Chapter 5: Membrane Structure and Function

Vocabulary flashcards covering the fluid-mosaic model, classes of membrane proteins, principles of selective permeability, tonicity effects, and bulk transport mechanisms from Chapter 5.

Fluid-Mosaic Model

Describes the plasma membrane as a fluid lipid bilayer in which diverse protein components form a shifting, mosaic pattern. It is used to describe the structure of the plasma membrane

Why is the membrane selectively permeable

The hydrophilic (polar) heads face water, while the hydrophobic (non polar) tails form an inner barrier. Because the center is hydrophobic, small non-charged molecules can cross easily, while charged and polar substances generally cannot cross without assistance.

What substances cannot cross the plasma membrane freely, and how do they cross?

Ions and polar molecules cannot cross the hydrophobic interior on their own, so they need transport proteins such as channels, aquaporins, or carrier proteins. Large molecules are too large to cross directly and must use vesicles through endocytosis or exocytosis.

Components of Cell Membranes

include phospholipids, proteins, carbohydrates, and cholesterol that contribute to its structure and function.

Components of Cell Membrane: Lipids

Phospholipids are the primary structural components of cell membranes, forming the bilayer that provides fluidity and barrier properties.

Components of Cell Membrane: Choelterol

Cholesterol is a lipid that helps to stabilize membrane fluidity and structure by fitting between phospholipids in the bilayer.

Components of Cell Membrane: Proteins

They are associated with or inside the membrane and include two options: Integral and peripheral

Integral Proteins

Are embedded within the membrane and span across it, playing key roles in transport, signaling, and cell adhesion. They are exposed on both sides of the membrane

Peripheral Proteins

Only on one side of the membrane; they play roles in signaling and maintaining the cell's shape (Cytoskelton = inside) (Extracellular matrix = outside).

Channel Proteins

Membrane proteins that form openings for free passage of molecules across the membrane. They are very specific because one channel allows only one specific substance to pass through

Carrier Proteins

Membrane proteins that bind specific substances and change shape to transport them.

Cell Recognition Proteins

Glycoproteins acting as cellular barcodes, helping the immune system distinguish self cells from pathogens.

Receptor Proteins

Proteins with specific binding sites that receive external signaling molecules (e.g., hormones), triggering internal responses to bring info/instructions. It is very specific (key to a lock)

Enzymatic Proteins

Membrane proteins that catalyze metabolic reactions.

Junction Proteins

Membrane proteins that mediate direct adhesion and communication between cells.

Properties of Substances to pass through the Membrane

Small, noncharged molecules can pass through the membrane

Substances that cannot pass through the Membrane

Anything with a charge (no matter the size) cannot cross the membrane without help from transport proteins.

Large Molecules passing through the membrane

Large molecules need vesicles via bulk transport to move across the membrane

Simple Diffusion

Passive transport down a concentration gradient ($\text{High} \rightarrow \text{Low}$) where small, uncharged, nonpolar molecules ($O_2$, $CO_2$) slip through the core.

Facilitated Transport

Passive transport down a concentration gradient with assistance from channel or carrier proteins, requiring zero $ATP$.

Active Transport

Transport against a concentration gradient ($\text{Low} \rightarrow \text{High}$) that requires cellular energy ($ATP$) and specific pumps.

Passive transport

does not require energy because the substnace is moving to a lower concentration

Osmosis

A special type of diffusion that must be in water, and the ater must diffuse across a seletively permeable membrane (only allows specific molecules to pass through).

Osmosis Net Movement

The movement of water is from the higher concentration to the lower concentration. Water can move both ways, while solutes cannot.

Diffusion

Net movement of molecules to a lower concentration from a higher concentration (high to low)> It happes the fastest with warmer temperatures and smaller molecules

Equilibrium

When net movement stops

Isotonic Solution

A solution where solute concentrations inside and outside the cell are equal, leading to no net movement of water and dynamic equilibrium.

Hypotonic Solution

A solution with lower solute concentration outside the cell, causing water to rush in and leading to animal cell lysis or plant cell turgor pressure.

Hypertonic Solution

A solution with higher solute concentration outside the cell, causing water to leave the cell and leading to animal cell crenation or plant cell plasmolysis.

Exocytosis

A form of transport where vesicles fuse with the plasma membrane to release products out of the cell.

Endocytosis

A form of transport where the plasma membrane folds inward to bring materials into the cell.

Phagocytosis

A subtype of endocytosis characterized as the cell taking larger, solid material via vesicle information (commonly is bacteria)

Pinocytosis

A subtype of endocytosis characterized by the cell taking in liquid and small particles via vesicles.

Receptor-mediated endocytosis

It is a specialized pinocytosis that uses receptor proteins to bind the cell to a specific receptor on the cell membrane. It is used for genetic disorders

Integrin / ECM

A structure that connects the internal cytoskeleton of a cell to the external extracellular matrix. It is made of different proteins and polysaccharides and is found outside the cell

Cytoskeleton

The structural framework inside the cell made of actin filaments

Not Selectively Permeable

Plant cell walls are permeable, which allows any substance to pass through the membrane