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Chapter 7 Membrane Structure and Function - Coggle Diagram
Chapter 7 Membrane Structure and Function
Cellular Membranes are Fluid Mosaics
Differences in Membrane Lipid Composition
lipid composition of the cell membrane
appears to be adapted to environmental conditions
in many species
Organisms living in variable temperature conditions
are able to change lipid composition in response to
changing temperature
EX: winter wheat, the percentage of
unsaturated phospholipids increases in autumn to
prevent membrane solidification during winter
Membrane Proteins and Their Functions
A membrane is a collage of different proteins, often
clustered in groups, embedded in the fluid matrix of
the lipid bilayer
Two types of membrane proteins:
Integral proteins - penetrate the hydrophobic core
Peripheral proteins - are bound to the surface of the
membrane
Transmembrane proteins - integral proteins
that span the membrane
Fluidity of Membranes
Membranes rich in unsaturated fatty acids are more
fluid than those rich in saturated fatty acids
Membranes must be fluid to work properly; fluidity
affects both permeability and movement of
transport proteins
Membranes are held together mainly by weak
hydrophobic interactions
Membrane Carbohydrates in Cell-
Cell Recognition
Glycolipids - carbohydrates bonded to lipids
Glycoproteins - carbohydrates bonded to
proteins
surface molecules are bonded to chains of carbohydrates:
Membrane structure results in
selective permeability
Transport Proteins
Hydrophilic substances cross membranes more
quickly by passing through transport proteins
Channel proteins - a hydrophilic channel that
certain molecules or ions can use as a tunnel
composed of four polypeptide subunits
that each form a channel for the passage of water
3 billion water molecules pass
through per second
Hydrophobic (nonpolar) molecules dissolve in the
lipid bilayer and pass through the membrane
rapidly
Carrier proteins - bind to molecules and change
shape to shuttle them across the membrane
Membranes exhibit selective permeability; some
substances cross more easily than others
.
selective permeability of a membrane is
dependent on both the lipid bilayer and the specific
transport proteins it contains
Passive transport is diffusion of
a substance across a membrane with no energy
investment
concentration gradient - density of a
chemical substance increases or decreases
passive transport - diffusion of a substance across a biological membrane
Diffusion - movement of particles of any
substance so that they spread out evenly into the
available space
Effects of Osmosis on Water Balance
Osmosis - diffusion of free water
Free water molecules diffuse across a membrane
from the region of lower solute concentration to the
region of higher solute concentration
Water Balance of Cells Without Cell Walls
isotonic - solute concentration is
the same as that inside the cell
Tonicity - the ability of a surrounding solution to
cause a cell to gain or lose water
hypertonic - solute concentration
is greater than that inside the cell
Water Balance of Cells with Cell Walls
cells of plants, prokaryotes, fungi and some
protists have cell walls
flaccid - plant starts to wilt
turgid - healthy state for most plant cells
Facilitated Diffusion
Ion channels - facilitate the transport of ions
facilitated diffusion - transport proteins speed
the passive movement of molecules across the
plasma membrane
Active transport uses energy to
move solutes against their gradients
sodium-potassium pump energizes the transport
of K+ into the cell and Na+ out of the cell
Active transport requires energy, usually in the
form of ATP hydrolysis moves substances against
their concentration gradients
Ion Pumps Maintain Membrane Potential
electrochemical gradient - Two combined forces driven by diffusion of ions across a membrane
Membrane potential - voltage across a
membrane
A chemical force (the ion’s concentration gradient)
An electrical force (the effect of the membrane
potential on the ion’s movement)
electrogenic pump is a transport protein that
generates voltage across a membrane storing
energy that can be used for cellular work
proton pump - actively transports hydrogen ions (H+) out of
the cell
Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
EX: cells in the pancreas secrete insulin by
exocytosis
Endocytosis - macromolecules are taken into the
cell in vesicles
Exocytosis - transport vesicles migrate to the
membrane, fuse with it, and release their contents
outside the cell
three types of endocytosis
Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis
Phagocytosis - cell engulfs a particle by
extending pseudopodia around it and packing it in a
membranous sac called a food vacuole
Pinocytosis - molecules are taken up when
extracellular fluid is “gulped” into tiny vesicles
Receptor-mediated endocytosis - a vesicle
formation is triggered by solute binding to receptors