Membrane fluidity and proteins

Why is membrane fluidity important to proteins

Some need to change shape to functon

What type of proteins do not diffuse in the membrane

Proteins used for anchorage

How is the rate of lateral diffusion measured

• Tracked using fluorophores (fluorescent molecules on lipids in the membrane

• Intense light exposure bleaches the fluorophores

• New lipids move into the area and regenerate the fluorescence

• Rate measures

What movements of lipids lead to membrane fluidity

• rotation of lipids

• Flexion of tails

• Lateral diffusion

• Transverse diffusion / flip flop

How do proteins move in membranes compared to lipids and why

• similar mechanisms

• Slower

• Not energetically favourable

What factors increase membrane fluidity

• shorter chains (less atoms to interact)

• Unsaturated lipids (kinks, less tight packing)

What factors decrease fluidity

• saturated lipids

• Long chains

How do organisms ensure their membranes are appropriately fluid

• regulation of lipid composition

How do plants know to prepare for heat stress

• sensors in CM detect changes in fluidity

What is the structure of cholesterol

• polar head

• Rigid steroid ring

• Non polar floppy tails

What is the function of cholesterol

• minimises effects of temperature on the membrane

• Restrains lipid movement at high temperatures

• Prevents close pacing at low temperatures

What effect does ethanol have on the cell membrane

• increases fluidity

• Its a small molecule

• Prevents membrane packing

How do bilateral ensure lipids stay in the correct monolayer

• transverse diffusion is catalysed by a flippase

How is the asymmetrical distribution of proteins lipids and carbs in the bilayer determined

• endoplasmic reticulum

• Synthesises and modifies the membrane

• Proteins synthesises on ER membrane then move by vesicles to CM

Can membrane proteins flip flop

• no

• They have a fixed orientation

Where are carbs found on the cell membrane

• cell exterior

What are integral proteins

Span the membrane

What are peripheral proteins

• found on a membrane face

• Either side of membrane

What are the types of integral proteins

• single span alpha helix (hydrophobic)

• Multi spanning alpha helices (multiple)

• Beta barrel

What is membrane topology

• arrangement in relation to the membrane

How is membrane topology maintained

• hydrophobic interactions

• Electrostatic interactions

Membrane protein domains

• protein chains extending from the membrane proteins

• Can be intra or extra cellular

• Some domains are used repeatedly in several proteins

How can secondary structure be predicted

• hydrophobicity of the AA in primary structure

How are side chains arranged in beta strands

• alternate facing up and down

How do peripheral membrane proteins interact with membranes

• no interaction with the core

• Cytoplasmic or exoplasmic (this doesn’t change)

• Interacts with lipid heads and integral proteins

• Non covalent, electrostatic , H bonds, VDW

• Anchor through HC group( the protein covalently bonds to a HC group which enters the core)

What linkages are between proteins and HC groups

• thioether

• Thioester

• Amide linkages

What is the role of ankytin and spectrum

Determine cell shape

What is spectrin

• cytoskeleton protein

• Creates scaffolding intracellularly

What is the function of ankyrin

• binds to integral groups and spectrin for cell shape determination

Where are carbs found on the membrane

• exoplasmic side only

• Attach to lipids and proteins

What is an example of a glycoprotein network

• glycocalyx

• Carbs bind to water

• Acts as a physical barrier against microbes

Glycoproteins. Vs glycolipids

• glycoproteins tend to have longer sugar chains

What are the functions of carbs on membranes

• recognition

• Communication

• Adhesion