Cell Structures, Transport, and Communication Practice

This set covers cell structures, organelles, transport mechanisms, and cellular communication methods based on the lecture notes.

Cell

The smallest unit of life.

Organelle

An interior structure found within a cell.

Prokaryotes

Simple and less compartmentalized organisms that lack a nucleus and store genetic information as a single circular DNA molecule in a nucleoid.

Eukaryotes

Complex and orderly cells that contain two membrane layers for extra protection and specialized organelles.

Nucleoid

The region in a prokaryote where the circular DNA molecule floats freely within the cytoplasm.

Shared Organelles

The three structures present in both prokaryotes and eukaryotes: cytoplasm, ribosome, and cell membrane.

Plant-specific Organelles

Organelles unique to plant eukaryotes, including the cell wall, chloroplast, and vacuoles.

Centrioles

Organelles found specifically in animal cells.

Cilia

Hair-like structures on the exterior of the cell used for movement or clearing mucus and debris, as seen in the lungs.

Flagella

Tail-like structures on the exterior of the cell used for movement, such as those found on sperm cells.

Intracellular

Occurring within the cell, particularly within the cytosol.

Intercellular

Occurring between cells and across cell membranes.

Vesicles

Transport sacs within a cell that carry a variety of molecules.

Phospholipid Bilayer

The structure of the cell membrane comprised of polar, hydrophilic phosphate heads and nonpolar, hydrophobic fatty acid interiors.

Cholesterol

A lipid molecule present in the cell membrane used for maintaining structure and fluidity.

Passive Transport

The transport of molecules that require no energy and occurs via constant, random motion.

Diffusion

Random movement causing molecules to spread from a region of higher concentration to a region of lower concentration.

Facilitated Diffusion

Diffusion of molecules down their concentration gradient that is facilitated by membrane proteins like ion channels or carrier proteins.

Active Transport

Transport of molecules against the concentration gradient across membranes that requires energy in the form of $ATP$.

Osmosis

The movement of water to higher solute environments; 'where salt goes, water follows.'

Hypertonic

A state where the outside of the cell is more solute concentrated than the interior, causing water to flow out and the cell to shrink.

Hypotonic

A state where the outside of the cell is less solute concentrated than the interior, causing water to flow in and the cell to swell or burst.

Isotonic

A state where the inside and outside of the cell are in solute balance.

Symporters

Active transport proteins that move two molecules in the same direction, such as sodium-glucose linked together ($SGLT$).

Antiporters

Active transport proteins that move two molecules in opposite directions, such as the sodium-potassium pump ($Na^+-K^+$ pump).

Endocytosis

A process where the cell takes in food or fluids by creating a vesicle from the cell membrane.

Phagocytosis

A specific type of endocytosis where pathogens or other solids are engulfed by cells.

Pinocytosis

A specific type of endocytosis where liquids are engulfed by cells.

Exocytosis

A process where the cell releases materials at the cell surface.

Ligand

Signaling molecules used in cell communication that bind to specific receptors.

Direct Communication

Cell communication involving direct contact with the target cell, characterized as targeted and close.

Indirect Communication

Cell communication where a cell releases a signal to numerous nearby or distant cells, characterized as broad and distant.

Autocrine

Communication occurring when a cell secretes molecules that bind to itself or other cells.

Paracrine

Indirect communication where a cell secretes a molecule that spreads to nearby cells in close proximity; common in the nervous system for immediate signals.

Endocrine

Cell signaling occurring over long distances through the bloodstream, primarily utilizing hormones.

Connexons

The main proteins that connect gap junctions in direct communication, extending from cytosol to cytosol.

Signal Transduction

The second step of cell communication where a signal is transmitted on an intracellular pathway to the target area of the cell.

Conformation Change

A change in the shape of a receptor protein caused by ligand binding, which sets off the signaling cascade.

GPCR

G protein-coupled receptors, which consist of $7$ transmembrane domains.

Secondary Messenger

Molecules that speed up and amplify messages within a cell, with cyclic $AMP$ ($cAMP$) being the most common type.

Apoptosis

Programmed cell death used to control cell count, prevent tissue damage, and eliminate worn-out or potentially cancerous cells.