Sequence analysis of a membrane protein shows four 20-amino acid long stretches of residues that are predominantly hydrophobic. Between each of these stretches of hydrodophobic residues, a stretch of predominantly hydrophilic residues is found. From this observation one can reasonably postulate that: A. this is a peripheral membrane protein which interacts with the membrane via hydrophobic interactions B. this protein has 4 alpha helical segments that span the membrane C. this protein can be removed from the membrane by dramatically increasing the salt concentration. D. this is a 4 stranded beta barrel which spans the membrane E. this is a glycoprotein Facilitated diffusion (passive transport) through a biological membrane is A. driven by a concentration gradient. B. generally irreversible. C. endergonic. D. driven by the ATP to ADP conversion
Structure and Composition of Cell Membrane
Despite differences in structure and function, all living cells in multicellular organisms are surrounded by a cell membrane. Just like the outer layer of the skin separates the body from its environment similarly, the cell membrane, also known as 'plasma membrane,' separates the inner content from its exterior environment.
Cell Membrane
The cell membrane is known by different names like plasma membrane or cytoplasmic membrane, or biological membrane. The term "cell membrane" was first introduced by C. Nageli and C. Cramer in the year 1855. Later on, in 1931, the term "plasmalemma" for cell membrane was given by J. Plowe. The cell membrane separates the cell's internal environment from the extracellular space. This separation allows the protection of cells from their environment.
Prokaryotes vs Eukaryotes
The cell is defined as the basic structural and functional unit of life. The cell membrane bounds it. It is capable of independent existence.
Sequence analysis of a membrane protein shows four 20-amino acid long stretches of residues that are predominantly hydrophobic. Between each of these stretches of hydrodophobic residues, a stretch of predominantly hydrophilic residues is found. From this observation one can reasonably postulate that:
| A. |
this is a peripheral membrane protein which interacts with the membrane via hydrophobic interactions |
|
| B. |
this protein has 4 alpha helical segments that span the membrane |
|
| C. |
this protein can be removed from the membrane by dramatically increasing the salt concentration. |
|
| D. |
this is a 4 stranded beta barrel which spans the membrane |
|
| E. |
this is a glycoprotein |
Facilitated diffusion (passive transport) through a biological membrane is
| A. |
driven by a concentration gradient. |
|
| B. |
generally irreversible.
|
|
| C. |
endergonic. |
|
| D. |
driven by the ATP to ADP conversion |
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