Chapter 4 & 5: Cell Structure and Membranes

Flashcards covering key vocabulary terms and definitions from lectures on cell structure and membranes, including cell theory, prokaryotic/eukaryotic cells, organelles, cytoskeleton, cell-cell interactions, and membrane transport mechanisms.

Cytoskeleton

A network of protein filaments within the cytoplasm that supports the shape of the cell and anchors organelles.

Actin filament (microfilament)

Long, thin protein fibers responsible for cell movements like contraction and 'pinching'.

Microtubule

Hollow tubes, the largest of the cytoskeleton fibers, that facilitate cellular movement and move materials within the cell.

Intermediate filament

Durable, tough fibrous protein molecules twined together, providing stable structural support (e.g., keratin).

Centriole

Barrel-shaped organelles, occurring in pairs near the nuclear membrane, part of the centrosome.

Cytoplasm

Semifluid matrix filling the interior of the cell, containing sugars, amino acids, and proteins.

Lysosome

Vesicles derived from the Golgi apparatus that contain hydrolytic digestive enzymes to digest worn-out organelles and cell debris.

Nucleus

The largest organelle in eukaryotic cells, containing genetic information (DNA) and acting as the information center.

Nuclear envelope

The surface of the nucleus bounded by two phospholipid bilayer membranes, continuous with the endoplasmic reticulum.

Nucleolus

An area within the nucleus of concentrated RNA synthesis and ribosome assembly.

Nuclear pore

Openings across the nuclear envelope that allow ions and small molecules to diffuse freely and control transport of proteins into the nucleus.

Ribosomes

Small, complex assemblies of protein and RNA, responsible for protein synthesis; often bound to the ER or free in the cytoplasm.

Rough endoplasmic reticulum (RER)

A network of internal membranes studded with ribosomes, a site of protein synthesis for proteins destined for export, lysosomes, vacuoles, or membranes.

Smooth endoplasmic reticulum (SER)

A network of internal membranes without ribosomes, involved in the synthesis of carbohydrates and lipids, Ca2+ storage, and detoxification.

Microvilli

Finger-like projections on the cell surface that increase surface area for absorption.

Plasma membrane

A phospholipid bilayer enclosing the cell and separating its contents from its surroundings; regulates what passes into and out of the cell.

Peroxisome

Vesicles containing oxidative and other enzymes, isolating particular chemical activities from the rest of the cell.

Mitochondrion

Bound by two membranes, metabolizes sugar to generate ATP through oxidative metabolism; considered the 'power plant' of the cell.

Exocytosis

The process by which materials leave the cell when vesicles fuse with the plasma membrane and eject their contents.

Vesicle

A small membrane-bound sac that stores and transports substances within a cell.

Golgi apparatus

A complex of flattened stacks of membranes (cisternae) that sorts, packages, and distributes molecules synthesized at one location and used at another.

Cell Theory

Modern cell theory states that all organisms are composed of one or more cells, cells are the smallest living things, and cells arise only by division of a previously existing cell.

Diffusion

The movement of solutes from a region of high concentration to low concentration, occurring across cell membranes to maintain homeostasis.

Surface area to volume ratio

A principle where as a cell’s size increases, its volume increases much more rapidly than its surface area, giving small cells an advantage for efficient diffusion.

Prokaryotic cells

Cells lacking a membrane-bound nucleus and internal membrane system/organelles; characteristic of Bacteria and Archaea.

Eukaryotic cells

Cells characterized by compartmentalization through an endomembrane system and organelles; includes plants, animals, and fungi.

Peptidoglycan

A carbohydrate matrix cross-linked with short polypeptide units, forming the bacterial cell wall to protect the cell, maintain shape, and prevent water loss/uptake.

Compartmentalization

The hallmark of eukaryotic cells, where cells are broken up into compartments through the endomembrane system and organelles, allowing for simultaneous and independent biochemical processes.

Chromatin

A complex structure in eukaryotes where DNA is organized into chromosomes.

Messenger RNA (mRNA)

Carries coding information from DNA and is used to direct protein synthesis in ribosomes.

Endomembrane system

The system of internal membranes within a cell that divides cells into compartments, including the ER, Golgi apparatus, lysosomes, and vacuoles.

Glycosylation

The process of adding short sugar chains to proteins or lipids in the ER and Golgi apparatus, forming glycoproteins or glycolipids.

Vacuole (plant cell)

Specialized membrane-bounded structures in plant cells; the central vacuole holds water, aids in maintaining water balance, and stores dissolved substances.

Tonoplast

The membrane surrounding the central vacuole in plants, containing channels for water to help maintain cell water balance.

Chloroplast

Photosynthetic organelles in plant cells that use light to generate ATP and sugars, containing thylakoids and stroma.

Cristae

The folded inner membrane of mitochondria, partitioning the mitochondrion into matrix and intermembrane space.

Matrix (mitochondria)

The compartment inside the inner membrane of the mitochondrion.

Intermembrane space (mitochondria)

The compartment between the two membranes of the mitochondrion.

Grana

Closed compartments of stacked membranes within chloroplasts, each containing disk-shaped thylakoids.

Thylakoids

Disk-shaped structures within grana in chloroplasts, containing light-capturing photosynthetic pigments on their surface.

Stroma

The fluid matrix surrounding the thylakoids in chloroplasts, containing enzymes to synthesize glucose.

Endosymbiosis Theory

Proposes that eukaryotic cells evolved by a symbiosis arising between two cells that were free-living, with mitochondria and chloroplasts believed to be descendants of engulfed prokaryotes.

Centrosome

A microtubule-organizing center near the nuclear membranes, containing a pair of centrioles and pericentriolar material.

Extracellular matrix (ECM)

A mixture of glycoproteins and other tough proteins/fibers secreted by animal cells, forming a protective layer over the cell surface.

Integrins

Proteins embedded in the plasma membrane of animal cells that extend into the cytoplasm, linking the ECM to the cytoskeleton and coordinating cell behaviors.

Glycolipids

Lipids with a carbohydrate head, acting as tissue-specific cell-surface markers (e.g., A, B, O blood type).

MHC proteins (Major Histocompatibility Complex)

Proteins that mark cells, allowing the immune system to recognize self and non-self cells.

Adhesive junctions

Cell junctions that mechanically attach the cytoskeleton of a cell to the cytoskeletons of other cells, common in muscle and skin.

Cadherin molecules

Transmembrane proteins on the surface of cells that form adhesive junctions by interacting with cadherin molecules on other cells.

Tight junctions

Separate junctions in vertebrates that form a barrier to prevent substances from passing between cells, creating a wall within the tissue (e.g., intestinal lining).

Communicating junctions

Permit small molecules or ions to pass directly from one cell to another; includes Gap Junctions (animals) and Plasmodesmata (plants).

Gap Junctions

Complexes of six transmembrane proteins arranged in a circle in animal cells, allowing cytoplasmic connections between cells.

Plasmodesmata

Cytoplasmic connections through the cell walls into the plasma membrane of neighboring plant cells, functioning similar to gap junctions.

Fluid mosaic model

A model describing biological membranes, where proteins float in or on a lipid bilayer, allowing for movement of components.

Phospholipid bilayer

Two layers of phospholipids that form the foundation of biological membranes, providing a permeability barrier.

Transmembrane proteins

Proteins embedded in and spanning the lipid bilayer, involved in transport, communication, and cell-surface marking.

Interior protein network

Intracellular proteins that reinforce the membrane's shape, often anchored to both membrane and cytoskeleton.

Cell-surface markers

Glycoproteins and glycolipids on the cell surface that identify different cell types.

Integral membrane proteins

Proteins embedded within the cell membrane.

Peripheral membrane proteins

Proteins associated with the surface of the cell membrane.

Amphipathic structure

A characteristic of phospholipids, having both a polar (hydrophilic) head and a nonpolar (hydrophobic) tail, causing them to spontaneously form bilayers in water.

Transmembrane domain

Each membrane-spanning region of a transmembrane protein, typically composed of hydrophobic alpha-helices.

Porin proteins

Transmembrane proteins with beta-pleated sheets (beta-barrels) that form polar cylinders through the membrane, allowing molecules to pass.

Passive transport

Movement of substances in or out of the cell without expending energy, typically with the concentration gradient via diffusion.

Facilitated diffusion

Passive transport of molecules across a membrane with the assistance of channel proteins or carrier proteins.

Channel proteins

Proteins that form a hydrophilic interior channel, allowing polar molecules and ions a passage through the membrane.

Carrier proteins

Proteins that bind specifically to the molecule they assist in transport across the membrane.

Selectively permeable

A characteristic of the cell membrane, meaning it allows some substances to pass through while impeding others, often due to assistance from proteins.

Ion channels

Hydrated (polar) channels that span the membrane, allowing ions to move between the cytoplasm and extracellular fluid; some are gated.

Osmosis

The net diffusion of water across a selectively permeable membrane toward a region of higher solute concentration (down its free water molecule concentration gradient).

Aquaporins

Specialized water channels that facilitate water transport across the cell membrane.

Osmotic concentration

The concentration of all solutes in a solution, determining the direction of water movement during osmosis.

Hypertonic solution

A solution with a higher solute concentration compared to another solution or a cell, causing water to diffuse out of the cell.

Hypotonic solution

A solution with a lower solute concentration compared to another solution or a cell, causing water to diffuse into the cell.

Isotonic solution

Solutions that have the same solute concentration, resulting in no net movement of water.

Turgor pressure

The high internal pressure in plant cells due to being hypertonic to their environment, helping plants maintain their shapes.

Active transport

Movement of substances across the cell membrane against their concentration gradient, requiring an input of energy (ATP).

Sodium-potassium pump

A carrier protein that directly uses ATP to actively pump 3 Na+ ions out of the cell and 2 K+ ions into the cell per cycle, maintaining ion gradients and electrical potential.

Bulk transport

Mechanisms for moving large polar molecules or large quantities of substances in or out of the cell, including endocytosis and exocytosis, both requiring energy.

Endocytosis

The process of bringing material INTO the cell by engulfing it in a vesicle formed from the plasma membrane.

Phagocytosis

A type of endocytosis where the material taken up is particulate matter (e.g., bacterial cells, organic matter); 'cell eating'.

Pinocytosis

A type of endocytosis where the material taken in is liquid; 'cell drinking'.

Receptor-mediated endocytosis

A type of endocytosis where specific molecules bind to receptors on the plasma membrane and are then brought into the cell in clathrin-coated vesicles.