Unit 3- Membranes and Movement across membranes Flashcards
A structure that surrounds every cell and protects internal cellular components from the outside
Plasma membrane
What is the Plasma Membrane?
A Two-ply sheet of phospholipids with embedded or peripheral proteins
True or False: the Plasma membrane is permeable to polar/hydrophilic/water-soluble molecules
False: It is generally not very permeable to these molecules
True or False: The Plasma Membrane is impermeable to charged molecules or Ions ( by itself)
TRUE
What are the activities the Plasma Membrane is involved in?
Information Transmission Import/Export of small molecules Capacity for movement/expansion All Properties linked to proteins found within the plasma membrane
Compartmentalization in the Plasma Membrane
This allows the cell to compartmentalize within the eukaryotic cells to create the membranes around organelles.
What environment are cells typically in
An Aqueous Environment
What will the membrane lipids do if they are present in large enough numbers?
They will automatically form a bilayer.
What is the most abundant lipid in the plasma membrane?
The Phospholipid
How are phospholipids amphipathic?
They have hydrophobic tails and hydrophyllic head regions (which facilitate bilayer formation)
Describe the self-sealing membrane layer:
Hydrophobic regions inability to form interactions with water results in highenergy cage-like formation of water molecules around molecule • Energy demand decreases if hydrophobic regions interact with each other as opposed to water • Hence, phospholipids, with both hydrophobic and –philic regions spontaneously coalesce into phospholipid bilayers with hydrophilics facing outward and –phobics interacting with each other with minimal exposure of any hydrophobic region to aqueous environment
What types of movement do phospholipids perform within the membrane?
Within plane Flip-Flop Spin in place Flexion: Fatty Acid Tails flexing
True or false: Flip flops of phospholipids across the membrane is a common occurance.
False: These rarely occur unless catalyzed by an enzyme
What is the difference between a saturated and an unsaturated fatty acid?
Saturated Fatty acids have at least one double bond, which will result in a bent tail. Unsaturated fatty acids have no double bonds, so both tails are straight.
What is choleterol and what is its function in relation to phospholipids?
Cholesterol is a rigid planar ring with one polar head group and a nonpolar tail. It is used to fill spaces between neighboring phospholipids, hindering movement and permeability
Describe this process
Membrane Assembly:
beginning in the cytosolic face of the Endoplasmic Reticulum
Where are phospholipids made?
On the cytosolic face of the ER
Define: Scramblases
Enzymes that randomly select phospholipids to move from one side to the opposite side of the ER Membrane.
How are phospholipids distributed to other organelles
As vesicles leave ER, new membrane gets distributed to other organelles and cell membrane
True or False: All membranes are symmetrical
False:
Some membranes are asymmetrical (have different types of phospholipids on one face of membrane vs. other)
What is the function of flippase?
It helps the golgi sequester specific phospholipids on one face
What is the result of golgi phospholipid sequestration:
It results in membranes having a distinct inside and outside face, which is important in fuction of the associated organelles.
What are the types of membrane proteins?
Anchors, transporters, Ion Channels, Receptors, and Enzymes
What is the function of the Na+ pump?
Actively pumps Na+ out of cells and K+ in the cells
What is the function of the K+ leak channel
It allows K+ ions to leave cells, thereby having a major influence on cell excitability
What is the function of an integrin (anchoring) protein?
They link intracellular actin filaments to extracellular matrix proteins
What is the function of a PDFG (Platelet-derived growth factor) receptor?
Binds Extracellular PDGF and, as a consequence, generates intracellular signals that cause the cell to grow and divide.
What is the function of adenylyl cyclase (enzyme in the membrane)
Catalyzes the production of the small intracellular signaling molecule Cyclic AMP (cAMP) in response to extracellular signals.
Define: Transmembrane Proteins:
Transmembrane proteins have portion(s) that span the membrane with parts of the protein on both sides of the membrane.
What structures do Transmembrane Proteins typically have?
Alpha-Helix or Beta Pleated sheets (several required)
What is the most common polypeptide structure to pass through the membrane?
The Transmembrane Alpha helices
True or False: Transmembrane Alpha-Helixes have hydrophyllic residues that stick out from helix, favoring interaction with nonpolar tails of phospholipids in bilayer
FALSE:
They have hydrophobic residues that stick out from helix, favoring interaction with nonpolar ta
True or false: If Multiple Alpha-Helices are present, it is possible for them to form a hydrophyllic core?
TRUE
What are Beta Barrels?
Very large Beta Sheets that are required for formation of pores in the membrane. Those residues that face outside of the barrel or pore are hydrophobic
What is the Cell Cortex?
The underlying framework of proteins attached to the plasma membrane, which provides support and strengthens the membrane.
What are the functions of the cell’s cortex?
- Withstand shear forces (blood cells)
- Selective uptake of materials
- Cortex can restrict movement of membrane proteins
- Change shape
- Move (amoeboid movement)
True or False:
Many proteins cannot move freely within plane of plasma membrane like phospholipids
FALSE:
Many proteins move freely within plane of plasma membrane just like phospholipids
What are the methods of restricition for protein movement?
Attachment to adjacent cells
- Tethered to cortex or cytoskeleton
- Attachment to extracellular matrix (ECM)
- Barriers (tight junctions) restrict movements to specific domains
- Important characteristic of epithelial (polarized) cells
What are membrane Domains?
Regions of restriction to proteins’ movement
What is FRAP? What is its function?
Fluorescence Recovery After Photo Bleaching:
It involves bleaching membrane proteins with a laser beam and observing the unbleached molecules migrate into the bleached area and recovering completely to prove ***
True or False: Most outer Leaf phospholipids have carbohydrates attached?
TRUE
True or False:
Many extracellular-exposed membrane proteins also have attached carbohydrates (Oligosaccharides)
TRUE
What two molecules together form the glycocalyx or carbohydrate layer?
The Outer Leaf Phospholipids with the Extracellular-Exposed membrane proteins (both with carbohydrates)
What is the function of the Glycocalyx?
Protect the Cell from Mechanical damange
Serve as Lubricant for movement between other cells
Cell-Cell Recognition
- Lectin Proteins from one cell recofnize specific carbohydrates present on other cells.
What does it mean when it is said that the cell membranes are “selectively Permeable”?
Cell membranes allow certain substances to pass and other not to pass
What determines the selective permeability of the membranes?
Usually the Transport Proteins.
But, sometimes the chemical nature of the phospholipids
What types of molecules can pass through the membrane with ease?
Small, non-polar molecules such as O2 and CO2
True or False:
The Lipid interior of the phospholipid Bilayer cannot serve as a barrier to molecules
False:
Lipid interior of phospholipid bilayer serves as barrier to many molecules
What is the permeability of small uncharged polar molecules ( like water) with respect to the membrane?
They are able to pass directly through the membrane, but do so at slow rates.
Large uncharged polar molecules may pass through, but at even slower rates.
What molecules are absolutely impermeable through the cell membrane’s phospholipid bilayer?
All Charged molecules, including ions. No matter how small, they cannot pass through the membranes.
How do cells get items that won’t easily pass through the membrane in or out?
Transport proteins
Why must the cell maintain it’s ion concentration?
It would not function if overloaded on either side of the membrane.
What are the important Ions in the cell?
Na+ (Sodium)
K+ (Potassium)
Ca2+ (Calcium)
Cl- (Chloride)
H+ (Hydrogen)
What are the functions of the ions in the cell?
They aid in ATP production and cellular communication.
What would occur if the cell’s charges inside and outside were not balanced?
The cell would be torn apart.
What is the most abundant positively charged ion outside the cell?
What is it balanced by outside the cell?
Sodium (Na+)
Balanced by Chlorine (Cl-) Outside the cell.
What is the most abundant positively charged ion inside the cell?
what is it balanced by?
K+ (Potassium)
It is balanced by negaticely charged organic molecules inside the cell such as amino acids, nucleotides, or other metabolites.
Is sodium (Na+) concentration greater inside or outside the cell?
Outside (145mM)
Is potassium (K+) concentration greater inside or outside the cell?
Inside (140mM)
Is the concentration of Magnesium (Mg2+) greater inside or outside the cell?
Outside (1-2 mM)
Is the concentration of Calcium (Ca2+) greater inside or outside the cell?
Outside (1-2 mM)
Is the concentration of hydrogen (H+) ions greater inside or outside the cell?
Inside (barely)
Is the concentration of Chloride (Cl-) greater inside or outside the cell?
Outside (110 mM)
Define Membrane Potential:
Small differences in charges near the plasma membrane generate small voltage across the membrane, called membrane potential.
What is the state of an unstimulated cell
There is a precisely balanced cation/anion presence.
What is resting membrane potential?
In an unstimulated cell, resting membrane potential can range between -20 to -200 millivolts (mV) depending on the cell type.
Why is the resting membrane potential negative?
There are slightly more anions inside the cell compared to outisde, resulting in a negative charge.
What does resting membrane potential allow for?
Transport of some metabolites across the membrane and for communication in some cells.
What are the two types of membrane transport proteins?
Transporters or Channels
What is the difference between a transporter and a channel ?
Channels discriminate by charge and size
Transporters discriminate by shape- and are very specific.
Define:
Passive Transport
Unless acted upon by some force, molecules will move down their concentration gradient, from area of high concentration to area of low concentration (diffusion)
Is diffusion acitive or passive transport?
If molecule/ion moves into/out of cell via diffusion, it is passive transport because no input energy is required
True or False:
Passive Transport can be mediated by simple diffusion or facilitated diffusion via channels or transporters
TRUE
Define Active Transport:
If molecule/ion is moved against its gradient, membrane protein and energy are required
What is the difference between active and passive transport?
The requirement of energy for the process to be completed.
What is mediated by specific transporters called pumps, powered by Ion gradients, ATP, or Sunlight?
Active Transport
If molecules are uncharged, they are only subject to ______ gradients
Concentration
If molecules are charged, they are subject to________ and _____, which make an electrochemical gradient.
Concentration Gradient
Membrane potential
True or False: Voltage and gradient work in the same direction no matter what.
False:
Sometimes voltage and gradient work in same direction (Na+ ) and sometimes, they work in opposite directions (K+ )
What molecule will readily enter the cell if given the opportunity?
Na+ (Sodium)
What molecule cannot exit the cell when given the opportunity due to the outside of the cell being more positively charged than the inside?
K+ (Potassium)
What is the main passage of transport for water down its concentration gradient (osmosis) in the cell?
Aquaporins
If a solute cannot move across the membrane, what will move in response?
Water
What would drive water into the cell?
A High Solute concentration
How do animal cells control water driving into the cells?
The Cytoplasm resists the swelling
How do plant cells control water driving into the cells?
They have a central vacuole and cell wall (Turgor Pressure)
How do protistan cells control water driving into the cell?
They shuttle water into vacuoles and discharge it
True or False:
Transporters mediate the cell membrane’s requirement of moving specific ions and molecules in specific directions
True:
Nucleotides (In)
Sugar (In)
Amino Acids (in)
Sodium/Potassium Pump ( *In/Out)
H+ (In) (Lysosome)
Pyruvate (In) (Mitochondria)
ATP (Out) Mitochondria
ADP (In) Mitochondria
How does the Glucose Transporter Function/Operate?
Glucose is only subject to the chemical gradient because it has no charge
When glucose is high outside the cell (After a meal), the transporter allows glucose to enter
When Glucose is low outside the cell (hungry), insulin stimulates liver cells to produce excess glucose
What operates against an Electrochemical gradient?
A pump
What type of transport do Pumps operate on?
Active transport
What are the three types of pumps?
ATP-Driven Pumps
Coupled Pumps
Light-Driven Pumps
What type of Pump is the Sodium-Potassium Pump (Na+ K+)
ATP-Driven
How much ATP is used in the Na-K Pump? And what are the results?
Uses 1 ATP to Expel 3 Na+ and Import 2 K+
True or False:
The Sodium-Potassium pump is not essential for the EC gradient along the cell membrane
FALSE:
Critical for establishing Na+ electrochemical gradient along cell membrane
Accounts for ~30% of ATP usage in cells
What mediates conformational changes in the Sodium-Potassium Pump that facilitates ion transfer?
ATP Hydrolysis
When does this pump operate? How does this relate to ATP Usage?
Pump only operates when Na+ and K+ are available, hence no useless ATP usage
Na+ is constantly entering the cell via methods outside the Na+ pump; therefore, the pump must (continually function/remained turned off)?
Continually function
The activity of the Na+ pump is required to create a steep _______ of Na+ across the membrane?
Electrochemical Gradient
What type of Pump is the Ca 2+ Pump?
ATP-Driven
True or false:
Cells must be sensitive to fluctuations in Ca2+ concentrations inside the cell.
TRUE
Cells must keep [Ca2+] _____ the cell very low in face of high ______ extracellular [Ca2+]
Inside
Extracellular
What is the rate of Ca2+ transfer in the Ca2+ pump?
2 Ca2+ exit the cell for every 1 ATP
What is the function of a Coupled Pump?
Use energy released by allowing one ion/molecule to move down its concentration gradient to power movement of another ion/molecule against that ion/molecule’s gradient
What are the two types of coupled pump activities?
Symport
Antiport
Define: Symport Coupled Pump Activity
Moves both solutes in the same direction across the membrane.
Define: Antiport Coupled Pump Activity
Moves solutes in opposite directions across the membrane
What drives pump functions in anumals?
The Electrochemical Na+ Gradient
Apical side of the cell faces:
The Lumen
Basolateral side of the cell faces
the Substratum
Epithelial cells lining the gut use the Glucose-Na+ ____ Protein on the ____ face of the cell to get glucose into cells
Symport
Apical
On the Apical side of epithelial cells, Na+ is allowed to enter and _____ is “dragged” along with it, creating a high [Glucose] inside the cell
Glucose
Describe the process of Cooperative binding in regard to the Glucose-Na+ relationship in epithelial cells
Binding of either solute enhances pump’s ability to bind the other solute (cooperative binding)
On the basolateral side of the cell, they have ______ _____ ______ that allow glucose the move down its gradient outside of the cell in this region
Passive Glucose Transporters
What useful solutes are imported via Na+ driven symporters
Amino Acids
Sugars
Na+ - H+ antiporters use the ___ gradient to move ___ out of the cell in order to adjust the intracellular pH. Why does this make sense?
Na+
H+
pH is based on the H+ ion concentration in the solute/specimen.
