Biology Chapter: Plasma Membrane Overview

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Questions and Answers

What is the primary function of the plasma membrane in animal and plant cells?

Provides structural support to the cell

Releases energy from nutrients

Serves as an external envelope that protects the cell (correct)

Stores genetic material

Which of the following best describes integral proteins in the plasma membrane?

Easily separated through mild treatments

Require detergents for separation (correct)

Soluble in aqueous solutions

Constitute less than 30% of membrane proteins

What model did J. David Robertson propose regarding the structure of the plasma membrane?

Lipid bilayer with proteins in globular conformation

Fluid mosaic model with proteins only on the surface

Static model with no protein presence

Mosaic model with proteins extending through the bilayer (correct)

Who proposed the fluid mosaic model of membrane structure?

Singer and Nicolson Signup and view all the answers

Which lipid types are primarily found within the plasma membrane?

Phospholipids and galactolipids Signup and view all the answers

What thickness is generally accepted for the plasma membrane?

7.5 nm Signup and view all the answers

Which type of carbohydrates are found within the plasma membrane structure?

Hexoses and hexosamines Signup and view all the answers

Which of the following statements about peripheral proteins is correct?

They are separated by mild treatment and are usually free from lipid Signup and view all the answers

What is the main function of exocytosis in cells?

To release secretory products from intracellular vesicles Signup and view all the answers

Which cellular process is primarily responsible for the uptake of large particles?

Phagocytosis Signup and view all the answers

What characterizes malignant tumor cells?

They can invade surrounding tissues and may metastasize. Signup and view all the answers

How does exocytosis affect the composition of the plasma membrane?

It introduces new membrane materials into the plasma membrane. Signup and view all the answers

What is the term for the process where tumor cells spread to form secondary growths?

Metastasis Signup and view all the answers

Which type of endocytosis involves specific binding to proteins on the cell's surface?

Receptor-mediated endocytosis Signup and view all the answers

What is required for the process of exocytosis to occur?

Energy from ATP hydrolysis Signup and view all the answers

Which of the following processes is most closely related to fluid uptake in cells?

Pinocytosis Signup and view all the answers

What is the primary function of active transport in plant cells?

To translocate ions, sugars, and amino acids using energy Signup and view all the answers

Which of the following correctly describes endocytosis?

Uptake of liquid from the environment Signup and view all the answers

Which statement about phagocytosis is true?

It allows cells to engulf large debris and microorganisms. Signup and view all the answers

What is the role of ATP in active transport?

It provides energy necessary for moving substances against their gradient. Signup and view all the answers

In the context of cytosis, what is exocytosis?

Release of substances from a cell into the extracellular space Signup and view all the answers

Which example describes a process that is not a form of endocytosis?

Exocytosis of neurotransmitters from nerve cells Signup and view all the answers

What distinguishes receptor-mediated endocytosis from other forms of endocytosis?

It requires binding of specific molecules to cell surface receptors. Signup and view all the answers

How does fluid endocytosis differ from other types of endocytosis?

The concentration inside the vesicle matches that outside the cell. Signup and view all the answers

What does the term 'fluid' in the fluid mosaic model refer to?

The flexibility and lateral movement of phospholipids and proteins Signup and view all the answers

Which type of proteins penetrate the lipid bilayer and may protrude from either side?

Integral proteins Signup and view all the answers

What characteristic of membrane lipids contributes to the structure of the fluid mosaic model?

They are hydrophilic and hydrophobic (amphipathic). Signup and view all the answers

What gives the fluid mosaic model its 'mosaic' appearance?

The varied distribution of different types of proteins on the membrane Signup and view all the answers

Which statement describes the forces that maintain the structure of the fluid mosaic model?

They arise from hydrophilic and hydrophobic interactions. Signup and view all the answers

How are peripheral proteins distinguished from integral proteins in the fluid mosaic model?

They are only found on the membrane surface. Signup and view all the answers

Which of the following statements is true regarding the lipid bilayer's consistency?

It exists in a relatively fluid state similar to light oil. Signup and view all the answers

Which component is NOT typically part of the fluid mosaic membrane model?

Nucleic acids Signup and view all the answers

What characteristic of phospholipids allows them to form a bilayer in the plasma membrane?

They are amphipathic, having both hydrophobic and hydrophilic parts. Signup and view all the answers

Why can steroid hormones easily penetrate the plasma membrane?

They are lipid soluble and can cross the lipid bilayer. Signup and view all the answers

What role do receptors on target cells play in hormone signaling?

They bind specifically to hormones and initiate a response. Signup and view all the answers

Which statement best describes the process of receptor binding with hormones?

The binding is concentration-dependent and reversible. Signup and view all the answers

What types of substances are primarily transported via micro-transfer mechanisms in plasma membranes?

Ions and small molecular species like amino acids and sugars. Signup and view all the answers

How do uncharged substances typically move across the plasma membrane?

Through simple diffusion and facilitated transport down the concentration gradient. Signup and view all the answers

How does the concentration of a hormone in the environment affect its binding to receptors?

The binding is concentration-dependent and decreases with lower hormone availability. Signup and view all the answers

What is a common feature of glycoprotein hormones like insulin in relation to the plasma membrane?

They bind to surface receptors without penetrating the plasma membrane. Signup and view all the answers

Study Notes

Plasma Membrane

The plasma membrane is a thin, external envelope surrounding the cell.
It separates and protects the cell from the external environment.
It also provides a connecting system for the cell to interact with its environment.
All cells are enveloped by a plasma membrane that is usually about 7.5 nm thick.
The membranes of prokaryotic and eukaryotic cells share a common overall structure, consisting of assemblies of lipids and proteins held together by noncovalent forces.

### Plasma Membrane Components

Lipid: Phospholipid, galactolipid, and cholesterol.
Proteins:
- Peripheral (extrinsic): Separated by mild treatment, soluble in aqueous solutions, and usually free from lipid.
- Integral proteins (intrinsic): Represent more than 70% of proteins. Separated by drastic procedures, insoluble in water, require the presence of detergents, and may be attached to other non-proteins (glycoprotein, phosphoprotein, and lipoproteins).
Carbohydrate: Hexose, hexoseamine, and fucose.
Enzymes: Approximately 30 enzymes.

### Molecular Organization of Membranes

The plasma membrane was first described as a lipid bilayer about sixty years ago.
Sandwich model OR Danielli- Davson Model (1935): Proposed by Davson and Danielle, this model suggested that the cell membrane is a lipid bilayer sandwiched with two monolayers of globular proteins.
Modified Danielli-Davson model (early 1960s): J. David Robertson modified this model to suggest that the proteins were extended rather than globular on both surfaces of the phospholipid bilayer.
Fluid Mosaic Membrane Model (late 1960s): Proposed by S. Jon Singer and Garth Nicolson, this model suggests that a mosaic of protein molecules is distributed in and on a fluid phospholipid bilayer. This model is widely accepted today, although certain details have been changed.
The model describes the plasma membrane as a flexible layer of lipid molecules interspersed with large protein molecules that act as channels for other molecules to enter and leave the cell.
Fluid: Individual phospholipids and some proteins can move sideways (laterally) in each layer, making the membrane fluid.
Mosaic: The range of different proteins, phospholipids, and cholesterol resting on the surface or through the phospholipid layer gives it a mosaic appearance.

Plasma Membrane Function

Steroid hormones (e.g., estrogen, progesterone): Pass through the plasma membrane easily because they are lipid-soluble. They readily cross the plasma membrane and enter the cell.
Glycoprotein hormones (e.g., insulin): Bind to the surface of their target cells and exert their influence from there without penetrating the plasma membrane.
Receptors: Target cells are stimulated by non-steroid hormones through receptors on the outer cell surface. These receptors are integral plasma membrane components and bind specifically to a particular hormone molecule.
Transport: The plasma membrane facilitates transport of substances across the membrane, including both micro-transfer and macro-transfer processes.

Micro-Transfer Processes

Passive and Facilitated Transport: Uncharged substances (non-electrolytes) move across the plasma membrane down the concentration gradient at a rate determined by their relative concentration on each side of the membrane (diffusion).
Active Transport: Specific carriers translocate ions, amino acids, or sugars from one membrane surface to the other, losing energy in the process. These carriers are likely integral transmembrane components.
Active Transport Examples in Plants:
- Ions moving from soil into plant roots.
- Transportation of chloride and nitrate from the cytosol to the vacuole.
- Sugars from photosynthesis moving from leaves to fruit.
- Calcium using energy from ATP to move between cells.
- Minerals traveling through a stem to various parts of the plant.
- Water moving from plant roots to other plant cells via root pressure.

Macro-Transfer Processes

Cytosis: Transport of macromolecules across the plasma membrane.
- Endocytosis: Movement into the cell.
  - Phagocytosis: “Cell eating.”
  - Pinocytosis: “Cell drinking.”
  - Receptor-mediated endocytosis: Uptake of specific particles based on recognition.
- Exocytosis: Movement into the extracellular space.

Endocytosis

Phagocytosis: Macrophages engulf and remove cellular and non-cellular debris from the body.
Pinocytosis & Micropinocytosis: Similar to phagocytosis but primarily concerned with the uptake of soluble materials dissolved in tissue fluids.
Fluid Endocytosis: The concentration of the substance within the enclosed vesicle is the same as that in the extracellular environment.

Exocytosis

Cellular secretion: Exocrine and endocrine secretory cells release their secretory products, nerve fibers release acetylcholine stores, and osteoclasts secrete lysosomal enzymes.
Vesicle Fusion: The transported material is packaged in a membrane-limited vesicle within the cytoplasm (e.g., secretory granule or lysosome). A demand for release triggers the vesicle to move to a specific region of the cell boundary where it fuses with the plasma membrane, releasing its contents.
Membrane Addition: Exocytosis adds intracellular membrane to the plasma membrane, which can become a significant contribution if it occurs repeatedly.

Plasma Membrane & Malignancy

Malignant Tumors: Can arise spontaneously or be induced by radiation, chemical agents, and virus infection.
Neoplasia: Malignant cells divide without stimulus and are not subject to normal growth control mechanisms.
Invasion: As malignant tumor cells proliferate, they invade surrounding tissues.
Metastasis: Groups of malignant cells detach from the tumor and disseminate throughout the body via circulatory systems or body cavities, leading to the formation of multiple secondary growths.

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Description

Explore the essential structure and function of the plasma membrane in cells. This quiz covers its components such as lipids and proteins, and how they protect and interact with the external environment. Test your knowledge of both prokaryotic and eukaryotic cell membranes.