Question

teins that pump hydrogen ions into the stomach. Another is the antidepress drug fluoxetine (Prozac), which prevents receptors on brain cell surfaces f absorbing a mood-altering biochemical called serotonin. 3.3 Mastering Concepts 1. How does the chemical structure of phospholipids enable them to form a bilayer in water? 2. Where in the cell do phospholipid bilayers occur? 3. What are some functions of membrane proteins? 4. How does a cell membrane differ from a cell wall? The Cytoskeleton Supports Eukaryotic Cells Cells Stick Together and Communicate

Answer 1

Answer to question 1.

The Phospholipid molecule is having Amphiphilic character. This means that it has both hydrophobic and hydrophilic heads.

It consists of glycerol molecule, two fatty acids and a Phosphate group. The Phosphate group is negatively charged polar head and is hydrophilic.On the other hand fatty acid chains are uncharged, non-polar tails which are hydrophobic.

In order to form the lowest free energy configuration , the phospholipids , when mixed with water they rearrange themselves .The hydrophilic regions interact with water and the hydrophobic regions remove themselves from water. Since water is present inside as well as outside of the cell , so two phospholipid layers interact with each other such that their hydrophilic ends face the inside and outside of the cell. And towards the centre face the hydrophobic ends of the two phospholipid molecules.

Thus forming a Phospholipid bilayer.

Surface Protein H₂O outside Surface Hydrophilic Hydro- Phobic H₂O inside Surface Through & thoolige protein CScanned with CamScanner

Answer to question 2.

Phospholipid bilayer is present in

a) All cell membranes ( also called plasma membrane).

It has a single layer of phospholipid bilayer.

b) Nucleus , mitochondria and chloroplast (in plants only) all have Two layers of phospholipid bilayer.

c) Golgi apparatus , lysosomes , endoplasmic reticulum all have single layer of phospholipid bilayer.

Answer to question 3.

Functions of membrane Proteins are :

a) They transport molecules and ions across the membrane.

b) They relay signals between inner and outer environment of the cell.

c) Some membrane Proteins have enzyme action , like transferase , hydrolase and oxidoreductase.

d ) Some membrane Proteins allow cell identification. These are involved in immune response.

e) Help in transport of chemical messenger - hormones.

Answer to question 4..

Cell Membrane Cell Wall 1. 2,9t is 9t is present in all plant of l. It is present in plant cell animal cells. bacteria, fungi Ralgae. Not in animals It is living 2.9t is non- is non-living It is made up of lipids and 3. It is made up of cellulose proteins. 4. It is this & flexible. 4. It is thick and rigid. 5. 96 is in approxiomation to 15. Cell membrane separates Cytoplasm. it from the cytoplasm CScanned with CamScanner 3.