BIOSCI 107 Cell Processes Short Answers Flashcards
What is the Basic Membrane Structure?
A thin, 8nm flexible and sturdy barrier surrounding the cytoplasm of a cell.
What are the 4 Characteristics of the Fluid Mosaic Model?
Sea of lipids with proteins floating like icebergs, membrane 50% lipid, 50% protein, barrier to entry or exit of polar substances, proteins regulate traffic.
Where are Cholesterol and Glycolipids?
Scattered among a double row of phospholipid molecules.
What does Amphipathic Mean? Give an Example.
Has both a polar and non-polar region - phospholipid molecules.
Which 3 Factors Determine Fluidity?
Lipid tail length (longer = less fluid), number of double bonds (more = increased fluidity), amount of cholesterol (more = less fluid).
What are Integral Proteins?
Extend into or completely across cell membrane.
What are Peripheral Proteins?
Attached to inner or outer surface of cell membrane (easily removed).
What do the Hydrophilic Ends of Proteins do?
Interact with the aqueous solution.
What are the 3 Characteristics of Integral Membrane Proteins?
Amphipathic, have hydrophobic regions, have regions of non polar amino acids coiled into helices.
What are the 6 Functions of Membrane Proteins?
Receptors, cell identity markers, linkers, enzymes, ion channels, transporter proteins.
What is Selective Permeability?
The membrane allows some substances to cross but excludes others.
What is the Lipid Bilayer Permeable to?
Non-polar molecules, lipid soluble molecules, small uncharged polar molecules.
What are some Examples of a Non-Polar, Uncharged Molecule?
O2, N2 benzene.
What are some Examples of a Lipid Soluble Molecule?
Steroids, fatty acids, some vitamins.
What are some Examples of a Small Uncharged Polar Molecule?
Water, Urea, Glycerol, CO2.
What are some Examples of a Large Uncharged Polar Molecule?
Glucose, amino acids.
What is the Lipid Bilayer Impermeable to?
Large uncharged polar molecules, ions.
How does Temperature Affect Rate of Diffusion?
Higher temp = Faster diffusion.
How does the Molecule Size Affect Diffusion Rate?
Larger = slower.
How does Diffusion Distance Affect Diffusion Rate?
Increased distance = slower rate of diffusion.
How can a Cell Increase Diffusion?
Increase membrane area available for exchange.
How do Molecules Interact with Concentration Gradients?
Non charged molecules will diffuse down their concentration gradients.
How do Molecules Interact with Electrical Gradients?
Ions will be influenced by membrane potential in addition to their concentration gradient.
What is Movement of Ions influenced by?
Electrochemical gradient.
What does the Selectivity Membrane enable?
A difference in concentration or gradient across the membrane to be established.
How do Cells Establish an Electrical Gradient?
Difference in charged ions between the membrane.
What is Osmosis?
Net movement of water through a selectively permeable membrane from an area of lower water concentration.
What is Osmotic Pressure?
The pressure applied by a solution to prevent the inward flow of water across a semi-permeable membrane.
What are the 3 Properties of a Water Permeable Membrane - Lipid Bilayer?
Small, mercury insensitive, temp dependent.
What are the 3 Properties of a Water Permeable Membrane - Channel?
Large, mercury sensitive, temp independent.
What is Pf is Mediated by?
The aquaporins (9 isoforms).
What is Non-Mediated Transport?
Does not directly used a transport protein.
What is Mediated Transport?
Moves materials with the help of a transport protein.
What is Passive Transport?
Moves substances down their concentration gradient with only their kinetic energy.
What is Active Transport?
Uses energy to drive substances against their concentration or electrochemical gradients.
What is Vesicular Transport?
Move materials across membranes in small vesicles either by exocytosis or endocytosis.
What is Non-Mediated Transport Important for?
Absorption of nutrients, excretion of wastes.
Which Molecules undergo Non-Mediated Transport?
Nonpolar, hydrophobic molecules - oxygen, co2, nitrogen, fatty acids, steroids, small alcohols.
What do Ion Channels Form?
A water filled pore that shields the ions from the hydrophobic core of the lipid bilayer.
Why is Ion Transport Rapid?
Ions do not bind to channel pore.
What is the Advantage of Ionic Selectivity?
Be being selective to a particular ion the channel can harness the energy stored in the different ion gradients.
What is Gating?
Channels contain gates that control opening and closing of the pore.
What are some Gate Stimuli?
Voltage, ligand binding, cell volume, pH, phosphorylation.
How is an Electrical Current Generated in Ion Channels?
The diffusion of over 1 million ions per second through a channel.
What do Fluctuations of Current in Ion Channels mean?
The opening and closing of single ion channels.
What is Carrier Mediated Transport?
The substrate to be transported directly interacts with the transport protein.
Which 4 Properties do Transport Proteins Exhibit?
Specificity, inhibition, competition, saturation.
What is the Function of Transport Proteins?
Mediate transport across the cell membrane at a faster than normal rate.
What do Transporter Proteins Display?
Enzyme kinetics.
When does Glucose Transport Occur?
Until all binding sites are saturated.
What is Active Transport?
An energy requiring process that moves molecules and ions against their concentration or electrochemical gradients.
What are the Two Forms of Active Transport?
Primary and secondary.
What is Primary Active Transport?
Energy is directly derived from the hydrolysis of ATP.
What is Secondary Active Transport?
Energy stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient.
What happens during Na/KTPase?
3 Na ions removed from cell as 2K brought into cell.
What is the Function of the Na Pump?
Maintains a low concentration of Na and a high concentration of K in the cytosol.
What are the 6 Reasons Difference in Ion Concentration are Important?
MECMUM: Maintain membrane potential, Electrical excitability, Contraction of muscle, Maintenance of cell volume, Uptake of nutrients, Maintenance of pH.
What is the Pump-Leak Hypothesis?
Na and K are continually leaking back into the cell down their respective gradients, so the pump works continuously.
What Energy does Secondary Active Transport use?
Uses energy stored in ion gradients created by primary active transporters to move other substances against the gradient.
What is an Example of Na Antiporter or Exchangers?
Na ions rush inward, Ca or H pushed out.
What is an Example of Na Symporters or Cotransporters?
Glucose or amino acids rush inward together with Na ions.
What are the 4 Basic Characteristics of Epithelial Tissue?
Cells arranged in continuous sheets in single/multiple layers, cells sit on basement membrane, boundary between organs and external environment, subject to physical breakdown and injury.
What is the Function of Tight Junctions?
Hold epithelial cells together at their luminal edges.
What are Tight Junctions Composed of?
Thin bands that encircle the cell, making contact with thin bands from adjacent cells.
How do Tight Junctions appear in EM and Freeze Fractures?
EM: Membranes are fused
Freeze fracture: Interlocking network of ridges in plasma membrane.
What are the 2 Major Functions of Tight Junctions?
A barrier and a fence - separating epithelial cells into two distinct membrane domains.
What is Apical Membrane?
Faces the lumen of the organ or body cavity.
What is the Basolateral Membrane?
Adheres to the adjacent basement membrane and interfaces with the blood.
How is Epithelial Tissue Functionally Classified?
Leaky epithelium - Paracellular transport dominates
Tight epithelium - Transcellular transport dominates
What are the 4 Characteristics of Proximal Tight Junctions?
Leaky epithelium, low electrical resistance, low number of strands, bulk transport.
What are the 4 Characteristics of Distal Tight Junctions?
Tight epithelium, high electrical resistance, high number of strands, hormonally controlled.
What is Absorption?
Transport from lumen to blood.
What is Secretion?
Transport from blood to lumen.
What are the 4 Rules of Trans-epithelial Transport about?
Entry and exit steps, electrochemical gradient, electroneutrality, osmosis.
What are Entry and Exit Steps for Trans-epithelial Transport?
The entry step for absorption is the apical but for secretion is the basolateral membrane.
What is the Electrochemical Gradient?
The entry or exit step; passive or active.
What is Electroneutrality?
Movement of a positive or negative ion will attract a counter ion.
How do Epithelial Cells Mediate Secretion and Absorption?
Using different collections of transporters and channels.
What is Exploited in Oral Rehydration Therapy?
The ability of glucose to enhance the absorption of Na and hence Cl and water.
What happens as a result of Glucose-Galactose Malabsorption Syndrome?
A mutation to the glucose symporter in the small intestine leads to sugar retention in the intestine lumen, increase in lumen osmolarity induces water efflux, increased water flow causes diarrhea.
What is the Treatment for Glucose-Galactose Malabsorption?
Remove glucose and galactose from diet, use fructose as a carb source (GLUT5).
Why is Glucose in the Kidney Filtered?
It must be filtered and reabsorbed or it will appear in urine.
What is Glucosuria?
Glucose in the urine.
What is the Renal Threshold?
Once the renal threshold is reached, glucose appears in urine.
What is the Rate Limiting Step?
Cl can’t leave unless channel is open (gated) - this channel opening is the rate limiting step.
What causes Secretory Diarrhoea?
Excessive stimulation of the secretory cells in the crypts of the small intestine and colon.
What effect do Enterotoxins have on the Colon?
Enterotoxins irreversibly activate adenylate cyclase causing a maximal stimulation of CFTR - leading to a secretion that overwhelms the absorptive capacity of the colon.
What cause Excessive Stimulation of the Colon?
Abnormally high concentrations of endogenous secretagogues produced by tumours or inflammation. Also Enterotoxins.
How can Secretory Diarrhoea be Treated?
Oral rehydration therapy.
How is Cystic Fibrosis Inherited?
In an autosomal recessive fashion - heterozygotes are carriers but show no symptoms.
How can Cystic Fibrosis affect Airways?
Clogging and impaired breathing.
How can Cystic Fibrosis affect the Liver?
Plugging of bile ducts impedes digestion.
How can Cystic Fibrosis affect the Pancreas?
Occlusion of ducts preventing delivery of critical enzymes to the bowel.
How can Cystic Fibrosis affect the Small Intestine?
Obstruction of the gut.
How can Cystic Fibrosis affect the Reproductive Tract?
Absence of fine ducts leads to infertility in males.
How can Cystic Fibrosis affect Skin?
Sweat gland malfunction (more salt in sweat).
What are the 4 Treatments for Cystic Fibrosis?
Chest percussion, antibiotics, pancreatic enzyme replacement, attention to nutritional status.
What is CFTR?
A Cl channel regulated by protein kinase A dependent phosphorylation of the R domain and binding of ATP to the NBD.
How do Normal Lung Epithelial Cells Behave?
Balance between secretion and absorption keeps lung surface most but prevents fluid build up.
How do Cystic Fibrosis Epithelial Cells Behave?
Defective Cl- channel prevents isotonic fluid secretion and enhances Na+ absorption to give
a dry lung surface.
What causes the Salty Sweat of CF Patients?
The failure of epithelial cells in the ducts of sweat glands to reabsorb NaCl.
What is the Two Stage Process of Sweat Formation?
A primary isotonic secretion of fluid by acinar cells, then a secondary reabsorption of NaCl to produce a hypotonic solution.
What is an Isosmotic Solution?
If the solution has the same osmolarity.
What is a Hyposmotic Solution?
If the solution has a lower osmolarity.
What is a Hyperosmotic Solution?
If the solution has a higher osmolarity.
Why does the Osmolarity of Extracellular and Intracellular Fluids have to be Equal?
So that no net water flow (osmosis) occurs, leading to a change in cell volume.
What is Tonicity?
The effect a solution has on cell volume.
Which Factor determines Tonicity?
The membrane permeability of the solute.
What is Lysis?
Cell swelling/explosion.
What is Crenation?
Cell shrinkage.
