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AL. AQA Biology > transport across cell membranes > Flashcards

transport across cell membranes Flashcards

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1
Q

stages of carb breakdown (simple)

A

1) amylase (starch) : starch -> maltose

2) maltase: maltose -> α-glucose

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2
Q

products of carbohydrate break down

A

maltose -> glucose

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3
Q

main carbs (2)

A

starch

glycogen

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4
Q

how is glucose absorbed

A

1) facilitated diffusion of glucose into epithelial cell of villa
2) glucose diffuses through the cell down concentration gradient
3) facilitated diffusion into capillary (initiated by active transport by Na+/K+ ion pump)

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5
Q

where is maltase?

- type of enzyme?

A

membrane-bound enzyme - in cell surface membrane of epithelial cells
- membrane-bound disaccharidase

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6
Q

stages of carb break down

A
  • saliva enters mouth - mixed salivary amylase with food
  • salivary amylase: carbs -> maltose
    (mineral salts in saliva keep pH around neutral - optimum temp for salivary amylase)
  • [swallowed] acid conditions in stomach denature salivary amylase - prevent further hydrolysis of starch
  • [into s. intestine] - mixed w. pancreatic juice
  • pancreatic amylase - hydrolysis of remaining starch -> maltose (alkaline slates keep pH neutral)
  • muscles push food along ileum - membrane-bound maltase
  • maltose -> α-glucose
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7
Q

endopeptidases

A

hydrolyse peptide bonds between amino acids in central region

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8
Q

exopeptidase

A

hydrolyse peptide bonds between terminal amino acids

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9
Q

dipeptidases

A

hydrolyse bond between 2 amino acids of dipeptides

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10
Q

adaptations of ileum (4)

A
  • increased SA (villi, microvilli) for diffusion
  • very thin-walled = short diffusion distance
  • contain muscle - can maintain diffusion gradient because movement mixed contents
  • well supplied with blood vessels to transport away absorbed molecules and maintain diffusion gradient
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11
Q

functions of surface proteins on plasma membrane (2)

A
  • mechanical support

- act as cell receptors for molecules eg. hormones

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12
Q

functions of proteins spanning the plasma membrane

+ what are they

A
  • channel proteins
  • carrier proteins
    movement of molecules across membrane
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13
Q

functions of plasma membrane (5)

A
  • structural support
  • act as receptors
  • form cell-surface receptors for identifying cells
  • help adhere cells together
  • control entry and exit of substances to the cell
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14
Q

functions of cholesterol in plasma membrane (4)

A
  • adds structural strength
  • v. hydrophobic - prevents waterless + dissolved ions from leaving
  • pulls together fatty acid tails of phospholipid molecules = makes membrane rigid and limits movement - reduces lateral movement of other molecules
  • makes membrane less fluid at high temps
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15
Q

functions of glycolipids in plasma membrane (3)

A
  • recognition site
  • maintain stability of membrane
  • help cells to attach to eachother and form tissues
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16
Q

what is a glycolipid

A

carbohydrate covalently bonded to lipid

17
Q

situation of glycolipid on phospholipid bi-layer

A

carbohydrate portion extends from bilayer into environment outside cell

18
Q

functions of glycoproteins in plasma membrane (3)

A
  • recognition sites - hormones and neurotransmitters
  • help cells to attach to eachother and form tissues
  • allows cells to recognise each other - eg. lymphatic cells recognising organisms own cells
19
Q

why dont molecules generally diffuse across plasma membrane? (4)

A
  • not lipid soluble - cant pass through phospholipid bilayer
  • too large to pass through channel proteins
  • of same charge as channel proteins - even if they are small enough they are repelled
  • electrically charge/polar - cant pass through hydrophobic tails of bi-layer
20
Q

why fluid mosaic model?

A

fluid - individual phospholipid molecules move relative to eachother - flexible structure
mosaic - proteins embedded vary in size and shape

21
Q

ways facilitated diffusion across a membrane occurs

A
  • channel proteins

- carrier proteins

22
Q

channel proteins

A
  • water-filled, hydrophilic channels across the membrane

- selective - open in presence of specific ion - binds to protein, closing it to one side and opening to another

23
Q

carrier proteins

A
  • molecule binds to it, changing shape, opening to one side and closing to the other
24
Q

how are amino acids and glucose absorbed?

A

diffusion and co transport

25
Q

how are triglycerides absorbed?

A
  • monoglycerides and fatty acids reman associated with bile salts in micelles
  • micelles come into contact with epithelial cell lining of villi (due to movement of material in lumen) causing micelle to break down and release monoglycerides and fatty acids
  • as are non-polar they diffuse easily across membrane
26
Q

what happens to products of lipid absorbtion once inside epithelial cells?

A
  • transported to endoplasmic reticulum where are reocmbined to make triglycerides
  • continuing in Golgi body, are combined with cholesterol and lipoproteins to make CHYLOMICRONS
  • chylomicrons move out of cell by exocytosis
  • enter lymphatic capillaries
  • pass into blood via lymphatic vessels
  • triglycerides in chylomicrons are hydrolysed by an enzyme in endothelial cells of capillaries, then diffuse into cells
27
Q

chylomicron?

A

special particles adapted for transport of lipids

28
Q

how are proteins digested [4]

A
  • hydrolysis of peptide bonds by peptidases
  • endopeptidases break polypeptides into smaller polypeptide chains
  • exopeptidase hydrolyse bonds between terminal amino acids producing amino acids
  • dipeptidases hydrolyse bond between 2 amino acids in dipeptide, releasing amino acids
29
Q

how is glucose absorbed (extended - incl. role of Na+)

A
  • NA+ is actively transported out of epithelial cell into blood by Na+/K+ ion pump creating concentration gradient through cell
  • Na+ diffuses down conc gradient into cell through protein carrier (co-transport protein) bringing glucose with it
  • glucose diffuses through cell into blood by facilitated diffusion using another type of carrier protein

AL. AQA Biology (18 decks)

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