Membranes - Structure and Function

Question 1

Regulating movement in and out of cell

Answer 1

• transports raw materials into the cell
• transports products and wastes out of the cell
• prevents entry of unwanted matter in
• prevents escape of matter needed for cell function

Question 2

What is the permeability of cell membrane?

Answer 2

Selectively permeable

Question 3

Membrane functions
MOVE TO 1ST POSITION!!!!!!!

Answer 3

1. Regulates movement in and out of cell
2. Separates cell from outside environment
3. Regulates molecular and ionic composition inside cell
4. Contains structures for transport
5. Internal membrane system (separates organelles)
6. Controls flow of information

Question 4

Giving cell individuality

Answer 4

• separates cell from external environment
• forms closed boundary between ICF (intracellular fluid) and ECF (extracellular fluid)

Question 5

Regulating molecular and ionic composition of ICF

Answer 5

• i.e. solutes like minerals, ions, glucose, gas molecules
• conditions inside cell must remain near constant for function = homeostasis

Question 6

Structures for transport

Answer 6

• contains specific pumps and gates for transport
• passage of materials (polar or nonpolar) through different methos
• i.e. passive and active

Question 7

Internal membrane system

Answer 7

• forms boundaries between organelles
• enables separate compartments to exist where specialized metabolic functions take place
• i.e. mitochondria, chloroplasts

Question 8

Controlling flow of information

Answer 8

• information exchange between cells and environment
• biological communication (i.e. hormones)
• infor into cell via messenger
• specific receptors or markers for external stimuli

Question 9

Features of plasma membrane

Answer 9

• sheetlike structures, two layrs thick (6-10nm) = BILAYER
• 50% lipids and 50% proteins
• main functional components: phopholipids (amphiphatic/amphiphilic in nature)

Question 10

Classification of Phospholipids

Answer 10

• differ in size, shape, and chemical makeup
• classes of phospholipids are determined by their type of molecule that is bound to the phosphate group

Question 11

Types of phospholipids involved in cell membrane

Answer 11

Phosphatidylcholine
Phosphatidylthanolamine
Phosphatidylserine

Question 12

How do membranes arrange themselves in water?

Answer 12

• when phospholipids are added to water, spontaneously (no energy added) from bilayers
• this is driven by thermodynamic
• hydrophobic tails face inwards
• hydrophilic heads are in contact with water through H-bonding (intermolecular)

Question 13

How do phospholipids act as selective permeable barriers?

Answer 13

• various substances will pass through at varying rates depending on type of material and transport across
• membrane lipid based: nonpolar substances can pass through
• also small uncharged substances (i.e. o2, co2)
• down the concentration gradient by simple diffusion

Question 14

Fluid Mosaic Model

Answer 14

1972 - Singer and Nicholson
- membrane is a dynamic structure, asymmetrical in nature
- floating protein “icebergs” in a lipid “sea”
- 10 main types of lipids
- each type of cell/organelle has a different percentage of each lipid, protein, carbohydrate

Question 15

Phospholipids

Answer 15

• foundation of bilayer
• composed of hydrophilic heads and hydrophobic tails
  i.e. phospatidylcholine
• regulate the passage of materials in and out of cel (selective permeability)
• lipid soluble substances pass through easily

Question 16

Internal (intrinsic) proteins

Answer 16

• proteins embedded in the lipid bilayer (one region interacts with hydrophobic core)
• many are transmembrane: span entire bilayer and peak out on either side
• transport small or large substances across the bilayer

Question 17

Peripheral (external or extrinsic) proteins

Answer 17

• proteins on the surface of membrane
• do not interact with hydrophobic core
• held to surface non-covalent bonds (H, ionic) usually interacting with exposed portions of integral proteins and directly with the lipid molecules
• most are on the cytosol side of membrane
• function as catalysts, cell identity markers
• anchor or reinforce membrane shape
• give the membrane different shapes
• i.e. red blood cell

Question 18

Carbohydrates

Answer 18

• covalently bonded to lipids or proteins forming glycolipids or glycoproteins
• function in cell recognition and also ensure cell interactions

Question 19

Cholesterol

Answer 19

• lipid molecule composed of 17 carbon atoms arranged in 4 rings found embedded between phospholipids
• controls the fluidity of the membrane

Question 20

What is membrane fluidity?

Answer 20

The viscosity (measure of resistance to flowing) of the lipid bilayer of the cell

Question 21

Factors that can influence membrane fluidity

Answer 21

1. Temperature
2. Degree of unsaturation
3. Length of the fatty acid chain
4. Presence of the steroid cholesterol

Question 22

Temperature

Answer 22

• increased temp leads to increased fluidity
• as temp lowers membrane switch from fluid state to solid state as phospholipids are more closely packed

Question 23

Degree of unsaturation

Answer 23

• presence of double bonds creates kinks in the chains which don’t allow fatty acid chains to allign = increased fluidity
• no double bonds = decreased fluidity (membrane very strong and stacked tightly)

Question 24

Length of the fatty acid chain

Answer 24

• longer chain = decreased fluidity
• because intermolecular interactions between the phospholipid tails adds rigidity to the membrane

Question 25

Presence of the steroid cholesterol

Answer 25

• reduce fluidity but help prevent solidification at low temp by preventing tight packaging of phospholipids