2. Functions of membranes Figure 7-2
Define the boundaries of the cell and its
organelles and act as permeability barrier.
They serve as sites for specific
biochemical functions such as electron
transport during mitochondrial respiration.
Provide for and regulate transport
processes.
2
Cell Biology, lecture 6
3. Functions of membranes Figure 7-2
Cell Biology, lecture 6 3
Contain protein receptors needed to
detect external signals.
Provide mechanisms for cell-cell
contact, adhesion and communication.
5. Functions of membranes; boundaries
and permeability
membrane defines outermost part of living cell
a) Separates physically cell from environment
b) Permeability barrier
c) w/o membranes, important stuff drifts away
d) Must maintain appropriate concentrations of
molecules in smaller volumes
5
Cell Biology, lecture 6
6. e) Compartmentalize functions, Isolate
incompatible reactions
eg: lysosomes contain hydrolytic enzymes not
compatible with other macromolecules
6
Cell Biology, lecture 6
membrane defines outermost part
of living cell
Some proteins in membranes act as
enzymes???? Examples
7. Membranes are sites of specific
functions
eg: reactions of oxidative e-transport and
phosphorylation found only
7
reactions of
photosynthetic
electron transport and
photophosphorylation
found only in the
thylakoid membranes
of chloroplast
Cell Biology, lecture 6
8. Plasma membrane interacts with other cells .
Cells must recognize other cells : immune
response to foreign cells.
receives communications from other cells
chemical communications = hormones
electrical communications = nerve impulse
mechanical communications = adhesion
cells transmit communication
role in cell communication and recognition
Cell Biology, lecture 6 8
9. 9
Gap junctions (also called communicating junctions) provide
cytoplasmic channels from one cell to an adjacent cell. Gap junctions
consist of special membrane proteins that surround a pore through
which ions, sugars, amino acids, and other small molecules may
pass. Gap junctions are necessary for communication between cells
in many types of tissues, including heart muscle and animal
embryos. Cell Biology, lecture 6
10. At tight junctions, the membranes of neighboring cells are very tightly
pressed against each other, bound together by specific proteins.
Forming continuous seals around the cells, tight junctions prevent
leakage of extracellular fluid across a layer of epithelial cells.
Cell Biology, lecture 6 10
11. Cell Biology, lecture 6 11
Desmosomes (also called anchoring junctions) function like
rivets, fastening cells Together into strong sheets. Intermediate
Filaments made of sturdy keratin proteins Anchor desmosomes
in the cytoplasm.
