Introduction to Cell Biology: Membrane Function

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Questions and Answers

What is a key tenet of cell theory?

The nucleus is the fundamental unit of structure in organisms.

Cells can spontaneously generate from non-living matter.

All living organisms are composed of one or more cells. (correct)

Viruses are the most basic unit of life.

Which of the following components contributes to the fluidity of the cell membrane?

A rigid protein scaffolding

A high proportion of saturated fatty acids

Fatty acids and cholesterol (correct)

Complete absence of cholesterol

What is the primary role of proteins embedded in the lipid bilayer of a cell membrane?

To maintain the rigidity of the membrane structure.

To completely block the passage of any molecules across the membrane.

To provide solutions to challenges created by the lipid bilayer, such as transport and signalling. (correct)

To prevent any interaction between the cell and its external environment.

Which type of transport involves the movement of molecules across the cell membrane without the input of energy?

Simple diffusion Signup and view all the answers

What process describes the movement of large molecules out of the cell by the fusion of vesicles with the plasma membrane?

Exocytosis Signup and view all the answers

What is a defining characteristic of all cells?

Presence of a membrane Signup and view all the answers

Which of the following organisms typically possess a rigid cell wall outside the plasma membrane?

Plants Signup and view all the answers

What is the primary function of the cell wall?

Providing structural support and protection Signup and view all the answers

What is the most likely theory about how the first cells may have formed?

Abiogenesis involving RNA capture within a lipid membrane Signup and view all the answers

Which molecules can readily cross a lipid bilayer?

Small hydrophobic molecules Signup and view all the answers

In the fluid mosaic model, what type of movement is restricted for lipids and proteins?

Transverse movement across the plane of the membrane Signup and view all the answers

According to the fluid mosaic model, what are the properties of cellular membranes?

Diverse set of lipids and proteins in the bilayer that are mobile within the plane of the membrane. Signup and view all the answers

What is one of the challenges presented by the high lateral fluidity and mobility of membranes?

Regulating fluidity across different temperatures Signup and view all the answers

What process describes the export of vesicle-bound contents from a cell by fusion with the plasma membrane?

Exocytosis Signup and view all the answers

Which type of endocytosis involves the uptake of large particles, such as pathogens, by immune cells?

Phagocytosis Signup and view all the answers

What is the primary mechanism for cells to capture bulk soluble material from the extracellular fluid?

Pinocytosis Signup and view all the answers

Which endocytotic process is specifically responsible for the cellular uptake of LDL (low-density lipoproteins)?

Receptor-mediated endocytosis Signup and view all the answers

What structural component drives the formation of vesicles during receptor-mediated endocytosis of LDL?

Clathrin coat Signup and view all the answers

What is the consequence of defects in the LDL receptor?

Heart disease Signup and view all the answers

What is the common feature of all endocytosis types?

Capture into vesicles Signup and view all the answers

Why do macromolecules require bulk transport routes to cross the plasma membrane?

They are too large to move through transport proteins Signup and view all the answers

Which of the following transport mechanisms requires energy to move substances against their concentration gradient?

Active transport Signup and view all the answers

What is the primary function of transport ATPases?

Moving substances up a concentration gradient using ATP hydrolysis Signup and view all the answers

Which type of molecule can freely pass through the cell membrane via simple diffusion?

Hydrophobic compounds Signup and view all the answers

What determines the direction of water movement across a semi-permeable membrane during osmosis?

The concentration gradient of solutes Signup and view all the answers

Which of the following best describes the external environment preferred by animal cells?

Isotonic Signup and view all the answers

How does facilitated diffusion assist in the transport of polar molecules across the cell membrane?

By providing a specific protein channel through which the polar molecules can pass Signup and view all the answers

What is the role of the GLUT transport protein?

Facilitated diffusion of glucose down its concentration gradient Signup and view all the answers

What is the function of the $Na^+/K^+$ ATPase?

To transport sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients Signup and view all the answers

How does co-transport function in indirect active transport?

It uses the movement of one solute down its concentration gradient to drive the movement of another solute up its concentration gradient Signup and view all the answers

What is the primary purpose of maintaining a membrane potential in cells?

To drive indirect active transport Signup and view all the answers

What is the cause of cystic fibrosis at the cellular level?

A mutation in a lung chloride ion transporter Signup and view all the answers

Which of the following describes the function of integral membrane proteins?

Signaling, and attachment to the cytoskeleton or extracellular matrix Signup and view all the answers

What is the role of exocytosis in bulk export?

To package macromolecules into vesicles and release them outside the cell Signup and view all the answers

What is the purpose of endocytosis?

Importing large particles and retrieving membrane components Signup and view all the answers

What distinguishes phagocytosis from other forms of endocytosis?

It involves the engulfment of very large particles Signup and view all the answers

What property of lipids contributes to membrane fluidity by preventing tight packing?

Incorporation of cholesterol Signup and view all the answers

Which type of molecule is typically unable to permeate a lipid bilayer?

Most polar molecules Signup and view all the answers

What is the effect of increasing the proportion of unsaturated fatty acids in a membrane's lipid bilayer?

Increased membrane fluidity Signup and view all the answers

How do cells maintain constant membrane viscosity despite temperature changes?

Regulating fatty acid content Signup and view all the answers

Which of the following best describes integral membrane proteins?

Proteins that span the lipid bilayer Signup and view all the answers

What is one of the primary roles of membrane proteins?

Facilitating transport across the membrane Signup and view all the answers

Compared to mammals that thermoregulate, what is different about the membrane composition within aquatic organisms and plants?

Higher unsaturated fatty acids Signup and view all the answers

What effect does low temperature typically have an a cell membrane?

Decreases fluidity and increases viscosity Signup and view all the answers

What is true about proteins spanning membranes?

Allows proteins to overcome the barriers of the membrane Signup and view all the answers

What are cell membranes formed from?

Amphipathic lipids Signup and view all the answers

Study Notes

Introduction to Cell Biology - Membrane Structure and Function

Cell theory establishes the cell as the fundamental unit of life.
- All living organisms are composed of one or more cells.
- The cell is the basic unit of structure and organization in organisms.
- Cells arise from pre-existing cells.
Cell membranes, specifically the plasma membrane (PM), are crucial for all cells.
Membranes are composed of a lipid bilayer.
- The bilayer is formed by amphipathic lipids (e.g., phospholipids).
- These lipids spontaneously form bilayers.
- The lipid bilayer is semi-permeable, meaning that some substances can pass through it easily while others cannot.
- Polar molecules generally cannot pass freely through the hydrophobic core, whereas gases and non-polar molecules can.
Membrane fluidity is affected by temperature, fatty acid saturation, and cholesterol.
- Unsaturated fatty acids create kinks, thus preventing tight packing and increasing fluidity.
- Cholesterol maintains fluidity at extreme temperatures.
Membrane proteins play vital roles.
- Integral proteins span the membrane and often act as channels or transporters for molecules.
- Peripheral proteins associate with one side of the membrane.
- Proteins are involved in transport (passive and active), signaling, cell-to-cell recognition, and other functions.
Transport across the cell membrane occurs through various mechanisms.
- Passive transport (no energy required):
  - Simple diffusion: substances move down their concentration gradient.
  - Facilitated diffusion: substances move down their concentration gradient with help of channel or carrier proteins.
- Active transport (energy required):
  - Primary active transport: uses ATP directly to move substances against their concentration gradient.
  - Secondary active transport: uses an established electrochemical gradient (e.g., Na+/K+ pump) to drive the movement of other substances against their concentration gradient.
Bulk transport involves the movement of large molecules or particles.
- Exocytosis: vesicles fuse with the membrane, releasing contents to the exterior.
- Endocytosis: vesicles form from the membrane, capturing material from the exterior and bringing it into the cell. Types include receptor-mediated endocytosis and phagocytosis.
Membrane potential is an electrical potential difference across the membrane.
- Maintained by an imbalance of ions (e.g., Na+, K+, Cl−).
- Used to drive indirect active transport.
Cystic fibrosis is a genetic disorder affecting lung function, a result of mutations in genes governing chloride ion transport.

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Description

This quiz explores the fundamental concepts of cell biology, focusing on membrane structure and function. It covers the composition of cell membranes, their semi-permeable nature, and factors affecting membrane fluidity. Dive deep into how these aspects are crucial for cellular capabilities.