Lecture 9 Review

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Questions and Answers

What is a key characteristic of passive transport?

It requires additional energy to move molecules.

Molecules move down their concentration gradient. (correct)

It only transports charged molecules.

Molecules are moved against their concentration gradient.

What distinguishes active transport from passive transport?

Active transport moves molecules up their concentration gradient. (correct)

Active transport transports molecules in a single direction only.

Active transport does not require a membrane potential.

Active transport occurs through channels only.

In terms of charged molecules, what factor primarily influences passive transport?

Electrochemical gradient. (correct)

Membrane thickness.

Concentration gradient only.

Temperature of the environment.

For uncharged molecules, what is the relationship between the electrochemical gradient and concentration gradient?

They are equal. Signup and view all the answers

Which statement correctly describes a transporter compared to a channel?

Transporters can only move one molecule at a time. Signup and view all the answers

What is the primary distinction between channels and transporters in membrane transport proteins?

Channels facilitate quick passage based on size and charge. Signup and view all the answers

Which statement accurately describes the principles driving passive transport?

It occurs along the concentration gradient without energy input. Signup and view all the answers

How is an electrochemical gradient primarily established in cells?

Through the differential distribution of ions across the membrane. Signup and view all the answers

Which of the following is NOT a characteristic of transport proteins?

They only function in the absence of an electrochemical gradient. Signup and view all the answers

Which mechanism would NOT be classified under the transport types discussed?

Endocytosis bringing large particles into the cell. Signup and view all the answers

What is the primary function of channels in passive transport?

To facilitate diffusion of specific molecules Signup and view all the answers

Which statement correctly describes transporters in passive transport?

They undergo conformational changes during transport. Signup and view all the answers

How do active transport mechanisms differ from passive transport mechanisms?

Active transport requires energy to move molecules up their gradient. Signup and view all the answers

What role does the Na+-K+-ATPase play in cellular transport?

It is a pump that uses ATP to move sodium and potassium ions. Signup and view all the answers

What is an electrochemical gradient?

The difference in ion concentration across a membrane, affecting molecule transport. Signup and view all the answers

Which type of transport utilizes energy derived from light?

Light-driven transport Signup and view all the answers

Which of the following best describes passive transport?

It allows molecules to move down their electrochemical gradient. Signup and view all the answers

What is a common characteristic shared by both channels and transporters in passive transport?

Both facilitate the movement of molecules down their gradients. Signup and view all the answers

What is true about the solution inside vesicles?

It contains both Na+ and K+. Signup and view all the answers

Which statement accurately describes the solution outside the vesicles?

It contains Na+, K+, and ATP. Signup and view all the answers

What happens to Na+ and K+ when the Na-K pump molecules are randomly oriented?

They cannot transport Na+ effectively. Signup and view all the answers

Which type of transport is described as driven by the flow of a molecule down its electrochemical gradient?

Gradient-driven transport Signup and view all the answers

In the context of transport mechanisms, which statement is correct?

Some transport is considered passive despite being presented as active. Signup and view all the answers

What is the role of ATP in the context of Na+ transport?

It powers the Na-K pump to transport Na+. Signup and view all the answers

What will generate a Na+ concentration gradient?

More than one of the conditions listed. Signup and view all the answers

What is a property of active transport mechanisms?

They always require energy input to move substances against their gradient. Signup and view all the answers

Which statement accurately describes the nature of symport transport?

Both molecules are transported into the cell. Signup and view all the answers

What is the role of the Na+-K+ ATPase in the context of active transport?

It creates an electrochemical gradient necessary for symport transport. Signup and view all the answers

Which transport mechanism allows for glucose to be transported without the use of energy?

Glucose uniport Signup and view all the answers

In the context of mitochondria, what role do H+ pumps play?

They create an electrochemical gradient necessary for ATP synthesis. Signup and view all the answers

Which of the following statements is true regarding active transport?

It can involve both symport and antiport mechanisms. Signup and view all the answers

What is a characteristic feature of passive transport?

It occurs when both molecules move down their gradients. Signup and view all the answers

What binds glucose and Na+ strongly during absorption into the cell?

Both glucose and Na+ must be present simultaneously. Signup and view all the answers

Which component is essential for ATP synthesis during cellular respiration?

The H+ gradient established across the inner mitochondrial membrane. Signup and view all the answers

Which solution configuration will allow the Na+-K+ pump to create a Na+ concentration gradient inside the vesicle?

Inside contains Na+ and K+ with ATP; outside contains Na+ and K+. Signup and view all the answers

What is the primary function of the Na+-K+ pump demonstrated in the vesicles?

To export Na+ and import K+ using energy from ATP hydrolysis. Signup and view all the answers

In which scenario will the Na+-K+ pump not be able to generate a concentration gradient?

The pump is oriented correctly, but there is no ATP. Signup and view all the answers

What is the direct consequence of ATP hydrolysis in the Na+-K+ pump's action?

It decreases the concentration of Na+ inside the cell. Signup and view all the answers

How does random orientation of the Na+-K+ pumps affect ion transport?

It can prevent the establishment of a Na+ gradient. Signup and view all the answers

Which of the following statements is true regarding the Na+-K+ pump's operation?

It functions optimally when there is ATP present to drive ionic movement. Signup and view all the answers

What will be the initial effect if both vesicle solutions contain only K+?

The Na+-K+ pump will not operate. Signup and view all the answers

What role does ATP play in the process of ion transport by the Na+-K+ pump?

It phosphorylates the pump, causing a conformational change. Signup and view all the answers

Study Notes

Learning Objectives

Understanding how transport proteins move specific molecules across a membrane is key
Understanding the principles driving passive, coupled, and active transport is essential
Understanding how several transport proteins work together in a cell context is important
Understanding the concept of channels and how electrochemical gradients are established is crucial

Today's Topics

Transporters versus channels
Electrochemical gradients
Passive transport
Active transport
How to make ATP

Eukaryotic Cells and Organelles

Eukaryotic cells contain membrane-bound organelles, like mitochondria, peroxisomes, Golgi apparatus, endoplasmic reticulum, and lysosomes.

Membrane Transport Proteins

Membrane transport proteins regulate cell composition
Small hydrophobic molecules (e.g., O₂, CO₂, N₂, benzene) cross the membrane easily
Small, uncharged, polar molecules (e.g., H₂O, glycerol, ethanol) also cross relatively easily
Larger polar molecules (e.g., amino acids, glucose, nucleosides) and ions (e.g., H⁺, Na⁺, HCO₃⁻, K⁺, Ca²⁺, Cl⁻, Mg²⁺) require proteins for transport

Channels vs Transporters

Two main types of membrane transport proteins: channels and transporters
Channels discriminate based on size and charge, allowing rapid ion passage
Transporters discriminate based on direct binding, moving one (or a few) molecule(s) at a time.

Passive Transport

Passive transport does not require additional energy
Molecules move "down" their concentration gradients through channels or transporters
Simple diffusion and channel-mediated transport are passive
Transporter-mediated transport is also passive when molecules move down their electrochemical gradient

Active Transport

Active transport requires energy to move molecules against their electrochemical gradients
Active transport uses the principle of energy coupling in enzyme-catalyzed reactions

Electrochemical Gradients

The electrochemical gradient is a combination of a voltage and concentration gradient
For charged molecules, the electrochemical gradient determines the direction of passive transport
For uncharged molecules, the electrochemical gradient equals the concentration gradient

The Na⁺-K⁺-ATPase

The Na⁺-K⁺-ATPase is an ATP-driven pump (Na⁺ pump) that utilizes about 30% of the total ATP hydrolysis in animals
The Na⁺-K⁺ pump transports Na⁺ to the outside and K⁺ to the inside of the cell per ATP hydrolysis cycle

Gradient-driven Transport

Gradient-driven transport is driven by the flow of a molecule down its electrochemical gradient
Types of gradient-driven transport include symport, antiport, and uniport

Mechanism for Glucose-Na⁺ Coupled Active Transport

Glucose moves up its concentration gradient because Na⁺ is moving down its electrochemical gradient across the membrane
These transporters move glucose and Na⁺ together into the cell

Glucose Transport

Glucose transporters mediate passive transport
The glucose transporter undergoes conformational changes to facilitate transport

Mitochondria: Inner Structure

Mitochondria have an outer and inner membrane
The inner membrane is folded into cristae

Mitochondrial Electrochemical Gradient (H⁺ Gradient)

Three H⁺ pumps generate an electrochemical gradient across the inner mitochondrial membrane
This H⁺ gradient is used by ATP synthase to synthesize ATP

ATP Synthase

ATP synthase uses the H⁺ gradient to synthesize ATP

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Description

Test your knowledge on the differences between passive and active transport mechanisms in biological systems. Explore the roles of transport proteins, channels, and electrochemical gradients. Understand how various transport types function within cell membranes.