Fluid Mosaic Membrane Model

Question 1

Membranes…

Answer 1

• cover the surface of every living cell
• form an intricate network with the cytoplasm
• surround most cell organelles
• same in all eukaryotes

Question 2

Visible under microscopes?

Answer 2

• optical -> barely visible

* electron -> visible

Question 3

Phospholipid bilayer size

Answer 3

7nm

Question 4

Glycocalyx width

Answer 4

0.5nm

Question 5

Cell surface membrane width

Answer 5

7.5nm

Question 6

Properties of phospholipid bilayer

Answer 6

• 45% lipid, 45% protein, 10% carbohydrate

* most of the lipid is phospholipid

Question 7

Phospholipid bilayer

Answer 7

• each phospholipid molecule has a hydrophobic tail of 2 fatty acids, and a hydrophilic phosphate head
• arrange themselves in a 2 molecule layer
• hydrophobic tails point inwards
• oily
• allows passage of certain lipid-soluble substances through the membrane (semi-permeable) - this is its function

Question 8

Why do hydrophobic tails point inwards?

Answer 8

away from the watery environments both inside and outside of the cell

Question 9

Why is the phospholipid bilayer oily?

Answer 9

• gives membrane flexibility and fluidity

Question 10

Proteins in the cell membrane - the basics

Answer 10

• need to have R-groups that anchor it in place and ones that facilitate movement of molecules
• hydrophilic/hydrophobic interactions
• intrinsic proteins
• extrinsic proteins
• glycoproteins
• channel protein
• carrier protein
• can act of pumps
• enzymes - digestion or microvilli

Question 11

Intrinsic proteins

Answer 11

• Span the width of the membrane
• carrier molecules
• enzymes

Question 12

Extrinsic proteins

Answer 12

• confined to the outer or inner surface
• combine with carbohydrate groups to form glycoproteins
• those on the inner surface attach onto the cytoskeleton right anchor the membrane in place

Question 13

Carbohydrate groups

Answer 13

Extend from the membrane

Question 14

Glycoproteins

Answer 14

cell signalling, cell recognition, binding cells together

Question 15

Channel proteins

Answer 15

• protein with a specific shape that complements the shape of a substance to be transported across the membrane
• used in facilitated diffusion

Question 16

Carrier proteins

Answer 16

• protein with a specific shape that complements the shape of a substance to be transported across the membrane
• used in facilitated diffusion and active transport
• allow the transport of water soluble and polar molecules

Question 17

Lipids in the cell membrane not involved in phospholipid bilayer

Answer 17

combine with carbohydrate groups to form glycolipids

Question 18

Glycolipid

Answer 18

• cell signalling, cell recognition (and cell-surface antigen recognition)
• receptors

Question 19

Cell signalling

Answer 19

• réceptors on cells bind to hormones, drugs and other cells
• leads to a series of reactions within the cell

Question 20

Cholesterol

Answer 20

• restricts the movement of other molecules
• regulates membrane fluidity and stability
• keeps phosphates in the bilayer

Question 21

Glycocalyx

Answer 21

• layer of carbohydrates on the outside of the bilayer

* glycoproteins/glycolipids

Question 22

Why call it the fluid mosaic model?

Answer 22

• fluid -> everything vibrates (esp. bilayer)

* mosaic -> made up of lots of different components

Question 23

How was the FMM discovered?

Answer 23

• freeze-fracturing using SEM on RBCs
• wanted to etch away at the membrane to investigate what it was made of
• blobs on image were glycoproteins sticking out

Question 24

Specialisations of the cell membrane

Answer 24

• properties, functions and capabilities depend on glycoproteins, carrier proteins, and channel proteins
• folds increase SA for transport/absorption (microvilli)
• fluidity allows membranes to be folded by the cytoskeleton to form vesicles; part of endocytosis; requires ATP
• vesicles can fuse with the membrane in exocytosis

Question 25

Functions of cell membranes

Answer 25

1) forms a barrier between the watery cell and its watery surroundings
2) controls transport of molecules into and out of cells (semi-permeable); fuse with itself for bulk transport
3) recognition of other cells
4) receptor sites for hormones and neurotransmitters
5) transmission of nerve impulses
6) insulation of nerves (resting potential maintenance)

Question 26

Properties of the barrier necessary

Answer 26

• strong -> offers mechanical support
• flexible -> allow cells to move, grow and divide
• self-sealing -> division without lysis

Question 27

Hydrophobic tails

Answer 27

Barrier to water soluble molecules

Question 28

Intracellular membranes

Answer 28

Proportions of molecules greatly vary

Question 29

Functions of intracellular membranes

Answer 29

• reaction surface
• intracellular transport system
• compartmentalisation; isolates différent chemical reaction pathways to avoid interference and maintain high substrate concentrations
• hold enzymes
• forms ATP with ATPase
• prevents disruption to the cell (e.g. lysozomes)
• formation of vesicles
• ER, Golgi
• exocytosis
• chloroplasts - contain chlorophyll

Question 30

How temperature affects cell membrane function

Answer 30

• affects permeability
• increase kinetic energy of component molecules and the transporting substances; membrane becomes more permeable
• too high - denature proteins - changes shape - destruction

Question 31

Kidney permeability - extra

Answer 31

• aquaporins (protein water channel) allow water to return to the medulla
• micelles fuse with the membrane
• ions cannot gets through because they’re charged
• lipid soluble substances can (hormones, O2, CO2, urea, glycerol)
• large molecules (glucose, amino acids) cannot
• water can, despite the hydrophilic tails