Lecture 3: Cell Membranes and Transport

Question 1

Selective Permeability

Answer 1

Allows some substances to cross it more easily than others

Question 2

Fluid Mosaic Model

Answer 2

• Cellular mebranes are fluid mosaics of lipids and proteins
• Phosolipids are he most abundant lipid in the plasma membrane, forming a phospholipid bilayer
• Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions
• The fluid mosaic model states that a membrane is a fluid structure wth a “mosaic” of various proteins embedded in it

Question 3

Steroid cholesterol

Answer 3

• Acts as essential building blocks of the plasma membranes, plays pivotal roles in maintaining the structural integrity and regulating the fluidity of cell membranes

Question 4

Cholesterol has different effects on membrane fluidity at different temperatures;

Answer 4

• Cholesterol restrains movement of phospholipids at warm temperatures
• Cholesterol maintains fluidity by preventing tight packing at cool temperatures

Question 5

Membrane Proteins (and functions-ish)

Answer 5

-Peripheral proteins (are not embedded)
- Integral proteins (penetrate the hydrophobic core and often span the membrane)
- Transmembrane proteins (integral proteins that span the membrane)

Question 6

6 Major functions of membrane proteins”

Answer 6

• Transport
• Enzymatic activity
• Signal transduction
• Cell-cell recognition
• Intercellular joining
• Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 7

3 different Movements across membranes

Answer 7

1. Passive Transport
   a) Diffusion
   b) Facilitated diffusion
2. Active Transport
   a) Primary
   b) Secondary
3. Excoytosis and Endocytosis

Question 8

Osmosis

Answer 8

The diffusion of water across a selectively permeable membrane (direction detrmined only by a difference on total solute concentration)

Question 9

Isotonic Solution:

Answer 9

Solute concentration is the same as that inside the cell; no net water movement across the PM

Question 10

Hypertonic Solution:

Answer 10

Solute concentration is greater than that inside the cell; cell loses water

Question 11

Hypotonic Solution:

Answer 11

Solute concentration is less than that inside the cell; cell gains water

Question 12

Active tansport:

Answer 12

• Active transport moves substances against their concentration gradient
• Active tranport requires energy, usually in the form of ATP
• Active transport is performed by specific proteins embedded in the membranes
• The sodium-potassiumm pump is one of the most important active transport system in animal cells

Question 13

Uniport

Answer 13

Movement of 1 molecule across a cell membrane inependant of the oher moleculles is known as a uniport

Question 14

Symport

Answer 14

Movement of 2 molecules in the same direction through a protein channel is known as symport

Question 15

Antiport:

Answer 15

Movement of 2 molecules in the opposite direction through a protein channel known as antiport (exchanger or counter-transporter)

Question 16

Cotransport

Answer 16

Cotranpost occurs when active transport of a solute indirectly drives transport of another

Question 17

2 Types of Active Transport:

Answer 17

Primary (direct) Active Transport- in which the energy is derived directly from the breakdown of adenosine triphosphate (ATP)
Secondary (Indirect) Active Transport- (co-transport) tha uses an electrochemical gradient created by the primary active transport

Question 18

Exocytosis

Answer 18

An active process of moving materials from within a cell to the exterior of the cell (many secretory cells use exocytosis to export their products)

Question 19

Endocytosis

Answer 19

An active cellular process in which substances are brought into the cell (is a reversal of exocytosis, involving different proteins)
3 types

Question 20

3 types of endocytosis:

Answer 20

• Phagocytosis (“cellular eating”): Cell engulfs particle in a vacuole
• Pinocytosis (“cellular drinking”): Cell creates vesicle around fluid
• Receptor-mediated endocytosis: Binding of ligan to receptors triggers vesicle formation