fluid mosaic model

Front

cell membrane basic desc

Back

1. 1. encloses the contents of the cells

2. 2. it forms a boundyr betwene the internal and external cell envrionment

3. 3. it is partially permeable --> allows only cetrain molecules to pass through it

Front

cell surface membrane strcuture

Back

1. 1. consists of a bilayer of phsopholipids with different protiens either attateched to it embedded with the bilayer

2. 2. carbohydrate chains are attatched to the phospholipids or portiens and are found on the side of the membrane in contact with the external environemnt

Front

phospholipids structure

Back

1. 1. phosphplipids are primarily repsonsible for the physcial properties of hthe cell membrane

2. 2. one molecule of phospholipid contains 2 fatty acid chians, one saturated and one unsaturated, linked to two or three carbons of the glycerol molecule,

3. 3. phospohate group that is attatched to the last carbon of the glycerol molecule

4. 4. fatty acid chains are hydrophobic --> hydrophobic tail

5. 5. phsophate group is electrically charged -->hydrohphillic --> hydrophilic heads.

6. phospholipid --> amphipathic molecule

--> phosphate group glycerol fatty acid chain

Front

fluid mosaic model

Back

1. 1. internal cytosol of cell and ext envt of cell are both aqueous , the phospholipid molecules arranged in a way such that hydrophilicheads are in aqueus solution and hydrophobic tails are shielded from aquous envt

2. 2. fluid referes to the phospholiipids and the embedded proteins moving freely and laterally within the phospholipid bilayer

3. 3. mosaic refers to the protein and cholestrol randomly embedded and scattered amongst the phospholipid moleuclues resulting in a mosaic arrangement of components in the cell membrane

--> all memrbane and membrane bound organesllls in the cell, have the bilyaer strcuture

Front

fucntions of cell membrane componeoned

Back

1. 1. transport proteins : carrier and channel proteins : allow the passage of specfic ions and molecules across the cell membrane

2. 2: enzymes which cataylse reactions

3. 3: receptors: have specific binding sites allowing chemical messengers like hormones to binf to the protein resulting in the relay of message to the isnide of the cell

4. 4. glycoproteins: play a role in cell-cell recognition and cell adhesion. they consit of carbohydrate chains covalently bonded to proteins and are found on the side facing ext of cell

5. 5:glycolipids are carbhydrate molecules that are covaently bonded to the phospholipid membrane . carbohydrate molecules are attatched to side facing ext of cell and involved in CELL RECOGNITION

6. 6: cholesterol which reduced fluidity of cell membrane

Front

membrane fluidity

Back

1. 1. increased at high temperatures and affected by

2. 1. presence of unsaturated fatty acids in phospholipids increase membrane fluidity

3. 2. presence of saturated fatty acids decrease membrane fluidity

4. 3. cholesterol increases membrane fluidity at low temperatures and decreases membrane fluidity at high temperatures

Front

transport across membranes

Back

1. 1. cell membranes are partially permable --> only certain moleuclues and ions pass thorugh

2. 2. can cross by simple diffusion, faciliated diffusion and active transport

Front

simple diffusion

Back

1. 1. small moleculues and lipid soluble substabnces can pass driectly thorugh the hydrohphobic core of the cell surface membrane by simple diffusion

2. 2. simple diffusion, transport proteins are not involved in moving the moleculues across membranes

3. 3. passive process, hence no energy from hydrolysis of ATP used

4. 4. moleculues are able to move from a region of higher concnentration to a region of lower concentration without the need for trasport proteins --> by simple diffusion

5. 5. oxygen carbon dioxide nitrogen water and glycerol

6. note water and glycerol are POLAR but RELATIVELY SMALL. usually polar moleculues are hydrohpilic cant cross because of hydrohpbic core

Front

facilitated diffusion

Back

1. 1. transport proteins ARE involved --> channel and carrier proteins are involved in the moving of HYDROPHILIC MOLECULES AND IONS across the hydrophobic bilayer

2. 2. passive process, as molecules move down a concentration gradient with the help of transport proteins embedded in the phospholipid bilayer

3. 3. most transport proteins are very specific and hence transport some substances but not others

1. 1. channel proteins: channel proteins provide a HYDROHPILIC PASSAGE to allow specific hydrophilic molecules and ions to move across the hydrophobic core of the cell membrane

2. --> protein channels called aquaporins are present to facilitate the movement of water molecules across the cell membrane

2. 2. channel proteins : alternates between two shapes, moving the ion or moleculue across the cell membrane with a change in shape (hydrophilic interior too)

3. --> change in shape is triggered by the binding and release of molecule at its binding site.

4. --> molecule to be transported is shielded from the hydrohphobic core of the cell membrane and it moves molculues across the cell membrane down a concentration gradient. --> no energy from hydrolysis of ATP is required.

--> both channel and carrier proteins : transport molecules in either direction from region of high to low concentration, net driecetion of movemnt is always down conentration gradient of moleuclue

Front

active transport

Back

1. 1. the movement of molecules or ions form a region of lower concentration to a region of higher concentration across the cell membrane, ENERGY FROM ATP IS REQUIRED.

2. 2. cells constantly using ACTIVE TRANPSORT TO TRANSPORT MOLCULES require lots of energy hence large number of mitochondria, - CARRIER PROTEINS also used in this process

3. 3. molecules present in higher concentration than in the cells are actively tranpsorted into the cell with the help of the protein tranpsorter, carrier portein.

4. 4. energy is required for the carrier protein to change its shape to tranpsort the molecule across the cell membrane and this energy is from the HYDROLYSIS OF ATP