The Cell Membrane
Purpose:
The cell membrane is a barrier that separates the cell
from the external environment and controls what enters
and leaves the cell.
Cells are semi-permeable because of selective
permeability:
This allows some but not all materials to cross the
membrane. This is purely based on the needs of the
cell. This allows the cell to maintain homeostasis
Homeostasis: The maintenance of a system to keep
internal balance, or stability of an
organism
Protein molecules embedded (stuck) in the cell
membrane help molecules cross through the cell
membrane in several ways:
Active Transport: Requires energy (ATP) to move
materials in & out of the cell.
Moves molecules against the
concentration gradient from low to high
concentration.
Passive Transport: Requires no energy to move
molecules in & out of the cell. Moves
molecules with the concentration
gradient from high to low
concentration.
Composition (what it’s made of):
Cell membranes are composed of 2 phospholipid
layers (C, H, O, P)
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Parts of a cell membrane
●Cholesterol: strengthens the cell membrane
●Channel Protein: Assists materials through the cell
membrane
●Carbohydrates: Acts as an ID tag allowing cells tell
one kind from another
●Surface protein: Helps materials through the
membrane, acts as a cellular ID &
helps with cell signaling
●Phospholipids: form most of the structure of the cell
membrane