CHAPTER 4
diffusion means random molecular movement of substances molecule by molecule, either
through inter- molecular spaces in the membrane or in combination with a carrier protein.
active transport means movement of ions or other substances across the membrane in
combination with a carrier protein in such a way that the carrier protein causes the substance to
move against an energy gradient, such as from a low-concentration state to a high-
concentration state.
The rate of simple diffusion is determined by:
, – the amount of substance available,
– the velocity of kinetic motion,
– the number and sizes of openings in the membrane through which the molecules or ions
can move.
– lipid solubility of a substance is an important factor for determining how rapidly it diffuses
through the lipid bilayer
protein channels are distinguished by two important characteristics:
1. they are often selectively permeable to certain substances
2. many of the channels can be opened or closed by gates that are regulated by electrical
signals (voltage-gated channels) or chemicals that bind to the channel proteins (ligand-
gated channels).
selectivity results from specific characteristics of the channel:
– its diameter,
– shape
– the nature of the electrical charges and chemical bonds along its inside surfaces.
Potassium channel’s selectivity filter is lined with carbonyl oxygens. When hydrated
potassium ions enter the selectivity filter, they interact with the carbonyl oxygens and
shed most of their bound water molecules, permitting the dehydrated potassium ions to
pass through the channel.
sodium channel’s selectivity filter, is lined with strongly negatively charged amino acid
residues. These strong negative charges can pull small dehydrated sodium ions away from
their hydrating water molecules into these channels
Voltage gating- the molecular conformation of the gate or its chemical bonds responds to
the electrical potential across the cell membrane.
Chemical (ligand) gating- opened by the binding of a chemical substance (a ligand) with
the protein, which causes a conformational or chemical bonding change in the protein
molecule that opens or closes the gate.
Some of these GLUT proteins transport other monosaccharides that have structures similar to
that of glucose, including galactose and fructose.
One of these, glucose transporter 4 (GLUT4), is activated by insulin, which can increase the rate
of facilitated diffusion of glucose
diffusion means random molecular movement of substances molecule by molecule, either
through inter- molecular spaces in the membrane or in combination with a carrier protein.
active transport means movement of ions or other substances across the membrane in
combination with a carrier protein in such a way that the carrier protein causes the substance to
move against an energy gradient, such as from a low-concentration state to a high-
concentration state.
The rate of simple diffusion is determined by:
, – the amount of substance available,
– the velocity of kinetic motion,
– the number and sizes of openings in the membrane through which the molecules or ions
can move.
– lipid solubility of a substance is an important factor for determining how rapidly it diffuses
through the lipid bilayer
protein channels are distinguished by two important characteristics:
1. they are often selectively permeable to certain substances
2. many of the channels can be opened or closed by gates that are regulated by electrical
signals (voltage-gated channels) or chemicals that bind to the channel proteins (ligand-
gated channels).
selectivity results from specific characteristics of the channel:
– its diameter,
– shape
– the nature of the electrical charges and chemical bonds along its inside surfaces.
Potassium channel’s selectivity filter is lined with carbonyl oxygens. When hydrated
potassium ions enter the selectivity filter, they interact with the carbonyl oxygens and
shed most of their bound water molecules, permitting the dehydrated potassium ions to
pass through the channel.
sodium channel’s selectivity filter, is lined with strongly negatively charged amino acid
residues. These strong negative charges can pull small dehydrated sodium ions away from
their hydrating water molecules into these channels
Voltage gating- the molecular conformation of the gate or its chemical bonds responds to
the electrical potential across the cell membrane.
Chemical (ligand) gating- opened by the binding of a chemical substance (a ligand) with
the protein, which causes a conformational or chemical bonding change in the protein
molecule that opens or closes the gate.
Some of these GLUT proteins transport other monosaccharides that have structures similar to
that of glucose, including galactose and fructose.
One of these, glucose transporter 4 (GLUT4), is activated by insulin, which can increase the rate
of facilitated diffusion of glucose
