Structure of the cell surface membrane

Question 1

plasma membranes

Answer 1

• allows different conditions to be established inside and outside the cell
• controls movement of substances

Question 2

phospholipids

Answer 2

• bilayer
• hydrophilic heads - attracted to water- point to inside cell and extracellular fluid
• hydrophobic tails - repel water- attracted to each other inside bilayer

Question 3

functions of phospholipids

Answer 3

• allow movement of lipid soluble substances
• prevent movement of water soluble substances
• make membrane flexible and self-sealing

Question 4

proteins

Answer 4

• embedded in the membrane
• carrier - bind to molecules changing tertiary structure to release molecule on the other side
• channels - water filled, allow movement of water soluble molecules

Question 5

functions of proteins

Answer 5

• provide structural support
• act as receptors e.g hormones
• channels for facilitated diffusion and active transport
• form cell surface receptors for identification
• help cells adhere together

Question 6

functions cholesterol

Answer 6

• add strengths to membranes
• prevent leakage of dissolved Ions and water
• reduce lateral movement of other molecules
• make membrane less fluid at high temperatures

Question 7

glycolipids

Answer 7

• carb covalently bonded with a lipid
• carb bit extends to extracellular fluid where it acts as a cell surface receptor

Question 8

functions of glycolipids

Answer 8

• act as recognition sites
• help maintain stability of the membrane
• help cells attach to form tissues

Question 9

glycoproteins

Answer 9

• carb chains attached to extrinsic proteins on the outer membrane surface
• acts as receptors for neurotransmitters and hormones

Question 10

functions of glycoproteins

Answer 10

• act as recognition sites
• help cells attach to form tissues
• help cells recognise own cells e.g. lymphocytes

Question 11

why do most molecules not freely diffuse across membranes?

Answer 11

because they’re:
- not lipid soluble
- too large
- charged/polar
- same charge as protein channels so repel

Question 12

How is the cell membrane fluid?

Answer 12

• individual phospholipid molecules can move relative to one another
• gives membrane flexible structure that’s constantly changing shape

Question 13

How is the cell membrane mosaic?

Answer 13

proteins embedded vary in shape size and pattern like the tiles of a mosaic