BIOLOGICAL MEMBRANES
(a) The roles of membranes within cells and at the surface of cells
● To include the roles of membranes as,
○ Partially permeable barriers between the cell and its environment,
between organelles and the cytoplasm and within organelles
○ Sites of chemical reactions
○ Sites of cell communication (cell signalling).
Role of cell-surface membranes
Mechanically, the cell membrane encloses and defines the boundary of the cell and is
maintains the integrity of the cell. It provides flexibility, which allows for the changing
shape of the cell to facilitate cytoplasmic streaming. Red blood cells have a shape
very specific to their function: the biconcave shape gives them a large surface area
for diffusion and its flexibility allows it to be manipulated and squeeze through the
narrow diameter of capillaries. Similarly, microvilli can be used to increase the
surface area of cells.
Defining the boundaries of the cell also means it separate the cell from the
environment forms a barrier between the inside of the cell and the environment
outside the cell. The cell membrane physically separates the intracellular components
(e.g. organelles in eukaryotic cells) from the extracellular environment, enclosing
cytoplasm and any organelles within the cell, and enabling different chemical
environments to exist on each side of the cell membrane. Providing only a selectively
permeable barrier, the cell membrane protects the cell from some harmful chemicals
in its external environment, protects the cell from loss of useful biological
macromolecules held within the cell by its plasma membrane and thus the
maintenance of solute potential.
Therefore, it controls the cell contents, and the conditions within the cell. This
happens through transport that the membrane allows, the molecules, that are small,
and needed most essentially and abundantly, can diffuse across the membrane, as
can larger molecules, facilitated by carrier and channel proteins. Molecules can be
moved against the concentration gradient through active transport, and large
molecules and liquids can also be moved across the membrane actively. This is
essential to provide the reactants for cellular processes, but they are also important
for function in other ways, such as storing energy. For example, electrochemical
gradients are needed for nerve transmission and muscle contraction.
The membrane also has a function in markers and signalling. Surface protein
markers embedded in the cell membrane identify the cell, enabling nearby cells to
communicate with each other, antigens, and glycocalyx, allow the organism’s immune
system can recognise the cell as being ‘self’ and not attack it. Cell membranes often
include membrane-bound receptor sites for interaction with specific biochemicals
such as certain hormones, neurotransmitters and immune proteins. In this way the
cell can recognize and process some signals received from the extracellular
environment. The membrane also allows cell adhesion. cells interact and attach to a
surface, substrate or another cell, mediated by interactions between molecules of the
cell surface, which can help tissue formation.
Lastly, cell-surface membranes can be sites of chemical reactions; they may
release molecules and signal to other cells and plasma membranes include as part of
(a) The roles of membranes within cells and at the surface of cells
● To include the roles of membranes as,
○ Partially permeable barriers between the cell and its environment,
between organelles and the cytoplasm and within organelles
○ Sites of chemical reactions
○ Sites of cell communication (cell signalling).
Role of cell-surface membranes
Mechanically, the cell membrane encloses and defines the boundary of the cell and is
maintains the integrity of the cell. It provides flexibility, which allows for the changing
shape of the cell to facilitate cytoplasmic streaming. Red blood cells have a shape
very specific to their function: the biconcave shape gives them a large surface area
for diffusion and its flexibility allows it to be manipulated and squeeze through the
narrow diameter of capillaries. Similarly, microvilli can be used to increase the
surface area of cells.
Defining the boundaries of the cell also means it separate the cell from the
environment forms a barrier between the inside of the cell and the environment
outside the cell. The cell membrane physically separates the intracellular components
(e.g. organelles in eukaryotic cells) from the extracellular environment, enclosing
cytoplasm and any organelles within the cell, and enabling different chemical
environments to exist on each side of the cell membrane. Providing only a selectively
permeable barrier, the cell membrane protects the cell from some harmful chemicals
in its external environment, protects the cell from loss of useful biological
macromolecules held within the cell by its plasma membrane and thus the
maintenance of solute potential.
Therefore, it controls the cell contents, and the conditions within the cell. This
happens through transport that the membrane allows, the molecules, that are small,
and needed most essentially and abundantly, can diffuse across the membrane, as
can larger molecules, facilitated by carrier and channel proteins. Molecules can be
moved against the concentration gradient through active transport, and large
molecules and liquids can also be moved across the membrane actively. This is
essential to provide the reactants for cellular processes, but they are also important
for function in other ways, such as storing energy. For example, electrochemical
gradients are needed for nerve transmission and muscle contraction.
The membrane also has a function in markers and signalling. Surface protein
markers embedded in the cell membrane identify the cell, enabling nearby cells to
communicate with each other, antigens, and glycocalyx, allow the organism’s immune
system can recognise the cell as being ‘self’ and not attack it. Cell membranes often
include membrane-bound receptor sites for interaction with specific biochemicals
such as certain hormones, neurotransmitters and immune proteins. In this way the
cell can recognize and process some signals received from the extracellular
environment. The membrane also allows cell adhesion. cells interact and attach to a
surface, substrate or another cell, mediated by interactions between molecules of the
cell surface, which can help tissue formation.
Lastly, cell-surface membranes can be sites of chemical reactions; they may
release molecules and signal to other cells and plasma membranes include as part of
