Cell Membranes

Front 1

What are the functions of cell membrane?

Back 1

• Defines the boundary of cells and cellular organelles;

• Separates the cellular environment from the extracellular environment;

• Separates aqueous regions of different composition within cells;

• Controls the movement of molecules between different environments;

• Regulates signal transduction between cells and within cells.

Front 2

outline the Fluid mosaic model of cell membranes

Back 2

Pattern of different molecules (lipids & proteins) put together in a cell membrane forms a mosaic, and these molecules are constantly moving in two dimensions, in a fluid fashion.

The movement of the mosaic of molecules makes it impossible to form a completely impenetrable barrier.

Front 3

What is the general structure of phopsholipids?

Back 3

# hydrophilic (polar) head {> consists of choline, phosphate, glycerol};

# 2 hydrophobic (non-polar) tails.

Front 4

What are the phosphoglycerides (glycerophospholipids)?

Back 4

# glycerol-based phospholipids,

# main component of the cell membranes.

Front 5

Which structures are the same in different phosphoglycerides?

Back 5

# in the hydrophilic cap:

> phosphate

> glycerol

# hydrophobic (non-polar) tail - fatty acid

Front 6

What are the 3 types of phosphoglycerides?

Back 6

1) phosphatidyl-ethanolamine

2) phosphatidyl-serine

3) phosphatidyl-choline

# ethanolamine, serine, choline - amino acids

Front 7

where can Sphingomyelin be found?

Back 7

- in the membranous myelin sheath surrounding axons of neurons.

- and in general, in some other animal cell membranes.

__________

# Sphingomyelin is a sphingolipid.

Front 8

What is the role of lipids in membrane structure and function?

Back 8

"A primary role of lipids in cellular function is in the formation of the permeability barrier of cells and subcellular organelles in the form of a lipid bilayer." (Dowhan and Bogdanov, 2002)

Front 9

What is the general structure of a cell membrane?

Back 9

Cell membrane is composed of:

a phospholipid bilayer,

> with the hydrophilic phosphate “head” groups facing the aqueous environment on either side,

> and the hydrophobic “tails” in middle.

The cell membrane is primarily made up of three things: 1. Phospholipids 2. Sterol 3. Proteins

Front 10

What are the functions of sterols?

Back 10

Sterols are essential in all eukaryotic cell membranes.

# reduce membrane fluidity and permeability,

# increase membrane rigidity and strength.

> chholesterol - mammalian sterol

Front 11

Useful resources about cell membranes

Back 11

http://bio1510.biology.gatech.edu/module-3-molecules-membranes-and-metabolism/02-membranes/

https://www.khanacademy.org/test-prep/mcat/cells/cell-membrane-overview/a/fluid-mosaic-model-cell-membranes-article

https://en.wikibooks.org/wiki/Structural_Biochemistry/Membrane_Proteins

Front 12

α-helical transmembrane proteins

Back 12

# the more common of the 2 types of transmembrane proteins.

# can be found in the inner membrane of bacterial cells or the plasma membrane of eukaryotes.

Examples:

Glycophorin A,

Bacteriorhodopsin.

Front 13

β-barrel transmembrane proteins

Back 13

# the less common type of transmembrane proteins;

# present in the...

> outer membranes of Gram -ve bacteria,

> cell wall of Gram +ve bacteria,

> outer membrane of mitochondria and chloroplasts.

Front 14

What are the common features of transmembrane proteins?

Back 14

# they span across the entire membrane.

# They may cross the membrane only once or several times, weaving in and out.

# The two kinds of transmembrane proteins are alpha-helical and beta-barrels.

Front 15

How fattiness of acids affects membrane fluidity?

Back 15

Fatty acids form the tails of phospholipids that make up cell membrane.

Saturated fatty acids - tightly packed & less permeable.

# chains of carbon atoms with single bonds between them => they are more straight => it's easier to pack tightly.

Unsaturated fatty acids - less tightly packed & more permeable.

# chains of carbon atoms with some double bonds between them => double bonds cause some sharp twists, so the tails are less straight => it is more complex to pack tightly.