Transport of Substances through Cell Membranes

PER 510 –HUMAN PHYSIOLOGY

GUYTON & HALL TEXTBOOK OF
MEDICAL PHYSIOLOGY 14TH EDITION
BY JOHN E. HALL and MICHAEL E. HALL




Special Thank You to George E. Haynes
for Preparation of Power Point Slides



Instructor: Michael Campisi CCP

Unit Two: Membrane Physiology, Nerve, and Muscle

Chapter 4: Transport of Substances through Cell Membranes




LEARNING OBJECTIVES
BY THE END OF THIS PRESENTATION, THE STUDENT SHOULD BE ABLE TO:

 Explain the structure and functions of the eukaryotic cell membrane

 Explain all the transport mechanisms that are used by the cell membrane to control the ECM and ICM
environments

 Understand the significance that these transport mechanisms play in the cell membrane potential

 Define, manipulate, and comprehend the significance of the Nernst Equation and the Goldman-Field
(GHK) equation in the overall control of cell membrane potential




 The Cell membrane or the plasma membrane
represents the boundary that separates the
ECM from the ICM. Its main function is to head is polr-hydrophilic
control the contents of the ECM and ICM
environments.

 It is best described in a “Fluid Mosaic
-
Molecules are always moving in layer
Model” where the membrane is
depicted as a Dynamic ever moving and
Recepta
changing ocean of two layers of
phospholipid (bilayer) with a mosaic of
floating and moving proteins
& -
more cholesterol = more movement




e
 it has an average diameter of 7 to 10 & ⑧ lipid raft-anchor Specific place
Proteins to Membrane
-



micrometers. in

 In some membranes, especially muscle,
as shown in the picture on the right, the
glycolipids and glycoproteins are so glucocalix = Outer Coating on Membrane
extensive that it forms a thin sugar-like
negative charged layer called the
Glycocalyx.
0- universal receiver


AB" = universal donor

transport Protein something binds conformation change Pulling
-
and
-


=

bound molecule into cell




1

,  About 20% of the membrane surface is covered with specialized regions called Lipid Rafts .

 Lipid raft as the name implies is a flat “raft-like” region  Some lipid raft regions, especially in smooth
-
keeps Proteins in one place of Membrane -

ex) digestive function ,
neuron receptors

of the membrane with a high concentration of muscle membranes, dip or collapse inward within
cholesterol and lipids called sphingolipids . the membrane to form specialized rafts called
Caveolae. caveole = Smooth Muscle allows larger surface area of cell membrane
,
 It is used to bind proteins and other substances that
trigger cell signaling reactions within the cell.  These help smooth muscle transport calcium ions
into the cell for contraction.




 Since the main function of the membrane is the control of substances within the ECM and the ICM, we should look at how this
is accomplished.
 Transport across the Membrane Active transport= Uses Air Passive = no ATP
,

1. In Vesicles: storage or transport

 ATP energy is used to alter specialized regions on the cell membrane called Coated
Pits to move large material or large amount of small of substances into a cell by the
-
Active = Pushing against gradient Passive-high to low
,
formation of a vesicle or out of the cell by dissolving back into the membrane an
existing vesicle.

 The membrane of the coated pit region reveals a complex series of various types of
proteins:
 Clathrin
 Actin
 Myosin
 Synaptotagmin (calcium binding protein)
 SNARE (specialized fusion proteins)
• AKA Soluble NSF Attachment proteins
• AKA N-ethyl- maleimide sensitive fusion proteins

 The next 2 slides show how the coated pit operates in the process of Endocytosis and in
the process of Exocytosis.




ENDOCYTOSIS
phagocytosis in
Substances bind to receptors
-
to bring into cell needs Atp
=
solids within the coated pit region. This
activates ATP and the energy
release causes conformational
change in the proteins within the
pit and the pit begins to collapse
in toward the cytosol.
-

energy used to pull in membrane


This inward collapse
continues until the
membrane is pinched off
creating a region on the
existing membrane with a
snare protein marker and
an internal vesicle within
-

Phagocytosis = solids
the cytosol with snare
protein markers and the
substances inside.
-

pinocytosis = water


-
ATP
used




↓ fusa
-
with

lysosome
-
peroxisome
-
for breakdown




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