Exam I | Membrane Transport Flashcards
State (in one sentence) what the sodium-potassium pump does.
moves 2 K+ ions into cell and 3 Na+ ions out of cell
List the 5 steps of how the sodium-potassium pump works.
1) ATP positions itself into ATPase
2) hydrolysis releases PO4-, which binds to exterior, causing conformational change
3) 3 Na+ ions are released
4) 2 K+ position themselves into ATPase, causing conformational change while PO4- gets released
5) K+ ions are expelled into interior and protein resumes original shape
What are the consequences of sodium-potassium pump activity?
- alters cell membrane osmotic balance
- alters membrane charge gradient
The sodium-potassium pump is essential to what 2 processes?
- generation of nerve impulses (use electrochemical gradient)
- metabolism
Will sodium-potassium pump activity cause water to move into or out of the cell?
out of the cell
What is another name for secondary active transport?
Sodium-dependent transport
What is secondary active transport?
the process of molecules moving into the cell against their concentration gradient using the electrochemical gradient caused by primary active transporters (usually sodium-potassium pump)
What is an antiporter?
- active transport protein that transports two molecules in OPPOSITE directions against their concentration gradient
- are also ATPases, using ATP to drive the transport
Where does sodium move in secondary active transport?
into the cell
What is a uniporter?
- active transport protein that moves molecule or a group of molecules in the same direction against concentration gradient
- are also ATPases, using ATP to drive transport
What is a symporter?
active transport protein that transports TWO DIFFERENT molecules across the cell membrane at the SAME time
What is SGLUT?
a transporter that moves glucose into the cell by secondary active transport (activity of sodium-potassium pump)
In what two ways can glucose move into the cell?
- secondary active transport
- passive transport
How many passive glucose transporters exist?
at least 4
Where is the GLUT2 protein found?
- liver
- pancreas
- small intestine
Where is GLUT4 protein found?
- skeletal (striated) muscle
- adipose tissue
- heart
what is the difference between GLUT 2 and GLUT 4 protein?
- GLUT2 is insulin-independent, GLUT4 is not
- GLUT4 requires binding of ligand
What is the charge inside the cell after Na-K pump activity?
negative
To what 2 processes is the calcium pump essential?
- neurotransmission
- contractile cells of the skeletal muscle, smooth muscle, and of the heart
is SGLUT a symporter or antiporter?
symporter
How do transport vesicles travel in the cell?
along microtubules by motor proteins( such as dyneins or kinesins)
Why might vesicular packaging be necessary?
- to maintain osmotic gradients
- to regulate intracellular concentrations
- to make sure contents are secreted and do not diffuse around the inside of the cell
How are vesicles generally formed?
through interactions with the ER, Golgi, and perhaps lysosomes
What are the 3 forms of endocytosis?
1) phagocytosis
2) pinocytosis
3) receptor-mediated endocytosis
What happens in phagocytosis?
cells use plasma membrane to engulf relatively large portions of material in ECF (such as bacterial cells) and takes them into the cell
What happens in pinocytosis?
the cell takes in fluid containing small particles
What happens in receptor-mediated endocytosis?
ligand-dependent incorporation of ECF (along with ligand)
What is the difference between basic endocytosis and phagocytosis?
- in basic endocytosis, the cell membrane INVAGINATES (incorporates vesicle into the membrane), rather than EXTRUDES (using the plasma membrane to package material) as in phagocytosis
- volume of membrane is decreased in phagocytosis
What is basic endocytosis?
a constitutive process in which plasma membrane surrounds macromolecules or fluid and then buds off inside the cells to form a vesicle with the ingested material inside
What is an example of receptor-mediated endocytosis?
cholesterol entering cells through LDL receptors
What are clathrins? What do they do?
- in receptor-mediated endocytosis, binds to inner cell membrane receptors following binding of the substrate to the membrane receptors, causing membrane to invaginate substrate
- coats intracellular vesicle which may be subsequently digested by lysosomes
Give 2 examples of cells that perform phagocytosis.
- paramecium
- white blood cells
What is the difference between constitutive and regulated secretion (exocytosis)?
- Constitutive secretion is ongoing. It does not stop. Substances are not stored after synthesis
- Regulated secretion requires binding of a ligand for it to happen. Substances are stored prior to release.
Give 3 examples of regulated secretion (exocytosis)
- release of insulin by beta cells
- release of neurotransmitters by neurons
- release of hormones by pituitary gland
Describe characteristics of transcytosis.
- transepithelial transport
- requires DIFFERENT types of transporter on the apical and basal surfaces
- important for virtually all tissues
What does it mean if a substance has a high partition coefficient?
can passively diffuse through plasma membrane
