Cell Membranes in Biology

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Questions and Answers

What are membrane receptors responsible for?

Transporting ions exclusively

Providing structural support to cells

Facilitating energy production

Recognizing and binding signal molecules (correct)

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.

oxygen

Which of the following is a main component of cell membranes?

Phospholipids Signup and view all the answers

Membrane receptors with intracellular protein subunits that catalyze chemical reactions are known as __________ receptors.

enzyme Signup and view all the answers

Integral proteins can be easily separated from biomembranes.

False Signup and view all the answers

Match the types of membrane receptors with their functions:

Ion channel receptors = Transport of cations and anions Enzyme-linked receptors = Catalyze chemical reactions G protein-coupled receptors = Signal transduction pathways Receptor tyrosine kinases = Insulin receptor activity Signup and view all the answers

Which of the following substances is primarily moved via facilitated diffusion?

Glucose Signup and view all the answers

Which process is specifically associated with the transport of solid particles?

Phagocytosis Signup and view all the answers

What is the average thickness range of cell membranes?

60 – 100 nm Signup and view all the answers

The cell membrane is a __________ permeable boundary.

selectively Signup and view all the answers

Diffusion is a directed movement of molecules toward lower concentration areas.

False Signup and view all the answers

Pinocytosis involves the transport of liquid substances into the cell.

True Signup and view all the answers

Match the following membrane components with their characteristics:

Integral proteins = Hardly separable from membranes Peripheral proteins = Easily separable from membranes Phospholipids = Form the bilayer structure Selectively permeable = Regulates substance movement Signup and view all the answers

What is the primary role of membrane receptors?

To interact with signal molecules and facilitate cellular responses. Signup and view all the answers

What restores the integrity of the plasma membrane after pinocytosis?

The membrane closes around the vesicle. Signup and view all the answers

What ensures the movement of phospholipids within the membrane?

Lateral movement Signup and view all the answers

In ________, substances are transported from the cell into the extracellular environment.

exocytosis Signup and view all the answers

Match each term with its correct description:

Pinocytosis = Transport of liquid substances Phagocytosis = Transport of solid particles Exocytosis = Substances released from the cell Cytoplasm = Inner environment of the cell Signup and view all the answers

Biomembranes have the same composition across all cell types.

False Signup and view all the answers

Name one function of membrane proteins.

Structural support, transport, signaling, or recognition. Signup and view all the answers

What is the primary substance that composes the cytoplasm of a cell?

Water Signup and view all the answers

Cytoplasm is a solid and rigid mass within the cell.

False Signup and view all the answers

What structures arise from the endoplasmic reticulum and Golgi apparatus to facilitate exocytosis?

Vesicles Signup and view all the answers

What energy source is primarily used in primary active transport?

Hydrolysis of ATP Signup and view all the answers

Cotransport involves transporting substances in opposite directions.

False Signup and view all the answers

Name one example of a primary active transport protein.

Na+–K+ pump or H+ pump Signup and view all the answers

The process by which substances are transported into cells is called ______.

endocytosis Signup and view all the answers

Match the type of transport with its description:

Primary active transport = Involves energy from ATP hydrolysis Secondary active transport = Uses ion gradients to transport substrates Cotransport = Transport of ions and substrates in the same direction Antiport = Transport of ions and substrates in opposite directions Signup and view all the answers

What type of transport occurs when the affinity of transport proteins changes due to phosphorylation?

Primary active transport Signup and view all the answers

Exocytosis is the process of transporting substances out of the cell.

True Signup and view all the answers

What is the primary function of the Na+–K+ pump?

To maintain the electrochemical gradient across the membrane Signup and view all the answers

Which type of organelle is characterized by having one membrane?

Golgi apparatus Signup and view all the answers

Mitochondria can reproduce independently of the cell they are in.

True Signup and view all the answers

What is the primary function of mitochondria in eukaryotic cells?

Generating energy Signup and view all the answers

The __________ cycle is where enzymes involved in the energy production are located within the mitochondria.

citric acid Signup and view all the answers

Which enzyme system is located in the inner membrane of the mitochondria?

H+ATP synthase Signup and view all the answers

Mitochondria only contain proteins necessary for energy production.

False Signup and view all the answers

What are the main structural components of the cytoskeleton?

Microtubules, microfilaments, intermediate filaments Signup and view all the answers

Match the organelle with its description.

Nucleus = Contains genetic material and controls cell activities Chloroplasts = Site of photosynthesis Lysosomes = Contains digestive enzymes Peroxisomes = Breaks down fatty acids and detoxifies harmful substances Signup and view all the answers

What is the primary function of Smooth Endoplasmic Reticulum?

Synthesis of saccharides and lipids Signup and view all the answers

Rough Endoplasmic Reticulum is responsible for the synthesis of proteins.

True Signup and view all the answers

What are the two types of endoplasmic reticulum?

Smooth ER and Rough ER Signup and view all the answers

The Golgi apparatus processes proteins and ________ coming from the endoplasmic reticulum.

lipids Signup and view all the answers

Match the following components with their functions:

Smooth ER = Synthesis of saccharides and lipids Rough ER = Protein synthesis Golgi Apparatus = Processing and packaging of proteins Sarcoplasmic Reticulum = Transport of Ca2+ for muscle contraction Signup and view all the answers

From which side do proteins enter the Golgi apparatus?

Cis side Signup and view all the answers

The main function of the Golgi apparatus is to synthesize proteins.

False Signup and view all the answers

What special form of endoplasmic reticulum do muscle cells have?

Sarcoplasmic reticulum Signup and view all the answers

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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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.