Cell Membranes Overview
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Questions and Answers

What is the name given to cell membranes?

Biomembranes

The discovery of cell membranes was not related to the advancement of microscopic techniques.

False

Biomembranes in all cells have the same chemical composition.

False

What is the average thickness of the cytoplasmic membrane?

<p>60 - 100 nm</p> Signup and view all the answers

What are the main functions of the cell membrane?

<p>All of the above</p> Signup and view all the answers

What is the main component of cell membranes?

<p>Phospholipids</p> Signup and view all the answers

Phospholipids are chemically bound to each other in the phospholipid bilayer.

<p>False</p> Signup and view all the answers

Which of the following describes the types of proteins found in cell membranes?

<p>both A and B</p> Signup and view all the answers

Integral proteins can easily be separated from the biomembranes.

<p>False</p> Signup and view all the answers

Peripheral proteins can be easily separated from the biomembranes.

<p>True</p> Signup and view all the answers

The number and types of proteins found in a biomembrane is constant across all cells.

<p>False</p> Signup and view all the answers

What is the role of membrane proteins?

<p>Membrane proteins perform various functions, including structural support, transport of molecules across the membrane, receptor activity, and enzymatic activity.</p> Signup and view all the answers

Some membrane proteins are involved in the transport of ions across the membrane.

<p>True</p> Signup and view all the answers

Membrane proteins can never be involved in facilitated diffusion.

<p>False</p> Signup and view all the answers

Membrane proteins are never involved in receptor activity.

<p>False</p> Signup and view all the answers

Some membrane proteins can act as enzymes.

<p>True</p> Signup and view all the answers

Proteins and Glycolipids are never part of the antigens.

<p>False</p> Signup and view all the answers

What is the primary function of membrane receptors?

<p>Membrane receptors are responsible for recognizing and binding signal molecules, including hormones, neurotransmitters, and other signaling molecules.</p> Signup and view all the answers

How can membrane receptors be classified?

<p>All of the above</p> Signup and view all the answers

Receptors that are part of ion channels can bind to cations and anions.

<p>True</p> Signup and view all the answers

Receptors with enzyme activity are only involved in catalyzing a limited number of reactions.

<p>False</p> Signup and view all the answers

G protein-coupled receptors represent a relatively small group of membrane receptors.

<p>False</p> Signup and view all the answers

What are the two basic mechanisms that regulate the transfer of substances into and out of cells?

<p>Both A and B</p> Signup and view all the answers

What is passive transport?

<p>Passive transport is the movement of substances across a membrane following their concentration gradient, without requiring energy from the cell.</p> Signup and view all the answers

What are the main types of passive transport?

<p>The two main types of passive transport are diffusion and osmosis.</p> Signup and view all the answers

The speed of passive transport is solely dependent on the size of the concentration gradient.

<p>False</p> Signup and view all the answers

Substances with low molecular weight can be transported across the cytoplasmic membrane via passive transport.

<p>True</p> Signup and view all the answers

What is active transport?

<p>Active transport is the movement of substances across a membrane against their concentration gradient, requiring energy expenditure by the cell.</p> Signup and view all the answers

Active transport relies on the movement of the membrane itself.

<p>False</p> Signup and view all the answers

Active transport is an example of a passive transport mechanism.

<p>False</p> Signup and view all the answers

Active transport involves the consumption of energy from the cell.

<p>True</p> Signup and view all the answers

What are the two basic types of active transport?

<p>The two basic types of active transport are primary active transport and secondary active transport.</p> Signup and view all the answers

Primary active transport is powered by the hydrolysis of ATP.

<p>True</p> Signup and view all the answers

How is primary active transport achieved?

<p>Primary active transport involves the phosphorylation and dephosphorylation of transport proteins, altering their affinity for the substrate and facilitating the movement of substances across the membrane.</p> Signup and view all the answers

What is an example of primary active transport?

<p>The sodium-potassium pump (Na+-K+-ATPase) is a classic example of primary active transport.</p> Signup and view all the answers

Secondary active transport directly utilizes ATP hydrolysis to move substances.

<p>False</p> Signup and view all the answers

How is secondary active transport achieved?

<p>Secondary active transport involves the attachment of ions to transport proteins, which alters the affinity for the transported substance.</p> Signup and view all the answers

Secondary active transport can be classified as either cotransport or antiport.

<p>True</p> Signup and view all the answers

What is endocytosis?

<p>Endocytosis is the process by which cells take in substances from the external environment by engulfing them into the cell.</p> Signup and view all the answers

Endocytosis is a passive transport mechanism.

<p>False</p> Signup and view all the answers

Which of the following describes the main types of endocytosis?

<p>Both A and B</p> Signup and view all the answers

What is pinocytosis?

<p>Pinocytosis is the process by which cells take in fluids and dissolved substances by forming small vesicles that pinch off from the cell membrane.</p> Signup and view all the answers

What is phagocytosis?

<p>Phagocytosis is the process by which cells engulf large particles, such as bacteria, cellular debris, or other cells, using their cell membrane to form a phagosome around the particle.</p> Signup and view all the answers

What is exocytosis?

<p>Exocytosis is the process by which cells release substances from their interior into the extracellular environment enclosed in vesicles that fuse with the cell membrane.</p> Signup and view all the answers

Exocytosis is a passive transport mechanism.

<p>False</p> Signup and view all the answers

Exocytosis involves the fusion of transport vesicles with the plasma membrane.

<p>True</p> Signup and view all the answers

What are cell organelles?

<p>Cell organelles are specialized structures within cells that perform specific functions and play crucial roles in cellular processes.</p> Signup and view all the answers

How are cell organelles classified?

<p>All of the above</p> Signup and view all the answers

Membrane-bound organelles consist of only one membrane.

<p>False</p> Signup and view all the answers

The cytoskeleton is composed of proteins.

<p>True</p> Signup and view all the answers

Ribosomes are composed of proteins and nucleic acids.

<p>True</p> Signup and view all the answers

What is the main function of mitochondria?

<p>Mitochondria are responsible for generating energy (ATP) for cellular processes by breaking down organic molecules through cellular respiration.</p> Signup and view all the answers

Mitochondria are only found in prokaryotic cells.

<p>False</p> Signup and view all the answers

Mitochondria are variable in shape and number depending on the cell type.

<p>True</p> Signup and view all the answers

The number of mitochondria in a cell is directly proportional to the intensity of the cell's energy metabolism.

<p>True</p> Signup and view all the answers

Mitochondria have their own DNA and ribosomes.

<p>True</p> Signup and view all the answers

Mitochondrial enzymes are exclusively synthesized on endoplasmic reticulum.

<p>False</p> Signup and view all the answers

What is the role of endoplasmic reticulum?

<p>Endoplasmic reticulum is a network of membranes that serves as a site for protein and lipid synthesis, detoxification, and storage.</p> Signup and view all the answers

Endoplasmic reticulum is only found in plant cells.

<p>False</p> Signup and view all the answers

Endoplasmic reticulum is directly connected to the nucleus.

<p>True</p> Signup and view all the answers

Endoplasmic reticulum is directly connected to the Golgi apparatus.

<p>True</p> Signup and view all the answers

What are the two main types of endoplasmic reticulum?

<p>Both A and B</p> Signup and view all the answers

Rough endoplasmic reticulum is the site of protein synthesis.

<p>True</p> Signup and view all the answers

The ratio of rough to smooth endoplasmic reticulum in a cell is fixed.

<p>False</p> Signup and view all the answers

What is the role of smooth endoplasmic reticulum?

<p>Smooth endoplasmic reticulum is involved in lipid synthesis, steroid hormone production, detoxification, and calcium storage.</p> Signup and view all the answers

What is the function of sarcoplasmic reticulum?

<p>Sarcoplasmic reticulum is a specialized type of smooth endoplasmic reticulum found in muscle cells. It stores and releases calcium ions, which are essential for muscle contraction.</p> Signup and view all the answers

What is the role of the Golgi apparatus?

<p>The Golgi apparatus processes, sorts, and packages proteins and lipids into vesicles for transport to various destinations within the cell or for secretion outside the cell.</p> Signup and view all the answers

The Golgi apparatus is composed of a single flattened sac.

<p>False</p> Signup and view all the answers

The Golgi apparatus is only involved in the packaging of proteins.

<p>False</p> Signup and view all the answers

What is the role of lysosomes?

<p>Lysosomes are membranous sacs containing digestive enzymes that break down worn-out cell components, engulf invading pathogens, and remove cellular debris.</p> Signup and view all the answers

Lysosomes are formed in the smooth endoplasmic reticulum.

<p>False</p> Signup and view all the answers

Vacuoles are only found in plant cells.

<p>False</p> Signup and view all the answers

What is the main function of peroxisomes?

<p>Peroxisomes are small, membrane-bound organelles that contain enzymes involved in the detoxification of harmful substances such as hydrogen peroxide.</p> Signup and view all the answers

Peroxisomes are directly involved in cellular respiration.

<p>False</p> Signup and view all the answers

What is the main function of ribosomes?

<p>Ribosomes are responsible for protein synthesis, reading the genetic code carried by messenger RNA (mRNA) to assemble amino acids into protein chains.</p> Signup and view all the answers

Ribosomes are only found in eukaryotic cells.

<p>False</p> Signup and view all the answers

Ribosomes are composed of two subunits: a large subunit and a small subunit.

<p>True</p> Signup and view all the answers

Ribosomes are directly involved in DNA replication.

<p>False</p> Signup and view all the answers

Study Notes

Cell Membranes (Biomembranes)

  • Cell membranes (biomembranes) are vital components of all cells.
  • Their discovery is linked to advancements in microscopic techniques, especially transmission electron microscopy.
  • A typical trilaminar structure was observed.
  • Cell membranes have similar structures, with slight differences in chemical composition relating to cell differentiation and specialization.

Functions of Cell Membrane

  • Every cell is surrounded by a cytoplasmic membrane separating intracellular and extracellular space.
  • Average membrane thickness is 60-100 nm.
  • The membrane is selectively permeable, maintaining dynamic equilibrium between the cell and its environment.
  • It includes enzymes, receptors and transport proteins, signaling systems, and antigens.
  • The membrane performs functions such as substance intake, signal interactions, and recognition.
  • It's a vital part of many cellular organelles.

Main Components of Cell Membranes

  • Phospholipids are the major components.
  • A phospholipid molecule consists of a polar (hydrophilic) head and two non-polar (hydrophobic) fatty acid tails.
  • In an aqueous environment, the hydrophilic heads of phospholipids are oriented towards water, while the hydrophobic tails point inwards, creating a phospholipid bilayer.
  • Phospholipids are chemically independent, enabling lateral movement.

Other Important Components of Biological Membranes

  • Integral proteins: embedded within, or spanning the bilayer, affecting its hydrophobic sections; difficult to separate from the membrane.
  • Peripheral proteins: situated outside the bilayer linked by ionic bonds; easily isolated from the membrane.
  • Protein type and number vary dependent on cellular differentiation and cell cycle phase.
  • Cell regulation controls the specific membrane protein composition.

Functions of Membrane Proteins

  • Membrane proteins perform diverse functions.
  • Some act as structural components (structural proteins).
  • Others facilitate ion transport across the membrane (pumps and ion channels).
  • Some facilitate substance movement along electrochemical gradients (facilitated diffusion).
  • Many act as receptors binding hormones, neurotransmitters, and signals.
  • Some proteins serve as enzymes.
  • Membrane proteins and glycolipids contribute to the formation of antigens.

Membrane Receptors

  • Membrane receptors are protein structures in the cell membrane.
  • Their function is recognizing and binding signal molecules (e.g., hormones, neurotransmitters).
  • The membrane interacts with its surroundings.
  • Receptor types include those that are part of ion channels, receptors with enzymatic activity, and receptors coupled to G proteins (the largest family).

Transport of Substances Through the Membrane

  • Transfer of substances into or out of cells is facilitated by two basic mechanisms:
  • Passive transport
  • Active transport

Passive Transport

  • Passive transport involves substance movement along the concentration gradient without energy expenditure.
  • The speed of transport is determined by the concentration gradient and the size of the substance.
  • Substances with low molecular weight (e.g., water, oxygen, carbon dioxide, urea, methanol, ethanol) are transported this way.
  • Diffusion is an unordered movement of dissolved molecules from high to low concentration across the membrane until equilibrium is reached.
  • Osmosis exemplifies passive transport.

Osmosis

  • Osmosis is the movement of water across a selectively permeable membrane from an area of high water concentration to one of low water concentration until equilibrium is reached.
  • Hypertonic solutions have higher solute concentrations outside the cell than inside, causing water to exit and cell shrinkage.
  • Hypotonic solutions have lower solute concentrations outside the cell than inside, causing water to enter and cell swelling.
  • Isotonic solutions have equal solute concentrations inside and outside the cell, leading to no net water movement.

Facilitated Diffusion

  • Facilitated diffusion is a form of passive transport employing plasma membrane proteins for substance movement across a concentration gradient without energy input.
  • The transport protein binds the substance and undergoes conformational change, releasing it into the cytoplasm. Glucose transport is a good example.

Active Transport

  • Active transport moves substances against a concentration or electrochemical gradient using cellular energy (ATP).
  • Systems like channels and pumps transport proteins through the membrane.
  • It's a selective and controlled process often regulated by receptors.
  • Primary active transport: Utilizes direct ATP hydrolysis to change transport protein's conformation facilitating the movement of substances against their gradient (e.g. Na+-K+ pump, H+ pump).
  • Secondary active transport: couples the movement of one substance along its gradient to the movement of another substance against its gradient (e.g. cotransport, antiport).

Endocytosis and Exocytosis

  • Endocytosis and exocytosis facilitate transport of large molecules.
  • Endocytosis: Transports molecules from outside the cell into vesicles within the cytoplasm.
    • Pinocytosis: movement of fluids and small dissolved substances into the cell.
    • Phagocytosis: movement of solids, large particles, or cells into the cell.
  • Exocytosis: Transports molecules from the vesicles within the cell to the outside.

Cell Organelles

  • Cytoplasm is the semi-fluid medium inside the cell, primarily composed of water and various organic and inorganic components.
    • Eukaryotic cells include various organelles, categorized by their membrane composition.
    • Organelles with one membrane include endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and vacuoles.
    • Organelles with two membranes include mitochondria and chloroplasts.
    • Additional organelles consist of proteins (cytoskeleton - microtubules, microfilaments, and intermediate filaments; flagella and cilia) and nucleic acids (ribosomes and nucleolus).

Mitochondria

  • Mitochondria are essential organelles involved in energy production in eukaryotic cells.
  • They generate energy by breaking down organic molecules.
  • Number and shape vary based on cell type.
  • They possess two membranes: an outer membrane and an inner membrane with cristae (folds) to maximize surface area.
  • ATP (adenosine triphosphate) synthesis occurs in the inner membrane.
  • Mitochondria contain their own DNA and ribosomes.

Endoplasmic Reticulum

  • Endoplasmic reticulum (ER) is a network of membranes (tubules and cisterns) linked to the nuclear membrane.
  • It plays a crucial role in protein and lipid synthesis and is involved in compartmentalization within the cell.
  • Two types of ER are distinguished based on structure and function:
    • Rough ER: Studded with ribosomes, responsible for protein synthesis.
    • Smooth ER: Lacks ribosomes and deals with lipid production, steroid hormone synthesis, and detoxification.

Golgi Apparatus

  • Golgi apparatus modifies, packages, and sorts proteins and lipids produced by the ER, often repackaging and targeting them to specific locations.
  • Composed of stacks of flattened membranes (cisternae).
  • Post-translational modifications of proteins in Golgi are performed.

Lysosomes and Vesicles

  • Lysosomes containing enzymes for digestion of materials internalized via endocytosis.
  • They break down excess or worn-out organelles, cellular debris.
  • They play a critical role in cell apoptosis.

Peroxisomes

  • Peroxisomes are single-membrane-bound organelles containing enzymes, especially catalase, for detoxification and lipid metabolism.

Ribosomes

  • Ribosomes are essential particles responsible for protein synthesis in cells.
  • They consist of large and small subunits.
  • They may be free in the cytoplasm or bound to the rough ER.

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Description

Explore the structure and functions of cell membranes in this quiz. Learn about their components, the role of phospholipids, and how they contribute to cellular activities. Test your understanding of the vital functions these biomembranes perform.

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