structure of the cell-surface membrane 4.1

What is the cell surface membrane?

the plasma membrane that surrounds the cells and forms the boundary between cell cytoplasm and the environment.
it controls the movement of substances in and out of the cell.

Why are phospholipids important components of cell-surface membrane?

-the hydrophilic heads of bot phospholipid layers point to the outside of the cell-surface membrane attracted by water on both sides.

-the hydrophobic tails on both phospholipid layers point into the centre of the cell membrane ,repelled by the water on both sides.

What are the functions of phosophlids in the membrane?

-allow lipid-soluble substances to enter and leave the cell.
-prevent water-soluble substances entering and leaving the cell.
-make the membrane flexible and self-sealing.

how are proteins embedded in the phospholipid bilayer in 2 main ways?

\-some proteins occur in the surface of the bilayer and never extend completely across it. (Peripheral proteins) Extrinsic

\
They act either to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors such as hormones.

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Intrinsic protein:

\-other proteins completely span the phospholipid bilayer from one side to the other.

\-Some are protein channels, which form water-filled tubes to allow water-soluble ions to diffuse across the membrane.

Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.

what are the functions of the proteins

-provide structural support
-act as channels transporting water-soluble substances across the membrane.
-allow active transport across the membrane through carrier proteins.
-form cell-surface receptors for identifying cells.
-help cells adhere together
-act as receptors

Function of cholesterol?

-add strength to the membrane

-reduce lateral movement of other molecules including phosoplilipds.
-make the membrane less fluid at high temperatures.
-prevent leakage of water and dissolved ions hydrophobic)

Function of glycolipids?

Made up of a carbohydrate covalently bonded with a lipid.

-act as recognition sites.
-help maintain the stability of the membrane.
-help cells to attach to one another and so form tissues.

glycoprotein?

Carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane.
the functions of glycoproteins
-act as recognition sites
-help cells to attach to one another and so form tissues.
-allow cells to recognize one another.

Permeability of the cell-surface membrane?

In general, most molecules do not freely diffuse across it because many are
--more soluble in lipids, cannot pass through the phospholipid layer.
-too large
-of the same charge
-ellectrically charged

Fluid mosaic model?

Fluid:because the individual phospholipid molecules can move relative to one another.
this gives the membrane a flexible structure that is constantly changing in shape.


mosaic-because the proteins that are embedded in the phospholipid bilayer vary in shape,size and pattern in the same way as the stone or tails of a mosaic.

the functions of the membrane?

-control exit and entry of substances
Separate organelles from cytoplasm so that specific metabolic reactions can take place
-provide an internal transport system
-isolate enzymes that might damage the cell
-provide surfaces on which reactions can occur.