Cell Membrane components and functions

In - depth analysis of the cell membrane, it's functions, and the functions of it's components.

Cells control movement of:

Water, Carbon Dioxide, Oxygen, Ions, and Sugar..

Cell membrane keeps Homeostasis how?

• Defines cell border

• Let’s cell interact w/ environment controlledly

• Let’s cells talk to other cells + identify itself

• Selectively Permeable, only some things pass through.

Fluid Mosaic Model

Used to describe the dynamic and fluid nature of the cell membrane. Molecules move fluidly and freely.

Phospholipids

• Main component of membrane

• Polar head, hydrophilic

• Nonpolar 2 tails, hydrophobic

• Tails turn towards each other to exclude most water

Phospholipid bilayer

• Each layer, phobic tails face each other for phobic core. Only some things go through.

  • (must be small + nonpolar / polar, eg. O², CO². Not charged or large, eg. Glucose.)

• Outer + Inner layer different functions;

  • Outer has glycoproteins (sugar chains on proteins) + glycolipids (sugar chains on some phosopholipids)

  • Inner specializes in binding elements of cytoskeleton

Integral Protein

• aka. Intrinsic Proteins

• >= 1 region in phobic core of bilayer

• Most typical are transmembrane proteins span whole bilayer

• Some associated w/ one side of membrane, not all

Peripheral Protein

• aka. Extrinsic Proteins

• Lie on + secured to inner / outer membrane surface.

• No interaction with phobic core of bilayer.

Cholesterol

• Play a role in providing membrane with proper fluidity + stability

• Adjust fluidity based on temp

  • High temps = reduce fluidity by restrict movement of phospholipids

  • Low temps = more fluidity by preventing fatty acids forming non - fluid gel

• Hydrophilic end for polar sections of phospholipids

• Hydrophobic end extend to non - polar core of phosopholipid bilayer.

• Plant + bacteria cells no cholesterol

Glycolipid

• Phospholipid that contains sugar chain on surface

• Markers for cell recognition + source of energy

Oligosaccharide / sugar chain

• Short chain / branch chain of sugars

• Attach to certain proteins / phosopholipids of membrane

• This modification of membrane only on outer layer

Glycoprotein

• Protein contains sugar chain on surface

• Many functions;

  • Structural Components

  • Receptors

  • Enzymes, ect…

• Glycocalyx = glycoprotein + polysaccharide covering that surrounds cell membrane

Transport protein

• Help substances that can’t cross lipid bilayer move across membrane

  • Can’t cross b/c;

    • Too large, eg. Glucose

    • Charged, eg. Proton

    • Both, eg. Amino Acids

• For facilitated transport + molecular active transport

Attachment and Recognition proteins

• Proteins exposed on intra + extracellular side of membrane, can have attachment sites for diff. elements on either side.

  • Intracellular suface:

    • Components of Cytoskeleton

  • Extracellular surface:

    • Components of extracellular matrix

      • Secreted by cells, structural + biochem. support for cells

      • Elements needed for cell to cell recognition

Receptor for Signalling

• Bind to hormones / growth factors

  • Then trigger signal for cascade of chain reactions in cell

Enzymatic Activities

• Some proteins involved in catalysing biochemical reaction, eg. ATP synthase in inner mitochondrial membrane