Bio 201: Chapter 7 Study Guide — Membrane Structure, Transport, & Function

Primary components of biological membranes

Phospholipids, carbohydrates, and proteins

Cytosolic leaflet

The inner layer of a membrane bilayer facing the cytoplasm

Extracellular leaflet

The outer layer of a membrane bilayer facing the outside environment

Transmembrane protein

An integral membrane protein with one or more hydrophobic regions inserted into the hydrophobic interior of the bilayer

Lipid-anchored membrane protein

A protein covalently attached to a lipid molecule inserted within the membrane bilayer

Peripheral membrane protein

A protein non-covalently bound to hydrophilic phospholipid heads or integral membrane proteins

Secondary structure used for ER membrane protein insertion

An $\alpha$-helix formed from $\sim 20$ hydrophobic amino acids

Glycosylation

The covalent attachment of a carbohydrate to a lipid or protein, occurring in the ER and Golgi apparatus

Flippase

An enzyme that uses ATP energy to flip a phospholipid from one leaflet to another

Effect of shorter phospholipid tails on membrane fluidity

Increases fluidity due to reduced intermolecular interactions between tails

Effect of unsaturated phospholipid tails on membrane fluidity

Increases fluidity because double bonds introduce kinks that prevent tight packing

Effect of cholesterol at high temperatures

Decreases membrane fluidity by restricting phospholipid movement

Effect of cholesterol at low temperatures

Increases membrane fluidity by preventing tight packing of phospholipids

Simple diffusion

Movement of solutes down a concentration gradient directly through the phospholipid bilayer without transport proteins or ATP

Facilitated diffusion

Passive movement of solutes down a concentration gradient aided by transport proteins

Primary active transport

Direct utilization of ATP to pump solutes across a membrane against their concentration gradient

Secondary active transport

Movement of a solute against its gradient driven indirectly by a pre-existing solute concentration gradient

Uniporter

A membrane transport protein that moves a single solute in one direction

Symporter

A membrane transport protein that moves two different solutes in the same direction

Antiporter

A membrane transport protein that moves two different solutes in opposite directions

Osmosis

The movement of water across a semi-permeable membrane from a hypotonic region to a hypertonic region

Animal cell in a hypertonic solution

Undergoes crenation as water exits the cell

Plant cell in a hypertonic solution

Undergoes plasmolysis as water exits and the plasma membrane pulls away from the cell wall

Animal cell in a hypotonic solution

Undergoes lysis as water enters, causing it to swell and burst

Plant cell in a hypotonic solution

Becomes turgid as water enters, maintaining normal structural rigidity

Exocytosis

Export of macromolecules out of the cell via vesicle fusion with the plasma membrane

Pinocytosis

A type of endocytosis involving the uptake of liquid materials into small vesicles

Phagocytosis

A type of endocytosis involving the uptake of large solid materials or particles into large vesicles

Receptor-mediated endocytosis

Targeted uptake of specific solutes triggered by binding to cell-surface receptors and forming coated vesicles