Chapter 4 Flashcards
What do cells and organelles need to separate internal and external contents?
Barrier
What are the qualities the barrier must have:
Impermeable to most molecules and ions (semi-permeable)
Ability to exchange specific molecules/ions between compartments
Insoluble in water
Permeable to water
What is the cellular membrane?
· A permeability barrier that consists of:
· Phospholipids (fabric of membrane), glycolipids
▪ Sterols (except in bacteria):
- Cholesterol (animals)
- Ergosterols (fungi)
- Phytosterols - no cholesterol (plants)
- Membrane protein
What are membrane proteins?
Integral and peripheral membrane porteins
What are Integral proteins?
transmembrane, embedded in the membrane
What are Peripheral membrane proteins
not embedded in the membrane
Are membranes rigid?
No
What do membranes consist of?
Fluid lipid bilayer in which proteins are embedded and float freely (they can move around)
What is the membrane structure according to the fluid mosaic model?
The model proposes that integral proteins are suspended individually in a fluid lipid bilayer. Peripheral proteins are attached to integral proteins or membrane lipids mostly on the cytoplasmic side of the membrane (shown only on the inner surface in the figure). Carbohydrate groups of membrane glycoproteins and glycolipids face the cell exterior.
What is the Fluid Mosaic Model supported by and what does it demonstrate?
Fluid Mosaic Model is Supported by Experimental Evidence: Membranes are Fluid
Experimental Research: The Frye–Edidin experiment demonstrates that the phospholipid bilayer is fluid
What is involved in cell chemistry review?
· Properties of water
- Water as a solvent
- Polarity
· What does Hydrophilic mean?
· What does Hydrophobic mean?
Are water molecules polar?
Yes
What is polarity?
Polarity is an uneven distribution of charge
Electronegative oxygen atom associates with electropositive hydrogen atoms of adjacent water molecules to form hydrogen bonds
Polar/charged molecules form hydrogen/ionic bonds with water molecules
What is a solvent?
a fluid in which another substance, called a solute, can be dissolved
Is water an excellent solvent?
Yes
Polar/charged molecules form hydrogen/ionic bonds with water molecules
What does hydrophilic mean?
(“water-loving”): sugars, DNA, RNA, organic acids, and some of the amino acids
What does hydrophobic mean?
(“water-fearing”): Do not dissolve in water, lipids (hydrocarbons), or some amino acids (e.g. those in integral membrane proteins that associate with lipids)
· No polar regions
· Do not interact electrostatically with water
· Disrupt hydrogen-bonded structure of water
· Tend to coalesce with each other in the water
· Water molecules tend to exclude molecules that disrupt hydrogen bonding
· Hydrophobic interactions are a major driving force in the folding of molecules (like proteins), assembly of cellular structures and membrane organization.
What does amphipathic mean and are phospholipids amphipathic
having both hydrophilic and hydrophobic parts.
Yes
What happens to phospholipids in aqueous solutions?
In an aqueous environment, phospholipids self-assemble into micelles, liposomes, or bilayers (the hydrophobic effect)
What happens to phospholipids in aqueous solutions?
In an aqueous environment, phospholipids self-assemble into micelles, liposomes, or bilayers (the hydrophobic effect)
Phospholipid structure
(a) Chemical formula of phosphatidylcholine. The polar head group consists of glycerol (shown in pink) linked to the organic molecule choline (shown in blue) by a phosphate group (shown in yellow). In addition, glycerol is linked to two fatty acids, each 18 carbons long. The structure of phospholipids is also often represented as space-filling models (b) and as an icon (c). As shown in the space-filling model, the presence of a carbon-carbon double bond (denoted by the arrow in (a)) imparts a bend to one of the fatty acids.
Why is the fluidity of a membrane important?
for its function
- Fluidity is dependent on how densely individual lipid molecules can pack together
What are the two major factors that influence fluidity?
- Composition of lipid molecules
- Degree of unsaturation of fatty acid tails
- Presence of sterols
2. Temperature
What do the lipid molecule compositions affect?
how closely the molecules interact. Lipid molecules that contain saturated hydrocarbon tails are closely packed (a), whereas unsaturated hydrocarbon tails have kinks that prevent lipid molecules from packing closely together (b).