DS: Macromolecules Flashcards

1
Q

What is the main source of energy in the diet?

A

Carbohydrates

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2
Q

How are carbohydrates used to provide energy for the body?

A

Carbohydrates are broken down into gluocse which is then converted into intermediates for ATP and energy production by a process called glycolysis.

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3
Q

What are the 3 monosaccharides of carbohydrates?

A
  1. Gluocse
  2. Fructose
  3. Galactose
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4
Q

What are the 3 disaccharides of carbohydrate?

A
  1. Sucrose
  2. Maltose
  3. Lactose
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5
Q

What are the monosaccharide units of sucrose?

A

Fructose + glucose

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6
Q

What are the monosaccharide units of maltose?

A

2 x glucose monomers

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7
Q

What are the monosaccharide units of lactose?

A

Glucose + Galactose

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8
Q

How are gluocse monomers linked together?

A

Gluocse mongers are linked together by alpha 1,4 glycosidic bonds to form polymer chains. These polymer chains can be linked by alpha 1,6 glycosidic bonds to form branched chains.

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9
Q

What are the 3 polysaccharides of carbohydrate?

A
  1. Amylose
  2. Amylopectin
  3. Glycogen
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10
Q

Describe the structure of amylose

A

Starch composed of long chains of glucose linked by alpha 1,4 glycosidic bonds

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11
Q

Describe the structure of amylopectin

A

Starch composed of branched polymer chains of glucose, containing both alpha 1,4 and alpha 1,6 glycosidic bonds.

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12
Q

Describe the structure and function of glycogen

A

Glycogen is composed of long chains fo glucose monomers, synthesised by the enzyme glycogen synthase. Important for the storage of excess glucose molecules when blood sugar levels are high.

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13
Q

Where is carbohydrate digestion initiated?

A

Carbohydrate digestion is initiated in the oral cavity by salivary amylase.

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14
Q

What is the role of salivary amylase?

A

Salivary amylase breaks down starch (and glycogen) into disaccharides (maltose) and trisaccharides (maltotriose) and limit dextrins by cleaving alpha glycosidic bonds between glucose molecules. Breakdown into smaller monomers helps aid in the uptake of carbohydrates by the small intestine for utilisation by the rest of the body

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15
Q

What are the 3 main macronutrients?

A
  1. Carbohydrates
  2. Lipids (fats)
  3. Protein
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16
Q

Why does the amount of carbohydrate digestion decrease between the oral cavity and the stomach?

A

Salivary amylase production is low. Carbohydrate digestion also ceases temporarily in the stomach as the pH is too low to activate salivary amylase, plus being a protein means the enzyme would be digested itself.

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17
Q

What happens to carbohydrates that are still present in the duodenum of the small intestine?

A

Remaining complex carbohydrates are broken down by pancreatic alpha-amylase (PAA) from the pancreases.

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18
Q

Why cant PAA breakdown amylopectin?

A

PAA cannot break bonds at ends of chains or at branch points

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19
Q

What is the role of brush border enzymes in the duodenum of the small intestine?

A

Complete the hydrolysis of complex carbohydrates to monosaccharide monomers so they are in a readily absorbable form to be taken up by intestinal (enterocyte) mucosal cells for distribution around the body

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20
Q

What are the brush border enzymes present in duodenum and what are their functions?

A
  1. Sucrase: sucrose to fructose + glucose
  2. Lactase: lactose to galactose + glucose
  3. Maltase: maltose to 2 x glucose monomers
  4. Glucomylase: amylose to gluocse
  5. Dextrinase: amylopectin and limit dextrins to glucose
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21
Q

How are monosaccharides transported into and across the intestinal mucosal cell?

A
  1. Monosaccharides move across the apical membrane of enterocytes for the intestinal lumen. Glucose and galactose are cotransported with sodium ions, down their concentration gradient, via secondary active transport. Fructose enters via facilitated diffusion using a GLUT5 transporter.
  2. Monosaccharides are secreted across the basolateral membrane, into the capillaries, and transported to the liver via the hepatic portal vein.
22
Q

How does fructose enter intestinal mucosal cells?

A

Via GLUT5 transporters

23
Q

How does galactose and glucose enter intestinal mucosal cells?

A

Via sodium-facilitated cotransporters; secondary active transport

24
Q

What is secondary active transport?

A

Using the movement of one molecule (ie. ions) down its concentration gradient to provide the energy to move another molecule against its concentration gradient.

25
Q

What is the function of the sodium-potassium ATPase pumps in the basolateral membrane of the enterocytes?

A

Help maintain the sodium concentration gradient in the enterocyte to facilitate the secondary active transport of glucose and galactose into the enterocyte for the intestinal lumen, against their concentration gradient.

26
Q

What is the average daily intake of protein?

A

Roughly 125g from the diet, plus an extra 20-60g of protein from secreted fluid and shed cells entering the GI tract

27
Q

What is the structure of proteins?

A

Proteins are comprised of chains of amino acids.

28
Q

What is the difference between EAAs and NEAAs?

A

EAA cannot be produced by the body from the carbon skeleton of glucose, therefore they must be obtained through the diet.
NEAA can be produced by the body so they are not necessary in the diet.

29
Q

What is the role of pepsin?

A

Enzyme that breaks the peptide bonds in proteins to form short chain polypeptides and amino acids.

30
Q

What is pepsinogen?

A

Pepsinogen is the inactive form of pepsin, and it is secreted by chief cells.

31
Q

How is pepsin formed?

A

Pepsinogen, secreted by chief cells, is activated by HCL, secreted by parietal cells in the stomach, to form pepsin.

32
Q

What happens to pepsin that is transported to the duodenum?

A

Pepsin becomes inactivated due to the rise in pH caused by the alkaline mucous and pancreatic juice in the duodenum to protect against the acidity of the stomach

33
Q

What are the brush border enzymes present in the duodenum of the small intestine?

A
  1. Trypsinogen: converted to trypsin
  2. Chymotrypsinogen: converted to chymotrypsin
  3. Procarboxypeptidase: converted to carboxypeptidase
  4. Proaminopeptidase: converted to aminopeptidase
  5. Proelastase: converted to elastase
34
Q

What is the role of trypsin?

A

Trypsin, formed from trypsinogen, activates the other proenzymes in the duodenum so they can become active brush border enzymes

35
Q

What are examples of endopeptidases?

A

Trypsin, chymotrypsin and elastase

36
Q

What is the function of endopeptidases?

A

Cleave peptide bonds in the interior of polypeptide molecules that enter the duodenum of the small intestine

37
Q

What are examples of exopeptidases?

A

Carboxypeptidase and aminopeptidase

38
Q

What is the function of exopeptidases?

A

Remove amino acids from the ends of polypeptide chains that are still present in the duodenum of the small intestine

39
Q

How are amino transported into and through the enterocytes for absorption and utilisation by the body?

A

Amino acids are co-transported across the apical membrane and into enterocytes with sodium ions, down their concentration gradient, in a process called secondary active transport. Amino acids are transported across the basolateral membrane of enterocyte into the interstitial fluid/capillaries by amino acid carriers.

40
Q

How are dipeptides/tripeptides transported into and through the enterocytes for absorption and utilisation by the body?

A

Dipeptides and tripeptides enter the enterocyte, across the apical membrane from the intestinal lumen, via a carrier system. They are then further digested by cytoplasmic dipeptidases and tripeptidases, before being secreted into the capillaries as free amino acids.

41
Q

What is the average daily intake of lipids in the diet?

A

Roughly 25-160g of lipids, of which roughly 95% are triacylglycerides

42
Q

Describe the structure of lipid/ fat droplets

A

Fat droplets are hydrophobic (water-repelling)

43
Q

What is the first stage of processing for lipids for transport within the body?

A

Fat droplets must first be emulsified by bile salts, produced by the liver, to make them more hydrophilic (water-loving)

44
Q

How are lipids taken up by the body?

A

Triglyceride fat droplets are converted to free fatty acids and monoacyl glycerol.

Some end-products are absorbed by the jejunum whereas others aggregate into small particles called micelles which contain fat-soluble vitamins, monoglyceride, fatty acids and bile salts.

Within the enterocyte, triacylglycerides are re-synthesised and combine with phospholipids and protein (Apo B48) to form chylomicrons which are secreted across the basolateral membrane of jejunal enterocytes and enter the lymphatic system.

45
Q

How are fat-soluble vitamins absorbed by the epithelial cells of the small intestine?

A

Absorbed in parralel with lipids/fats.

46
Q

How are water-soluble vitamins absorbed by the epithelial cells of the small intestine?

A

Absorbed by action of special transport proteins

47
Q

What are some examples of fat-soluble vitamins?

A

Vitamin A, D, E and K

48
Q

What is an example of a water-soluble vitamin?

A

Vitamin B12

49
Q

How is vitamin B12 transported to the ileum of the small intestine?

A

Vitamin B12 needs to bind to intrinsic factor (IF)- which is secreted in the lumen of the stomach- in the duodenum for transport to the ileum for later absorption by the body.

50
Q

What is the role of vitamin B12?

A

DNA synthesis