biology - unit 2

What are the main fonction of cell membranes ?

The form biyndaries, enable selective transport, receive signals, support cell communication and maintain the electrochemical gradient.

Why the membrane is semipermeable ? ( type of molecules can only pass)

Only small uncharged molecules diffuse through the lipid bilayer

What properties allow the membrane to make action like endocytoss ?

They are self sealing

What is the composition of the cell membrane ?

Lipids ( phospho/sphingo lipids, cholesterol and carbohydrates)

What is the thickness of the plasma membrane ?

75 A ( 7,5 nm)

What the railroad track mean ?

It’s showing two polar layers constituent with a phospholipid bilayer

What does freeze fracture electron microscopy reveals ?

It splits the lipid bilayer into two leaftetes and reveals embedded membrane proteins

What are the three characteristics of fluid mosaic model ?

Membranes are fluid, dynamic and asymmetric

What membrane fluidity allow proteins and lipids to do ?

They allows proteins to move laterally within the plane of the membrane

On which side of the membrane the carbohydrates are present ?

Only on the extracellular one ( glycolipids and glycoproteins)

What makes phospholipids amphi^hilic ?

Their hydrophilic ( lipophobic) polar head and hydrophobic (non polar/ lipophilique) tail .

What is the basic composition of phospholipid?

Glycérol / sphingosine backbone, fatty acid/ phosphate and polar group ( alcohol ) or nitrogenous alcohol ( choline)

How is cholesterol positioned in the phospholipid bilayer ?

It’s polar head lies near phospholipid head while the hydrophobic region lies among fatty acid tails .

What is the main role of cholesterol ?

Mb fluidity and stability

Which lipids are mostly found on the outer layer ?

Phosphatidylcholine and sphingomyeline

Which lipids are mostly found on the inner layer ?

Phosphatidylethanolamine and phosphatidylserine

Wher is mostly found phosphatidylinositol ? For what are they important ?

In the cytosol layer/ important for signals transduction

Where is mostly found cholesterol ? With which molecules have they high affinity ?

In both side but + affinity for sphingomyeline ( outer )

For what is membrane fluidity is important ? 4

Cell signaling : diffusion in the plane of lipid bilayer

Transport of lipids and protéines =facilitates the transport to other regions of the celle

Celle division : ensures that membrane molecules are distributed evenly between daughter cells when they are divided

Membrane fusion : membrane fluidity to fuse their protein and lipid components

What factors determine membrane fluidity ?

Fatty acid chain length, unsaturation, cholesterol content and temperature

What length of fatty acids increase fluidity ?

Shorter chains

What conformation of saturation is the best ?

CIS cause they introduce kinks that reduce packing and increase fluidity

How temperature affect fluidity ?

Hight increase fluidity

What membrane state occurs below normal physiological temperature ?

Semisolid with strongly constrained lipid movement

What membrane state occurs above normal temperature ?

Disorder liquid state = hydrocarbon of fatty acids are in constant motion

What effect does cholesterol have at high temperature ?

It makes the membranes less fluid ( restricts mov of polar head of fatty acids and disperses tails)

What effect cholesterol have on low temperature ?

Help to keeps the membrane in a fluid state

What are the three main types of lipid movement in membranes ?

Rotation, lateral diffusion and flipflop

Why flip flop movements are rare ?

Cause moving thought polar head is energetically unfavorable and require enzymes

Which proteins mediate transbilayer lipid movement ?

Flip passes floppies (ATP) and scrambles ( gradient)

What are glycoprotéines and glycolipids ?

Membrane proteins or lipids covertly linked to carbohydrates chains

What is glycocalyx ?

The carbohydrates rich outer cell surface layer formes by glycoproteins/lipids

What are key functions of membrane carbohydrates ?

Celle recognition and communication, protection, interaction, endocitosis (binding And recruitment of bacteria)

With what carbohydrates can interacts ?

EC matrix, lectins, growth factors and antibodies

About what proportion of the plasma membrane mass do proteins constitute animals cells ?

About 50%

How are membrane proteins distributed and how can they move ?

Asymmetrically, diffuse laterally within the lipid bilayer

How are integral membrane proteins can be extracted

With strong agent such as detergents or organic solvents

What are the three type of integral proteins ?

Transmembranaire( lipides tails,ionic reaction with phospholipid group) anchored with helix alpha(amphiiphilic) , anchored with lipid

With which interaction are accroched the periphical prot ?

Non covalent bound ( hydrogène or electrostatic)

What structural forms can transmembrane proteins can form ?

Hydrophilic channels ( curved b sheets ( barrels) pr multiple amphiphilic alpha helices)

What can be the functions of integral membrane proteins ? ( 4)

Transporters, anchors, receptions, enzymes

What can transports transporters?

Ions or small molecules (active or passive)

What do membrane anchors do ?

They link the cytoskeleton to the membrane and or to the extracellulr matrix components .

What do receptors do ?

Bind the extracellular signal molecules and relay to the cells

What enzyme make?

Catalyse the production of specific molecules

Where are periodical membrane are located ?

On the cytotoxic face or the outer surface of the plasma membrane

By what the non covalent interactions can be destroyed ?

By pH or high salts concentration

What are lipids raft ?

Microdomains where cholesterol et sphingolipidds cluster with specific proteins

How the lipid rafts regions differ ?

They are thicker, less fluid and more rigid .

What is the composition of those rafts?

Spgingolipid/ cholesterol/ glycoproteins / proteins anchored bu GPI

What are the role of lipid raft ?

Cells receptions/ signalisation / facilitate endocarditis