Lecture 11 Plasma Membrane Flashcards
Why are membranes important?
They allow cells to compartmentalize and control their chemical environment making it conducive for life
How do membranes “work”? (based on what principle/s)
Cellular chemistry/biochemistry occurs in water, so by making membranes primarily out of lipids it separates aqueous environments as it is energetically unfavorable for water soluble/fat insoluble molecules to cross lipid membranes
What is an amphipathic molecule?
A molecule that is both water and lipid soluble. Membrane lipids are typically amphipathic with both hydrocarbon fatty acids, which are lipid soluble, and one or more charged groups, which are water soluble.
What does hydrophobic mean?
Same as lipophilic. Hates water, loves lipids.
What does hydrophilic mean?
Same as lipophobic. Water loving, lipid hating.
An amphipathic molecule has:
1) Hydrophobic/Hydrophilic region
2) Lipophobic/Lipophilic region
3) Hydrophobic/Lipophobic region
4) Hydrophilic/Lipophilic region
Glycolipids are mainly found in the extracellular face of cell/plasma membranes: T or F?
True
Water is a polar molecule so why can it cross biological membranes?
Because it is very small
Can you predict what can and cannot cross a cell membrane?
Only relatively small, hydrophobic molecules (ethanol) plus the polar, universal solvent water: certainly nothing charged (ions) or larger polar molecules (glucose).
How do you overcome membrane impermeability?
There are 2 mechanisms; one is utilizing transport proteins while the other involves fusing with membranous vesicles (endocytosis for exporting and endocytosis for importing).
All cells are surrounded by a _______ _______ with ________ __________
Plasma membrane, selective permeability
The selective permeability of a membrane allows a regulated _______ where the chemistry necessary for life can occur.
environment
All ____ ______ are bounded by membranes: compartmentalization.
intracellular organelles
Our cellular chemistry/biochemistry occurs in ______ phase/solution.
aqueous
Fats are typically _______ formed from glycerol with 2 or 3* fatty acids (hydrocarbon “tails”).
Triglycerides
These are principally for fuel storage.
Triglycerides
Membrane lipids typically contain a hydrophilic group in the ____ position*
third
Different hydrophilic groups in the membrane lipids confer different properties to the membrane. List some examples.
Phosphatidylcholine (a phospholipid), a modified sugar (glycolipid), and many variations.
The hydrophilic group substitution in the membrane lipids makes these lipids _____ with a hydrophobic part that will avoid a water and a hydrophillic part that will interact with water.
amphipathic
Amphipathic membrane lipids will naturally form a bilayer with hydrophilic parts, these lipids arranged externally to interact with water while the hydrophobic parts self-associate to form the true barrier away from water; this is _______ favorable.
energetically
The membrane presents a barrier to water-soluble ____ and most molecules bigger than ~7.5 to 10nm diameter.
ions
________ is a major membrane component which inserts in between the hydrocarbon “tails” stabilizing and affecting membrane permeability.
cholesterol
Cell membranes are typically ___% protein by weight, (very large/high molecular weight molecules that confer specific functions), ___% phospholipids, (relatively small/low molecular weight molecules: ~ x1/50 that of proteins), ___% cholesterol, ___% other lipids and __% carbohydrate, (combined with lipids as glycolipids or proteins as glycoproteins)
55% Protein 25% Phospholipids 13% Cholesterol 4% other lipids 3% Carbohydrate
The CARBOHYDRATE portions of GLYCOLIPIDS and GLYCOPROTEINS are invariably on the EXTERNAL cell surface where they are important in forming a protective “coat” against ______ and _______ ________.
mechanical; chemical damage
The “coat” is also involved in _____-_____ recognition and _______.
Cell to cell; adhesion
Membranes are synthesized primary in the ______ _______
endoplasmic reticulum
During synthesis of the membrane in the ___, new lipids are added to the _____ face of the bilayer.
ER; cytosolic
_______ move half of lipids to the non-cytosolic face so both sides of the membrane are expanded equally.
flippases
T or F: Membrane polarity is altered during synthesis.
False; polarity is maintained
T or F: The inner and outer membrane of the cell are symmetrical.
False; different proteins and lipids forming the bilayer makes them asymmetrical
Membrane protein function is often dependent on the surrounding ______ _______.
Lipid environment
The cell membrane is ___ and allows for ____ movement of embedded molecules/proteins necessary for cellular function.
fluid; lateral movement
A flexible membrane also allows for ____, _______ _____, _________ and various forms of endo- and exocytosis: this is also vital for cell function.
growth, cell division, movement
Fluidity of the membrane depends on lipid _______.
Composition
T or F: the longer the hydrocarbon “tails” the more fluid the membrane.
False, the less fluid it is
Unsaturated fatty acids (double bonds) makes the membrane more or less fluid?
More; (the unsaturated “leg” makes it less packed together than the straight, tighter hydrocarbon “tails”)
Planar cholesterol molecules can interlock with the hydrocarbon “tails” and affect the ______ of membrane.
fluidity
Bacteria and yeasts adjust the lipid composition of their membranes to maintain appropriate ________ especially to overcome temperature changes
fluidity
Some membrane proteins must be ______ to certain regions of the cell membrane.
localized
Some membrane protein are grouped together with other proteins for their function, this is achieved by a network of structural proteins. (such as _____)
Spectrin
The network of structural proteins is necessary for mechanical support of the thin, delicate membrane and helps determine cell shape; this is called the ____ _____
Cell cortex
What could cause the cell cortex to have an inappropriate or flattened shape?
Genetic abnormalities in spectrin structure
T or F; the cortex is linked to the cytoskeleton.
true
Can cells “rearrange” their membranes?
Yes, in cells that move. (actin cytoskeleton)*
Membrane protein position can also be determined by links to _____ ______.
extracellular structures
Membrane protein movement is limited by _____ ______ where adjacent cell membranes are actually fused providing a physical barrier.
tight junctions
T of F; membrane proteins are beneficial vital functions necessary for life.
true
_____ ______ (integral proteins), cross the lipid bilayer typically either as single or multiple alpha-helices composed of approximately 20 amino acid residues with hydrophobic side chains (R-groups: alanine, valine, etc.) arranged peripherally allowing integration with membrane lipids.
Transmembrane protein
T or F: There are single alpha helix, multiple alpha helix, and rolled up beta sheet types of transmembrane protein.
true
Many transmembrane proteins are receptors allowing chemical signals that cannot enter the cell to be recognized and produce an effect inside the cell: this is ___ ____
signal transduction
T or F; Many transmembrane proteins have recognizable amino acid sequences that can indicate their function:
True
Give 4 examples of how proteins can associate with membranes.
- Transmembrane
- Monolayer associated
- Lipid Linked
- Protein attached
Many receptors have 12 transmembrane domains, while many sugar transporters for example have 7 transmembrane domains. T or F?
False, reversed, 7;12
Can some membrane protein be involved in cell communication, cell to cell adhesion and regulation of growth.
Yes
Disruption of cell communication, cell to cell adhesion and regulation of growth can cause _______
cancer
