2.5.1 the structure of cell membranes

Question 1

fluid mosaic model

Answer 1

theory of cell membrane structure with proteins embedded in sea of phospholipids

Question 2

glycolipid

Answer 2

lipid/phospholipid with chain of carbohydrate molecules attached to

Question 3

glycoprotein

Answer 3

protein with chain of carbohydrate molecules attached to

Question 4

plasma membrane

Answer 4

cell surface membrane

Question 5

role of membranes at surface of cells

Answer 5

• separates cell components from external environment
• regulate transport of materials into/out of cell
• may contain enzymes used in specific metabolic pathways
• has antigens (recognised by immune system)
• may release chemicals to signal to other cells
• contain receptors for chemical signals = site for cell communication/signalling
• may be site of chemical reactions

Question 6

role of membranes within cells

Answer 6

• mitochondria have folded inner membranes (cristae) = large SA for reactions (eg. aerobic respiration) & localise some of enzymes needed for respiration
• inner membrane of chloroplasts (thylakoid membranes) house chlorophyll = some of reactions of photosynthesis occur
• some digestive enzymes on plasma membranes of epithelial cells lining small intestine

Question 7

history of fluid mosaic model

Answer 7

1972 - singer & nicolson

Question 8

what did fluid mosaic model propose

Answer 8

• fabric of membrane consisted of phospholipid bilayer (double layer) with proteins floating in it
• lipid molecules can change places & some proteins may move = fluidity

Question 9

describe the lipid bilayer

Answer 9

• 2 layers of phospholipid molecules
• hydrophilic heads in contact with watery exterior/interior (cytoplasm)
• hydrophobic tail regions in centre of membrane (away from water)

Question 10

role of cholesterol in phospholipid bilayer (eukaryotic cells)

Answer 10

• helps regulate fluidity of membrane
• maintains mechanical stability
• resist effects of temperature changes on structure

Question 11

describe the different types of proteins in a phospholipid bilayer

Answer 11

1. some have pores & act as channels to allow ions (with electrical charge & surrounded by water molecules) to pass through
2. some are carrier & change shape to carry specific molecules across
3. other proteins attached to carrie proteins & act as enzymes, antigens or receptor sites for complementary shaped signalling chemicals

Question 12

integral proteins

Answer 12

= channel & carrier proteins

• span whole membrane
• membrane-spanning regions interact with hydrophobic region of phospholipid bilayer

Question 13

glycocalyx

Answer 13

(carbohydrate molecules)
- on outside of membrane
- formed by carbohydrate chains attached to lipids (glycolipids) or proteins (glycoproteins)
- very hydrophilic
- attract water with dissolved solutes
- helps cell interact with watery environment & obtain dissolved substances