1.3 Membrane Structure

Question 1

membrane structure essential idea

Answer 1

The structure of biological membranes make them both fluid and dynamic

Question 2

Phospholipid

Answer 2

Lipid where one fatty acid is replaced by a phosphate group, in membranes characterized by phosphate (polar) head and lipid (non polar) tails

Question 3

Hydrophilic

Answer 3

Polar/ charged unit that is attracted to water

Question 4

Hydrophobic

Answer 4

Non polar unit that is repelled by water

Question 5

Phospholipid emergent properties

Answer 5

When put into water, an emergent property is that phospholipids self-organize to keep heads wet and tails dry

Question 6

Amphipathic

Answer 6

Molecule made form bio the hydrophilic and hydrophobic subunits

Question 7

Phospholipid movement

Answer 7

Phospholipids flow past each other laterally but can’t move vertically

Question 8

Integral proteins

Answer 8

Permanently embedded proteins that go all the way through membranes. They are

Question 9

Integral protein

Answer 9

Protein thats permanently embedded in the cell and goes all the wya through, penetrating one surface (mono topic), or many surfaces (poly-topic). Integral proteins are amphipathic.

Question 10

Glycoproteins/ glycolipids

Answer 10

Proteins with oligosaccharide (few sugar) chain attached, used for cell recognition by immune system and as hormone receptors

Question 11

Peripheral proteins

Answer 11

Temporary association with cell membrane, polar molecules that reside on the outside of the membrane

Question 12

Protein functions

Answer 12

Transport, receptors, anchorage, cell recognition, intercellular joining, enzymatic activity

Question 13

Role of cholesterol in cell membrane

Answer 13

Makes phospholipids pack more tightly and regulates fluidity and flexibility of the membrane by providing structure and rigidity as well as regulating permeability to hydrophilic molecules

Question 14

Attachment to membrane

Answer 14

Hydroxyl group makes the head of the molecule hydrophilic and attracted to phosphate heads on membrane periphery. The hydrophobic tail attracts to lipid tails within the membrane

Question 15

Describe the nature of membrane fluidity

Answer 15

Maintained in mammalian membranes by cholesterol as the hydrophobic tails behave as a liquid while the phosphate head behaves as a solid, making the membrane neither solid nor liquid but fluid

Question 16

Why should membrane fluidity be regulated

Answer 16

Fluidity required for cell movement and material exchange, however overly fluid membranes cannot effectively regulate and restrict the movement of substances in and out of the cell

Question 17

Cholesterol and Fluidity

Answer 17

Presence of cholesterol in membranes restricts phospholipid movement and therefore reduces fluidity

Question 18

Cholesterol and fluidity in cold temperatures

Answer 18

The presence of cholesterol prevents crystallization and solidification at cold temperatures, therefore increasing fluidity by disrupting regular packing of hydrocarbon tails

Question 19

Description of the Singer-Nicholson Fluid Mosaic Model

Answer 19

Considered the most accurate model to date. Phospholipids form a bilateral that is fluid and moves laterally. The membrane also consists of proteins that can be either peripheral or integral. The membrane is a fluid mosaic of phospholipids and proteins. Proposed in 1972.

Question 20

Evidence of the singer-Nicholson model as opposed to davson-danielli model

Answer 20

Membranes proteins were found to be globular and varied in size so they would be unable to form a continuous layer on the membranes periphery. Membrane proteins also has hydrophobic tendencies, suggesting they would embed within the membrane as opposed to outside of it.

Question 21

Davson-Danielli model

Answer 21

A phospholipid membrane surrounded by a layer of protein on either side

Question 22

Evidence of the Davson-Danielli model

Answer 22

High magnification electron microscopes show membranes appearing as two dark lines with lighter space in-between, leading to the belief that proteins surrounded the phospholipid bilayer as proteins are darker beneath the microscope.

Question 23

Falsification of the Davson-Danielli model through freeze fracturing

Answer 23

Freeze fracturing that demonstrated fractures along lines of weakness including the center of the membrane. The fracture also revealed an irregular and rough surface within the bilayer with globular structures that were then interpreted as trans-membrane proteins

Question 24

Falsification of Davson-Danielli model through flourescent antibody tagging

Answer 24

Red and green fluorescent markers attached to the antibodies that bind to membrane proteins. Within 40 minutes the red and green proteins had mixed throughout the membrane, showing that proteins were not fixed to the peripheral layer

Question 25

Calculating magnification

Answer 25

Scale bar measurement / scale bar label

Question 26

Calculating actual size

Answer 26

Measured length / magnification

Question 27

Shortcomings of the davson-danielli membrane model

Answer 27

• assumed all membranes had an identical structure which didn’t;t explain how different membranes had different functions
• proteins are amphipathic though largely non polar and hydrophobic, making it strange for them to be situated on periphery of membrane