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what is the main function of the plasma memebrane
The main function of the plasma membrane is to regulate the movement of substances in and out of the cell, maintaining homeostasis and protecting the cell's internal environment.
What term describes the plasma membrane’s ability to allow some substances to pass while blocking others?
selective permeability
What is the process called where the cell maintains a stable internal environment despite external changes?
Homeostasis
What type of transport moves molecules from high to low concentration without using energy?
diffusion
What is the special type of diffusion that involves the movement of water across the plasma membrane?
osmosis
What type of transport requires energy (ATP) to move molecules against their concentration gradient?
Active transport. This process uses energy to move substances from areas of low concentration to areas of high concentration, allowing cells to maintain necessary concentrations of ions and molecules.
What is the structure of the plasma membrane called, consisting of two layers of phospholipids?
Phospholipid bilayer
What type of transport involves carrier proteins helping molecules cross the membrane without using energy?
Facilitated diffusion
What process does the cell use to expel large molecules, like waste or hormones, out of the cell?
exocytosis.
What is the name of the transport process where the cell engulfs large molecules or particles to bring them inside?
endocytosis.
What part of the phospholipid bilayer is hydrophilic (water-loving) and where is it located?
The polar heads face inside and outside of the cell where water is present.
What part of the phospholipid bilayer is hydrophobic (water-fearing) and where is it located?
The hydrophobic tails face each other in the interior of the membrane, away from water.
What role do steroids, such as cholesterol, play in the plasma membrane of animal cells?
Cholesterol stiffens and strengthens the plasma membrane in animal cells.
What are the two types of membrane proteins, and how do they differ in their location?
Peripheral proteins are attached to only one side of the membrane.
Integral proteins span the membrane and can be embedded within it
What are peripheral proteins, and where are they found in the membrane?
Peripheral proteins are membrane proteins that are not embedded in the lipid bilayer but are attached to the exterior or interior surfaces of the membrane, often interacting with integral proteins.
What are integral proteins, and how do they interact with the membrane?
Integral proteins are membrane proteins that span the lipid bilayer, interacting with both the hydrophobic interior and the aqueous environment, often functioning as channels or transporters.
How are integral proteins positioned in the plasma membrane?
span the entire membrane and can protrude from one or both sides.
What ability do membrane proteins have that allows them to move within the membrane?
Membrane proteins can move laterally within the lipid bilayer, allowing for fluidity and flexibility in membrane structure.
What is the fluid-mosaic model, and what components make up this pattern in the membrane?
The fluid-mosaic model describes the flexible structure of the membrane, where phospholipids, proteins, and steroids (like cholesterol) are arranged in a dynamic pattern.
What types of molecules in the plasma membrane can have attached carbohydrate chains?
Both phospholipids and proteins can have attached carbohydrate chains.
What are glycolipids?
Glycolipids are lipids with attached carbohydrates.
What are glycoproteins?
Glycoproteins are proteins with attached carbohydrates.
What type of membrane protein is involved in the passage of solutes through the membrane?
Channel proteins are involved in the passage of solutes through the membrane.
How do substances move across the membrane using channel proteins?
Substances simply move across the membrane through channel proteins.
What special feature do some channel proteins have?
Some channel proteins have gates that must be opened in response to a signal.
How do carrier proteins assist in the movement of solutes across the membrane?
Carrier proteins bind to solutes and change shape to help them move across the membrane.
How do channel proteins, carrier proteins, and gated channels work together to regulate the movement of solutes across the plasma membrane, and why is this important for homeostasis?
Channel proteins provide open passageways for solutes to move freely across the membrane.
Some channels have gates that only open in response to specific signals, controlling when and how substances enter or exit.
Carrier proteins, in contrast, bind to specific molecules, change shape, and actively help move them across the membrane when needed.
Together, these proteins regulate the movement of essential substances like ions, glucose, and water, ensuring the cell maintains balance (homeostasis).
Without proper function of these proteins, cells could lose control over nutrient intake, waste removal, and ion balance, leading to cell damage or dysfunction.
What type of membrane proteins are responsible for cell recognition?
Cell recognition proteins, which are glycoproteins, help with cell identification.
Why are cell recognition proteins important for the immune system?
They help the body recognize and defend against pathogens (harmful invaders).
What is the function of receptor proteins in the membrane?
Receptor proteins bind to specific molecules, triggering a shape change that initiates a cellular response
What happens when a receptor protein binds to its specific molecule?
It changes shape, which starts a cellular response such as activating an enzyme or signaling pathway.
How do cell recognition proteins and receptor proteins work together to protect the body from infection, and why is their function critical for immune response and cell communication?
Answer:
Cell recognition proteins (glycoproteins) help the immune system distinguish between "self" cells and foreign invaders (like bacteria or viruses).
When the body detects a pathogen, immune cells use these proteins to identify and attack the invader.
Receptor proteins play a role in cell signaling by detecting foreign molecules or signals from the immune system.
When a pathogen-specific molecule binds to a receptor protein, the receptor changes shape, triggering an immune response such as releasing antibodies or activating white blood cells.
If these proteins fail, the body might not recognize infections, leading to disease, or could mistakenly attack its own cells, causing autoimmune disorders.
What is the main function of enzymatic proteins in the plasma membrane?
Enzymatic proteins carry out metabolic reactions directly within the cell.
What is an example of enzymatic proteins at work?
The proteins of the electron transport chain, which carry out the final steps of aerobic respiration to produce ATP
How do enzymatic proteins in the membrane, such as those in the electron transport chain, contribute to cellular energy production, and why is their proper function essential for cell survival?
Answer:
Enzymatic proteins facilitate metabolic reactions, allowing cells to efficiently break down molecules and extract energy.
In aerobic respiration, enzymatic proteins in the electron transport chain (ETC) play a key role in producing ATP, the cell’s main energy source.
The ETC is located in the mitochondrial membrane and uses enzymatic proteins to transfer electrons, creating a gradient that powers ATP synthesis.
If these proteins malfunction, the cell cannot efficiently produce ATP, leading to energy depletion, cell damage, or even cell death.
This process is critical for high-energy-demanding cells like muscle and nerve cells, making enzymatic proteins essential for overall bodily function
What is the function of channel proteins in the plasma membrane?
Channel proteins allow specific molecules or ions to cross the membrane freely.
How does a faulty chloride channel lead to cystic fibrosis?
A faulty chloride channel causes thick mucus buildup in airways and pancreatic/liver ducts.
What is the role of carrier proteins, and how do GLUT carriers work?
Carrier proteins selectively transport molecules or ions across the membrane
GLUT carriers transfer glucose in and out of different cell types based on blood glucose levels.
Why do organ transplants face challenges related to cell recognition proteins?
MHC glycoproteins are unique to each person, making it difficult for the immune system to accept foreign organs, leading to rejection.
How do receptor proteins contribute to dwarfism?
Some types of dwarfism occur when growth hormone receptors are faulty, preventing proper interaction with growth hormone.
What is the role of enzymatic proteins in ATP metabolism, and how does cholera affect them?
Adenylate cyclase is a membrane enzyme involved in ATP metabolism.
Cholera bacteria release a toxin that disrupts adenylate cyclase function, leading to severe diarrhea
How do channel, carrier, receptor, and enzymatic proteins work together to maintain cellular homeostasis, and what can go wrong when one of these proteins is faulty? Provide real-world examples.
Channel proteins regulate ion balance by allowing ions (like chloride) to pass freely, ensuring proper cellular hydration and signaling.
Example: Faulty chloride channels cause cystic fibrosis, leading to mucus buildup.
Carrier proteins control nutrient transport, moving glucose in and out based on cellular demand.
Example: GLUT carriers regulate blood glucose levels.
Receptor proteins receive chemical signals (like growth hormone) to trigger cellular responses.
Example: Faulty growth hormone receptors lead to some types of dwarfism.
Enzymatic proteins speed up critical reactions, such as ATP metabolism for energy production.
Example: Cholera toxin disrupts enzymatic proteins, causing severe diarrhea due to fluid imbalance.
What types of molecules can freely cross the plasma membrane?
Small, uncharged molecules like CO₂, O₂, glycerol, and alcohol can freely cross.
How do small, uncharged molecules move across the membrane?
They slip between the hydrophilic heads and pass through the hydrophobic tails of the phospholipid bilayer.
What drives the movement of molecules across the membrane?
The concentration gradient drives molecular movement.
What does it mean to move "down" a concentration gradient?
Moving from an area of higher concentration to an area of lower concentration (does not require energy).
What does it mean to move "up" a concentration gradient, and what does it require?
Moving from an area of lower concentration to an area of higher concentration (requires energy)
Why can’t water readily cross the plasma membrane?
Water is polar, and the hydrophobic tails of the membrane prevent it from crossing easily.
How does water move across the plasma membrane if it is polar?
Aquaporins are special protein channels that allow water to cross the membrane
Are aquaporins found in all cells?
Yes, aquaporins are present in the majority of cells
How do small, uncharged molecules, ions, and water cross the membrane differently, and why is each transport method important for cellular function? Provide examples of what happens if these processes fail.
Small, uncharged molecules (CO₂, O₂, glycerol, alcohol) can freely pass through the membrane without assistance, allowing gas exchange and metabolism to occur efficiently.
Example: If oxygen (O₂) could not freely cross, cells would suffocate due to lack of oxygen for respiration.
Ions and polar molecules (like water) cannot cross easily due to the hydrophobic nature of the membrane.
Water moves through aquaporins, allowing hydration and fluid balance inside the cell.
Example: If aquaporins malfunction, severe dehydration or swelling can occur.
Ions and large molecules must use transport proteins to move across the membrane, especially when going against the concentration gradient (requires energy).
Example: A failure in sodium-potassium pump function can lead to nerve signal disruption and muscle paralysis.
If these processes fail, cells cannot regulate their environment, leading to disruptions in respiration, hydration, and nerve function, ultimately causing cell death.
Why can the plasma membrane regulate the passage of molecules?
Because it is selectively permeable, meaning it allows some molecules to pass while blocking others.
What factors determine whether a molecule can freely cross the plasma membrane or requires assistance?
Size of the molecule.
Nature of the molecule (polarity and charge)
What types of molecules are more likely to freely cross the membrane?
Small, uncharged molecules (such as O₂, CO₂, glycerol, and alcohol)
What types of molecules may require carrier proteins and/or energy to cross the membrane?
Large molecules, polar molecules, and charged ions (such as glucose, sodium ions, and potassium ions).
How does selective permeability help maintain homeostasis in the cell, and what would happen if the membrane lost this ability? Provide specific examples of molecules and their transport methods.
Selective permeability allows the cell to control its internal environment, ensuring the proper balance of nutrients, ions, and water.
Small, uncharged molecules (O₂ and CO₂) cross freely, allowing gas exchange for respiration.
Example: If oxygen transport failed, cells would not produce enough ATP, leading to organ failure.
Large or charged molecules (glucose, sodium, potassium) require carrier proteins or energy to enter/exit.
Example: Glucose needs GLUT carriers to enter cells for energy production. If GLUT carriers malfunction, diabetes can occur.
Sodium and potassium require the sodium-potassium pump to maintain nerve function. If this pump stops working, muscle paralysis and nerve failure can occur.
If the membrane lost its selective permeability, harmful substances could enter, and vital molecules could escape, disrupting homeostasis and leading to cell death.
what types of melecules can freely cross the plasma membrane?
Small unchanged molecules such as Co2, o2, glycerol, and alcohol
how do small uncharged molecules move through the plasma membrane?
They slip between the hydrophilic heads and pass through the hydro phobic tails of the phospholipid bilayer
What drives the movement of these molecules across the membrane?
The concentration gradient, meaning they move from high concentration to low concentration without energy input
Why is the ability of small, uncharged molecules to freely cross the plasma membrane essential for cellular function, and what would happen if this process was disrupted? Provide specific examples.
Oxygen (O₂) must freely cross the membrane so cells can perform cellular respiration to produce ATP.
Disruption Example: If O₂ couldn’t pass freely, cells would suffer from oxygen deprivation, leading to energy failure and tissue death.
Carbon dioxide (CO₂) must exit the cell to prevent toxic buildup from respiration.
Disruption Example: If CO₂ couldn’t diffuse out, it would accumulate, lowering pH and causing cellular damage (acidosis).
Glycerol and alcohol diffuse freely, which is why alcohol rapidly affects the brain without needing a transporter.
Disruption Example: If alcohol required a transporter, its effects on the nervous system would be slower and less intense.
If these molecules couldn’t pass freely, cells would lose their ability to exchange gases and maintain energy production, leading to organ failure and death.
What is a concentration gradient?
A difference in the amount of a substance on one side of the membrane compared to the other.
what does it mean to move “down” a concentration gradient?
Moving from an area of higher concentration to lower concentration, which does not require energy
What does it mean to move “up” a concentration gradient, and what does it require?
Moving from an area of lower concentration to higher concentration, which requires energy (ATP)
Why is water not expected to readily cross the plasma membrane?
Because water is polar, and the hydrophobic tails of the membrane prevent easy passage
What are aquaporins, and what is their function?
Aquaporins are special protein channels that allow water to cross the membrane
Are aquaporins found in most cells?
Yes, aquaporins are present in the majority of cells
How does the concentration gradient affect water movement in cells, and why are aquaporins necessary for maintaining homeostasis? Provide an example of what happens if aquaporins fail.
Water moves down its concentration gradient (from high to low concentration) through a process called osmosis.
Since water is polar, it cannot pass freely through the hydrophobic membrane, so aquaporins provide specialized channels to allow rapid water movement.
Example: In kidney cells, aquaporins help reabsorb water to prevent dehydration.
If aquaporins malfunction, the body loses too much water, leading to severe dehydration and organ failure.
Aquaporins also regulate water during cell swelling and shrinking, preventing cell damage from excess water intake or loss.
Without aquaporins, cells would struggle to balance water levels, leading to dehydration, swelling, or bursting depending on external conditions.h
What is diffusion?
Diffusion is the movement of molecules from an area of higher concentration to lower concentration.
Does diffusion require energy?
No, diffusion occurs passively without requiring energy.
What drives diffusion across the plasma membrane?
The concentration gradient (molecules move down from high to low concentration)
When does diffusion stop?
When equilibrium is reached (when molecules are evenly distributed).
Give an everyday example of diffusion.
When a crystal of dye is placed in water, the dye molecules spread out until equilibrium is reached
What is a solution composed of?
A solute (solid) and a solvent (liquid)
What types of transport do not require energy?
Diffusion (movement down a concentration gradient).
What types of transport require energy?
Active transport, exocytosis, and endocytosis.
