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Questions and Answers
What are membrane receptors responsible for?
What are membrane receptors responsible for?
Active transport requires energy to move substances against a concentration gradient.
Active transport requires energy to move substances against a concentration gradient.
True
Name one example of a substance that can be transported via passive transport.
Name one example of a substance that can be transported via passive transport.
oxygen
Which of the following is a main component of cell membranes?
Which of the following is a main component of cell membranes?
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Membrane receptors with intracellular protein subunits that catalyze chemical reactions are known as __________ receptors.
Membrane receptors with intracellular protein subunits that catalyze chemical reactions are known as __________ receptors.
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Integral proteins can be easily separated from biomembranes.
Integral proteins can be easily separated from biomembranes.
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Match the types of membrane receptors with their functions:
Match the types of membrane receptors with their functions:
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Which of the following substances is primarily moved via facilitated diffusion?
Which of the following substances is primarily moved via facilitated diffusion?
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Which process is specifically associated with the transport of solid particles?
Which process is specifically associated with the transport of solid particles?
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What is the average thickness range of cell membranes?
What is the average thickness range of cell membranes?
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The cell membrane is a __________ permeable boundary.
The cell membrane is a __________ permeable boundary.
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Diffusion is a directed movement of molecules toward lower concentration areas.
Diffusion is a directed movement of molecules toward lower concentration areas.
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Pinocytosis involves the transport of liquid substances into the cell.
Pinocytosis involves the transport of liquid substances into the cell.
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Match the following membrane components with their characteristics:
Match the following membrane components with their characteristics:
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What is the primary role of membrane receptors?
What is the primary role of membrane receptors?
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What restores the integrity of the plasma membrane after pinocytosis?
What restores the integrity of the plasma membrane after pinocytosis?
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What ensures the movement of phospholipids within the membrane?
What ensures the movement of phospholipids within the membrane?
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In ________, substances are transported from the cell into the extracellular environment.
In ________, substances are transported from the cell into the extracellular environment.
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Match each term with its correct description:
Match each term with its correct description:
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Biomembranes have the same composition across all cell types.
Biomembranes have the same composition across all cell types.
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Name one function of membrane proteins.
Name one function of membrane proteins.
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What is the primary substance that composes the cytoplasm of a cell?
What is the primary substance that composes the cytoplasm of a cell?
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Cytoplasm is a solid and rigid mass within the cell.
Cytoplasm is a solid and rigid mass within the cell.
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What structures arise from the endoplasmic reticulum and Golgi apparatus to facilitate exocytosis?
What structures arise from the endoplasmic reticulum and Golgi apparatus to facilitate exocytosis?
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What energy source is primarily used in primary active transport?
What energy source is primarily used in primary active transport?
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Cotransport involves transporting substances in opposite directions.
Cotransport involves transporting substances in opposite directions.
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Name one example of a primary active transport protein.
Name one example of a primary active transport protein.
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The process by which substances are transported into cells is called ______.
The process by which substances are transported into cells is called ______.
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Match the type of transport with its description:
Match the type of transport with its description:
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What type of transport occurs when the affinity of transport proteins changes due to phosphorylation?
What type of transport occurs when the affinity of transport proteins changes due to phosphorylation?
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Exocytosis is the process of transporting substances out of the cell.
Exocytosis is the process of transporting substances out of the cell.
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What is the primary function of the Na+–K+ pump?
What is the primary function of the Na+–K+ pump?
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Which type of organelle is characterized by having one membrane?
Which type of organelle is characterized by having one membrane?
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Mitochondria can reproduce independently of the cell they are in.
Mitochondria can reproduce independently of the cell they are in.
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What is the primary function of mitochondria in eukaryotic cells?
What is the primary function of mitochondria in eukaryotic cells?
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The __________ cycle is where enzymes involved in the energy production are located within the mitochondria.
The __________ cycle is where enzymes involved in the energy production are located within the mitochondria.
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Which enzyme system is located in the inner membrane of the mitochondria?
Which enzyme system is located in the inner membrane of the mitochondria?
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Mitochondria only contain proteins necessary for energy production.
Mitochondria only contain proteins necessary for energy production.
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What are the main structural components of the cytoskeleton?
What are the main structural components of the cytoskeleton?
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Match the organelle with its description.
Match the organelle with its description.
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What is the primary function of Smooth Endoplasmic Reticulum?
What is the primary function of Smooth Endoplasmic Reticulum?
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Rough Endoplasmic Reticulum is responsible for the synthesis of proteins.
Rough Endoplasmic Reticulum is responsible for the synthesis of proteins.
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What are the two types of endoplasmic reticulum?
What are the two types of endoplasmic reticulum?
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The Golgi apparatus processes proteins and ________ coming from the endoplasmic reticulum.
The Golgi apparatus processes proteins and ________ coming from the endoplasmic reticulum.
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Match the following components with their functions:
Match the following components with their functions:
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From which side do proteins enter the Golgi apparatus?
From which side do proteins enter the Golgi apparatus?
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The main function of the Golgi apparatus is to synthesize proteins.
The main function of the Golgi apparatus is to synthesize proteins.
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What special form of endoplasmic reticulum do muscle cells have?
What special form of endoplasmic reticulum do muscle cells have?
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Study Notes
Cell Membranes (Biomembranes)
- Cell membranes are crucial parts of all cells.
- Their discovery was linked with advancements in microscopy, particularly transmission electron microscopy.
- Observations showed a typical trilaminar structure.
- Biomembranes within cells have similar structures, with minor chemical composition differences due to cellular differentiation and specialization.
Functions of Cell Membranes
- Every cell is enclosed by a cytoplasmic membrane, separating intracellular and extracellular spaces.
- The average membrane thickness is 60-100 nanometers.
- The membrane is a selective boundary, maintaining a dynamic equilibrium between the cell and its environment.
- The membrane contains enzymes, receptors, transport proteins, signaling systems, and antigens.
- It performs various functions, including substance intake, interactions with the environment, and signal recognition.
- Membranes are integral components of many cellular organelles.
Main Components of Cell Membranes
- Phospholipids are the main components.
- Phospholipid molecules have a hydrophilic (water-loving) head and two hydrophobic (water-fearing) fatty acid tails.
- In an aqueous environment, the hydrophilic heads face outward, and the hydrophobic tails face inward, forming a bilayer.
- Phospholipids are not chemically bound to each other, allowing for lateral movement.
Other Important Components of Biological Membranes
- Proteins are also crucial components.
- Integral proteins interact with the hydrophobic parts of the phospholipid bilayer and might span it completely.
- Peripheral proteins are located outside the lipid bilayer and can be easily separated.
- The type and number of proteins in the membrane vary depending on cell differentiation and the cell cycle.
- Cells control the specific protein composition of their membranes.
Functions of Membrane Proteins
- Membrane proteins carry out varied functions, serving as structural components and contributing to the transport of ions.
- Some proteins facilitate ion transport across membranes, either via pumps or channels, following electrochemical gradients (facilitated diffusion).
- Other proteins act as receptors, binding hormones, neurotransmitters, and other signal molecules.
- Some membrane proteins function as enzymes, playing a catalytic role within the cell.
- Others contribute to the formation of antigens.
Membrane Receptors
- Membrane receptors are proteins located in the cell membrane.
- They recognize and bind to signal molecules (hormones, neurotransmitters).
- These interactions trigger processes within the cell.
- Membrane receptors are classified into different categories.
Membrane Receptors - Types
- Receptors that form part of ion channels: involved in cation and anion transport.
- Receptors with enzymatic activity: intracellular proteins that catalyze certain chemical reactions (e.g., insulin receptor).
- Receptors coupled with G proteins: the largest group of membrane receptors (five families are known).
Transport of Substances Through the Membrane
- Substances enter and exit cells through passive or active transport mechanisms.
- Passive transport doesn't require energy.
- Active transport requires energy.
Passive Transport
- Passive transport follows the concentration gradient (moving from high to low concentration).
- The speed of transport depends on the concentration gradient and the size of the substance.
- Small, non-polar molecules (water, oxygen, carbon dioxide, urea, methanol, ethanol) can be transported passively.
Diffusion
- Diffusion is a passive transport process where substances move from high to low concentration.
- Diffusion continues until the concentration is equalized on both sides of the membrane.
Osmosis
- Osmosis is the passive transport of water across a selectively permeable membrane.
- Water moves from a low solute concentration (hypotonic) to a high solute concentration (hypertonic) area to dilute the higher solute concentration.
- Cells can become shrunken (crenation) due to high solute concentration or burst (lysis) due to low solute concentration in the surrounding environment.
Facilitated Diffusion
- Facilitated diffusion is a passive transport process where substances move across the membrane via protein channels or carriers.
- The process requires no energy directly; the driving force is the concentration gradient.
- The transport protein facilitates the movement of substances without affecting the direction of transport (high to low concentration).
Active Transport
- Active transport moves substances against a concentration or electrochemical gradient.
- It requires energy in the form of ATP (adenosine triphosphate) hydrolysis.
- The transport is performed by protein complexes called pumps and channels that pass across the membrane.
Primary Active Transport
- Primary active transport directly uses ATP to move substances against their concentration gradients.
- The transport protein changes its conformational shape during transport, binding and releasing the molecule transported.
- This is the case of Na+/K+-ATPase or H+-ATPase.
Secondary Active Transport (Co-transport and Anti-port)
- Secondary active transport uses the energy from the movement of one substance down its concentration gradient to move another substance against its concentration gradient.
- Co-transport (symport) means both substance move in the same direction.
- Anti-port means both substances move in opposite directions.
Endocytosis and Exocytosis
- Endocytosis and exocytosis are bulk transport processes for substances with high molecular weights.
- Endocytosis involves substances entering the cell.
- Exocytosis involves substances leaving the cell.
- These processes involve extensive changes in the cell membrane.
Pinocytosis
- Pinocytosis is a specialized cell endocytosis process that involves the ingestion of small liquid droplets.
- The cell membrane engulfs the liquid, forming a vesicle that eventually moves inside of the cytoplasm.
Phagocytosis
- Phagocytosis is the process by which cells engulf solid particles.
- These particles are enclosed within a membrane vesicle, transported into the cytoplasm, and later digested.
- Usually seen in immune cells engulfing pathogens.
Exocytosis
- Exocytosis involves the transport of substances outside of the cell.
- Materials are packaged in vesicles that move towards and fuse with the cell membrane.
- Substances are then expelled from the cell.
Cell Organelles
- The cytoplasm comprises various organelles with specific roles and structures.
- Some organelles have a single membrane (e.g., endoplasmic reticulum, Golgi apparatus, vesicles including peroxisomes, vacuoles and lysosomes).
- Other organelles have a double membrane (e.g., mitochondria, chloroplasts).
- Organelles are involved in distinct functions, including metabolism, synthesis, secretion, and degradation.
Mitochondria
- Mitochondria generate energy for eukaryotic cells through cellular respiration.
- They possess two membranes: an outer and inner membrane.
- The inner membrane is folded into cristae, increasing its surface area for reactions.
- Mitochondria have their own DNA (circular prokaryotic-type) allowing for their self-replication.
Endoplasmic Reticulum (ER)
- ER is a network of membrane tubules and cisterns in the cell.
- It is connected with the nuclear envelope.
- The ER has smooth and rough forms; the rough ER has ribosomes on its surface and is involved in protein synthesis.
- The smooth ER synthesizes lipids, steroid hormones, and cholesterol and detoxifies harmful substances.
Golgi Apparatus
- Golgi apparatus is a system of flattened sacs that modifies, packages, and transports proteins and lipids.
- It is involved in sorting and directing proteins and lipids to their respective cellular destinations.
- It receives materials from the ER and modifies them before they are packaged into secretory vesicles.
Lysosomes and Other Vesicles
- Lysosomes are membrane-bound vesicles containing hydrolytic enzymes.
- They participate in digesting and removing unwanted materials.
- Related vesicles have different roles from digestion, in transport, and other functions.
Peroxisomes
- Peroxisomes are vesicles that contain enzymes for reactions involving oxygen. Often involved in breakdown of fatty acids and other molecules.
Ribosomes
- Ribosomes are small organelles crucial for protein synthesis.
- They are composed of ribosomal RNA (rRNA) and proteins.
- Ribosomes can be found free in the cytoplasm; some associated with the endoplasmic reticulum.
Ribosomes of Eukaryotic Cells
- Ribosomes in eukaryotic cells are larger than prokaryotic ribosomes, with a sedimentation coefficient of 80S.
- They consist of four rRNA types and 82 proteins.
- They play essential roles in the cytoplasm and on the rough endoplasmic reticulum in protein synthesis.
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Description
Explore the crucial role of cell membranes in cellular structure and function. Learn about their unique trilaminar structure, key functions, and the importance of selective boundaries in maintaining cellular equilibrium. This quiz will enhance your understanding of biomembranes and their components.
