Lecture 2a: Cell Membrane Structure Flashcards
The cell membrane is ____ and allows a ____ to move
> flexible
unicellular organism
Functions of the Cell Membrane
- Acts as a boundary
Gateway to the Cell - Controls what enters and leaves cell
- Regulates chemical composition
- Maintains homeostasis
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
Proposed the Sandwich Model
Danielli & Davson
Proposed the Unit Membrane Model
Robertson
States that the cell membrane is composed of an outer layer of protein with phospholipid bilayer inside; believed all cells same composition,
Unit Membrane Model
Proposed the Fluid Mosaic Model
Singer & Nicholson
States that the cell membrane is composed of a phospholipid bilayer with proteins partially or fully imbedded
Fluid-Mosaic Model
What makes the cell membrane “Fluid”?
It has the consistency of olive oil at body temp which allows it and proteins to move freely within the layer like its liquid.
What makes the cell membrane a “Mosaic”?
Due to the proteins that forms a collage that differs on either side of membrane and from cell to cell
A harsh ionic detergent
Sodium Dodecyl Sulfate (SDS)
A gentler, non-ionic detergent
Triton X-100
Formation of sphere is ______ .
Energetically favorable
What happens to the cell membrane at low temperatures?
Hydrocarbons are tightly packed, cell membrane is in a gel phase.
What happens to the cell membrane at higher temperatures?
The bilayer “melts” which allows movement in the cell membrane
How does the phospholipids move in the cell membrane?
Lipids can move laterally and rotate 360 degrees
How does proteins move in the cell membrane?
Proteins move laterally
How does cholesterol affect the cell membrane at body temperature?
It lessens fluidity by restraining the movement of phospholipids.
How does cholesterol affect the cell membrane at colder temperatures?
It maintains fluidity by not allowing phospholipids to pack close together.
The Planar Rings of Cholesterol Make the Membrane ______ , ______ , and ______ .
(1) More Rigid
(2) Less Permeable
(3) Resistant to Low Temperature Crystalization
Performs the same function as cholesterol but in plant cell membrane
Sterols
Classifications of Membrane Proteins
(1) Peripheral Membrane Proteins
(2) Integral Membrane Proteins
(3) 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 Protein
Types of Membrane Proteins
(1) Channel Protein
(2) Carrier Protein
(3) Cell Recognition Protein
(4) Receptor Protein
(5) Enzymatic Protein
(6) Attachment Protein
(7) Intercellular Junction Protein
A channel for lipid insoluble molecules and ions to pass freely through.
Channel Proteins
Binds to a substance and carries it across
the membrane; changes
shape in the process
Carrier Protein
Binds to chemical messengers (Ex. hormones) which sends a message into the cell causing cellular reaction
Receptor Proteins
Carry out enzymatic reactions right at the membrane when a substrate binds to the active site
Enzymatic Proteins
Attach to cytoskeleton (to maintain cell shape and stabilize proteins) and/or the extracellular matrix (integrins connect to both)
Attachment Proteins
Binds cells together
Intercellular Protein
Transmembrane Proteins of opposite cells attach in a tight zipper-like fashion
Tight Junctions
Channel proteins of opposite cells join together providing channels for ions, sugars, amino acids, and other small molecules to pass.
Gap Junctions
Cytoplasmic plaques of two cells bind with the aid of intermediate filaments of keratin
Desmosomes
What provided the first evidence that the cell membrane consists of lipid bilayers?
Studies of the red blood cell plasma membrane
