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Biology A1 > 5: Digestion & Absorption > Flashcards

5: Digestion & Absorption Flashcards

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1
Q

What is Digestion?

A
  • process by which large molecules in food we eat are hydrolysed into smaller, more soluble molecules that can be absorbed by the body
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2
Q

What is Physical Breakdown?
What is Chemical Breakdown?

A
  1. large food particles are mechanically broken down by the action of the teeth and churning of food in the stomach
  2. larger, insoluble molecules are hydrolysed into smaller ones by the action of enzymes
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3
Q

What is Hydrolysis?

A
  • breaking of a chemical bond, forming products from larger molecules with the addition of water
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4
Q

What are the functions of:
1. Salivary Gland
2. Pancreas
3. Small Intestine

A
  1. releases saliva - a mixture of amylase, water and ions required to digest starch into maltose
  2. releases pancreatic juice - mixture of enzymes in an alkaline solution, including amylase for release into small intestine
  3. main area of secretion of digestive enzymes/bile and absorption of products
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5
Q

Why are so many different digestive enzymes used?

A
  • to make sure digestion is rapid
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6
Q

What group of Enzymes are used to break down Starch?
Which 3 areas does digestion occur for Starch?

A
  1. carbohydrases
  2. mouth, small intestine lumen, small intestine brush border
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7
Q

Explain Starch Digestion “in the mouth”

A
  • starch digestion begins here
  • salivary glands secrete saliva - containing amylase enzymes and ions
  • amylase catalyses the hydrolysis of starch into maltose
  • glycosidic bonds broken
  • incomplete hydrolysis of starch
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8
Q

Explain Starch Digestion “in small intestine lumen”

A
  • starch digestion continues in the duodenum
  • pancreatic amylase secreted from pancreas
  • catalysing the hydrolysis of any undigested starch molecules into maltose
  • glycosidic bonds broken
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9
Q

Explain Starch Digestion “on small intestine brush border”

A
  • maltose is a disaccharide, so is too large to be absorbed across the lining of the small intestine
  • therefore, the enzyme maltase hydrolyses MALTOSE into Glucose, breaking glycosidic bonds
  • Maltase enzyme is embedded into the microvilli (brush border) of the small intestine epithelial cells
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10
Q

Why does Starch Digestion stop in Stomach?

A
  • amylase is denatured, due to low pH of Stomach Acid
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11
Q

Why is there “undigested Starch”?

A

food only in mouth for little time before being swallowed

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12
Q

What group of Enzymes break down Protein?
Where does Protein Digestion occur?

A
  • proteases
  • begins in stomach and continues in small intestine
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13
Q

Explain the Digestion of Proteins:

A
  1. Endopeptidases: hydrolyse peptide bonds between amino acids in the central region of the protein molecule, forming smaller peptide molecules
    - produced by stomach + pancreas
  2. Exopeptidases: hydrolyse peptide bonds between terminal amino acids of the protein molecule, releasing dipeptides and single amino acids
    - produced by pancreas, and found on brush border of small intestine wall
  3. Dipeptidases: hydrolyse peptide bonds in dipeptides, forming 2 amino acids
    - intracellular, and found on brush border of small intestine of small intestine epithelial cells
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14
Q

Why is it beneficial to digest polypeptides in the middle to produce smaller peptides?

A
  • increases S.A to provide more “ends”, for exopeptidases to carry out hydrolysis of terminal peptide bonds faster
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15
Q

Where does the Digestion of Lipids take place?

A
  • begins in the duodenum and completed in the ileum
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16
Q

Explain the Digestion of Lipids:
(hint- both physical and chemical)

A
  1. Physical Change:
    - lipids form large droplets when mixed with water
    - liver produces bile salts, which break down large droplets into smaller droplets. This is emulsification
    - this increases S.A of lipids, speeding up the action of lipases
  2. Chemical Change:
    - lipids are then hydrolysed by lipases, which hydrolyse ester bonds in triglycerides, forming 3 fatty acids and 1 glycerol
    - sometimes monoglycerides are formed
17
Q

Are Bile Salts enzymes?

A

no

18
Q

How are Amino Acids & Monosaccharides absorbed?

A
  • co-transport
19
Q

Explain Co-Transport for Glucose:
(hint- 5 steps)

A
  1. Sodium Ions are Actively Transported out of the Epithelial cell into the blood
  2. This reduces the concentration of Sodium Ions in the Epithelial cell, compared to the ileum lumen
  3. This therefore means that Sodium ions can transport from the lumen into epithelial cells via Facilitated Diffusion
  4. However the membrane protein of the microvilli, is a co-transport protein.
    - this means as Na+ is transported into the epithelial cell via facilitated diffusion, glucose can also be transported with the Na+ against the concentration gradient (by active transport)
  5. As the glucose concentration increases in the epithelial cell, the glucose can then move into the bloodstream via Facilitated Diffusion
20
Q

How does the blood capillary near the epithelial cells always have a lower Glucose concentration than in the epithelial cells?

A
  • the blood is constantly flowing in the capillaries, so the high glucose concentration blood is quickly transported away from the epithelial cells, and low glucose concentration blood is brought to the epithelial cells
21
Q

How are Epithelial Cells adapted for Co-Transport?

A
  • microvilli increase S.A for the co-transport proteins to be present
22
Q

Explain the Formation of Micelles:
Describe the properties of Micelles:

A
  • once lipids are hydrolysed by lipase into glycerol, fatty acids and monoglycerides, the come together with Bile Salts to form Micelles
  • micelles are water-soluble
23
Q

Explain the Absorption of Lipids “once the micelles are formed”:

A
  • micelles will transport their contents to the cell-surface membrane of the epithelial cells
  • since these micelles are water-soluble they can’t pass in between phospholipids
  • therefore, the micelles release their contents (glycerol + fatty acids), which are lipid-soluble and non-polar so easily diffuse across the phospholipid bilayer
  • once in the epithelial cells, they reform to chylomicrons
    . these are lipoproteins, formed by the Golgi by adding protein to products
  • these are then transported out of the cell by exocytosis
  • they are first absorbed into lacteal vessels then into the blood

Biology A1 (15 decks)

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