Lecture 6: Cell Membranes And Transport Flashcards
Which of the following best describes the structure of a biological membrane?
A. Two layers of phospholipids with proteins embedded between the layers
B.a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane
C. Two layers of phospholipids with proteins either crossing the layers or on the surface of the layers
D. A fluid structure in which phospholipids and proteins move freely between sides of the membrane
C
You are a peripheral membrane protein synthesized by the rER that will ultimately be found associated with the intracellular leaflet (cytoplasmic side) of the cell’s plasma membrane. During your journey as part of a vesicle traveling from the Golgi body to the plasma membrane, where would you be found?
A. Associated with the external surface of the vesicle’s membrane
B. Associated with the internal surface of the vesicle’s membrane
C. Integrated in the vesicular membrane
D. Packaged within the vesicle
A
What is the method of transport across the membrane?
Diffusion
What is diffusion?
The tendency d=for molecules to spread out evenly into the available space.
Diffusion: each molecule moves _______ but substances _______________________, from _________ to _________.
Randomly; diffuse down their conc. gradient; high conc.; low conc.
Which of the following molecules could move through a phospholipid membrane with the least difficulty? A. water B. glucose C. Na+ D. O2 E. an amino acid
Water is polar, glucose is large molecule, na is charged, amino acid is large
Oxygen is small/ nonpolar.D
Explain simply how transport across the plasma membrane occurs
Plasma membranes ares selectively permeable which means its able to regulate what is passing through the cell, its hydrophobic nonpolar molecules can dissolve in the lipid bilayer and pass through the membrane readily and the opposite is true to hydrophobic polar molecules, but the different transport proteins will allow hydrophilic substances to pass through the membrane.
Facilitated diffusion
:it moves substances like ions and small polar molecules down their conc. Gradients through integral membrane proteins
Carrier proteins
Carrier proteins are the lock to a key: substance. They bind to the substance and change conformation/shape and translocate/carry it to the other side of the plasma membrane.
Channel proteins
Act like corridors that allows specific molecules or ions to cross the plasma membranes. Some are consistently open some are gated (ion channels) opening solely when it gets a signal.
How water crosses the membrane?
Water although polar can diffuse passively across the plasma membrane with considerable restraint OR through aquaporin channels
Diffusion of water
Diffusion of water is called osmosis. A difference in water concentration happens when a solute (like a sugar molecule) cannot pass through the selectively permeable membrane. Water will diffuse across the membrane from low solute conc. to high conc. until solute conc. is equal on both sides
Water balance in (animal/plant)cells?
Hypotonic: (low solute-low water)
Animal cell: shrivelled
Plant cell: plasmolyzed
Isotonic:
Animal: normal
Plant: flaccid
Hypotonic:
Animal: lysed/burst
Plant: turgid-normal
What do you expect to happen over time in the cell: outside the cell 250nM NaCl, inside the cell 300nM NaCI.
A. Water will move from inside to outside ONLY.
B. Water will move from outside to inside ONLY.
C. Water will move in both directions, but more water will move inside.
D. Water will move in both directions, but more water will move outside.
E. Water will not move.
The cell is hyper tonic relevant to its environment. C
Osmoregulation
Is the necessary adaptation organisms use to solve osmotic problems caused by hypertonic and hypotonic environments. It’s the control of solute concentrations and water balance.
What are the 2 types of passive transport? Similarities/differences?
Simple diffusion and facilitated diffusion both move along concentration gradient but facilitated diffusion requires transport protein but simple diffusion does not require transport protein.
Active transport
Uses energy like ATP to move a substance against:
Its concentration gradient
Or
its electrochemical gradient
What is the electrochemical gradient describe?
Movement of hydronium ions to a solution that is already more positively charged
Carrier proteins in active transport have …?
Pumps:
Uniporter: carries 1 molecule/ion
Symporter: carries 2 different molecules/ions, in same direction
Anti porter: carries 2 different molecules/ions in different directions
Is the sodium-potassium pump a uni-porter, sym-porter, or anti-porter?
Anti-porter
The sodium-potassium pump is an important example of _______ transport system.
An active
Describe the sodium-potassium pump.
- Sodium from the cytoplasm binds to sodium-potassium pump
- which stimulates phosphorylation by atp
- Which leads to a change in protein shapes releasing the sodium
- This attracts the potassium to bind to the pump’s extracellular sidewhich triggers the release of the phosphate groups
- Loss of phosphate group release potassium into intracellular fluid
Cotransport
Also known as secondary active transport as it occurs when active transport of a solute indirectly drives transport of other solutes by membrane proteins
Treatment of diarrhea
Drinking solution containing high concentrations of slat and glucose. The solutes are taken by the sodium-glucose cotransporters on the surface of intestinal cells and passed through the cells into the blood, because sodium waste wasnt able to reabsorb into the colon since diarrhea expels waste so fast that reabsorption cant occur (salt levels are thus not constant in the body).
