3.2.3 - Cells - Transport across cell membranes Flashcards
What is the structure of all cell-surface membranes and organelle membranes?
They have the same structure.
What model describes the arrangement of molecules in cell membranes?
Fluid-mosaic model.
What are the two main components of a phospholipid?
Hydrophilic head and hydrophobic tail.
What is the arrangement of phospholipids in cell membranes?
They align as a bilayer.
Why do phospholipids form a bilayer?
Hydrophilic heads are attracted to water, hydrophobic tails are repelled by water.
What type of membrane is created by the arrangement of phospholipids, proteins, glycoproteins, and glycolipids?
Partially permeable membrane.
What is the role of protein channels in cell membranes?
They function as transport proteins.
What type of proteins are glycoproteins?
Proteins with carbohydrate groups attached.
Fill in the blank: The _____ model describes the fluid nature of cell membranes.
fluid-mosaic
True or False: Cholesterol is a component of the phospholipid bilayer.
True.
What type of protein is an integral protein?
Globular protein.
What is the function of surface proteins in cell membranes?
They interact with the extracellular environment.
What are the two types of fatty acids found in phospholipids?
- Saturated fatty acid
- Unsaturated fatty acid
What are peripheral proteins?
Proteins that are attached to the surface of the membrane.
What is the role of the cytoskeleton filaments in relation to the cell membrane?
They provide structural support.
Fill in the blank: The phospholipid bilayer is formed by the alignment of phospholipids with _____ heads and _____ tails.
hydrophilic; hydrophobic
What are glycolipids?
Lipids with carbohydrate groups attached.
What is the role of cholesterol in cell membranes?
Cholesterol restricts the lateral movement of other molecules, making the membrane less fluid at high temperatures and preventing water and dissolved ions from leaking out of the cell.
Define glycoprotein.
A protein with carbohydrate attached.
Define glycolipid.
A lipid with carbohydrate attached.
What are the two types of membrane proteins?
- Peripheral membrane proteins
- Integral membrane proteins
What is the function of peripheral membrane proteins?
Provide mechanical support and facilitate cell recognition through carbohydrate chains.
What do integral membrane proteins do?
Span across the bilayer and are involved in the transport of molecules across the membrane.
What is the function of channel proteins?
Form tubes that fill with water to enable water-soluble ions to diffuse.
How do carrier proteins transport molecules?
They bind with molecules and change shape to transport them into the cell or organelle.
Fill in the blank: The phospholipid bilayer is a key component of cell membranes, composed of _______.
[phospholipids]
True or False: Glycoproteins are involved in cell recognition.
True
What is the primary function of glycolipids?
Cell recognition and signaling.
What type of membrane allows certain molecules to pass while blocking others?
Partially permeable membrane
Name two types of molecules that can pass through the plasma membrane.
- Lipid soluble substances (e.g. some hormones)
- Very small molecules (e.g. CO2, O2, H2O)
What type of molecules cannot pass through the membrane?
- Water-soluble (polar) substances (sodium ions)
- Large molecules (glucose)
What is the process called where molecules move from an area of higher concentration to an area of lower concentration?
Simple diffusion
What is meant by equilibrium in the context of diffusion?
Equal concentration of molecules on both sides of the membrane
Is simple diffusion an active or passive transport process?
Passive
What energy allows molecules to move in fluids during simple diffusion?
Kinetic energy
What are the four key types of transport across cell membranes?
- Simple diffusion
- Facilitated diffusion
- Active transport
- Osmosis
What adaptations do many cells have to increase the rate of transport across membranes?
- Increasing the surface area
- Increasing the number of protein channels and carrier molecules
Fill in the blank: Simple diffusion requires _______ to occur.
No ATP
True or False: Simple diffusion can occur with large molecules.
False
For molecules to diffuse across the membrane, they must be _______ and _______.
- Lipid-soluble
- Small
What is facilitated diffusion?
A passive process that uses membrane proteins to transport molecules
It does not require ATP and differs from simple diffusion.
What types of molecules can be transported by facilitated diffusion?
Ions and polar molecules
These cannot simply diffuse across the membrane.
What are the two types of protein structures involved in facilitated diffusion?
- Protein channels
- Carrier proteins
These are intrinsic proteins that help transport molecules.
How do protein channels function?
They form tubes filled with water that allow water-soluble ions to pass through
The channels open selectively in the presence of certain ions.
What triggers the opening of channel proteins?
The binding of certain ions to the protein
This binding is necessary for the channel to open due to the protein’s specific tertiary structure.
What happens when a carrier protein binds with a molecule?
It causes a change in the shape of the protein, enabling release to the other side
An example molecule is glucose.
Define osmosis.
The net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane
This process is crucial in maintaining cellular homeostasis.
Fill in the blank: Osmosis is the net movement of water from an area of higher water potential to an area of lower water potential across a _______.
[partially permeable membrane]
What is the significance of a partially permeable membrane?
It allows selective movement of substances while restricting others
This is essential for maintaining cell integrity and function.
What is the water potential at a specific point in this context?
- 0.5 kPa or - 3.1 kPa
These values indicate the potential energy of water in relation to solute concentration.
What is water potential?
The pressure created by water molecules, measured in kPa and represented with the symbol Ψ.
What is the water potential of pure water?
Zero.
What happens to the water potential when solutes are dissolved in water?
It becomes negative.
What does a more negative water potential indicate?
More solute must be dissolved in it.
Define hypotonic solution.
A solution with a water potential more positive (closer to zero) than the cell.
Define hypertonic solution.
A solution with a water potential more negative than the cell.
Define isotonic solution.
A solution with the same water potential as the cell.
What happens to animal cells in a hypotonic solution?
They take in a lot of water and may burst (lyse).
Why do plant cells not burst in a hypotonic solution?
They have a strengthened cell wall, causing them to become turgid.
What occurs to both animal and plant cells in hypertonic solutions?
They shrink and become shriveled due to water leaving the cell by osmosis.
What is active transport?
The movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins.
What role do carrier proteins play in active transport?
Carrier proteins act as pumps to move substances across the membrane.
What is required for active transport to occur?
ATP and carrier proteins.
In active transport, what happens to ATP?
ATP binds to the protein and is hydrolysed into ADP and Pi.
What does the hydrolysis of ATP cause in carrier proteins?
It causes the protein to change shape and open towards the inside of the membrane.
What is released on the other side of the membrane during active transport?
The molecule being transported.
What happens to the carrier protein after the molecule is released?
The Pi molecule is released, and the protein reverts to its original shape.
True or False: Active transport is non-selective.
False
Fill in the blank: Active transport moves substances _______ the concentration gradient.
against
What concentration gradient does active transport work against?
From lower concentration to higher concentration.
What is the significance of receptor sites on carrier proteins?
Certain molecules can bind to the receptor site to be pumped.
Which ions are mentioned in the context of active transport?
Sodium (Na) and Potassium (K).
What happens to the structure of a carrier protein during active transport?
It changes shape to facilitate the transport of molecules.
What is co-transport?
A process that allows the transport of substances against their concentration gradient by coupling it with the movement of sodium ions down their concentration gradient.
Co-transport is essential for the absorption of glucose and amino acids in epithelial cells.
Why is active transport needed for glucose absorption in epithelial cells?
Because there is usually more glucose in the epithelial cells than in the lumen, necessitating the movement against the concentration gradient.
Facilitated diffusion cannot occur when the concentration of glucose is higher inside the cell.
Describe the first step in the co-transport of glucose and amino acids.
Sodium ions are actively transported out of the epithelial cell into the blood in the capillary.
This step creates a concentration gradient that allows sodium ions to diffuse back into the cell.
What happens to the sodium ion concentration in the epithelial cell after active transport?
The sodium ion concentration in the epithelial cell decreases.
This decrease enables sodium ions to diffuse from the lumen into the epithelial cell.
How do sodium ions enter the epithelial cell after active transport?
Sodium ions diffuse from the lumen down their concentration gradient into the epithelial cell.
This diffusion is facilitated by a co-transporter protein.
What function does the co-transporter protein serve in the absorption process?
It allows the simultaneous transport of sodium ions and either glucose or amino acids into the epithelial cell against their concentration gradient.
This process is critical for nutrient absorption in the intestines.
What occurs after glucose is transported into the epithelial cell?
Glucose moves by facilitated diffusion from the epithelial cell to the blood.
This step completes the absorption process of glucose into the bloodstream.
Fill in the blank: The process of absorbing glucose from the lumen of the intestines into the epithelial cells relies on the active transport of _______.
sodium ions
True or False: Co-transport can only occur with glucose.
False
Co-transport can occur with various substances, including amino acids.
List the main components involved in the co-transport process.
- Sodium ions
- Glucose
- Amino acids
- Co-transporter protein
- ATP
What model describes the structure of the cell surface membrane and organelle membranes?
Fluid mosaic model
The fluid mosaic model illustrates the dynamic and complex nature of cell membranes, comprising various lipids and proteins.
Name the five key types of transport across membranes.
- Simple diffusion
- Facilitated diffusion
- Osmosis
- Active transport
- Co-transport
Co-transport is a specific type of active transport that involves the simultaneous transport of multiple substances.
True or False: Active transport and osmosis are linked to urine creation in the nephron of the kidney.
True
The nephron utilizes both active transport and osmosis to regulate water and solute concentration in urine.
Fill in the blank: Cholera releases toxins affecting ______ ion channels, leading to diarrhoea.
[chloride]
The disruption of chloride ion channels by cholera toxins causes an imbalance in water potential, resulting in water leaving cells and entering the intestinal lumen.
How is glucose absorbed into liver cells?
Facilitated diffusion
This process helps to maintain homeostasis by reducing blood glucose levels.
Co-transport and facilitated diffusion are related to which physiological processes in the nervous system?
Resting potentials and generating an action potential
These processes are crucial for the transmission of nerve signals.
Active transport and facilitated diffusion occur in which processes related to energy production?
Chemiosmosis in photosynthesis and respiration
Chemiosmosis is vital for ATP synthesis in both processes, linking transport mechanisms to energy production.
