5.1 Structure and function of memebranes

Question 1

whats the roles of membranes at the surface of cells

Answer 1

• partially permeable barriers between the cell
  and its environment, between organelles and
  the cytoplasm and within organelles
• sites of chemical reactions
• sites of cell communication (cell signalling)

Question 2

whats the roles of membranes within cells and

Answer 2

• Some membranes are found within cells
• Around organelles (allow internal environment of organelle to be different and so its functions more efficient).
• Partially permeable so control what enters / leaves
  oganelle.
• Within organelles to compartmentalise the contents.
• Can be the site of chemical reactions within some organles – folded to increase surface area.
• Form vesicles for transport within cell – membranes can fuse together and seal without any content loss.

Question 3

Cell membranes have a ….. …… sturucture becuase

Answer 3

1972 – ‘Fluid Mosaic Model’.

Fluid – Phospholipids constantly moving

Mosaic – Protein molecules scattered throughout
like tiles in a mosaic.

Question 4

The different components pf cell memebranes

Answer 4

• phosphlipids
• cholestrol
• proteins
• glycolipids and glycoproteins

Question 5

Phospholipids role in cell membranes

Answer 5

• Phosphate ‘head’ and fatty acid ‘tails’.
• Polar head Hydrophilic head attracts water
• Non-polar tail Hydrophobic tail repels water
• Automatically arrange themselves into a ‘bilayer’
  because the heads face outwards towards the aqueous solution either side of the membrane.
• Acts as a barrier to water-soluble substances (ions and polar molecules).
• Fat-soluble dissolve in the bilayer and pass through the membrane.

Question 6

Cholesterol role in the membrane

Answer 6

• Gives the membrane stability.
• Type of lipid present in all membranes apart from bacterial cell membranes
• Fit between phospholipids.
• Bind to tails causing them to pack more closely together.
• More cholesterol in membrane = less fluid and more rigid.
• Has hydrophobic regions to create a further barrier to polar substances.

Question 7

Proteins role in cell membranes

Answer 7

Control what enters and leaves the cell.

• Channel proteins in membrane allow small charged
  particles through.
• Carrier proteins transport larger molecules and
  charged particles across the membrane by ‘active
  transport’ or ‘facilitated diffusion’.
• Receptors for molecules in cell signalling
  (hormones) so when a molecule binds to the
  protein on the cell surface membrane, a
  chemical reaction is triggered within the cell.

Question 8

Channel proteins

Answer 8

hydrophilic chnnel for passive movment of polr molecules and ions down a conc gradient

Question 9

Carrier proteins

Answer 9

roles: passive transport down a conc gradient and active transport invoves the protein shape changing

Question 10

Membrane-bound
receptors.

Answer 10

• Specific shape. Only messenger molecules with complementary shape can bind.
• Different cells have different types of receptors – respond to different messenger molecules.
• A cell that responds to a particular messenger molecule is a ‘target cell’.
• Drugs can bind.
• Trigger a response or block a receptor.

Question 11

Glycolipids and glycoproteins role in cell membranes

Answer 11

Act as receptors for messanger molecules

Glycolipids – carbohydrates attached to lipids
Glycoproteins – carbohydrates attached to proteins
Stabilise membrane by forming hydrogen bonds with
surrounding water molecules.

Examples of functions
* Act as receptors for cell signalling because they are sites where drugs, hormones and antibodies bind.
* Antigens – cell surface molecules involved in
self-recognition and immune response.

Question 12

Biological membranes consists of a _________a_______ bilayer

Phospholipids consist of a polar, hydrophilic _________ head and a non-polar,
hydrophobic tail consisting of ______ _____ chains.

_________ also occur in the membrane and float freely throughout it.

The model for membrane structure is known as the fluid _______ model.

Membrane bound enzymes occur allowing structured metabolic pathways.

Glycoproteins form the glycocalyx and allow cell to cell recognition.

Glycocalyx is layer outside of bilayer for cell __________ so cells group
together to form tissues.

__________ proteins can act as binding sites for hormones and other
substances and can transmit the information to the interior of the cell.

A variety of ________ proteins allow for the controlled movement of substance
through the membrane using both passive diffusion or active transport.

____-______ and lipid soluble molecules diffuse through the phospholipid
bilayer.

Ionic, polar molecules require ________ proteins to enable them to pass
through the membrane.

Membrane structure loses integrity with high __________ or presence of
organic solvents such as alcohol, thereby increasing permeability.

Answer 12

1. phospholipidbilayer
2. phosphate
3. fatty acid
4. proteins
5. mosaic
6. recognition
7. receptor
8. carrier
9. non polar
10. channel
11. temprture

Question 13

Extrinsic proteins

Answer 13

present on one side of the bilayer

Question 14

Intrinsic proteins

Answer 14

embeded throughout the membrane whith hydrophobi r group holding them in place
eg. carrier channel proteins

Question 15

cells comunicate via

Answer 15

cell signalling

cells need to comunicate control processes inside the body and respond to changes in the environment