Cell Structure and Function

Vocabulary flashcards covering cellular organization, membrane structure, organelles, transport processes, energy metabolism, and motility based on Chapter 2 lecture notes.

Protoplasm

The collective group of substances that compose the cell, primarily consisting of water, electrolytes, proteins, lipids, and carbohydrates.

Structural Proteins

Intracellular proteins existing mainly as long filaments that polymerize to form microtubules, cytoskeleton, cilia, axons, and mitotic spindles, comprising $10\%\text{ to }20\%$ of total cell weight.

Functional Proteins

Mobile globular proteins in the cytoplasm that act primarily as enzymes, catalyzing specific intracellular chemical reactions either in solution or attached to cellular membranes.

Adipocytes

Fat cells in which stored triglycerides account for approximately $95\%$ of total cellular volume, serving as the body's main energy reserve.

Glycogen

An insoluble polymer of glucose stored within cells that can be rapidly depolymerized to provide glucose for cellular energy needs.

Cell Membrane (Plasma Membrane)

An elastic structure $7.5\text{ to }10\,\text{nm}$ thick that envelopes the cell, composed of $55\%$ proteins, $25\%$ phospholipids, $13\%$ cholesterol, $4\%$ other lipids, and $3\%$ carbohydrates.

Phospholipids

The most abundant lipids in the cell membrane, containing a hydrophilic (water-soluble) phosphate end and a hydrophobic (fat-soluble) fatty acid end.

Sphingolipids

Membrane lipids derived from the amino alcohol sphingosine that provide protection, signal transmission, and cell-binding sites.

Cholesterol

A steroid-based membrane lipid dissolved in the lipid bilayer that regulates membrane permeability to water-soluble components and controls membrane fluidity.

Integral Proteins

Membrane-spanning proteins that serve as selective channels, carrier proteins for active transport, receptors for water-soluble ligands, or enzymes.

Peripheral Proteins

Proteins attached only to one surface of the cell membrane without penetrating its core, functioning mainly as enzymes or regulators of membrane transport.

Glycocalyx

A loose carbohydrate coat covering the entire outer surface of the cell, providing a net negative electrical charge, aiding cell adhesion, and acting as hormone receptors.

Cytosol

The clear fluid portion of the cytoplasm in which cellular particles, organelles, proteins, electrolytes, and glucose are dispersed.

Endoplasmic Reticulum (ER)

A network of tubular structures (cisternae) and flat vesicles formed by a lipid bilayer, responsible for synthesizing, processing, and transporting cellular molecules.

Rough (Granular) Endoplasmic Reticulum

The portion of the ER studded with ribosomes on its outer membrane, directly continuous with the nuclear envelope, and dedicated to synthesizing new proteins.

Smooth (Agranular) Endoplasmic Reticulum

The portion of the ER lacking ribosomes that synthesizes lipids (phospholipids and cholesterol), breaks down glycogen, and detoxifies drugs.

Golgi Apparatus

An organelle composed of stacked flat vesicles located near the nucleus that works with the ER to process, package, and direct cellular secretions and proteins.

Lysosomes

Intracellular digestive organelles ($250\text{ to }750\,\text{nm}$ in diameter) containing about $40$ acid hydrolase enzymes enclosed by a membrane operating at an acidic $\text{pH} \approx 4.8$.

Tay-Sachs Disease

A rare genetic lysosomal storage disorder caused by a mutation in the Hexosaminidase A enzyme gene, leading to ganglioside accumulation in nerve cells and early childhood death.

Peroxisomes

Organelles containing oxidases (which produce $\text{H}_2\text{O}_2$) and catalase that function to detoxify sytemic toxins and catabolize long-chain fatty acids.

Zellweger Syndrome

A congenital peroxisomal disorder characterized by a reduced number of cell peroxisomes, causing severe neurological and metabolic dysfunction, typically fatal in the first year of life.

Secretory Vesicles

Storage vesicles formed by the ER-Golgi system that carry inactive proenzymes or proteins and release them outside the cell via exocytosis.

Mitochondria

The 'powerhouse of the cell', featuring an outer membrane with porins and an inner membrane forming cristae, generating over $95\%$ of cellular ATP.

Mitochondrial DNA (mtDNA)

Circular DNA within the mitochondrial matrix encoding $37$ essential genes, inherited almost exclusively through the maternal egg cell.

Heteroplasmy

A genetic state in which normal and mutated mitochondrial DNA ($mtDNA$) molecules coexist within a cell.

Cytoskeleton

An intracellular network of fibrillar proteins organized as microfilaments, intermediate filaments, and microtubules that maintains cell shape, aids division, and directs organelle transport.

Intermediate Filaments

Strong, thread-like protein filaments (e.g., desmin in muscle, neurofilaments in neurons, keratins in epithelial cells) that provide mechanical support to cells.

Microtubules

Rigid tubular structures ($25\,\text{nm}$ in diameter) composed of polymerized tubulin that act as structural tracks, centrioles, mitotic spindles, and ciliary cores.

Nuclear Envelope

A double-membrane boundary enclosing the nucleus containing several thousand nuclear pores with a central channel diameter of $9\,\text{nm}$.

Nucleolus

A non-membrane-bound structure within the nucleus composed of RNA and proteins where ribosomal subunits are synthesized and assembled.

Endocytosis

The active mechanism by which cells ingest extracellular material by invaginating the cell membrane, taking the form of pinocytosis or phagocytosis.

Pinocytosis

The ingestion of minute extracellular fluid vesicles ($100\text{ to }200\,\text{nm}$) formed at clathrin-coated pits, requiring ATP and extracellular calcium ions ($\text{Ca}^{2+}$).

Phagocytosis

The ingestion of large particles such as bacteria or dead tissue cells by specialized cells (macrophages and white blood cells), facilitated by antibody opsonization.

Autophagy

The housekeeping process in which cellular structures and worn-out organelles (e.g., liver mitochondria with a ~10-day lifespan) are enclosed in autophagosomes and degraded by lysosomes.

Exocytosis

The extrusion mechanism where intracellular vesicles fuse with the cell membrane to release contents into the extracellular space, triggered by $\text{Ca}^{2+}$ influx.

Adenosine Triphosphate (ATP)

A nucleotide composed of adenine, ribose, and three phosphate groups, featuring high-energy phosphate bonds carrying approximately $12000\,\text{cal/mol}$ of energy.

Chemotaxis

The movement of a cell toward (positive) or away from (negative) a chemical stimulus along a concentration gradient.

Axoneme

The structural complex of $9+2$ microtubules and associated cross-links inside a motile cilium, powered by dynein arms with ATPase activity.

Primary Cilia

Non-motile single cilia found on cell surfaces acting as sensory antennae to monitor fluid flow and chemical signals; defects in renal primary cilia cause polycystic kidney disease.