MODULE 1.3

Question 1

surrounds the cytoplasm within cells, which in eukaryotes is filled with membrane-bound organelles.

Answer 1

cell or plasma membrane

Question 2

all cellular membranes are _________ allowing only certain substances to cross the membrane.

Answer 2

selectively permeable

Question 3

All cellular membranes are composed of two layers of __________ embedded with ______ and _______.

Answer 3

phospholipids;
proteins and glycoproteins

Question 4

A bilayer membrane structure was predicted by_____ and _______ as early as ______.

Answer 4

Gorter and Grendel (1925)

Question 5

Gorter and Grendel knew that red blood cells (____________) have no nucleus or other organelles, and thus have only a plasma membrane.

Answer 5

erythrocytes

Question 6

also knew that a major chemical component of these membranes were lipids, specifically phospholipids.

Answer 6

Gorter and Grendel

Question 7

Phospholipid structure (2)

Answer 7

hydrophilic head
hydrophobic tail

Question 8

had experimentally measured the surface area of red blood cells, disrupted them and calculated the amount of phospholipid in the membranes that remained.

Their estimate that that there were enough lipid molecules per cell to wrap around each cell twice was ‘correct’.

Answer 8

Gorter and Grendel

Question 9

what part of the phospholipid bilayer is polar

Answer 9

polar hydrophilic heads

Question 10

In 1935, __________ suggested that proteins might be more or less fortuitously bound to the polar heads of the phospholipids.

Answer 10

In 1935, Davson and Danielli

Question 11

first observed membranes in the transmission electron microscope at high power some decades later, revealing them to have a trilamellar structure.

Answer 11

J.D Robertson

Question 12

Trilamellar Membrane Structure in the Electron Microscope:

electron-dense layer: _________
electron-transparent layer:_____

Answer 12

electron-dense layer: proteins bound to phospholipids

electron-transparent layer:
fatty acid layer

Question 13

Robertson offered his ________in which only proteins with specific functions associated with a membrane were actually bound to the phospholipid heads.

Answer 13

Unit Membrane theory

Question 14

proposed the Fluid Mosaic model of membrane structure

Answer 14

Singer and Nicolson (1972)

Question 15

They suggested that in addition to peripheral proteins that do bind to the surfaces of membranes, many integral membrane proteins actually span the membrane.

Answer 15

Singer and Nicolson (1972)

Question 16

were imagined as a mosaic of protein ‘tiles’ embedded in a phospholipid medium. (the protein ‘tiles’ were predicted to be mobile (fluid) in a phospholipid sea)

Answer 16

integral membrane proteins

Question 17

The key to the fluid mosaic is that embedded proteins are held in membranes by a __________, while they expose their ________ to the external aqueous and cytosolic environments. Thus, like phospholipids themselves, membrane proteins are _________.

Answer 17

hydrophobic domain

hydrophilic domains

amphipathic (have both hydrophilic and hydrophobic part)

Question 18

Because the hydrophilic domains of each integral membrane protein are different from each other, we say that cellular membranes are _______. In other words, cells expose different surface structural (and functional) features to opposite sides of the membranes.

Answer 18

asymmetric

Question 19

peripheral proteins are also known as

Answer 19

surface protein

Question 20

are a natural barrier to the free passage of charged molecules across the membrane because of their own aqueous hydrophilic domains

Answer 20

membrane proteins

Question 21

are responsible for the selective permeability of membranes, facilitating the movement of specific molecule in and out of cells.

Answer 21

membrane proteins

Question 22

also account for specific and selective interactions
with their extracellular environment, including the adhesion of cells to other cells, their attachment to
surfaces, communication between cells (both direct and via hormones and neurons).

Answer 22

membrane proteins

Question 22

The extracellular surface of plasma membranes is ‘sugar-coated’ with _________ covalently linked to membrane proteins (as _______) or to phospholipids (as _______).

Answer 22

oligosaccharides;
glycoproteins;
glycolipids

Question 22

The __________ components of glycosylated membrane proteins inform their function.

Answer 22

carbohydrate

Question 22

enable specific interaction of cells with each other to form tissues. They also allow interaction with extracellular surfaces to which they must adhere. And they figure prominently as part of receptors for many hormones and other chemical communication biomolecules.

Answer 22

glycoproteins

Question 23

Protein domains exposed to the cytoplasm are not ______. They are often connected to components of cytoskeleton, giving cells their shape and allowing cells to change shape when necessary

Answer 23

glycosylated.

Question 24

Integral membrane proteins are also called

Answer 24

trans-membrane proteins

Question 25

Evidence for membrane structure (mosaic organization) and asymmetry of membranes

Answer 25

freeze-fracture electronic microscopy technique

Question 26

proteins embedded in the membrane are not static, but are able to move laterally in the membrane, in effect diffusing within a “____________”.

Answer 26

sea of phospholipids

Question 27

substances that can cross membrane through simple diffusion (3),

cant cross (2)

Answer 27

can cross:
- gases
- hydrophobic molecules
- small polar molecules

can’t cross:
- large polar molecules
- charged molecules (ions)