Exam 2 Chapter 5 Flashcards
Biological membranes consist of ___ and ___ in a thin film
lipids, proteins
What are the two major types of lipids in cell membranes?
Phospholipids and sterols (in animal cell membranes, cholesterol)
Does the proportion of lipids and proteins vary or stay the same across the cell and across different cells?
Varies across the cell and across different cells
What are four of the main polar groups attached to the phosphate group in phospholipids?
Either an alcohol or an amino acid
- Phosphatidyl choline
- Phosphatidyl serine
- Phosphatidyl ethanolamine
- Phosphatidyl inositol
Describe the structure of phospholipids
Phosphate group linked to a polar amino acid or alcohol and a glycerol on the other side; the glycerol is attached to two fatty acid nonpolar tails that are hydrophobic
How are the hydrophobic tails of phospholipids attracted to other nonpolar molecules?
Via Van Der Waals forces
Phospholipids are _____ molecules
Amphiphilic
What structure is spontaneously formed by the phospholipid molecules?
A bilayer
Describe the characteristics of a fluid and frozen bilayer
Fluid:
- Individual molecules are free to flex, rotate, and exchange places
Frozen:
- Molecules remain fixed in place
Which end faces the aqueous solution in a bilayer?
The polar phosphate heads
What happens when a phospholipid bilayer sheet is shaken in water?
Vesicles are spontaneously formed
Phospholipids are ____ molecules
amphiphilic (both hydrophobic and hydrophilic properties)
True or false: membrane sterols have dual solubility properties
True; sterols have an outward facing polar OH group that extends into the aqueous surface, and the four carbon rings and nonpolar chain that face inwards are nonpolar
What sterols are found in plants?
Phytosterols
True or false: the similarity of membrane structure in eukaryotes and prokaryotes tells us that basic membrane structure evolved during the earliest stages of life on earth
True
What role does cholesterol play in animal cell membranes?
Helps in membrane fluidity
True or false: plants produce cholesterol
False
True or false: membrane proteins have hydrophobic and hydrophilic regions, so also display amphiphilic properties
True
Describe the fluid mosaic model
The membrane consists of a fluid phospholipid bilayer in which proteins are embedded and float freely. The molecules are fluid in that they freely exchange places with one another within a sheet. “Mosaic” refers to the fact that membrane proteins float freely in the membrane/lipid bilayer.
How are the hydrophobic sections of membrane proteins formed?
Segments of polypeptide chains are enriched in amino acids with nonpolar R groups. These segments are often coiled into alpha helices with loops of hydrophilic amino acids that face the aqueous exteriors.
How do secondary structures contribute to membrane proteins?
Alpha helices may form a hydrophobic channel with a hydrophilic loop through the center. Beta sheets may ‘weave’ together.
Where are integral proteins found?
Embedded in phospholipid bilayer
Where are peripheral proteins found?
Held to membrane surfaces by noncovalent bonds
Describe structure and function of bacteriorhodopsin
Bacteriorhodopsin absorbs light for energy in photosynthetic archeans.