble into larger polymers; subunit dissociation and reassembly enable relocation, while single protofilaments are thermally unstable.

The cytoskeleton supports the cell and maintains its shape, interacts with motor proteins to drive movement, and provides monorails for vesicle transport, with emerging evidence of regulating biochemical activities.

Explore the cytoskeleton's structure and function, comparing microtubules, microfilaments, and intermediate filaments, their tubulin and actin subunits, and roles in cell shape, motility, division, organelle movement, and nuclear anchorage.

Explore how the cytoskeleton provides structural support, mechanical stability against osmotic pressure and injury, acts like a geodesic dome, anchors organelles, and dynamically reassembles subunits to shape the cell.

Explore how the cytoskeleton powers selective cell movement and organelle transport with ATP-powered motor proteins along microtubules, guided by receptors, and organized by centrosomes and centrioles.

Cilia and flagella share a nine-plus-two microtubule core, anchored by a basal body and driven by dynein arms, with cilia beating perpendicularly and flagella undulatory along the axis.

Microfilaments are the thinnest actin filaments forming a 3D network beneath the plasma membrane, resisting tension. Actin and myosin slide past each other to drive muscle contraction and cytoplasmic streaming.

Describe intermediate filaments as 8–12 nm cytoskeletal threads built from keratin subunits, bearing tension and serving as permanent fixtures that reinforce cell shape and fix organelle location.

Explore how extracellular components coordinate cell activities, focusing on plant cell walls—made of cellulose fibers with polysaccharides and proteins—and their roles in protection and shape.

Identify and describe the three plant cell wall layers—the primary cell wall, middle lamella, and secondary cell wall—and explain how plasmodesmata connect plant cells and relate to the central vacuole.

The extracellular matrix in animal cells comprises collagen, proteoglycans, and fibronectin, which bind to integrin receptors on the plasma membrane, linking the extracellular matrix to the cell interior.

Explore how the extracellular matrix provides support, adhesion, movement, and regulation, links cells into tissue networks, enables intercellular communication via fibronectin and integrins, and guides development.

Discover intercellular junctions, including plasmodesmata, tight junctions, desmosomes, and gap junctions. Understand how tight junctions prevent leakage, desmosomes anchor cells to intermediate filaments, and gap junctions enable molecule exchange.

Explore plasmodesmata in plant cells as channels that connect adjacent cell membranes, enabling water, small solutes, and sometimes proteins and RNA to move between cells.

Describe tight junctions that seal membranes and prevent glucose flow between cells, desmosomes that anchor cells into strong sheets, and gap junctions that form cytoplasmic channels for intercellular passage.

Explore cell adhesion molecules (cams) in animal cells, including cadherins, Ig-like cams, selectins, and integrins, their calcium dependence, binding modes, and interactions with extracellular matrix and cytoskeleton.

The extracellular matrix is a dynamic network that provides structural support and guides tissue growth. It has three types—basement membrane, elastic fibers, and interstitial matrix—with laminin as a key component.

Collagens provide tensile strength in connective tissue, with types I, II, III, and V forming fibrils, while proteoglycans and hyaluronan create extracellular matrix gels; fibronectin supports adhesion and wound healing.