12.7 Transport Across Membranes

Question 1

Phospholipids cell membrane

Answer 1

They have a hydrophilic phosphate head and a hydrophobic fatty acid tail which means they can form a bilayer by the head facing water and tail repelling water.

Question 2

the cell surface membrane controls…

Answer 2

the entry and exit of molecules in cells

Question 3

the cell surface membrane surrounds…

Answer 3

the cytoplasm of a cell

Question 4

the cell surface membrane is described as…

Answer 4

selectively permeable

Question 5

the cell surface membrane consists of…

Answer 5

proteins, glycoproteins, phospholipids, cholesterol and carbohydrates

Question 6

phospholipid molecules form… that are… giving the membrane a… structure

Answer 6

1 a bilayer (double layer)
2 constantly moving around relative to 1 another
3 fluid

Question 7

the selective permeability of the cell-surface membrane is related to the type and distribution of…

Answer 7

specific proteins and phospholipid molecules present in the membrane

Question 8

components in the fluid mosaic model

Answer 8

• phospholipids
• cholesterol
• channel proteins (complementary to specific charged molecules & ions)
• carrier proteins
• receptor proteins
• enzymes
• glycoproteins
• aquaporins

Question 9

function of the phospholipids in the fluid mosaic model

Answer 9

• hydrophobic tails (fatty acid chains) of phospholipid molecules are attracted towards each other
• hydrophilic heads are orientated either inwards towards the cytoplasm or outwards towards the watery extra-cellular fluid
• forms the phospholipid bilayer (PB)
• most abundant molecule found in all membranes
• PB allows lipid-soluble (non-polar) molecules to pass through by simple diffusion
• prevents passage of small polar / charged molecules (like ions) and larger molecules (glucose)

Question 10

function of the cholesterol in the fluid mosaic model

Answer 10

• decreases permeability and increases the stability of the membrane
• more cholesterol = less fluidity of the membrane is and vice versa
• different types of cells have different proportions of cholesterol

Question 11

function of the channel proteins (complementary to specific charged molecules & ions) in the fluid mosaic model

Answer 11

• like pores within the membrane
• only allows specific charged ions / small molecules to move across the membrane by facilitated diffusion
• can be open or closed + intrinsic (allow ions to pass straight though)
• Na+ only pass through sodium ion channel proteins embedded within and through the membrane
• proteins have specific tertiary structures -> they are specific and can only transport molecules that are complementary to the shape of the channel protein

Question 12

function of the carrier proteins in the fluid mosaic model

Answer 12

• aid the transport of ions / polar molecules and large molecules (glucose and amino acids by facilitated diffusion and active transport)

Question 13

function of the receptor proteins in the fluid mosaic model

Answer 13

• other protein molecules act as specific receptors for complementary molecules (hormones - insulin - may bind to the insulin receptor protein -> allows a cell to respond by increasing the cells permeability to glucose)
• proteins have specific tertiary structures -> only specific molecules can bind to specific receptor proteins -> specific cells have specific receptors

Question 14

function of the enzymes in the fluid mosaic model

Answer 14

• found embedded in the cell membrane (maltase + dipeptidases)
• shape of enzyme’s active site is specific + complementary to its substrate

Question 15

function of the glycoproteins in the fluid mosaic model

Question 16

function of the aquaporins in the fluid mosaic model