Chapter 6: Membrane Flashcards
The Na+/K+ ATPase pumps Na+ from the cell into the lumen of the intestine. T/F
False.
The Na+/K+ ATPase pump does not pump sodium ions from the cell into the lumen of the intestine. Its primary function is to transport sodium ions out of the cell.
The K+ channel is gated closed to Na+ and only opens when its “senses” K+. T/F
False
K+ channels are selective for potassium ions (K+), but they are not completely closed to sodium ions (Na+). While K+ channels do preferentially allow the passage of K+ ions, they can also allow the passage of Na+ ions to some extent, although at a lower rate compared to K+ ions.
So, in summary, the statement is false. While K+ channels preferentially allow the transport of K+ ions, they are not completely closed to Na+ ions and can permit the passage of Na+ ions to a limited extent.
K+ ions have a smaller hydration shell than Na+ ions, allowing the passage of hydrated K+, but not Na+, through the selectivity filter of the K+ channel. T/F
False
K+ ions and Na+ ions have different characteristics when it comes to their hydration shells. Na+ ions are smaller in size compared to K+ ions, and they have a stronger affinity for water molecules. As a result, Na+ ions have a smaller and more tightly bound hydration shell, while K+ ions have a larger and less tightly bound hydration shell.
The action of the Na+/K+ ATPase pumps maintains am excess of Na+ ions outside the cells and an excess of K+ ions inside the cell. The K+ ion channels are unidirectional and only allow the transport of ion out of the cell. T/F
True
The Na+/K+ ATPase pumps do maintain an excess of Na+ ions outside the cells and an excess of K+ ions inside the cell. This is accomplished by actively pumping three Na+ ions out of the cell for every two K+ ions brought into the cell.
Regarding K+ ion channels, they are primarily responsible for the movement of K+ ions out of the cell, which makes the statement “K+ ion channels are unidirectional and only allow the transport of ions out of the cell” true.
To summarize:
True: The Na+/K+ ATPase pumps maintain an excess of Na+ ions outside the cells and an excess of K+ ions inside the cell.
True: K+ ion channels are unidirectional and primarily allow the transport of ions out of the cell.
The permease (transporter) allows glucose and Na+ into the cell requires ATP. T/F
False
- Permeases or transporters involved in the facilitated diffusion of glucose and the passive movement of Na+ ions do not require ATP.
- ATP is utilized in active transport processes, such as the Na+/K+ ATPase pump, which actively transports ions against their concentration gradients.
Glucose and Na+ are transported across the cell membrane through specific transporter proteins known as glucose transporters (GLUTs) and sodium-glucose co-transporters (SGLTs), respectively. These transporters utilize the concentration gradient of glucose and Na+ to facilitate their movement into the cell, and they do not directly require ATP for their function.
The permease (transporter) pumps glucose from the cell into the blood requires ATP. T/F
False.
The statement is incorrect. The permease (transporter) responsible for glucose transport does not pump glucose from the cell into the blood, and it also does not require ATP. Glucose transporters (GLUTs) are responsible for facilitating the movement of glucose across the cell membrane. These transporters use facilitated diffusion, meaning they allow glucose to passively move down its concentration gradient without the need for ATP. In the case of glucose transport, GLUTs primarily function to transport glucose into the cell from the blood, not the other way around.
The Na+/K+ ATPase pumps Na+ from the cell into the blood, maintaining low Na+ levels in the cell. T/F
True.
The Na+/K+ ATPase, also known as the sodium-potassium pump, is responsible for pumping sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. This process requires ATP (adenosine triphosphate) to actively transport the ions against their concentration gradients. By pumping Na+ out of the cell, the Na+/K+ ATPase helps to maintain low Na+ levels inside the cell, which is essential for various cellular processes and maintaining cell volume.
What types of transport would increase at a linear rate (no saturation) proportional to the concentration gradient?
The types of transport that would increase at a linear rate (no saturation) proportional to the concentration gradient are simple diffusion and facilitated diffusion.
In simple diffusion, molecules move from an area of high concentration to an area of low concentration, driven solely by the concentration gradient. The rate of diffusion is directly proportional to the concentration gradient, and it increases linearly as the gradient becomes steeper.
Passive transport (at least until the gradient is destroyed). Note: Active transport cannot, and any receptor mediated transport essentially would become saturated (reach a maximum transport level.
Co-transport of nutrients across the intestinal cell membranes is an active process that can move glucose against a concentration gradient. What is the energy requiring step for co-transport?
Co-transport of glucose across intestinal cell membranes is an active process that moves glucose against its concentration gradient. The energy-requiring step in co-transport involves the movement of sodium ions. The sodium-potassium pump actively pumps sodium ions out of the cell, creating a high concentration of sodium outside and a low concentration inside the cell. The sodium-glucose co-transporter (SGLT) uses the energy from this sodium concentration gradient to transport glucose into the cell against its concentration gradient. This process allows for the absorption of glucose from the intestinal lumen into the body.
Potassium ion (K+) channels are very selective for K+, although the ion sodium (Na+) has the same charge as K+ and is even smaller. What feature of the K+ ion channel explains this selectivity?
The selectivity of potassium ion (K+) channels for K+ over sodium (Na+) ions is due to a feature called the selectivity filter. This filter is a narrow region in the channel that interacts with ions. The selectivity filter of K+ channels is designed to accommodate and stabilize K+ ions but not Na+ ions effectively. It has the right size and shape to fit K+ ions, while excluding smaller Na+ ions. This size and charge selectivity in the selectivity filter allow K+ ions to pass through the channel while restricting the movement of Na+ ions. This selective flow of K+ ions contributes to important cellular processes and the establishment of the membrane potential.
K+ channels have a selectivity filter that is specifically designed to accommodate the larger K+ ions while excluding smaller Na+ ions. The selectivity filter consists of carbonyl oxygen atoms that interact favorably with the K+ ions, forming stable interactions. The size of the selectivity filter is critical in determining the selectivity of K+ channels.
While it is true that dehydrated Na+ ions are smaller than hydrated Na+ ions, and dehydration of ions generally requires energy, the selectivity of K+ channels is primarily determined by the size and fit of the ions within the selectivity filter, rather than the energetic favorability of dehydration.
Membrane proteins called _________ channels open to allow ions to flow in and out of the cell when the concentration of ions nearby is changed.
Ion channels
The central cavity of the K+ channel can only accommodate hydrated K+ but not
hydrated Na+. T/F
False
The hydrated Na+ ions (or any other small ion) can indeed enter the central cavity of the K+ channel. The central cavity is large enough to accommodate hydrated ions of similar size, including hydrated Na+ ions. However, it is at the selectivity filter, which is located deeper within the channel, where the selectivity between K+ and Na+ ions occurs.
In summary, the central cavity of the K+ channel can accommodate hydrated Na+ ions, but it is at the selectivity filter where the selectivity between K+ and Na+ ions occurs.
Specific amino acids that line the selectivity filter of the K+ channel can dehydrate K+ and allow passage of that ion but cannot coordinate the dehydration of Na+. T/F
True.
The selectivity filter of the K+ channel contains specific amino acids that can dehydrate K+ ions, removing water molecules and allowing the passage of dehydrated K+ ions through the channel. However, the selectivity filter is less effective in coordinating the dehydration of Na+ ions due to their smaller size. This selectivity allows K+ ions to pass through the channel while restricting the passage of hydrated Na+ ions.
Concerning ion transport, how can passive carriers be distinguished from active transporters (pumps)?
Passive Carriers:
- Operate without energy input.
- Allow ion movement down their concentration gradients.
- Exhibit saturation kinetics.
- Generally exhibit broad specificity for similar ions.
Active Transporters (Pumps):
- Require energy, usually ATP.
- Can move ions against their concentration gradients.
- Often do not exhibit saturation kinetics.
- Display high selectivity for specific ions.
By considering the energy requirement, direction of ion movement, kinetics, and specificity, one can differentiate between passive carriers and active transporters involved in ion transport.
(Anytime ATP is required, or an ion is moving from low concentration to high concentration, it is active transport. Passive transport will always move ions down the concentration gradient).
Explain the mechanism of a voltage-gated channel.
Mechanism of Voltage-Gated Channels:
1- Closed State: In the absence of a voltage stimulus, the channel is closed, and an activation gate blocks ion passage.
2- Activation: When the membrane potential reaches a threshold, voltage-sensing regions in the channel undergo conformational changes in response to the electric field.
3- Opening: Conformational changes in the voltage-sensing regions cause the activation gate to open, allowing ions to pass through the channel.
4- Ion Conduction: Open channel allows ions (Na+, K+, Ca2+) to flow down their electrochemical gradient across the membrane.
5- Inactivation: After a period of time or specific membrane potential, an inactivation gate closes within the channel, blocking ion passage.
6- Reset: The channel returns to its closed state, ready to respond to subsequent changes in voltage.
Voltage-gated channels play a critical role in electrical signaling of cells, allowing selective ion passage in response to changes in membrane potential.