Cell Biology: Plasma Membrane Structure and Function

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Questions and Answers

What model do biologists use to describe the structure of the plasma membrane?

Rigid layer model

Fluid mosaic model (correct)

Solid-state model

Dynamic layer model

Which of the following defines the permeability of the plasma membrane?

Selective permeability (correct)

Complete permeability

Impenetrable barrier

Universal permeability

What key component spontaneously self-assembles to form simple membranes?

Proteins

Phospholipids (correct)

Carbohydrates

Cholesterol

Which of the following functions are performed by proteins within the plasma membrane?

Selective transport and signaling Signup and view all the answers

What characteristic of membranes is essential for cellular survival and function?

Membrane fluidity and diversity Signup and view all the answers

Why is the selective permeability of the plasma membrane important?

It regulates the internal environment of the cell Signup and view all the answers

Which statement about the fluid mosaic model is correct?

Membranes are dynamic and flexible Signup and view all the answers

What is a significant step in the origin of life, according to the evolution connection?

Spontaneous formation of membranes Signup and view all the answers

What is the primary reason for monitoring control eggs in a hypotonic solution?

To compare osmotic responses with test eggs Signup and view all the answers

What is required for a cell to perform active transport?

Energy in the form of ATP Signup and view all the answers

Which statement accurately describes exocytosis?

It exports bulky materials like proteins. Signup and view all the answers

What process is described by phagocytosis?

Engulfment of large particles by the cell Signup and view all the answers

During active transport, where is calcium typically more concentrated?

Outside the cell Signup and view all the answers

What distinguishes receptor-mediated endocytosis from regular endocytosis?

It requires specific receptors for certain solutes. Signup and view all the answers

What role does ATP play in cellular transport mechanisms?

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

Which of the following is NOT a function of endocytosis?

Exporting proteins outside the cell Signup and view all the answers

Why is a simple lipid bilayer membrane insufficient for the formation of the first cells?

It lacks the ability to perform metabolic functions. Signup and view all the answers

What defines diffusion across a cell membrane as passive transport?

It occurs without energy investment. Signup and view all the answers

What happens during osmosis when a 0.5% sucrose solution is separated from a 2% sucrose solution?

Water moves from the 0.5% solution to the 2% solution. Signup and view all the answers

In a hypertonic solution, what is the likely effect on a cell?

The cell will lose water and shrink. Signup and view all the answers

What is the purpose of a selectively permeable membrane in osmosis?

To allow only water to cross while blocking solutes. Signup and view all the answers

What is the term used to describe the ability of a solution to alter cell water balance?

Tonicity Signup and view all the answers

Which of the following statements about passive transport is FALSE?

It only occurs in the presence of water. Signup and view all the answers

How does water movement across a membrane during osmosis occur?

Down its own concentration gradient. Signup and view all the answers

What is the primary distinction between exergonic and endergonic reactions?

Exergonic reactions release energy; endergonic reactions require energy. Signup and view all the answers

How does kinetic energy differ from potential energy?

Kinetic energy is energy associated with movement; potential energy is stored energy. Signup and view all the answers

What term describes the totality of chemical reactions occurring within a cell?

Metabolism Signup and view all the answers

According to the second law of thermodynamics, what happens to energy during transformations?

It can increase disorder or entropy, with some energy lost as heat. Signup and view all the answers

What happens to the energy that is extracted from food during cellular respiration?

It is transformed into usable energy for cellular functions. Signup and view all the answers

What is the result of energy transformations according to thermodynamic laws?

Some energy becomes unusable form, usually lost as heat. Signup and view all the answers

Which process is associated with the uptake of large particles into a cell?

Phagocytosis Signup and view all the answers

What role does ATP play in cellular work?

It facilitates the transfer of energy between exergonic and endergonic reactions. Signup and view all the answers

Which type of energy is stored in chemical bonds and released during exergonic reactions?

Potential energy Signup and view all the answers

What is the primary function of enzymes in biochemical reactions?

They decrease the activation energy needed for a reaction. Signup and view all the answers

What is the active site of an enzyme?

The part of the enzyme where substrates fit specifically. Signup and view all the answers

What process does ATP use to drive cellular work?

By coupling exergonic reactions to endergonic processes. Signup and view all the answers

How do enzymes impact the energy profile of a reaction?

They decrease the activation energy without changing the overall energy of the reaction. Signup and view all the answers

What forms of work does ATP support in the cell?

Chemical, transport, and mechanical work. Signup and view all the answers

Which statement correctly describes enzyme activity?

Enzymes are specific to their substrates. Signup and view all the answers

What does an enzyme-catalyzed reaction typically illustrate?

A lower activation energy than the same reaction without an enzyme. Signup and view all the answers

What distinguishes phagocytosis from receptor-mediated endocytosis?

Phagocytosis involves engulfing large particles, while receptor-mediated endocytosis targets specific molecules. Signup and view all the answers

Which statement about kinetic and potential energy is accurate?

Kinetic energy can be converted into potential energy and vice versa. Signup and view all the answers

Which of the following best describes endergonic reactions?

They absorb energy and are non-spontaneous in nature. Signup and view all the answers

How do competitive inhibitors affect enzyme activity?

They bind to the enzyme's active site, blocking substrate access. Signup and view all the answers

Which law of thermodynamics states that energy cannot be created or destroyed?

First Law of Thermodynamics. Signup and view all the answers

Which is an example of how ATP functions as an energy shuttle?

By capturing energy from exergonic reactions to power endergonic reactions. Signup and view all the answers

Which of the following best defines exergonic reactions?

They release energy and often occur spontaneously. Signup and view all the answers

What role do enzymes play in biochemical reactions?

They speed up reactions by lowering the activation energy. Signup and view all the answers

Study Notes

Chapter 5: The Working Cell

The plasma membrane and its proteins allow cells to survive and function.
This chapter explores how working cells use membranes, energy, and enzymes.

Introduction

Plasma membranes and their proteins enable cells to survive and function.
This chapter clarifies how working cells use membranes, energy, and enzymes.

Figure 5.0_1

Shows a detailed representation of a cell membrane.

Figure 5.0_2

Visualizes the relationship between membrane structure and function and cellular respiration.
Demonstrates how enzymes function within the cell.

Membrane Structure and Function

Discusses the fluid mosaic model, explaining membranes' structure as a mosaic of diverse protein molecules in a fluid phospholipid bilayer.
Highlights selective permeability, where the plasma membrane controls which substances enter and exit the cell.
Explains various protein functions in cell membranes.

5.1 Visualizing the Concept: Membranes Are Fluid Mosaics of Lipids and Proteins with Many Functions

Biologists utilize the fluid mosaic model to describe membrane structure.
Membrane structure entails a fluid phospholipid bilayer with diverse protein molecules suspended within it.
Plasma membranes exhibit selective permeability.
Membrane proteins perform diverse functions.

Figure 5.1

Depicts the various components of a cell membrane.
Illustrates the extracellular matrix (ECM).
Shows the cytoskeleton's microfilaments.

Figure 5.1_1

Displays different kinds of membrane proteins and molecules.
Illustrates oxygen and carbon dioxide diffusion across the cell membrane.

Figure 5.1_2

Shows small nonpolar molecules diffusing across cell membranes.

Figure 5.1_3

Shows channel and active transport proteins.
Emphasizes how these transport proteins allow specific ions or molecules to enter or exit cells.

Figure 5.1_4

Introduces Membrane enzymes.
Explains how enzymes may be grouped to facilitate sequential reactions.

Figure 5.1_5

Depicts attachment proteins, which attach to the extracellular matrix and cytoskeleton.
Highlighting their role in supporting cell membranes and coordinating external and internal cell changes.

Figure 5.1_6

Demonstrates receptor proteins.
Explains how signaling molecules bind to receptor proteins, triggering other intracellular processes.

Figure 5.1_7

Highlights junction proteins that form intercellular junctions to attach adjacent cells.

Figure 5.1_8

Explains the function of glycoproteins as identification tags on cell membranes.
Emphasizes how these tags facilitate cell recognition and interactions.

Figure 5.1_9

Provides a comprehensive overview of cell membrane components including diffusion, enzymes, and proteins.

Animation: Overview of Cell Signaling

Illustrates the overall process of cell signaling.

Animation: Signal Transduction Pathways

Shows cell signaling through receptors and G proteins.

5.2 Evolution Connection: The Spontaneous Formation of Membranes Was a Critical Step in the Origin of Life

Phospholipids spontaneously self-assemble into simple membranes.
The formation of membrane-enclosed collections of molecules was crucial in the evolution of the first cells.

Figure 5.2

Illustrates water-filled bubbles composed of phospholipids.

5.3 Passive Transport Is Diffusion Across a Membrane with No Energy Investment

Diffusion is the spreading of particles evenly in an available space.
Passive transport, encompassing diffusion across cell membranes, does not require energy input.

Figure 5.3a

Demonstrates net diffusion and equilibrium across a membrane.

Figure 5.3b

Demonstrates net diffusion and equilibrium across a membrane.

Animation: Diffusion

Visualizes the random movement of particles in diffusion.

Animation: Membrane Selectivity

Shows how cell membranes regulate movement of substances across them.

5.4 Osmosis Is the Diffusion of Water Across a Membrane

Osmosis is water diffusion across a selectively permeable membrane.
Water moves from a high concentration to a low concentration across the membrane until solute concentration is equal on both sides.

Figure 5.4

Illustrates how water moves across a semi-permeable membrane during osmosis.

Animation: Osmosis

Demonstrates the movement of water across a selectively permeable membrane in osmosis.

5.5 Water Balance Between Cells and Their Surroundings Is Crucial to Organisms

Tonicity describes a solution's ability to change cell water content.
Cells shrivel in hypertonic solutions, swell in hypotonic solutions, and remain normal in isotonic solutions.

Figure 5.5

Depicts animal and plant cells in hypotonic, isotonic, and hypertonic solutions, highlighting how their cells respond to the solutions.

5.6 Transport Proteins Can Facilitate Diffusion Across Membranes

Hydrophobic substances easily diffuse across cell membranes, while polar or charged substances do not.
Facilitated diffusion involves specific transport proteins that aid polar or charged molecules across the membrane down their concentration gradient, requiring no energy.
Water rapidly diffuses via aquaporins, specialized protein channels.

Figure 5.6

Illustrates facilitated diffusion using a transport protein.

5.7 Scientific Thinking: Research on Another Membrane Protein Led to the Discovery of Aquaporins

Dr. Peter Agre received the 2003 Nobel Prize for his work in discovering aquaporins.
Aquaporin research was influenced by his Rh protein studies used in blood typing.

Figure 5.7

Presents graph of water permeability rates comparing control and RNA-injected eggs in varying conditions.

5.8 Cells Expend Energy in the Active Transport of a Solute

In active transport, cells use energy to move solutes against their concentration gradients.
ATP powers active transport.

Figure 5.8.1 - 5.8.3

Illustrates the four main stages of active transport.

Animation: Active Transport

Visualizes how active transport involves molecular movement against concentration gradients using energy

5.9 Exocytosis and Endocytosis Transport Large Molecules Across Membranes

Exocytosis expels large molecules, whereas endocytosis takes them in.
Material is enclosed in vesicles that fuse with the membranes during exocytosis and endocytosis.

Figure 5.9 & 5.9.1 & 5.9.2

Displays phagocytosis and receptor-mediated endocytosis processes depicting how substances enter.

Animation: Exocytosis and Endocytosis Introduction, Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis

Visualizations of the endocytosis processes.

5.10 Cells Transform Energy and Matter as They Perform Work

Energy is the capacity for change.
Kinetic energy is energy of motion and potential energy stored and includes chemical energy.
The laws of thermodynamics stipulate that energy transformation increases disorder and involves heat loss. Illustrates energy transformation in cars and cells.

Figure 5.10 & 5.10.1 & 5.10.2

Shows a comparison of energy conversion between a car and a cell. This illustrates cellular respiration and the role of ATP.

Animation: Energy Concepts

Presents an animated overview of energy concepts relevant to cell function.

5.11 Chemical Reactions Either Release or Store Energy

Exergonic reactions release energy, whereas endergonic reactions require it.
Metabolism, encompassing all cellular chemical reactions, either releases or stores energy.

Figure 5.11a

Illustrates exergonic reactions releasing energy.

Figure 5.11b

Illustrates endergonic reactions requiring energy.

5.12 ATP Drives Cellular Work by Coupling Exergonic and Endergonic Reactions

ATP powers nearly all cellular work.
The transfer of a phosphate group from ATP powers cellular processes like chemical, transport, and mechanical work.

Figure 5.12a_1 & 5.12a_2 & 5.12b & 5.12c

Illustrates ATP structure and its role in transferring energy.
Shows how ATP transfers energy from exergonic to endergonic processes, providing an example of energy coupling in the cell.

5.13 Enzymes Speed Up the Cell's Chemical Reactions by Lowering Energy Barriers

Enzymes catalyze reactions by lowering the activation energy needed to initiate reactions, without consumption by the reaction itself.

Figure 5.13 & 5.13_1 & 5.13_2 & 5.13_3 & 5.13_4

Depicts an enzyme's role in lowering activation energy needed before a reaction can begin.
Illustrates the process of enzyme-catalyzed reactions and how enzymes reduce activation energy.

Animation: How Enzymes Work

Illustrates how enzymes speed up reactions by lowering activation energy.

5.14 A Specific Enzyme Catalyzes Each Cellular Reaction

An enzyme's substrate fits precisely within its active site.
The figure showcases the catalytic cycle of an enzyme.

Figure 5.14_1 & 5.14_2 & 5.14_3 & 5.14_4

Illustrates the cycle of an enzyme reacting with a substrate via an active site.

5.15 Enzyme Inhibition Can Regulate Enzyme Activity

Competitive inhibitors block substrates from entering active sites.
Noncompetitive inhibitors bind elsewhere on enzymes, altering the enzyme's shape to prevent substrate binding.
Feedback inhibition regulates metabolic pathways.

Figure 5.15a & 5.15b

Depicts how competitive and noncompetitive inhibitors function in a reaction.
Illustrates feedback inhibition on enzyme pathways and how the product can inhibit enzymes.

5.16 Connection: Many Drugs, Pesticides, and Poisons Are Enzyme Inhibitors

Many drugs and beneficial chemicals function as enzyme inhibitors.
Enzyme inhibitors are used as pesticides or for warfare.
Enzyme inhibition reversibility depends on factors affecting the binding and release of the inhibitor.

You Should Now Be Able To

These are learning objectives covering membrane structure, functions, transport, thermodynamics, energy reactions, enzymes, and inhibition.

Figure 5.UN01 & 5.UN02 & 5.UN03 & 5.UN04 & 5.UN05

Diagrams and tables to better understand important concepts: examples of passive transport including osmosis and facilitated diffusion, active transport, enzyme pathways.

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Description

Test your knowledge on the plasma membrane's structure and functions, including its permeability and the roles of proteins. This quiz covers essential concepts about the fluid mosaic model, active transport, and endocytosis. Perfect for students studying cell biology.