The Cellular Level of Organization - Flashcards

Vocabulary flashcards covering cellular organization, organelles, membrane transport mechanisms, gene expression, and cell division based on Chapter 3 lecture notes.

Cytoplasm

All the cellular contents located between the plasma membrane and the nucleus, consisting of two components: cytosol and organelles.

Cytosol

The fluid portion of cytoplasm surrounding organelles, consisting of $75\text{--}90\text{\%}$ water plus dissolved and suspended components, serving as the site of many chemical reactions.

Organelles

Specialized subcellular structures with characteristic shapes and specific functions, each possessing its own set of enzymes.

Nucleus

A large spherical or oval organelle containing DNA organized into chromosomes, which house thousands of hereditary units called genes.

Plasma membrane

A flexible, selective barrier forming the outer boundary of the cell that regulates the flow of materials and plays a role in cellular communication.

Cytoskeleton

A network of protein filaments extending throughout the cytosol that provides structural support and generates movement for the cell and its organelles.

Microfilaments

The thinnest cytoskeletal components made of actin, prevalent at the edge of the cell, which aid in cell movement (muscle contraction, migration) and provide mechanical support.

Intermediate filaments

Exceptionally strong cytoskeletal filaments found in areas subject to mechanical stress that help stabilize organelle positions and assist in cell-cell junctions.

Microtubules

The largest cytoskeletal components, composed of long, unbranched hollow tubes of tubulin assembled in the centrosome that determine cell shape and move vesicles, cilia, and flagella.

Centrosome

An organelle located near the nucleus consisting of two centrioles and pericentriolar matrix, serving as the organizing center for microtubule formation and mitotic spindles.

Cilia

Short, hair-like projections containing a core of $20$ microtubules anchored to a basal body that move fluids along a cell surface in an oarlike pattern.

Flagella

Long cell surface projections that move an entire cell (such as a sperm cell) through rapid, wave-like wiggling.

Ribosomes

Structures composed of rRNA and proteins, made of large and small subunits created in the nucleolus, that serve as the sites of protein synthesis.

Rough Endoplasmic Reticulum (ER)

A series of flattened membrane sacs continuous with the nuclear envelope, studded with ribosomes, that synthesizes glycoproteins and phospholipids.

Smooth Endoplasmic Reticulum (ER)

A network of membrane tubules extending from the rough ER lacking ribosomes that synthesizes fatty acids and steroids, and detoxifies certain drugs.

Golgi complex

An organelle consisting of $3\text{--}20$ flattened membranous sacs (cisternae) divided into entry (cis) face, medial cisternae, and exit (trans) face that modifies, sorts, and packages proteins.

Lysosomes

Golgi-derived vesicles containing digestive and hydrolytic enzymes operating at pH $5$ that digest endocytosed material and carry out autophagy and autolysis.

Autophagy

The process by which lysosomal enzymes digest worn-out cellular structures to recycle their components.

Autolysis

The complete destruction of an entire cell by its own lysosomal enzymes.

Tay-Sachs Disease

An inherited condition caused by the absence of the lysosomal enzyme Hex A, leading to glycolipid accumulation in neurons, seizures, blindness, and death before age $5$.

Peroxisomes

Vesicles containing oxidases that break down amino acids and fatty acids, detoxify alcohol, and utilize catalase to decompose byproduct $H_2O_2$.

Proteasomes

Tiny barrel-shaped protein structures containing proteases that continuously degrade unneeded, damaged, or faulty proteins into small peptides.

Mitochondria

Double-membrane organelles termed the powerhouses of the cell that generate ATP through aerobic cellular respiration and possess self-replicating maternal circular DNA containing $37$ genes.

Cristae

The internal series of folds of the inner mitochondrial membrane containing enzymes required for cellular respiration reactions.

Mitochondrial matrix

The large central fluid-filled cavity enclosed by the inner mitochondrial membrane containing respiratory enzymes.

Nuclear envelope

A double lipid bilayer membrane separating the nucleus from the cytoplasm, perforated by nuclear pores that control substance movement.

Nucleolus

A cluster of protein, DNA, and RNA inside the nucleus responsible for assembling ribosome subunits.

Chromatin

A complex mass of DNA, proteins (histones), and RNA present in non-dividing cells.

Nucleosome

A structural unit of chromatin consisting of double-stranded DNA wrapped twice around a core of eight histone proteins.

Fluid mosaic model

The model describing the plasma membrane structure as a dynamic sea of lipids containing floating or anchored proteins.

Amphipathic

Molecules having both polar (hydrophilic) and nonpolar (hydrophobic) regions, such as membrane phospholipids.

Glycocalyx

An extracellular carbohydrate coating formed by glycolipids and glycoproteins that serves as a molecular signature for cell recognition.

Integral proteins

Membrane proteins that extend into or through the lipid bilayer, most of which are transmembrane proteins spanning both sides.

Peripheral proteins

Membrane proteins attached to inner or outer surfaces associated with polar lipid heads or integral proteins without spanning the bilayer.

Electrochemical gradient

The combined influence of a concentration gradient and an electrical gradient driving the movement of a specific ion across a plasma membrane.

Passive processes

Transport mechanisms moving substances across cell membranes down concentration gradients using particle kinetic energy without cellular ATP expenditure.

Active processes

Transport mechanisms requiring cellular energy (primarily ATP hydrolysis) to move substances against concentration gradients or via vesicles.

Simple diffusion

Passive transport where nonpolar, hydrophobic molecules move freely through the lipid bilayer without transport protein assistance.

Facilitated diffusion

Passive transport of polar or charged solutes across a membrane assisted by channel or carrier proteins.

Osmosis

Net movement of water through a selectively permeable membrane from an area of higher water concentration to one of lower water concentration.

Aquaporins

Integral membrane proteins that act as specialized channels to facilitate water movement across plasma membranes.

Tonicity

The ability of an extracellular solution to modify cell volume and shape by altering its water content.

Hemolysis

The swelling and bursting of red blood cells placed in a hypotonic solution.

Crenation

The shrinking and spiction of red blood cells placed in a hypertonic solution.

Primary active transport

Active transport mechanism where energy from ATP hydrolysis powers carrier pumps to move solutes against gradients (such as the $Na^+/K^+$ ATPase).

Secondary active transport

Coupled transport driven by energy stored in ionic concentration gradients ($Na^+$ or $H^+$) created by primary active transport pumps.

Symporters

Secondary active transport carriers that transport two substances across a membrane in the same direction.

Antiporters

Secondary active transport carriers that transport two substances across a membrane in opposite directions.

Endocytosis

Active vesicular transport moving materials into a cell via plasma membrane invagination (includes receptor-mediated endocytosis, phagocytosis, and pinocytosis).

Phagocytosis

A form of endocytosis ('cell eating') where phagocytes extend pseudopods to engulf solid particles into a phagosome.

Bulk-phase endocytosis

A form of endocytosis ('cell drinking' or pinocytosis) involving non-selective uptake of extracellular fluid and dissolved solutes into a vesicle.

Exocytosis

Active process where secretory vesicles fuse with the plasma membrane to release contents into extracellular fluid.

Transcytosis

A transport process combining endocytosis on one side of a cell and exocytosis on the opposite side to transport substances across cell barriers.

Transcription

Process in the nucleus where a DNA template sequence is transcribed into complementary RNA strands (mRNA, rRNA, tRNA).

Translation

Process carried out by ribosomes where nucleotide sequences in mRNA dictate specific amino acid sequences to assemble proteins.

Base triplet

A sequence of three DNA nucleotides that encodes specific genetic instructions for protein synthesis.

Codon

A sequence of three mRNA nucleotides complementary to a DNA base triplet that specifies a single amino acid.

Introns

Non-coding regions of pre-mRNA transcripts located between exons that are removed by snRNPs prior to translation.

Exons

Coding regions of pre-mRNA spliced together to form functional mRNA that exits the nucleus.

Apoptosis

Genetically programmed cell death in which self-destructive enzymes shrink cytoplasm and fragment DNA without triggering inflammation.

Necrosis

Pathologic cell death resulting from severe tissue injury, characterized by cell swelling, bursting, and inflammation.

Telomeres

Specific DNA sequences at chromosome tips that protect against erosion and shorten with each round of cell division.