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Biology > Transport Across Membranes and Digestion > Flashcards

Transport Across Membranes and Digestion Flashcards

1
Q

Fluid mosaic model of cell membrane

A

Dynamic structure consisting of different molecules constantly moving in relation to each other

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2
Q

Reasons for membranes in cells

A
  • control entry and exit of materials (barrier)
  • control cell signalling
  • site of chemical reactions
  • isolate enzymes/ separate organelles from cytoplasm so reactions can occur
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3
Q

Describe phospholipid layer

A
  • form a bilayer
  • hydrophilic heads are attracted to water so face outwards
  • hydrophobic heads repel water so face inwards
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4
Q

Role of glycoproteins/lipids in cell membrane

A
  • cell recognition sites
  • provide stability to membrane
  • helps cells attach to form tissues
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5
Q

Intrinsic Protein

A
  • span complete membrane
  • protein channels allow diffusion of water soluble ions
  • carrier proteins bind to ions and molecules (e.g. glucose) and change their shape to allow their passage
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6
Q

Extrinsic Protein

A
  • found on either side of cell membrane
  • mechanical support
  • cell receptors
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7
Q

Role of cholesterol in cell membrane

A
  • strength
  • ensures membrane in less fluid at high temperatures
  • membrane less soluble so prevents leakage of water/dissolved ions from cell
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8
Q

Reasons molecules do not diffuse freely through cell membrane

A
  • not lipid soluble or are polar

- too large

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9
Q

Simple Diffusion

A
  • net movement of molecules from high to low concentration (until equilibrium reached)
  • passive (no ATP)
  • no carrier proteins / protein channels
  • very small, lipid soluble substances e.g. gases
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10
Q

Facilitated Diffusion

A
  • net movement of molecules from high to low concentration (until equilibrium reached)
  • passive (no ATP)
  • carrier proteins/protein channels
  • large, polar molecules/charged ions
  • binds to carrier proteins by complementarity of shape or pass through selective channels
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11
Q

Osmosis

A
  • net movement of water molecules from a high to low water potential across a partially permeable membrane
  • passive (no ATP)
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12
Q

Active Transport

A

Movement of molecules from a low to high concentration

  • using carrier proteins
  • requires (hydrolysis of) ATP (active process)
  • large, polar molecules (e.g. glucose) /charged ions
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13
Q

Hypertonic

A

High solute concentration and high osmotic pressure

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14
Q

Hypotonic

A

Low solute concentration and low osmotic pressure

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15
Q

Describe active transport across cell membrane

A
  • molecule binds to carrier protein
  • ATP attaches to carrier protein and donates phosphate group
  • addition of phosphate group changes tertiary structure of carrier protein
  • molecule released moving against concentration gradient
  • phosphate group leaves and protein returns to original shape
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16
Q

Adaptations of villi to increase absorption

A
  • microvilli to increase surface area
  • thin walls for short diffusion path
  • rich blood supply to maintain concentration gradient
17
Q

Explain reason for active transport of glucose and amino acids across ileum

A
  • maximum absorption of glucose and amino acids

- since not all glucose and amino acids absorbed by facilitated diffusion since equilibrium is reached

18
Q

Describe co-transport of glucose into ileum

A
  • Na+ actively transported out of cells into capillary by sodium-potassium pump
  • low Na+ concentration in cell means it diffuses by facilitated diffusion back into cells from lumen of ileum carrying either glucose or amino acids with it (co-transport=passive)
  • glucose diffuses into capillary due to high concentration in cell
19
Q

Digestion

A
  • large molecules are hydrolysed by enzymes

- forming smaller soluble molecules that can be absorbed into the blood through the ileum

20
Q

Describe physical digestion

A

Teeth break down food to increase surface for chemical digestion and stomach muscles churn food

21
Q

Endopeptidase

A

Enzymes found in stomach that hydrolyse INTERNAL peptide bonds between amino acids in a polypeptide / from shorter chains

22
Q

Exopeptidase

A

Enzymes produced in pancreas and used in duodenum that hydrolyse peptide bonds on terminal amino acids of a polypeptide

23
Q

Dipeptidase

A

Membrane bound enzymes found ileum that hydrolyses bond between amino acids in a dipeptide

24
Q

Purpose of endopeptidase

A

Speeds up digestion because it provides more ends for action of exopeptidase

25
Q

Amylase

A

Enzyme produced in salivary glands/pancreas and found in mouth and stomach that digests starch into maltose

26
Q

Maltase

A

Membrane-bound found in the small intestine that digests maltose into glucose

27
Q

Lipase

A

Enzyme produced in pancreas and used in duodenum that digests triglycerides into fatty acids and glycerol

28
Q

Bile

A
  • produced in liver and stored in gall bladder
  • emulsifies fats thus increasing surface area for action of lipase
  • neutralises stomach acid
29
Q

Describe digestion of triglycerides

A
  • lipid globules are emulsified by bile to form smaller emulsion droplets
  • triglycerides are hydrolysed by pancreatic lipase into monoglycerides and fatty acids
  • these associate with bile salt and phospholipids to form even smaller micelles
  • lipid soluble and small enough to pass between microvilli
  • monoglycerides and fatty acids move out of micelles and enter cells by SIMPLE diffusion
30
Q

Suggest why rehydration therapy hydrates the body better than water alone

A

Contains glucose which increases uptake of Na+ ions so more water enters cells by osmosis than it would otherwise

31
Q

Suggest why cholesterol and many other lipids are incorporated into the cell membranes of cells

A
  • provides stability to cell membrane (less fluid)

- accelerates diffusion of non polar substances, e.g. O2 and CO2

32
Q

Describe the role of micelles in lipid absorption

A
  • transport poorly lipid soluble monoglycerides and fatty acids to SURFACE of epithelial cell
  • small enough to pass between microvilli
33
Q

Describe action of membrane-bound dipeptidases and explain their importance

A
  • hydrolyse peptide bond in dipeptide to release amino acids
  • amino acids can cross cell-surface membrane but dipeptides cannot
  • maintain concentration gradient of amino acids/ maximum break down of dipeptides
34
Q

Explain the difference between facilitated diffusion with carrier proteins and channel proteins

A
  • substrate binds to carrier protein by complementarity of shape and changes shape so substrate transported to other side of membrane
  • selective channel protein allows passage of mostly ions based on size and charge
35
Q

Compare and contrast carrier proteins and protein channels

A
  • both intrinsic proteins
  • both involved in facilitated diffusion
  • both transport large, polar molecules and charged ions
  • only carrier proteins involved in active transport
  • molecule/ion must bind to carrier protein which changes shape to transport substrate
  • molecule/ion passes through water filled pathway in protein channels
  • substrate must be complementary to carrier protein where molecule/ion must be certain size or charge to pass through channel protein
36
Q

Describe how sodium-potassium pump works

A
  • active transport
  • carrier protein which binds to three Na+ ions and molecule of ATP
  • ATP hydrolysed which induces change in shape of carrier protein so Na+ released across membrane
  • two potassium ions bind to newly shaped carrier protein on opposite side
  • release of phosphate reverts carrier protein to original shape so potassium ions are released across membrane
37
Q

Co-transport

A

movement of one molecule with its concentration gradient and another against its concentration gradient

38
Q

Explain why higher temperatures result in more leakage out of cells

A
  • damage cell-surface membrane / denature proteins

- increase fluidity

Biology (14 decks)

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