Chapter 3: Cell Structure and Membrane Transport — Vocabulary Flashcards

A comprehensive set of vocabulary cards covering cell theory, cell shapes, membrane structure, membrane transport, organelles, and cytoskeletal components based on the lecture notes.

Cell Theory

All living organisms are made of one or more cells; the cell is the basic unit of structure and function; all cells arise from existing cells.

Squamous

Thin, flaky, or scaly cell shape that lines the esophagus and alveoli of the lungs and the epidermis.

Cuboidal

Cube-like cell shape; appears squash-shaped, as seen in liver cells.

Columnar

Tall, column-like cells; inner lining of stomach and intestines.

Polygonal

Irregularly angular cells with four or more sides; densely packed in glands.

Stellate

Star-shaped cell type, such as certain nerve cells.

Spheroid (ovoid)

Round to oval cells, such as white blood cells (WBCs).

Discoidal

Disc-shaped cells, such as red blood cells (RBCs).

Fusiform

Thick in the middle and tapered at the ends; seen in some smooth muscle cells and axons.

Fibrous

Threadlike cells, such as skeletal muscle fibers and certain axons.

Limit on cell size

Reasons:

• cells may rupture if overly large (overfilled water ballon)

• large cells cannot support themselves

• If a cell is too large, molecules can’t diffuse fast enough to support metabolism and life

• Organs composed of many small cells instead of fewer large ones

Major components of a cell

•       Plasma (cell) membrane:

•       Defines cell boundaries

•       Made of proteins and lipids

•       Composition can vary between regions of the cell (basal, lateral, apical surfaces)

Extracellular fluid (ECF)

• Fluid outside cells

•       ECF includes any fluid outside of cells

•       ECF among the cells tissue (interstitial) fluid

E.g.: blood plasma, lymph, and cerebrospinal fluid

Plasma membrane

•       defines the boundaries of the cell

•       Governs the interactions with other cells

•       Controls the passage of material into and out of the cell

Phospholipids

-         75% of membrane lipids

Amphipathic molecules arranged in a bilayer

-          Hydrophilic phosphate heads face water on each side of membrane

-          Hydrophobic tails—are directed toward the center, avoiding water

-          Drift laterally, keeping membrane fluid

Cholesterol

• About 20% of membrane lipids

•   Found near membrane surfaces among phospholipids

• Holds phospholipids still, stiffening the membrane

 

Glycolipids

• About 5% of membrane lipid

• Phospholipids with short carbohydrate chains on extracellular face

• Contribute to glycocalyx—carbohydrate coating on cell surface

Transmembrane proteins

• pass completely through membrane/phospholipid bilayer

•       Hydrophilic regions contact the water on both sides (cytoplasm/extracellular fluid)

•       Hydrophobic regions pass through lipids of the membrane

Peripheral proteins

Adhere to either the inner OR outer face of the membrane

• Those on inner face are usually tethered to a transmembrane protein AND the cytoskeleton

Receptors

Bind chemical signals to trigger internal changes

•       Specific for a particular messenger

•       Can activate second messengers inside the cell

Enzymes (membrane enzymes)

• catalyze (speed up) reactions including digestion of molecules

• production of second messengers,

• breakdown hormones and other signaling molecules whose job is complete

Channel proteins

Proteins that create passages for hydrophilic solutes and water to pass through the membrane.

Leak channels

Channels that are always open, allowing continuous passage of ions or materials.

Gated channels

open and close under different circumstances allowing solutes through sometimes

Ligand-gated channels

Channels that open in response to chemical messengers (ligands).

Voltage-gated channels

respond to electrical potential (voltage) across plasma membrane

Mechanically gated channels

respond to physical stress on cell (e.g.: stretch, pressure)

Carriers

  Transmembrane proteins that bind to glucose, electrolytes and other solutes and CARRY them to the other side of the membrane

Cell identity markers

Glycoproteins contribute to the glycocalyx, acting like an ID tag, enabling the immune system to identify cells belonging to the body / foreign invaders

Glycocalyx

Carbohydrate coating on the cell surface formed by glycoproteins and glycolipids.

Cell adhesion molecules (CAMs)

Mechanically link cell to another cell and to extracellular material

Second Messenger system

Epi (1^st messenger) -> receptor -> G protein -> Adenylate cyclase

ATP to cAMP (2^nd messenger) -> kinases -> + phosphate groups -> cell changes

Functions of Glycocalyx

Microvilli

Extensions (1–2 μm) of the plasma membrane that increase surface area.

Cilia

Hair-like projections (7–10 μm)

•       Single, nonmotile primary cilium found on nearly every cell; serves as “antenna” for monitoring nearby conditions

•       Helps with balance in inner ear; light detection in retina

•       Multiple nonmotile cilia found on sensory cells of nose

Cystic fibrosis

Hereditary disease in which chloride pumps exist but are not properly inserted into the plasma membrane.

Flagellum

Whiplike tail (sperm) that moves in an undulating, snake-like fashion; longer than a cilium.

Pseudopods

Cytoplasm-filled extensions of the cell

• used by white blood cells to crawl and engulf particles

• platelets use them to adhere and form plugs.

Membrane transport

Movement of substances across the plasma membrane; selective permeability.

Selective permeability

• Membrane property that allows some substances to cross more easily than others.

• preventing (barrier) others from passing between the cytoplasm and ECF

Passive transport

Movement of substances across the membrane without energy input (no ATP).

Active transport

Movement of substances against their gradient requiring energy (ATP).

Carrier-mediated transport

Transport via membrane carriers that bind and move solutes across the membrane.

Filtration

•       particles are driven through membrane by physical pressure

•       Example: Blood capillaries – BP forces fluid through gaps in capillary wall.

Simple diffusion * KNOW FOR EXAM

Factors affecting diffusion rate and how they are affected:

-Temperature: ↑ temp., ↑ motion of particles, ↑  diffusion rate

-Molecular weight: small molecules move faster, ↑ diffusion rate

-Concentration gradient: ↑ difference (“steepness”), ↑ diffusion rate

  -Membrane surface area: ↑ surface area, ↑ diffusion rate

-Membrane permeability:↑ permeability, ↑ diffusion rate

 

Osmosis

Net flow of water through a selectively permeable membrane

•       Water moves from an area of higher water (lower solute) concentration to an area of lower water (higher solute) concentration

•       Crucial consideration for IV fluids

Osmotic pressure

Hydrostatic pressure required to stop osmosis; reflects solute concentration.

•    Increases as amount of nonpermeating solute rises

•       Nonpermeating solutes cannot pass through membrane

•       Example: proteins

 

Hydrostatic pressure

fluid pressure on the membrane, opposing filtration.

Reverse osmosis

Forcing water through a membrane by applying pressure to override osmotic pressure.

Osmolarity

Total solute concentration of a solution.

•       Includes all solutes that cannot cross the membrane

•       E.g.: Blood plasma, tissue fluid, and intracellular fluid are all about 300 milliosmoles per liter (mOsm/L)

Tonicity

How a solution affect’s a cell’s water movement, volume, and pressure.

Isotonic solution

Same solute concentration inside & outside the cell

•       No net water movement -> cell stays the same size

•       E.g.: 0.9% NaCl (normal saline)

Hypotonic solution

Lower osmolarity than the cell; water enters the cell and it may swell.

Hypertonic solution

Higher osmolarity than the cell; water leaves the cell and it may shrink (Crenation).

Carrier-mediated transport

•       proteins (carriers) in cell membrane carry solutes into or out of cell (or organelle)

Carriers exhibit specificity for their specific solutes

•       Solute (ligand) binds to receptor site on carrier protein

•       Solute is released unchanged on other side of membrane

•       Carriers also exhibit saturation

•       Transport rate increases with solute concentration, but only to a point called the transport maximum

Uniport

Moves one solute at a time

•       E.g.: Calcium pump

Symport

Moves 2+ solutes in the same direction at the same time.

•       Secondary Active Transport

•       E.g.: Sodium-glucose symporter (SGLT)

Antiport

Moves 2+ solutes in opposite directions at the same time

•       Secondary Active Transport

E.g.: Sodium-potassium pump, sodium-calcium exchanger

Facilitated diffusion

carrier moves solute DOWN its concentration gradient

•       No ATP needed

•       Solute attaches to binding site on carrier, carrier changes shape, then releases solute on other side of membrane

Primary active transport

• carrier moves solute through a membrane UP its concentration gradient

• Active transport powered directly by ATP (e.g., Na+/K+ pump).

Sodium-potassium pump

Sodium and potassium ions are pumped against their gradients; maintains Na+ outside and K+ inside the cell.

Functions of the Sodium-potassium pump

•       Maintains Na+ gradient, allowing for secondary active transport

•       Regulates solute concentration and thus osmosis and cell volume

•       Maintains negatively charged resting membrane potential

•  Produces heat

Secondary active transport

Carrier moves solute through membrane

•       Uses ATP indirectly

•       E.g.: Sodium-glucose transporter (SGLT)

•       Moves glucose into cell, up its concentration gradient, while simultaneously carrying sodium down its gradient

Vesicular transport

Moving stuff through the membrane using vesicles

•       Stuff moved: Large particles, fluid droplets, or numerous molecules at once

•       Vesicles = little “bubbles” of membrane that carry things

Endocytosis

brings material INTO cell

Phagocytosis (“Cell eating”)

Cell engulfs large particles (e.g.; bacteria, debris)

•       Pseudopods (extensions) wrap around large particles -> internalize it into a vesicle = phagosome -> fuses with a lysosome -> phagolysosome -> break down/digested -> Eliminated through Exocytosis

Pinocytosis (“cell drinking”)

Cell takes in droplets of ECF containing useful molecules in the cell

Receptor-mediated endocytosis (“Picky”)

Cells internalize specific molecules (ligands)

•       E.g.: liver cell absorbing cholesterol from the blood by binding LDL particles to receptors on its membrane

•       Entry of viruses/toxins

Transcytosis

•       Transport of material across the cell by capturing it on one side and releasing it on the other

•       E.g.: movement of molecules across capillary walls

Exocytosis

Moves material OUT of the cell

•       Vesicle fuses with membrane, releasing contents outside

•       Also replaces any plasma membrane lost during endocytosis

Cytosol

is a clear, viscous, watery colloid within the cell

•       Contains enzymes, other proteins, amino acids, ATP, electrolytes, dissolved gases, metabolic wastes

Cytoskeleton

is a network of protein filaments and cylinders

   Functions:

•       Structural support, determines cell shape, organizes cell contents

•       Directs movement of materials within cell and contributes to movements of the cell as a whole

•       Composed of microfilaments, intermediate fibers, microtubules

 

Microfilaments

Thin (about 6 nm) Actin filaments; support, movement, and cell surface changes.

Intermediate filaments

8–10 nm filaments; provide mechanical support and integrity.

Microtubules

25 nm hollow tubes; tubulin-based; form the mitotic spindle, move organelles, and shape the cell.

Nucleus

Largest organelle; control center housing genetic material and regulating gene expression.

Nuclear envelope

Double membrane surrounding the nucleus; barrier between nucleus and cytoplasm.

Nucleoplasm

Gel-like fluid inside the nucleus that suspends components and supports replication/transcription.

Rough Endoplasmic Reticulum

Flattened sacs studded with ribosomes; synthesizes phospholipids and proteins.

Smooth Endoplasmic Reticulum

Tubular ER without ribosomes; makes lipids and steroids; detoxifies substances.

Golgi Complex

Stack of flattened sacs; packages, modifies proteins, and synthesizes carbohydrates.

Lysosomes

Membrane-bound packages of enzymes; sites of autophagy and autolysis.

Peroxisomes

Organelle like lysosomes but with different enzymes; detoxifies harmful substances and fatty acids.

Mitochondria

Double-membrane-bound organelle; powerhouse producing ATP via cellular respiration.

Proteasomes

Hollow, cylindrical organelles that degrade damaged or unneeded proteins.

Ribosomes

Tiny particles that synthesize proteins by linking amino acids.

Centrosome

Region near the nucleus serving as the organizing center for microtubules during cell division.

Centriole

Paired short cylinders (9 triplets) that organize the formation of cilia and flagella.

Basal bodies

9 triplet microtubules arranged as a cylinder; anchor cilia and flagella to the cell.

Inclusions

Non-membrane-bound substances stored in the cell; not essential for survival.