BIO 1140 - Cell Transport Across Plasma Membrane (Pt. 1) Flashcards
What do Cell Membranes contain?
Cell membranes contain specialized membrane transport proteins
- Membrane transport proteins facilitate the passage of selected small water-soluble molecules
- Liposomes are impermeable to most water-soluble molecules
What determines diffusion rate?
The molecule’s size and solubility determine the diffusion rate
- Simple diffusion
What are the most important Inorganic ions for Cells?
Na+, K+, Ca2+, Cl–, and H+ (protons) are among the most important inorganic ions for cells.
- Na+ is most abundant outside the cell.
- K+ is most abundant inside the cell.
What are the Electrical Charges inside and out?
Electrical charges inside and outside are generally balanced (Na+ by Cl- and K+ by organic molecules).
What is a Voltage Difference?
Small excesses of positive or negative charge on the two sides of the plasma membrane create a voltage difference
What is a Membrane Potential?
This voltage difference across the membrane is called the membrane potential
- The activity of membrane transport proteins create and maintain the membrane potential
What is a Resting Membrane Potential?
For a cell at rest, the exchange of anions and cations across the membrane is steady (resting membrane potential)
What are the Two Classes of Membrane Transporter Proteins?
Membrane transport is mediated by two classes of membrane proteins
- Transporters: transfer small organic molecules or inorganic ions
- Channels: form tiny hydrophilic pores and allow substances to pass by diffusion
- Most channels are ion channels
What is Passive Transport?
Molecules flow from a region of high concentration to a region of low concentration (downhill movement)
- Downhill movement is passive and requires no energy(passive transport)
- Passive transporters change conformation to mediate transport across the membrane
What is Active Transport?
The uphill movement requires energy (active transport)
- against a concentration / electrical gradient requires an input of energy
- Only transporters can carry out active transport
What are Active Transporters / Pumps?
Transmembrane proteins responsible for active transport are called active transporters or pumps
What is Movement Direction of an Uncharged Molecule determined by?
For an uncharged molecule movement direction is determined only by its concentration gradient
What does Concentration Gradient and Membrane Potential of a Charged Molecule exert?
For a charged molecule, both concentration gradient and the membrane potential exert forces
What is an Electrochemical Gradient?
The net driving force moving a charged solute is called electrochemical gradient
- The electrochemical gradient is the sum of a force from the membrane potential and a force from the concentration gradient of the solute
What is Osmosis?
Osmosis is the diffusion of water across membranes
- Water molecules diffuse rapidly through aquaporin channels in the plasma membrane of some cells
What are Aquaporins responsible for?
Aquaporin channels responsible for water reabsorption in our kidneys
- A nephron tissue
What is an important example of a Passive Transporter?
Glucose Transporter
What are the Three types of Proteins for Active Transport?
- Uniporter: transports one substance in one direction
- Symporter: transports two different substances in the same direction
- Antiporter: transports two different substances in opposite directions
What are the Three Types of Energy Sources used in Active Transport?
- ATP (used by primary active transporters)
- Electrochemical gradient (used by secondary active transporters)
- Light
What do ATP-driven Ca2+ Transporters maintain?
ATP-driven Ca2+ transporters (pumps) keep the cytosolic Ca2+ concentration low
- Ca2+ binds to a variety of proteins in the cell and alters their activities
- An influx of Ca2+ into the cell serves as an intracellular signal
- It triggers cell processes, such as muscle contraction, fertilization and nerve cell communication
What do ATP-driven Na+ Transporters use?
ATP-driven Na+ transporters (pumps) uses energy supplied by ATP to expel Na+ and bring in K+
- The ATP-driven Na+ pump plays a pivotal role in the energy economy of animal cells
- This pump accounts for 30% or more of their total ATP consumption
- This pump is also called Na+-K+ ATPase or the Na+-K+ pump
What do ATP-driven Na+ Transporters generate?
ATP-driven Na+ transporter generates a steep concentration gradient of Na+ across the plasma membrane
- With the Na+ pump, Na+ concentration remains about 10–30 times lower and K+ concentration about 10–30 times higher inside the cell
- High Na+ concentration outside the cell represents a huge store of energy
What are Coupled Transporters?
Coupled transporters (pumps) are secondary active transporters
- Coupled transporters mediate coupled transport using electrochemical gradients.
- Symport & Antiport
What does Glucose–Na+ transporters use to drive Active Import of Glucose?
Glucose–Na+ transporters use the electrochemical Na+ gradient to drive the active import of glucose
What are Both Active and Passive Transporters involved in?
Active and passive transporters are involved in glucose transfer across the epithelial lining of the gut
How do Larger Molecules Enter and Leave the Cell?
Large molecules enter and leave the cell by endocytosis and exocytosis
- Proteins, polysaccharides, and nucleic acids are too large and too charged or polar to pass through biological membranes
- import extracellular materials by endocytosis
- secrete intracellular materials by exocytosis.
What are the Three Types of Endocytosis?
- Receptor-Mediated: Specific uptake of large molecules
- Receptor-mediated endocytosis is a highly specific process - Pinocytosis: Nonspecific uptake of extracellular fluid (fluids and dissolved substances from blood)
- Phagocytosis: Nonspecific uptake of large undissolved particles (invading bacteria by cells of the immune system
What is Exocytosis?
Release of large molecules:
- Vesicle fusion with cell membrane (digestive enzymes in the pancreas)
Release of small molecules:
- Vesicle fusion with cell membrane (Neurotransmitters at synapse)
What is Receptor Mediated Endocytosis responsible for?
Receptor-mediated endocytosis is responsible for LDL uptake
What is Cholesterol and LDL?
Cholesterol is a hydrophobic molecule that is transported in the blood as part of huge lipoprotein complexes such as the low-density lipoprotein (LDL).
What is Phagocytosis Responsible for?
Smaller cells and large particles are taken up by phagocytosis
What is Insulin Secreted from?
Insulin is secreted from pancreatic β cells by exocytosis
What happens to Secretory Vesicles during Exocytosis?
During exocytosis, secretory vesicles fuse with the plasma membrane and releases (secretes) its content into the extracellular space.
