Lecture 4: Cell Membrane

Question 1

Discovered by Singer and Nicholson, the ___________ describes the structure of the plasma membrane as a composition of components –including phospholipids, cholesterol, proteins, and carbohydrates – together they give the membrane a fluid character

Answer 1

FLUID MOSAIC MODEL

Question 2

Consisting of a polar, hydrophilic head and a non polar hydrophobic tail

Answer 2

AMPHIAPATHIC

Question 3

The ratio of lipid to protein varies with the cell _____ and _____

Answer 3

Ratio of lipid to protein varies with the cell type and function

Question 4

Plasma membranes contain carbohydrate linked to both lipid (__________) and protein

(________) components

Answer 4

Plasma membranes contain carbohydrate linked to both lipid (glycolipid) and protein (glycoprotein) components

Question 5

All _________ face outwards into extracellular space. Example?

Answer 5

Carbohydrates

Blood group antigens A,B O

Question 6

__________ stiffens membranes

Answer 6

Cholestorol

Question 7

Two main categories of membrane proteins: _______ and _________

Answer 7

Integral proteins - permeate the surface of the membrane

Peripheral proteins - bound to the surface of the membrane

Question 8

Phospholipids and Glycolipids are Distributed __________ in the Plasma Membrane and Lipid Bilayer

Answer 8

Phospholipids and Glycolipids are Distributed Asymmetrically in the Plasma Membrane and Lipid Bilayer

Question 9

Four Mechanisms of Transport across Plasma Membrane

Answer 9

1. Passive diffusion
2. Facilitated diffusion
3. Active transport
4. Bulk transport

Question 10

Small Hydrophobic Molecules can pass easily through the Plasma Membrane (T/F)

Examples?

Answer 10

True

O₂ , CO₂ N₂, Benzene

Question 11

Small uncharged Polar Molecules cannot pass through the polar membrane. (T/F)

Examples?

Answer 11

False

H₂O, Glycerol, Ethanol

Question 12

Large Uncahrged molecules can diffuse through the plasma membrane. (T/F)

Examples?

Answer 12

False

Amino Acids, Glucose, Nucleosides

Question 13

Ions can diffuse through the Plasma Membrane

Examples?

Answer 13

False

H+, Na+, K+, Ca2+, Cl-

Question 14

___________: Dependent on the presence of a concentration gradient across the plasma membrane

– Lipids and lipid-soluble molecules eg ethanol

– Small molecules eg. water and urea

– Small ________ molecules such as O₂, CO₂, NO and H₂O₂

Answer 14

Passive Difusion: Dependent on the presence of a concentration gradient across the plasma membrane

– Lipids and lipid-soluble molecules eg ethanol

– Small molecules eg. water and urea

– Small INORGANIC molecules such as O₂, CO₂, NO and H₂O₂

Question 15

In a ______ solution a cell shrinks

In a _________ solution the cell swells

Answer 15

HYPERTONIC shrinks

HYPOTONIC swells

Question 16

Osmosis is facilitated by a family of membrane proteins called ________ that form channel through which the water can flow. Where commonly found?

Answer 16

Aquaporins

Cells of Kidney tubule

Question 17

Ion Channel whose conformational state depends on the difference in ionic charge on two sides of the membrane

Answer 17

Voltage Gated Channels

Question 18

Ion Channel whose conformational state depends on the binding of the specific molecule which is usually not the solute that passes through the channel

Answer 18

Ligand Gated Channels

Question 19

Ion Channel whose conformation is affected by stretching of the cell membrane

Answer 19

Mechanically-Gated Channels

Question 20

_____________:

• Involves movement of large hydrophilic molecules –concentration dependent
• Can occur in _________
• Strictly passive but requires protein carrier molecules (gated pores), molecules bind specifically but reversibly

Answer 20

Facilitated Diffusion:

• Involves movement of large hydrophilic molecules –concentration dependent
• Can occur in Either Direction
• Strictly passive but requires protein carrier molecules (gated pores), molecules bind specifically but reversibly

Question 21

Mediated transport occurs at a ________ rate than passive diffusion

Answer 21

SLOWER

Question 22

________________:

• Independent of concentration gradients
• Often acts against extreme gradients
• Depends on integral membrane proteins that selectively bind a solute and move it across the membrane in a process driven by changes in the protein’s conformation
• Movement of a solute against a concentration gradient requires the coupled input of energy –direct use of ATP

Answer 22

Active Transport

Question 23

Proteins that carry out active transport are often referred to as _______. Example?

Answer 23

Pumps

ATPase enzyme: a transmembrane protein complex that pumps potassium into cells while pumping sodium out of cells, against each of their gradients

Question 24

___________________uses the stored energy of an electrochemical gradient to move both an ion and a second solute molecule across a plasma membrane.

Answer 24

Secondary Active Transport

Question 25

Bulk Transport:

• Phagocytosis
• Receptor-mediated ______
• Exocytosis–secretion of cell product
• _________–uptake of small volume of extracellular fluid in non-specificmanner
  
  • _________–taken up and then secreted

Answer 25

Bulk Transport:

• Phagocytosis
• Receptor-mediated endocytosis
• Exocytosis–secretion of cell product
• Pinocytosis–uptake of small volume of extracellular fluid in non-specific manner
  
  • Transcytosis–taken up and then secreted

Question 26

Receptor Mediated Endocytosis:

• Only occurs at the specific site along the cell membrane
• ______ binds to receptors
• ______ proteins form a pit around the Ligand which buds off as a vessicle
• Proteins are then recycled back to the membrane

Answer 26

Receptor Mediated Endocytosis:

• Only occurs at the specific site along the cell membrane
• Ligands bind to receptors
• Cathrine proteins form a pit around the Ligand which buds off as a vesicle
• Proteins are then recycled back to the membrane