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Chapter 3
The Plasma Membrane: transport across cell
I. Definitons
1.Passive transport
Transport of a solute across a membrane down its concentration gradient or its electrochemical
gradient, in which the cell expends no metabolic energy.
2.Ion channel
Transmembrane protein complex that forms a water-filled channel across the membrane
through which specific ions can diffuse down their electrochemical gradients.
3.Active transport
Movement of a molecule across a membrane driven by energy.
Uptake of material into a cell by an invagination of a the plasma membrane and its
internalization in a membrane-bounded vesicle.
Process by which most molecules are secreted from a eucaryotic cell. These molecules are
packaged into membrane-bounded vesicles that fuse with the plasma membrane and release their
contents to the extracellular space.
II. True or False
1. H+ can move across the membrane by simple diffusion.
2. Transport by channel protein can be either active or passive.
3. Carrier proteins transfer the solute across the cell membrane by undergoing reversible
conformational changes.
4. Most channel proteins have a gate which selectively opened in response to extracellular
5. Most cells are able to ingest microorganisms or cell debris.
6. Cells use receptor-mediated endocytosis to import selected extracellular macromolecules.
7. Pinocytosis is the uptake of fluid and dissolved material.
III. Choose the Best Answer
1. Which of the following molecules move across the cell membrane by endocytosis?
A. CO2
B. glucose
C. protein
D. K+
E. ethanol
2. Cell secrete enzyme by:
A. active transport
B. pinocytosis
C. phagocytosis
D. exocytosis
E. endocytosis
3. LDLs are transported in cell by:
A. facilitated diffusion
B. receptor-mediated endocytosis
C. simple diffusion
D. carrier protein
E. pinocytosis
4. Red blood cells take in O2 by:
A. active transport
B. facilitated diffusion
C. simple diffusion
D. phagocytosis
E. channel protein
5. Many of the particles and molecules ingested by cells end up in:
A. endosomes
B. endoplasmic reticulum
C. Golgi complex
D. Lysosome
E. Mitochondria
8. The higher concentration of K+ inside cells and the higher concentration of Na+ outside cells
are maintained by:
A. endocytosis and exocytosis
B. facilitated diffusion
C. ions exchange
D. active transport
E. simple diffusion
9. The process which transport certain solutes across the cell membrane against their
concentration gradient is:
A. active transport
B. facilitated diffusion
C. simple diffusion
D. endocytosis
E. exocytosis
10. Which statement following is true about facilitated diffusion?
A. transport solutes against their concentration gradients
B. needs no carrier protein
C. transport ions only
D. transport solutes down their concentration gradients with the help of carrier
E. needs no transport protein
IV. Multiple Choice
1. Small molecules are transported into cell by:
A. facilitated diffusion
B. active transport
C. simple diffusion
D. endocytosis
2. The features of facilitated diffusion include:
A. specificity
B. saturation
C. need receptor
D. high speed
3. Using the energy of ATP hydrolysis, Na+-K+ pump:
A. pump Na+ out of cell
B. pump K+ out of cell
C. pump Na+ into cell
D. pump K+ into cell
4. The Na+-K+ pump consists of:
A. α subunit
B. β subunit
C. γ subunit
D. δ subunit
5. Step of receptor-mediated endocytosis include:
A. Macromolecules bind receptor specifically
B. Macromolecule-receptor complexes migrate to coated pit
C. Membrane pinches off as internal coated vesicles
D. Vesicles approach to the cell membrane