1. B 2.1 SL Membranes and transport

Phospholipids

Molecules that form the basis of cell membranes, consisting of hydrophobic tails and hydrophilic heads.

Amphipathic

Molecules that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.

Hydrophobic

Substances that repel water; nonpolar.

Hydrophilic

Substances that attract water; polar

Fluid Mosaic Model

A model describing the structure of cell membranes as a mosaic of various components, including phospholipids, proteins, and cholesterol, that move fluidly.

Integral Proteins

Proteins that are embedded in the lipid bilayer, some spanning the entire membrane.

Peripheral Proteins

Proteins that are attached to the outer or inner surfaces of the membrane, not embedded.

Osmosis

The passive movement of water molecules from a hypotonic to a hypertonic region until equilibrium

Facilitated Diffusion

The process by which specific molecules are transported across cell membranes through protein channels or carrier proteins, no energy needed (ions and charged and/or polar particles)

Active Transport

The movement of substances across a cell membrane against their concentration gradient, requiring energy or ATP (hydrophilic and charged molecules)

Aquaporins

Channel proteins that facilitate the transport of water molecules across cell membranes.

Selective Permeability

The property of cell membranes that allows certain substances to pass through while restricting others.

Glycoproteins

Molecules consisting of proteins with carbohydrate groups attached, playing roles in cell recognition and communication.

Glycolipids

Lipids with carbohydrate groups attached, contributing to cell membrane structure and function.

Channel Proteins

Proteins that provide passageways for specific ions or molecules to cross the membrane.

Protein Pumps

Proteins that transport substances across membranes using energy in the form of ATP.

Concentration Gradient

A difference in the concentration of a substance across a space, which drives diffusion.

Simple Diffusion

The passive movement of small, nonpolar molecules across a membrane without the need for energy.

Dynamic Equilibrium

The state reached when the concentrations of substances on either side of a membrane are equal, resulting in no net movement.

Glycocalyx

A carbohydrate-rich layer on the cell surface, composed of glycoproteins and glycolipids, important for cell recognition.

Endocytosis

A process by which cells engulf substances into a pouch, which becomes a vesicle in the cytoplasm (vesicular transport)

Exocytosis

The process of expelling materials from a cell via vesicles that fuse with the plasma membrane. (vesicular transport)

diffusion

the passive transport of molecules from a region of high concentration to a region of low concentration across a semi-permeable membrane until a dynamic equilibrium has been reached

solute

substance that is dissolved in a solvent (water) to form a solution

lipid bilayer

a double layer of phospholipids that makes up the cell membrane

molecules for simple diffusion

small and non-polar (eg. oxygen, water) or polar (ethanol)

molecules not able to simple diffuse

charged (ions) or large polar molecules (eg. glucose, fructose) or non-polar

factors influencing rate of diffusion

include concentration gradient, temperature, surface area, membrane permeability, thickness of membrane

uniporter

carries on specific ion or molecule, same direction (active transport)

symporter

carries two different ions or molecules, same direction (active transport)

antiporter

carries two different ions or molecules in different directions (active transport)

which molecules diffuse across a membrane

hydrophobic molecules, small uncharged polar molecules

which molecules don’t diffuse across a membrane

large uncharged polar molecules, ions

why are glycoproteins important in tissues

cell to cell binding

how cell membrane adapts to temperature?

through modifications in the types and proportions of lipids (eg. colder temperatures, cells increase proportion of fatty acids in phospholipids, which have kinks in their tails that prevent the lipids from packing too tightly, aka freezing, maintaining membrane fluidity)

first use for sodium ions in membrane

sodium potassium pumps, mechanism moves sodium ions out of cell and potassium ions into cell against concentration gradients, use energy/ATP

second use for sodium ions in membrane

sodium ions are transported into the cell along with other molecules (eg. glucose) through symporters, ions move down concentration gradient, providing energy required to move other substances into the cell against their gradients