Cell Biology Active Transport

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Questions and Answers

What is the primary function of the sodium-potassium pump?

To establish an electrochemical gradient (correct)

To facilitate passive transport of glucose

To transport proteins out of the cell

To neutralize cellular waste

Which of the following describes exocytosis?

The diffusion of ions across a membrane

Substances entering the cell via vesicle formation

The exit of substances from the cell through vesicle fusion (correct)

Breakdown of large particles for energy

Which transport process does glucose utilize when sodium ions move into the cell?

Simple diffusion

Bulk transport

Facilitated diffusion

Secondary active transport (correct)

What role do vesicles play in bulk transport?

They facilitate the secretion and intake of large molecules Signup and view all the answers

Phagocytosis is primarily used for what purpose?

Engulfing large particles or small cells Signup and view all the answers

What characterizes endocytosis?

It involves forming vesicles from the plasma membrane Signup and view all the answers

Which of these molecules are typically secreted via exocytosis?

Hormones and digestive enzymes Signup and view all the answers

What is the main distinction between passive and active transport mechanisms?

Active transport requires energy, while passive does not Signup and view all the answers

Which of the following correctly describes channel proteins?

They provide a hydrophilic passage for specific ion transport. Signup and view all the answers

What type of diffusion allows polar molecules to enter the cell using specific proteins?

Facilitated diffusion Signup and view all the answers

How do carrier proteins function in facilitated diffusion?

They bind to solutes and change shape to transport them. Signup and view all the answers

Which protein type is specifically involved in transporting glucose into red blood cells?

Glucose transporter 1 (GLUT 1) Signup and view all the answers

What determines the direction of ion movement through channel proteins?

Relative concentration gradient across the membrane Signup and view all the answers

What triggers the opening or closing of gated channel proteins?

Hormonal stimulation or electrical impulses Signup and view all the answers

Which process uses energy to move substances against their concentration gradient?

Active transport Signup and view all the answers

What is a key characteristic of the sodium-potassium pump?

It transports sodium out and potassium into the cell using ATP. Signup and view all the answers

What role does ATP play in active transport?

It provides energy required for the transport process. Signup and view all the answers

Which type of carrier protein is responsible for transporting two different molecules in the same direction?

Symporter Signup and view all the answers

How many potassium ions are moved into the cell for every three sodium ions pumped out by the sodium-potassium pump?

2 Signup and view all the answers

Which step in the sodium-potassium pump involves the binding of sodium ions to the carrier protein?

Sodium ion binding Signup and view all the answers

What defines secondary active transport (cotransport)?

Transport that relies on the concentration gradient established by primary active transport. Signup and view all the answers

What happens to the carrier protein after potassium ions bind to it in the sodium-potassium pump process?

It releases phosphate and returns to its original shape. Signup and view all the answers

Which process entails the transport of large molecules or particles into or out of the cell?

Bulk transport Signup and view all the answers

Which of the following statements about the sodium-potassium pump is true?

It helps maintain an electrochemical gradient. Signup and view all the answers

Study Notes

Active Transport

Involves moving molecules or ions across a membrane against their concentration gradient, requiring energy
Energy source is Adenosine Triphosphate (ATP) converted to Adenosine diphosphate (ADP) by the enzyme ATPase
Achieved by carrier proteins:
- Uniporters: Carry one specific ion or molecule
- Symporters: Carry two different ions or molecules in the same direction
- Antiporters: Carry two different ions or molecules in opposite directions
Carrier proteins bind to specific molecules, change shape to move them across the membrane, and require energy for this conformational change
Example: sodium-potassium pump
- Pumps ions against concentration gradients (high sodium outside, low sodium inside; low potassium outside, high potassium inside)
- Maintains electrochemical gradient, moving 2 potassium ions into the cell for every 3 sodium ions moved out
- Process:
  1. Three sodium ions bind to the carrier protein
  2. Phosphate group from ATP is transferred to the carrier protein
  3. Phosphorylation causes the carrier protein to change shape, releasing three sodium ions outside the cell
  4. Two potassium ions bind to the carrier protein
  5. Phosphate is released from the carrier protein
  6. Phosphate release causes the carrier protein to return to its original shape, releasing two potassium ions inside the cell

Secondary Active Transport (Cotransport)

Uses the electrochemical gradient created by primary active transport (like the sodium-potassium pump) to move other substances against their concentration gradients
Example: Glucose cotransport
- Carrier protein transports both sodium and glucose
- Sodium moves into the cell along its gradient, releasing energy that's used to transport glucose into the cell

Bulk Transport

Transport of large molecules (polypeptides, polysaccharides, polynucleotides) and even small cells across the plasma membrane
Requires energy, often referred to as energy-intensive
Achieved through exocytosis and endocytosis

Exocytosis

The exit of substances from the cell
Vesicles containing substances fuse with the plasma membrane, releasing their contents
Hormones, neurotransmitters, and enzymes can be secreted this way
Golgi apparatus produces vesicles that carry these cell products to the membrane
Vesicle membrane becomes part of the plasma membrane upon fusion
Content of vesicles can adhere to the cell surface or become part of the extracellular matrix
Cells of specific organs specialize in producing and exporting materials (e.g., pancreatic cells produce digestive enzymes, pituitary cells produce growth hormones)
Secretory vesicles typically accumulate near the plasma membrane and release their content only when stimulated by a signal (e.g., rise in blood sugar signals pancreatic cells to release insulin)

Endocytosis

The entry of substances into the cell
A portion of the plasma membrane invaginates to envelope the substance, pinches off to form an intracellular vesicle
Three types:
- Phagocytosis: Taking in of large food particles or small cells (viruses, bacteria)
- Pinocytosis: Taking in of fluids and dissolved solutes
- Receptor-mediated endocytosis: Specific binding of substances to receptors on the cell surface, triggers vesicle formation

Facilitated Diffusion

Movement of polar molecules (glucose, amino acids, ions, water) across the plasma membrane through specific membrane proteins (channel proteins and carrier proteins)
Dependent on concentration gradient across the membrane, like simple diffusion
Makes the membrane permeable to ions and polar molecules
Channel proteins:
- Non-gated channels: Permanent pores (porins) allow substances of specific size to pass
- Gated channels: Open or close in response to stimuli (hormones, electrical impulses)
Carrier proteins:
- Bind to solutes on one side of the membrane, change shape, and transport the molecule to the other side
- Example: Glucose transporter 1 (GLUT 1) facilitates glucose diffusion from plasma into red blood cells, thousands of times faster than simple diffusion

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Description

Explore the details of active transport in cells, focusing on the mechanisms that move molecules across membranes against their concentration gradients. This quiz covers the role of ATP, different types of carrier proteins, and the example of the sodium-potassium pump. Test your knowledge on how these processes maintain essential cellular functions.