Foundations of Biology Chapter 5

plasma membrane

Biomembrane which separates the internal contents of a cell from its external environment

Selective uptake of substrates, compartmentalization, protein sorting, anchoring cytoskeleton, signaling, division, adhesion

Name a few functions of cell membranes

Phospholipid bilayer

The basic framework of the cellular membrane, consisting of two layers of lipids

Fluid mosaic model

States that a plasma membrane is a semifluid phospholipid bilayer with a mosaic of proteins that can have carbohydrates attached

Leaflet

Half of a phospholipid bilayer

Extracellular

Glycolipids are more concentrated on the (extracellular/intracellular) leaflet

Transmembrane protein

A protein that has 1+ regions physically embedded in the hydrophobic region of membrane bilayer

Nonpolar

The amino acids making up the transmembrane region on a protein are (polar/nonpolar)

Lipid anchored protein

Integral membrane protein that has amino acid side chain covalently attached to a lipid molecule

Integral membrane protein

A protein that can't be released from the membrane unless it is dissolved with organic solvents

Peripheral membrane protein

Protein non-covalently bonded to regions of integral membrane proteins or phospholipid heads

Freeze fracture electron microscopy

Analyzes bilayer interiors by freezing and splitting with a knife; transmembrane proteins remain attached to one of the leaflets

Fluidity

Individual molecules remain in close association yet have the ability to move rotationally or laterally within the plane of a membrane

Spontaneous

Lateral and rotational movement is (spontaneous/nonspontaneous)

Flippase

Enzyme which flips phospholipids from one leaflet to another using ATP

Lipid raft

A group of lipids that have a different composition from surrounding lipids and float together as a unit

Increase

Shorter phospholipid tails (increase/decrease) fluidity

Increase

Unsaturated lipid tails (increase/decrease) fluidity

Increases

At low temperatures, cholesterol (increases/decreases) fluidity

Decreases

At high temperatures, cholesterol (increases/decreases) fluidity

Glycosylation

Process of covalently attaching a carbohydrate to a lipid or protein

N linked

Glycosylation which occurs in archaea which attaches carbohydrates to asparagine

O linked

Glycosylation which occurs in the Golgi which adds sugar to oxygen on polypeptides to produce proteoglycan to organize the ECM

Membrane transport

The movement of ions and molecules across biological membranes

Selective permeability

Property of membranes that allows for the passage of certain ions or molecules but not others to maintain favorable internal environment

Passive transport

Membrane transport which does not require energy

Simple diffusion

A substance moves from high to low concentration without the help of proteins

Facilitated diffusion

Proteins help substances move from high to low concentration

Active transport

Membrane transport which requires energy

Concentration gradient

Concentration of a solute is higher on one side of a membrane that on the other

Electrochemical gradient

Combined effect of both an electrical and chemical gradient across a membrane which determines ion movement

Isotonic

Solute concentration is the same on both sides of the membrane

Hypertonic

Solute concentration is higher outside of the cells

Shrink

Cells (shrink/grow) in hypertonic solutions

Out

Water moves (in/out) of a cell in hypertonic solutions

Hypotonic

Solute concentration is higher inside cell

Grow

Cells (shrink/grow) in hypotonic solutions

In

Water moves (in/out) of a cell in hypotonic solutions

Osmosis

Facilitated diffusion of water across a membrane to balance solute concentrations

Plasmolysis

The shrinkage of algal or plant cytoplasm that occurs when water leaves the cell by osmosis, with the result that the plasma membrane no longer presses on the cell wall.

Transport proteins

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Channel protein

Transmembrane protein that forms an open passageway for facilitated diffusion; can be gated by ligands

Transporters

Transmembrane proteins that bind solutes in a hydrophilic pocket then undergo a conformational change to allow the solute to be moved across the mebrane

Uniporter

Moves a single ion/molecule in one direction at a time

Symporter

Moves 2+ ions/molecules in the same direction at once

Antiporter

Moves 2+ ions/molecules in opposite directions at once

Primary active transport

Active transport which involves pumps that use ATP/energy to transport solutes against a gradient

Secondary active transport

Active transport that transports solutes against gradients by taking advantage of a pre-existing gradient (i.e. sym or anti porter)

Sodium potassium pump

Transports three sodium ions out of the cell and two potassium ions into the cell

Electrogenic pump

Pump which generates an electrochemical gradient

Exocytosis

Material inside a cell is packaged into vesicles and excrected extracellularly

Endocytosis

Plasma membrane folds inwards to form a vesicle that brings substances into the cell

Receptor mediated endocytosis

Endocytosis which requires cargo molecules to bind to receptors for vesicles to form and transport them into the cell

Pinocytosis

Formation of membrane vesicles to internalize extracellular fluid

Phagocytosis

Formation of huge membrane vesicles that engulf large particles like bacteria (ex. macrophages)