Structure of the cell-surface membrane

Question 1

Plasma membrane

Answer 1

+All membranes around and within all cells
+Forms the boundary between cytoplasm and the environment
+Maintains the environment of inside the cell and controls the movement of substances in and out of the cell

Question 2

Phospholipids in cell-membrane

Answer 2

Hydrophyllic heads and hydrophobic tails
∴, forms a bilayer of lipids.
Allow lipid soluble subtances enter and leave the cell.
Prevents water soluble substances entering or leaving the cell
Membrane is flexible and self-healing

Question 3

Proteins in cell-membrane

Answer 3

Proteins are interspersed throughout the cell in two ways
1.Some are on the surface of the cells and don’t cross it. They give mechanical support or form cell receptors with glycolipids.
2. Others span across the membrane. Some are protein channels. which form water filled tubes, which allow water soluble ions to diffuse across the membrane.
Others are carrier proteins. They bind to ions or molecules like glucose and amino acids, change shape in order to move these molecules across the membrane.

Question 4

Functions of proteins in cell-membrane

Answer 4

+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
+Helps cells adhere together
+Act as receptors, e.g for hormones

Question 5

Cholesterol

Answer 5

+Cholesterol molecules occur within the phospholipids and add strength
+Cholesterol is very hydrophobic and prevents loss of water and dissolved ions
+Also pull together the fatty acid tails and the phospholipid molecules.

Question 6

Function of cholesterol in cell-membrane

Answer 6

+Reduce lateral movement of other molecules including phospholipids
+Make make membrane less fluid at high temperature
+Help cells to attach to one another and form tissues

Question 7

Glycolipids in cell-membrane

Answer 7

Made from a carbohydrate covalently bonded to a lipid.
The carbo part extends from the phospholipid bilayer into the watery environment
Acts as a cell-surface receptor.

Functions
+Act as recognition sites
+Help maintain the stability of the membrane
+Help cells to attach to one another and so form tissues

Question 8

Glycoproteins in cell-membrane

Answer 8

Carbohydrates attached to the extrinsic proteins.
Also act as a receptor mainly hormones and neurotransmitters

Functions
+Act as recognition sites
+Help cells attach to one another and form tissues
+Allow cells to recognise each other

Question 9

Permeability of the cell-surface membrane

Answer 9

-Controls the movement of substance in and out of the cell
-Most molecules don’t diffuse across it because
+Not soluble in lipids
+Too large to pass through the channels in the membrane
+Of the same charge as the proteins.
So they get repelled
+Electrically charged, so can’t pass through the non-polar tails.

Question 10

Fluid Mosaic model of the cell -surface membrane

Answer 10

The arrangement which all the various molecules are combined into the structure of the membrane
Fluid- because the individual phospholipid molecules can move relative to one another (Flexibility)

mosaic- the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern.