LESSON 2a: CELL MEMBRANE STRUCTURE Flashcards
-Gateway of the cell
-Acts as boundary
-Controls what enters and exits the cell
-regulate chemical composition
-Maintains homeostasis
Cell Membrane
The cell membrane
is _______ and
allows a
unicellular
organism to
move
flexible
Studies of the_______________ provided the first evidence that biological membranes consist of lipid bilayers
red blood cell plasma
membrane
Plasma Membrane models
- Sandwich Model
- Unit Membrane Model
- Fluid-Mosaic Model
-2 layers of globular proteins with phospholipid inside to make a layer
and then join 2 layers together to make a channel for molecules to pass
Sandwich Model
Proponent of Sandwich Model
Danielli and Davson
-Outer layer of protein with phospholipid bilayer inside,
-believed all cells same composition,
-does not explain how some molecules pass through or the use of
proteins with nonpolar parts
-used transmission electron microscopy
Unit Membrane Model
Proponent of Unit Membrane Model
Robertson
Phospholipid bilayer with proteins partially or fully imbedded, electron
micrographs of freeze-fractured membrane
Fluid Mosaic Model
Proponent of Fluid Mosaic Model
Singer and Nicolson
How did they examine the plasma membrane under SEM?
1) Rapidly freeze specimen
2) Use special knife to cut membrane in half
3) Apply a carbon + platinum coating to the surface
4) Use scanning electron microscope to see the surface
According to the electron micrograph which membrane model is
correct?
Fluid-Mosaic Model
The lipids in a membrane are organized into a _____________
liquid crystalline lattice.
The lattice becomes a _____________ at
the transition temperature
frozen crystalline gel
The Plasma Membrane is composed of two layers of lipids. Why is this important?
This allows the membrane to repel too much water around it to prevent the cell to burst.
-plasma membrane has consistency of olive oil at body temperature,
due to unsaturated phospholipids.
-phospholipids and proteins move around freely within the layer, like it’s a
liquid
Fluid
plasma membrane has consistency of olive oil at body temperature,
due to ______________
unsaturated phospholipids
– proteins form a collage that differs on either side of membrane
and from cell to cell (greater than 50 types of proteins)
-proteins span the membrane with hydrophilic portions facing out and
hydrophobic portions facing in.
-mosaic pattern produced by scattered protein molecules when membrane
is viewed from above.
Mosaic
Hydrocarbons are tightly packed
Gel phase- Low temperature
Bilayer “Melts”, movement is allowed
Higher temperature-moves to fluid state
Formation of sphere is _____________
energetically favorable
a harsh ionic detergent
SDS
a gentler non-ionic detergent, are
commonly used solubilizing agents
Triton X-100
A Scheme to Study a
Membrane Protein
-Solubilization,
-Purification, and
-Reconstitution in Liposomes
Membrane Proteins Can Be
Solubilized by _________ That
Disrupt the Membrane
Detergents
*Most of the lipids and some proteins drift _________ on either
side.
laterally
Phospholipids _________ switch from one layer to the next.
do not
The lipids and proteins in the cell membrane are not fixed in position but _________ moving
constantly
The ________ move laterally within the cell membrane –lateral diffusion
proteins
While the ______ can move both laterally and rotate 360 degrees – flip-flop diffusion
lipids
Cholesterol Affects fluidity: At Body Temp
- it lessens fluidity by restraining the movement of phospholipids;
-also reduce permeability to small mol
Cholesterol Affects fluidity: colder temp
maintains fluidity by not allowing
phospholipids to pack close together.
The Planar Rings of Cholesterol Make
the Membrane More _____, ___________, and ___________
-Rigid
-Less Permeable
-Resistant to Low Temperature Crystalization
Major component of animal cell
Cholesterol
Cholesterol is not found in _________, how ever it has ______ that perform the same function.
-Plant Membrane
-Sterols
Cholesterol has same molar amounts as _____________
Phospholipids
Heat produces motion of acyl side chains this resulted to change from solid to ___________ transition.
Fluid
By change in solid to fluid state, ________ in the plane bilayer is made possible
Lateral Diffusion
Classification of Membrane Proteins
-Peripheral Proteins
-Integral Proteins
-Transmembrane Proteins
are proteins that dissociate
from the membrane following
treatments with polar
reagents that do not disrupt
the phospholipid bilayer.
Peripheral membrane proteins
can be released only by
treatments that disrupt the
phospholipid bilayer.
Integral membrane proteins
span the lipid bilayer with
portions exposed on both
sides of the membrane
Transmembrane proteins
Types of Membrane Proteins
- Transport Proteins (Channel and Carrier)
- Cell Recognition Protein
- Receptor Protein
- Enzymatic Protein
- Intercellular Junction Proteins
- Attachment Proteins
-channel for lipid
insoluble molecules
and ions to pass freely
through
Channel Protein
An inherited disorder that is caused by faulty Cl- channel creating a collection of thick mucus in the airways and in pancreatic and liver ducts
Cystic Fibrosis
– bind
to a substance and
carry it across
membrane, change
shape in process
Carrier Proteins
The inability of some persons to use energy for ___________ has been suggested as the cause of their obesity.
Sodium-Potassium Transport
Bind to chemical
messengers (Ex.
hormones) which
sends a message into
the cell causing
cellular reaction
Receptor Proteins
Some types of _____ result not because the body does not produce enough growth hormone but because the plasma membrane growth hormone receptor is faulty.
Dwarfism
Carry out enzymatic
reactions right at the
membrane when a
substrate binds to the
active site
Enzymatic Proteins
____________ releases toxin that interferes with the proper functioning of adenylate cyclase which is involved in ATP metabolism resulting to severe diarrhea.
Cholera Bacteria
Glycoproteins (and
glycolipids) on
extracellular surface
serve as ID tags
(which species, type of
cell, individual).
Carbohydrates are
short branched chains
of less than 15 sugars
Cell Recognition Proteins
The ______________ are different for each person, so organ transplant are difficult to achieve. When this is introduced and considered foreign the WBC (responsible for immunity) attacked it .
MHC (Major Histocompatibility Complex) Glycoproteins
Attach to cytoskeleton (to
maintain cell shape and stabilize
proteins) and/or the extracellular
matrix (integrins connect to
both)
Attachment Proteins
– protein fibers and carbohydrates
secreted by cells and fills the
spaces between cells and
supports cells in a tissue.
-can influence activity inside the cell
and coordinate the behavior of
all the cells in a tissue
Extracellular Matrix
Bind cells together
Intercellular Junction Proteins
Types of Cell Junctions
- Tight Junctions
- Desmosomes
- Gap Junctions
- Transmembrane Proteins of opposite cells attach in a tight zipper-like
fashion - No intercellular space, No leakage Ex. Intestine, Kidneys, Epithelium of skin
-bar the movement of dissolved materials from the lumen through space between epithelial cells.
Tight Junctions
Long rows of tight junction protein form a ___________.
Complex meshwork
- Cytoplasmic plaques of two cells bind with the aid of
intermediate filaments of keratin - Allows for stretching
- Ex. Stomach, Bladder, Heart
Desmosomes
- Channel proteins of opposite cells join together providing
channels for ions, sugars, amino acids, and other small
molecules to pass. - Allows communication between cells.
- Ex. Heart muscle, animal embryos
Gap Junctions
Example of Mobility of Membrane Proteins
- The fusion of human cell and animal cell.
- After 40 minutes of incubation, the human and mouse protein spread out forming uniform distribution and no separation.
Many Membrane Proteins
Move _____ in the Plane
of the Membrane
Freely
________ membrane proteins
have this freedom of
motion
Not all
Can Establish
the Rate of Membrane Component Movement
Fluorescence Recovery After Photobleaching (FRAP)
