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Alimentary > Lecture 5 - Nutrient Digestion I (Carbohydrates and Proteins) > Flashcards

Lecture 5 - Nutrient Digestion I (Carbohydrates and Proteins) Flashcards

1
Q

What is the basic principle of digestion?

A

Taking large complex molecules and breaking them down into monomeric units

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2
Q

What is the problem with digestion?

A

You unlock all these tiny molecules which causes water to flood in

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3
Q

How do you get past the problem with digestion?

A

Stomach releases small amount of content at once to prevent influx of water
Molecules are repackaged into larger molecules (e.g. liver stores glycogen)

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4
Q

What is dumping syndrome?

A

A condition where the stomach moves its contents to the duodenum too quickly –> massive water influx

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5
Q

What are the principle dietary constituents?

A 
Carbs - main energy source
Protein - build + repair body 
Fat - most calorie rich 
Vitamins
Minerals
Water
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6
Q

What are monosaccharides?

A

Sugars that cannot be hydrolysed to give a simpler sugar

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7
Q

What are the 3 monosaccharides we absorb in the GIT?

A

3 Hexose sugars (6C): galactose, fructose, glucose

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8
Q

Where are the monosaccharides absorbed?

A

Small intestine

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9
Q

What bond links two monosaccharides to form a disaccharide?

A

Glycosidic

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10
Q

Where and by what are disaccharides broken down?

A

Brush border enzymes break them down in the small intestine

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11
Q

What are the 3 important disaccharides?

A

Lactose
Sucrose
Maltose

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12
Q

What is lactose?

A

Glucose + galactose

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13
Q

What is sucrose?

A

Glucose + fructose

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14
Q

What is maltose?

A

Glucose + glucose

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15
Q

What enzyme breaks down lactose?

A

Lactase

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16
Q

What enzyme breaks down sucrose?

A

Sucrase

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17
Q

What enzyme breaks down maltose?

A

Maltase

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18
Q

Can the body absorb disaccharides?

A

No

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19
Q

What causes diarrhoea in lactose intolerance?

A

Lack of expression of lactase –> inability to breakdown lactose –> brings in too much water from lumen of small intestine

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20
Q

What are the three main polysaccharides?

A

Starch
Cellulose
Glycogen

21
Q

What is the starch?

A

Plant form of glucose

22
Q

What is the composition of starch?

A

Alpha-amylase (glucose linked in straight chains)

Amylopectin (glucose chains highly branched)

23
Q

What bonds link the glucose monomers in starch?

A

Alpha-1, 4 glycosidic bonds

24
Q

What enzymes can hydrolyse the alpha 1-4, glycosidic bonds?

A

Salivary and pancreatic amylases

25
Q

What is cellulose?

A

Constituent of plant cell walls

26
Q

What is the composition of cellulose?

A

Unbranched, linear chains of glucose monomers linked by beta-1, 4, glycosidic bonds

27
Q

How is cellulose broken down?

A

It is a dietary fibre, i.e. require bacterial cellulase to break it down

28
Q

What is glycogen?

A

Animal storage form of glucose

29
Q

What bonds link the glucose monomers in glycogen?

A

Alpha 1, 4 glycosidic bonds

30
Q

What kind of bonds can be broken down by alpha-amylase?

A

Alpha 1, 4 glycosidic bonds

31
Q

What are the function of the villi in the GIT?

A

Increase surface area for absorption

32
Q

What are found on the surface of the villi?

A

Microvilli

33
Q

What are the two membranes on the epithelial cells?

A

Basolateral and apical membrane (outward facing)

34
Q

What is present between the columnar cells in the small intestine?

A

Tight junctions

35
Q

How do the molecules travel into the small intestine?

A

Molecules have to get through apical membrane

36
Q

What are the two ways that molecules can get across the apical membrane?

A

Can go through the cells (transcellular pathway)

Can go between epithelial cells (paracellular pathway)

37
Q

What are the different transcellular pathways?

A

Lipid soluble - cross lipid membrane

Transport proteins for charged molecules

38
Q

What pump creates a driving force for sodium to enter cells on the intestinal epithelium?

A

Na-K-ATPase

39
Q

How is glucose absorbed in the small intestine?

A

Sodium-glucose linked transporter 1 co-transports glucose and sodium into the epithelial cell
Glucose moved across basolateral membrane via GLUT2 transporter
NaK-ATPase on basolateral membrane maintains a concentration gradient that favours Na moving in from the gut

40
Q

How is water absorbed in the small intestine?

A

Follows Na absorption paracellularly

41
Q

How is fructose absorbed from the gut?

A

GLUT5 receptor on apical membrane and GLUT2 out basolateral membrane

42
Q

What are proteins?

A

Polymers of amino acids linked together by peptide bonds

43
Q

What are amino acid chains of 3-10 known as?

A

Peptides

44
Q

What are the names of enzymes which hydrolyse peptide bonds?

A

Proteases - breakdown proteins

Peptidases - breakdown peptidases

45
Q

Where do endopeptidases work?

A

Centre of protein

46
Q

Where do exopeptidases work?

A

Terminal amino acid

47
Q

How are proteins absorbed in the small intestines?

A

Sodium coupled amino acid transporter - sodium electrochemical gradient driven by pump, sodium pulls in amino acid with it and specific transporter transports it across basolateral membrane

48
Q

How are dipeptides absorbed across the small intestine?

A

PepT1 transporter absorbs di and tripeptides by coupling up with hydrogen ions (proton motive force)

Can be transported across basolateral membrane as intact dipeptide or broken down to AAs in cell

NHE3 transporter transports H out of cell again (this is important for creating acid microclimate)

Alimentary (6 decks)

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