Pharmacokinetics and Membrane Transport

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Questions and Answers

What is the outcome when the pH is lower than the pKa for a weak acid?

Absorption occurs mainly in the stomach.

The un-ionized form predominates in the stomach. (correct)

The ionized form predominates in the stomach.

The drug is completely ionized in the plasma.

For a weak base with a pKa of 4.4, which statement is true regarding its presence in the stomach?

The drug is absorbed more effectively in an acidic medium.

Most of the drug remains un-ionized.

The drug has equal ionization in both the stomach and small intestine.

Most of the drug is ionized in the stomach. (correct)

In which part of the gastrointestinal tract does most drug absorption occur?

Esophagus due to rapid transit time.

Colon because of permeability.

Stomach due to pH levels.

Small intestine because of larger surface area. (correct)

What is the ratio of un-ionized to ionized forms for a weak acid with a pKa of 4.4 in gastric fluid (pH 1.4)?

1000:1 (A) Signup and view all the answers

Which type of drug is more readily absorbed from an acidic medium like the stomach?

Weakly acidic drugs. (A) Signup and view all the answers

What is a primary characteristic of active transport proteins?

They are highly selective. (A) Signup and view all the answers

What role does ATP play in active transport?

ATP provides energy necessary for the transport process. (B) Signup and view all the answers

Which of the following statements about the transport cycle is accurate?

The transport protein changes shape after binding with 'X'. (C) Signup and view all the answers

What happens to the transport protein after the phosphate group is released?

It resumes its original shape to repeat the process. (A) Signup and view all the answers

In relation to nerve and muscle function, why is active transport essential?

It controls ion concentrations vital for signaling. (C) Signup and view all the answers

What is the primary role of the plasma membrane in a cell?

To control the traffic of molecules in and out (A) Signup and view all the answers

Which statement best describes the structure of cell membranes according to the fluid mosaic model?

Cell membranes are composed of a mosaic of proteins embedded in a phospholipid bilayer. (D) Signup and view all the answers

What is the significance of selective permeability in cell membranes?

It maintains a stable internal environment by regulating molecule passage. (B) Signup and view all the answers

What is the primary component that helps in the movement of proteins and phospholipids within the membrane?

Fluid nature of the membrane (B) Signup and view all the answers

What is the role of internal membranes within a cell?

They compartmentalize chemical reactions and form organelles. (A) Signup and view all the answers

What drives passive transport in biological membranes?

Concentration gradient potential energy (C) Signup and view all the answers

Which of the following statements about channel proteins is true?

Channel proteins allow for rapid transport of multiple molecules simultaneously. (D) Signup and view all the answers

How do carrier proteins differ from channel proteins in their transport mechanism?

Carrier proteins transport solutes through conformational changes. (D) Signup and view all the answers

What is the primary function of potassium-specific channel proteins in animal cells?

To establish the resting electric potential across the plasma membrane (A) Signup and view all the answers

What characterizes the transport rate of carrier proteins in contrast to channel proteins?

Carrier proteins transport solute molecules at a slower rate than channel proteins. (C) Signup and view all the answers

What is a primary source of energy for secondary active transport?

Ion gradients established by primary active transport (D) Signup and view all the answers

Which statement accurately describes the speed of transport through ion channels?

Transport through channels can reach rates of up to 10^8 ions per second. (B) Signup and view all the answers

Which feature distinguishes passive transport from active transport?

Passive transport is driven by concentration gradients. (A) Signup and view all the answers

What happens to an animal cell when placed in a hypotonic solution?

It lyses. (A) Signup and view all the answers

Which type of solution has a higher concentration of solute compared to the inside of the cell?

Hypertonic solution (C) Signup and view all the answers

How does an animal cell respond when placed in an isotonic solution?

It remains normal. (A) Signup and view all the answers

What is the outcome for a plant cell in a hypertonic solution?

It shrivels and plasmolyzes. (A) Signup and view all the answers

What characterizes a hypotonic solution?

Lower concentration of solute compared to the cell. (D) Signup and view all the answers

What is the primary function of active transport proteins?

To move substances against their concentration gradient. (B) Signup and view all the answers

What happens to plant cells in a hypotonic solution?

They become turgid. (D) Signup and view all the answers

Which statement about isotonic solutions is correct?

They maintain equal solute concentrations inside and outside the cell. (A) Signup and view all the answers

Study Notes

Movement and Transport Across Membranes

Pharmacokinetics is essential for understanding the fate of xenobiotics like drugs and pesticides in organisms.

Membrane Structure and Function

Cell membranes exhibit selective permeability, controlling the entry and exit of molecules.
Internal membranes organize cellular function and metabolic activities by forming organelles that compartmentalize reactions.

Fluid Mosaic Model

Membranes consist of a mosaic of proteins embedded in a phospholipid bilayer.
Proteins within the membrane facilitate most of its functions and can move laterally among lipids.

Acid-Base Behavior and Drug Absorption

Weak acids are more readily absorbed in acidic environments (like the stomach), where they remain un-ionized.
Weak bases predominate in alkaline environments (like plasma, pH 7.4), where they become ionized and absorbed less effectively.
Most absorption of drugs occurs in the small intestine due to its large surface area and higher permeability.

Tonicity and Osmosis

Isotonic solutions have equal solute concentrations, hypotonic solutions have lower concentrations, and hypertonic solutions have higher concentrations of solute.
In hypotonic solutions, animal cells lyse (burst), while plant cells become turgid (firm).
Hypertonic solutions cause animal cells to shrivel and plant cells to plasmolyze (dehydrate).

Active Transport Mechanisms

Active transport requires ATP to move substances against their concentration gradient.
This process is vital for the function of nerves and muscles, relying on highly selective transport proteins.

Active Transport Process

Active transport proteins span the plasma membrane, changing shape to move substances from one side to the other.
Phosphate groups from ATP energize transport proteins, allowing continued operation.

Channels vs. Carrier Proteins

Channel proteins facilitate the rapid transport of water or ions down their concentration gradients, forming a protein-lined passageway.
Carrier proteins undergo conformational changes, transporting one or a few solute molecules at a time, and never form open channels through the membrane.

Transport Rates

Transport via carrier proteins is faster than passive diffusion but slower than that through channels due to the number of solute molecules moved during each cycle.

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Description

Explore the principles of pharmacokinetics and how transport across membranes affects drug absorption and distribution. This quiz covers topics such as membrane structure, the fluid mosaic model, and the impact of acid-base behavior on drug efficacy.