1.3 Membrane structure Flashcards Preview

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Flashcards in 1.3 Membrane structure Deck (23)
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1
Q

Structure of phospholipids

A

Consists of a polar head (hydrophilic) - composed of a glycerol and a phosphate molecule
Consists of two non-polar tails (hydrophobic) - composed of fatty acid (hydrocarbon) chains
Amphipathic - contain both hydrophilic and lipophilic regions

2
Q

Arrangement in membranes

A

Phospholipids arrange into a bilayer

Hydrophobic tail regions face inwards and shielded from surrounding polar fluids

3
Q

Properties of the phospholipid bilayer

A

The bilayer is held by weak hydrophobic interactions
Restrict the passage of many substances
Individual phospholipids can move within the bilayer, allowing fluidity and flexibility

4
Q

Integral proteins

A

permanently attached to the membrane and are typically transmembrane (span across the bilayer).

5
Q

Peripheral proteins

A

temporarily attached by non-covalent interactions and associate with one surface of the membrane.

6
Q

Structure of membrane proteins

A

Non-polar (hydrophobic) amino acids associate directly with the lipid bilayer.
Polar (hydrophilic) amino acids are located internally and face aqueous solutions.

7
Q

Transmembrane proteins structures

A

Single helices/helical bundles

Beta barrels

8
Q

Functions of membrane proteins

A
Junctions
Enzymes
Transport
Recognition
Anchorage
Transduction
9
Q

Junctions

A

serve of connect and join two cells together

10
Q

Enzymes

A

fixing to membranes localises metabolic pathways

11
Q

Transport

A

responsible for facilitated diffusion and active transport

12
Q

Recognition

A

may function as markers for cellular identification

13
Q

Anchorage

A

attachment points for cytoskeleton and extracellular matrix

14
Q

Transduction

A

function as receptors for peptide hormones

15
Q

Cholesterol

A

a component of animal cell membranes, where it functions to maintain integrity and mechanical stability.

16
Q

Functions of cholesterol

A

Immobilise the outer surface of the membrane, reducing fluidity.
Makes the membrane less permeable to very small water-molecule molecules that would otherwise freely cross
Separate phospholipid tails so prevent crystallisation.
Secure peripheral proteins by high density lipid rafts capable of anchoring the protein.

17
Q

Cholesterol at high temperatures

A

it stabilises the membrane and raises the melting point.

18
Q

Cholesterol at low temperatures

A

it intercalates between the phospholipids and prevents clustering.

19
Q

Fluid

A

the phospholipid bilayer is viscous and individual phospholipids can move position

20
Q

Mosaic

A

the phospholipid bilayer is embedded with proteins, resulting in a mosaic of components

21
Q

First model of fluid-mosaic model

A

The first model was proposed in 1935 by Hugh Davson and James Danielli.
They proposed a model whereby two layers of protein flanked a central phospholipid bilayer
The model was described as a “lipo-protein sandwich” - the lipid layer was sandwiched between two protein layers

22
Q

Problems of the lipo-protein sandwich

A

Assumed all membranes were of a uniform thickness
All membranes would aave symmetrical internal and external surfaces
Did not account for the permeability of certain substances
Temperatures at which membranes solidified did not correlate with those expected under the proposed model

23
Q

Evidence of falsification

A

Membranes were discovered to be insoluble in water and varied in size.
They are mobile and not fixed in place.
Freeze fracturing was used to split open the membrane and releaved irregular rough surfaces within the membrane.