BIO 311C Chapter Notes - Chapter 7: Integral Membrane Protein, Peripheral Membrane Protein, Active Transport
Vocabulary:
● fluid mosaic model of membrane structure – a model that describes the phospholipid
bilayer as fluid and proposes that integral membrane proteins float freely in the lipid
bilayer
● endocytosis – process by which vesicles are internalized from the plasma membrane;
often used to absorb or ingest molecular contents into the cell
● integral membrane protein – protein that is permanently embedded in the cell membrane
● transmembrane protein – integral membrane protein that spans the entire width of a cell
membrane
● osmosis – diffusion of water across a selectively permeable membrane due to solute
differences on either side of the membrane
● isotonic solutions – solutions separated by a membrane and containing an equal
concentration of non-permeating solutes
● hypotonic solution – solution with a lower concentration of non-permeating solutes than
that of the solution on the other side of a membrane
● hypertonic solution – solution with a higher concentration of non-permeating solutes than
that of the solution on the other side of a membrane
● facilitated diffusion (passive transport) – movement of molecules across a membrane via
transport proteins without energy from ATP hydrolysis
● active transport – movement of molecules across a membrane, typically against a
concentration gradient, by transport proteins that require energy from ATP hydrolysis;
this energy requirement can be direct (primary active transport) or indirect (secondary
active transport)
● electrochemical gradient – combined electrical and chemical (diffusion) forces acting on
an ion between two sides of a cell membrane
● membrane potential – electrical potential or voltage between the two sides of the plasma
membrane
● aquaporin – transport protein for the facilitated diffusion of water through a cell
membrane
● ion channel – transport protein for the facilitated diffusion of ion(s) through a cell
membrane
● ion pump – protein that moves ion(s) through a cell membrane by primary active
transport
● cotransporter – protein that moves two or more molecules through a cell membrane by
secondary active transport
7.1 Cellular membranes are fluid mosaics of lipids and proteins
● In the fluid mosaic model, amphipathic proteins are embedded in the phospholipid
bilayer. Proteins with related functions often cluster in patches.
● Phospholipids and some proteins move laterally within the membrane. The unsaturated
hydrocarbon tails of some phospholipids keep membranes fluid at lower temperatures,
while cholesterol helps membranes resist changes in fluidity caused by temperature
changes. Differences in membrane lipid composition, as well as the ability to change
lipid composition, are evolutionary adaptations that ensure membrane fluidity.
● Integral proteins are embedded into the phospholipid bilayer; peripheral proteins are
attached to the membrane surface. The functions of membrane proteins include
transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular
joining, and attachment to the cytoskeleton and ECM. Short chains of sugars linked to
proteins (in glycoproteins) and lipids (in glycolipids) on the exterior side of the plasma
membrane interact with surface molecules of other cells.
● Membrane proteins and lipids are synthesized in the ER and modified in the ER and
Golgi apparatus, the inside and outside faces of membranes differ in molecular
composition.
-Function: The plasma membrane not only defines the borders of the cell, but also allows the
cell to interact with its environment in a controlled way. Cells must be able to exclude, take in,
and excrete various substances, all in specific amounts. In addition, they must able to
communicate with other cells, identifying themselves and sharing information.
-According to the fluid mosaic model, the plasma membrane is a mosaic of
components—primarily, phospholipids, cholesterol, and proteins—that move freely and fluidly in
the plane of the membrane. In other words, a diagram of the membrane is just a snapshot of a
dynamic process in which phospholipids and proteins are continually sliding past one another.
-The principal components of the plasma membrane are lipids (phospholipids and cholesterol),
proteins, and carbohydrate groups that are attached to some of the lipids and proteins.
Phospholipids:
-Phospholipids, arranged in a bilayer, make up the basic fabric of the plasma membrane.
They are well-suited for this role because they are amphipathic, meaning that they have
both hydrophilic and hydrophobic regions.
Protein:
-Proteins are the second major component of plasma membranes. There are two main
categories of membrane proteins: integral and peripheral.
-Integral membrane proteins are, as their name suggests, integrated into the membrane:
they have at least one hydrophobic region that anchors them to the hydrophobic core of
the phospholipid bilayer. Some stick only partway into the membrane, while others
stretch from one side of the membrane to the other and are exposed on either side.
Proteins that extend all the way across the membrane are called transmembrane
proteins.
-Peripheral membrane proteins are found on the outside and inside surfaces of
membranes, attached either to integral proteins or to phospholipids. Unlike integral
membrane proteins, peripheral membrane proteins do not stick into the hydrophobic
core of the membrane, and they tend to be more loosely attached.
Carbohydrates:
-Carbohydrates are the third major component of plasma membranes. In general, they
are found on the outside surface of cells and are bound either to proteins (forming
glycoproteins) or to lipids (forming glycolipids).
-Along with membrane proteins, these carbohydrates form distinctive cellular markers,
sort of like molecular ID badges, that allow cells to recognize each other. These markers
are very important in the immune system, allowing immune cells to differentiate between
body cells, which they shouldn’t attack, and foreign cells or tissues, which they should.
Main function: protection/ ability to maintain interior that is different from exterior
Permeable because protection is great but isolation is not
All cells require exchange of materials with the exterior environment
Move freely - non polar (hydrocarbon, co2, o2)
Polar move slowly
Water and glucose
Document Summary
Fluid mosaic model of membrane structure a model that describes the phospholipid bilayer as fluid and proposes that integral membrane proteins float freely in the lipid bilayer. Endocytosis process by which vesicles are internalized from the plasma membrane; often used to absorb or ingest molecular contents into the cell. Integral membrane protein protein that is permanently embedded in the cell membrane. Transmembrane protein integral membrane protein that spans the entire width of a cell membrane. Osmosis diffusion of water across a selectively permeable membrane due to solute differences on either side of the membrane. Isotonic solutions solutions separated by a membrane and containing an equal concentration of non-permeating solutes. Hypotonic solution solution with a lower concentration of non-permeating solutes than that of the solution on the other side of a membrane. Hypertonic solution solution with a higher concentration of non-permeating solutes than that of the solution on the other side of a membrane.
