Week 4 Cell Membrane Structure and Function

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Questions and Answers

What type of backbone do glycerol-based phospholipids possess?

Fatty acid backbone

Steroid backbone

Glycerol or sphingosine backbone (correct)

Cholesterol backbone

Which of the following statements about glycolipids is true?

Glycolipids are exclusively found in the human ABO blood groups.

Glycolipids do not contain carbohydrate groups.

All glycolipids are sphingosine-based.

Some glycolipids are glycerol-based and called glycoglycerolipids. (correct)

What role do glycosphingolipids have in relation to blood groups?

They are enzymes that process blood cells.

They are involved in energy storage.

They act as specific cell surface markers for blood groups. (correct)

They provide structural support to red blood cells.

What is sodium dodecyl sulfate (SDS) primarily used for in laboratories?

To disrupt membranes and solubilize membrane proteins. Signup and view all the answers

Which of the following correctly describes phosphosphingolipids?

They are sphingosine-based phospholipids. Signup and view all the answers

What primary function does the plasma membrane serve in relation to the cell?

It defines the boundary of the cell and its compartments. Signup and view all the answers

Which structure is embedded in the lipid bilayer and contributes to the membrane's function?

Integral proteins Signup and view all the answers

What component primarily constitutes the main fabric of biological membranes?

Phospholipids Signup and view all the answers

Which type of membrane protein is characterized by being amphipathic and may extend through the membrane?

Integral membrane proteins Signup and view all the answers

What is the role of cholesterol in the plasma membrane?

To maintain fluidity and stability. Signup and view all the answers

How do peripheral proteins primarily interact with the membrane?

By binding to integral membrane proteins. Signup and view all the answers

What is the function of membrane transporters and ion channels within the plasma membrane?

To enable transmembrane movement of specific solutes. Signup and view all the answers

What distinguishes integral membrane proteins from peripheral proteins?

Integral proteins are embedded within the membrane, while peripheral proteins are not. Signup and view all the answers

Which statement is true regarding the composition of the phospholipid bilayer?

The inner and outer layers differ in lipid, protein, and carbohydrate types. Signup and view all the answers

What type of membrane protein is specifically linked to the lipid bilayer through a fatty acid or isoprenyl group?

Lipid-anchored membrane proteins Signup and view all the answers

What impact do double bonds in hydrocarbon chains have on their arrangement?

They prevent the chains from fitting together snugly. Signup and view all the answers

How does cholesterol influence membrane fluidity at high temperatures in animal cells?

It maintains constant fluidity. Signup and view all the answers

What effect does cholesterol have on lipid chains at low temperatures?

It disrupts the ordered packing of lipid chains. Signup and view all the answers

What characterizes the fluid mosaic model of membranes?

Membranes are composed of lipids, proteins, and carbohydrates, giving them a fluid character. Signup and view all the answers

What percentage of the total membrane lipid in a typical animal cell is cholesterol?

Up to 50% Signup and view all the answers

What is the main role of transport proteins in cellular membranes?

To allow selective passage of molecules Signup and view all the answers

Which type of transport protein allows the movement of two different types of molecules in the same direction?

Symport Signup and view all the answers

What distinguishes ligand-gated ion channels from other types of ion channels?

They open in response to specific ligand binding. Signup and view all the answers

Which mechanism is primarily responsible for transporting materials against their concentration gradient?

Active transport Signup and view all the answers

What is the energy source for active transport processes in cells?

Adenosine triphosphate (ATP) Signup and view all the answers

How do coupled transporters function in cellular transport?

By linking the movement of one solute to another Signup and view all the answers

What occurs during exocytosis?

Large molecules are expelled from the cell. Signup and view all the answers

What is the primary function of gap junctions?

To allow communication between adjacent cells Signup and view all the answers

Which type of transport protein allows only a single type of molecule to pass through?

Uniport Signup and view all the answers

What occurs during endocytosis?

Cells engulf external substances Signup and view all the answers

What dynamic property do lipid bilayers exhibit in response to disruption?

They spontaneously reseal Signup and view all the answers

Which type of ion channel opens in response to changes in membrane potential?

Voltage-gated Signup and view all the answers

Which process allows the removal of various substances from the cell?

Exocytosis Signup and view all the answers

What results from the mechanical opening of ion channels in response to sound waves?

Creation of an electrical impulse Signup and view all the answers

What is the primary function of membranes in cells?

To act as permeable barriers Signup and view all the answers

Which type of transport requires energy?

Active transport Signup and view all the answers

How does passive transport occur across membranes?

Along a concentration gradient Signup and view all the answers

What plays a crucial role in the facilitated diffusion of solutes?

Transport proteins Signup and view all the answers

What is osmosis specifically concerned with?

Diffusion of water molecules Signup and view all the answers

What effect does a hypertonic solution have on red blood cells?

Cells shrink Signup and view all the answers

What is a characteristic of facilitated diffusion?

It is always passive Signup and view all the answers

Which substances typically require transport proteins to move across cell membranes?

Hydrophilic nutrients Signup and view all the answers

What happens to red blood cells in an isotonic solution?

Their volume remains unchanged Signup and view all the answers

How do membranes contribute to cellular communication?

By providing binding sites for receptors Signup and view all the answers

What defines the permeability barrier of the cell membrane?

The phospholipid bilayer structure Signup and view all the answers

What characterizes active transport processes?

Need for cellular energy Signup and view all the answers

What effect does a hypotonic solution have on a red blood cell?

Cell swells and may burst Signup and view all the answers

What drives the direction of movement in passive transport?

Concentration gradients or electrochemical potentials Signup and view all the answers

What are the three sub-phases of Interphase, and what key processes occur in each?

The three sub-phases of Interphase are G1 Phase (cell growth and preparation for DNA replication), S Phase (DNA replication occurs), and G2 Phase (further growth and preparation for mitosis). Signup and view all the answers

Describe the role of checkpoints in the cell cycle.

Checkpoints at G1, G2, and M phases regulate the cell cycle by ensuring proper conditions for cell division and preventing errors. If issues are detected, the cycle can be halted to fix problems or trigger apoptosis. Signup and view all the answers

What are the stages of Mitosis, and what occurs during Anaphase?

The stages of Mitosis include Prophase, Metaphase, Anaphase, and Telophase. During Anaphase, sister chromatids are pulled apart to opposite ends of the cell. Signup and view all the answers

What distinguishes Mitosis from Meiosis in terms of daughter cells produced?

Mitosis produces two identical daughter cells, while Meiosis produces four genetically diverse gametes. This difference is essential for asexual and sexual reproduction, respectively. Signup and view all the answers

Explain the significance of apoptosis in the context of the cell cycle.

Apoptosis is programmed cell death that eliminates damaged or unwanted cells, maintaining tissue homeostasis. It plays a crucial role in development and preventing cancer by removing cells that might proliferate uncontrollably. Signup and view all the answers

What happens during Cytokinesis, and how does it differ in plant and animal cells?

Cytokinesis is the division of the cytoplasm that results in two daughter cells. In animal cells, a cleavage furrow forms, while in plant cells, a cell plate is created. Signup and view all the answers

How do cyclins and cyclin-dependent kinases (CDKs) regulate the cell cycle?

Cyclins bind to CDKs to activate them, driving the cell cycle forward through checkpoints. Their levels fluctuate throughout the cell cycle, ensuring that division occurs only under favorable conditions. Signup and view all the answers

What is the main purpose of the S Phase in the cell cycle?

The S Phase is primarily for DNA replication, during which each chromosome is duplicated to form sister chromatids. This ensures that both daughter cells receive an identical set of chromosomes. Signup and view all the answers

What is the function of 'crossing over' during Meiosis, and when does it occur?

'Crossing over' is the exchange of genetic material between homologous chromosomes that occurs during Prophase I of Meiosis. This process increases genetic diversity among gametes. Signup and view all the answers

How does the structure of chromosomes change from Prophase to Telophase?

During Prophase, chromatin condenses into visible chromosomes, while in Telophase, chromosomes decondense back into chromatin and nuclear envelopes reform around each set of chromosomes. Signup and view all the answers

Study Notes

Cell Membrane Structure and Function

The plasma membrane defines the boundary of the cell and any of its internal compartments including organelles like mitochondria, nucleus, and chloroplasts.
The plasma membrane is semi-permeable, allowing selective passage of substances.
The biological membrane is a lipid bilayer with proteins embedded or associated with the bilayer.
Biological membranes are stable in water.
The lipid bilayer is impermeable to charged or polar solutes, but membrane transporters and ion channels allow passage of specific solutes.
All of the internal membranes of cells are part of an interconnected, functionally specialized, and dynamic endomembrane system.

Membrane Components

Components of the plasma membrane include phospholipids, integral proteins, peripheral proteins, carbohydrates, and cholesterol.
Phospholipids are the main fabric of the membrane.
Integral proteins are embedded in, and may or may not extend through, the phospholipid bilayer.
Peripheral proteins are attached to the phospholipid bilayer but not embedded in its hydrophobic core, or are attached to proteins or lipids on the extracellular side of the membrane.
Carbohydrates are attached to proteins or lipids on the extracellular side of the membrane, forming glycoproteins and glycolipids.
Cholesterol is tucked between the hydrophobic tails of the membrane phospholipids.
The composition of the two layers of the phospholipid bilayer membrane is not identical (e.g., bulkier molecules are more often found in the inner side of the membrane).

Integral Membrane Proteins

Integral membrane proteins are amphipathic, with at least one hydrophobic region at the membrane interior and at least one hydrophilic region extended outward.
Transmembrane proteins are a type of integral membrane protein that extend across the membrane.

Peripheral Proteins

Peripheral proteins can be either lipid-anchored membrane proteins or bound to integral membrane proteins.
Lipid-anchored membrane proteins are located on one of the surfaces of the lipid bilayer, and are attached by covalent linkage to a fatty acid, isoprenyl, or glycosylphosphatidylinositol (GPI).

Membrane Lipids

Phospholipids are composed of a small polar head group (such as choline) attached to a fatty acid-containing glycerol or sphingosine backbone.
Glycerol-based phospholipids are called phosphoglycerolipids (phosphoglycerides).
Sphingosine-based phospholipids are called phosphosphingolipids.
Glycolipids are formed by adding carbohydrate groups to lipids.
Glycoglycerolipids are glycerol-based glycolipids.
Glycosphingolipids are sphingosine-based glycolipids.
Human ABO blood groups are determined by glycosphingolipids called A and B antigens, which serve as cell surface markers.

Membrane Fluidity

Membrane fluidity is influenced by temperature and the degree of fatty acid saturation.
Kinks caused by double bonds in fatty acids prevent hydrocarbon chains from fitting together snugly, increasing membrane fluidity.
Cholesterol affects membrane fluidity, acting as a fluidity buffer and helping to maintain fairly constant fluidity despite temperature or saturation fluctuations.

Fluid Mosaic Model

The fluid mosaic model, proposed by S. Jonathan Singer and Garth Nicolson in 1972, describes the structure of membranes as a fluid lipid bilayer with embedded proteins and carbohydrates.

Membrane Functions

Membranes function as boundaries of cells and organelles, acting as permeable barriers between internal and external environments.
Membranes serve as sites for specific biochemical functions.
Membranes contain transport proteins that regulate substance movement across the cell.
Membranes possess protein receptors to detect extracellular signals.
Membranes provide mechanisms for cell-to-cell contact, adhesion, and communication.

Boundary and Permeability Barrier:

Membranes define the boundaries of cells and their compartments, separating the interior of the cell from the surrounding environment.
Membranes are an effective permeability barrier for polar molecules and ions, preventing their free passage.
Intracellular membranes compartmentalize functions within eukaryotic cells.

Specific Functions

Specific proteins embedded in or localized on membranes give the membrane a specific function.
Examples of specific membrane functions include:
- Cell membrane enzymes that secrete materials for the extracellular matrix.
- Ion transporters in nerve cell membranes essential for signal transmission to muscles.

Transport Across the Membrane

Most substances that move across membranes are not macromolecules.
Membrane proteins carry out and regulate the transport of nutrients, ions, gases, water, and other substances into and out of cells and organelles.
While some substances (gases, small or lipophilic molecules) can diffuse directly across membranes, most substances needed by the cell are hydrophilic and require transport proteins.
Cells may have specific transporters for importing glucose, amino acids, or other nutrients.

Transport Mechanisms

Transport mechanisms can be either passive or active.
Passive transport is the movement of substances across the membrane without energy expenditure, following concentration gradients or electrochemical potentials.
Active transport requires energy.
Types of passive transport include simple diffusion and facilitated diffusion.
Types of active transport include coupled transporters, ATP-driven pumps, and light-driven pumps.

Simple Diffusion

Simple diffusion is the movement of solutes or molecules from a region of higher concentration to a region of lower concentration.
Molecules move down a concentration gradient.
Simple diffusion is a passive process that requires no energy.

Osmosis

Osmosis is the diffusion of water molecules from one side of a selectively permeable (semi-permeable) membrane to the other.
The cell membrane is naturally permeable to water and water flow across membranes is always passive.
Tonicity describes the effect of an extracellular solution on the volume of a cell, determined by the relative concentration of non-penetrating solute molecules.
Hypertonic solutions cause cells to shrink as water leaves the cell.
Hypotonic solutions cause cells to swell as water enters the cell.
Isotonic solutions do not affect cell volume.

Facilitated Diffusion

Facilitated diffusion is the passive movement of solutes (molecules, ions) across the membrane through transport proteins (protein channels or carrier proteins).
Solutes move along the concentration gradient.
Facilitated diffusion is a selective process.
Facilitated diffusion is a passive process, requiring no energy.

Transport Proteins

Uniports transport a single type of molecule across the membrane.
Symports transport two different types of molecules in the same direction across the membrane.
Antiports transport two different types of molecules in opposite directions across the membrane.

Ion Channels

Ion channels allow passage of specific ions and can be gated by:
- Ligands: Triggered by binding of specific substances, like the nicotinic acetylcholine receptor for Na+ ions passage.
- Mechanical forces: Triggered by mechanical forces, such as sound waves bending cilia on hair cells, which open ion channels and create nerve impulses.
- Changes in membrane potential: Triggered by changes in the membrane potential, such as calcium channels at the synapse of neurons.

Active Transport

Active transport is a process that requires energy to move molecules against their concentration gradient, from a low concentration to a high concentration.
Active transport is mediated by transport proteins and uses cellular energy, such as ATP.
Major functions of active transport include:
- Uptaking essential nutrients from the environment.
- Removing waste products from the cells.
- Maintaining constant imbalance of electro-potential.
- Large molecules like starch are actively transported across the plasma membrane by processes known as exocytosis and endocytosis.

Exocytosis and Endocytosis

Exocytosis describes the release of substances from the cell through vesicle fusion with the plasma membrane.
Endocytosis describes the intake of substances into the cell through vesicle formation.
Active transport processes can involve coupled transporters, ATP-driven pumps, and light-driven pumps.

The Erythrocyte (Red Blood Cell)

Erythrocytes possess specific transport processes, such as the transport of glucose and sodium ions.

Exocytosis of Neurotransmitters at the Synapse

Exocytosis plays a vital role in the transmission of nerve impulses at the synapse through the release of neurotransmitters.

Function – Signal Transduction

Membrane proteins detect and transmit electrical and chemical signals, a process known as signal transduction.
Membrane proteins mediate cell adhesion and cell-to-cell communication.

Membrane Self-Sealing

Lipid bilayers can self-seal when disrupted due to the lateral flow of lipid molecules.
Small breaks in the cell membrane spontaneously seal.

The Cell Cycle

The cell cycle is a series of stages that a cell goes through to grow and divide.
Interphase, the longest phase of the cell cycle, is divided into three sub-phases:
- G1 Phase (Gap 1): The cell grows and performs its normal functions, preparing for DNA replication.
- S Phase (Synthesis): DNA replication occurs, creating two identical sister chromatids for each chromosome.
- G2 Phase (Gap 2): The cell continues growing, preparing for mitosis, and checks for DNA damage.
M Phase (Mitosis), the division of the nucleus, is comprised of several important stages:
- Prophase: Chromatin condenses into chromosomes, and the mitotic spindle begins to form.
- Metaphase: Chromosomes line up at the cell equator.
- Anaphase: Sister chromatids are pulled apart to opposite ends of the cell.
- Telophase: Chromosomes decondense, and nuclear envelopes reform around each set of chromosomes.

Cell Division

Mitosis: A type of cell division that produces two identical daughter cells. It's fundamental for growth, repair, and asexual reproduction. Mitosis involves only one round of division.
Meiosis: A type of cell division that produces four genetically diverse daughter cells, known as gametes. It is essential for sexual reproduction, and involves two rounds of division: Meiosis I and Meiosis II. Meiosis introduces genetic variation through crossing over and independent assortment.

Cell Cycle Regulation

The cell cycle is tightly controlled by checkpoints at G1, G2, and M phases to ensure proper cell division.
Cyclins and cyclin-dependent kinases (CDKs) are crucial proteins that regulate these checkpoints.
Errors in cell cycle regulation can lead to uncontrolled cell division, resulting in cancer.

Apoptosis

Apoptosis is a programmed cell death that is critical for eliminating damaged or unwanted cells during development and tissue homeostasis.

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Explore the intricate details of the cell membrane in this quiz. Learn about its structure, key components, and the essential role it plays in cell functionality. Test your knowledge on topics such as lipid bilayers, proteins, and selective permeability.