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MODULE 3 - Gastrointestinal System > CELLULAR BIOLOGY - Non-ruminant Digestion and Metabolism > Flashcards

CELLULAR BIOLOGY - Non-ruminant Digestion and Metabolism Flashcards

1
Q

What are the main nutritional energy sources used by most mammals?

A

Carbohydrates
Lipids
Proteins

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2
Q

Which enzyme cleaves alpha 1-4 glycosidic bonds?

A

Amylase

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3
Q

Where does carbohydrate digestion begin in pigs?

A

Carbohydrate digestion begins at the mouth by the actions of lingual amylase

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4
Q

Where in the digestive tract does the majority of carbohydrate digestion occur?

A

Carbohydrate digestion occurs predominately within the small intestine by the actions of pancreatic amylase

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5
Q

What are the four main steps of carbohydrate digestion?

A
  1. Enzymatic digestion of polysaccharides into disaccharides
  2. Enzymatic digestion of disaccharides into monosaccharides
  3. Absorption of monosaccharides into the small intestinal wall and into the bloodstream
  4. Transport of monosaccharides to target cells
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6
Q

Describe the process of enzymatic digestion of polysaccharides into disaccharides

A

Amylase cleaves the alpha 1-4 glycosidic bonds to break down polysaccharides into disaccharides

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7
Q

Describe the process of enzymatic digestion of disaccharides into monosaccharides

A

Cell surface enzymes on the enterocyte microvilli cleave disaccharides into monosaccharides (glucose)

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8
Q

Describe how glucose is absorbed into the small intestinal wall and into the bloodstream

A

Glucose in the small intestinal wall is absorbed into the enterocytes and into the bloodstream via active transport or facilitated diffusion

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9
Q

Describe the process of glucose transport to target cells

A

Glucose is transported around the body dissolved in the blood and taken up into target cells via GLUT proteins

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10
Q

What are the four metabolic processes that glucose is involved in?

A

Glycolysis
Glycogenesis
Glycogenolysis
Fatty acid synthesis

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11
Q

What is glycolysis?

A

Glycolysis is the breakdown of glucose into pyruvate

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12
Q

What is glycogenesis?

A

Glycogenesis is glycogen synthesis from glucose

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13
Q

What is the enzyme which converts glucose into glycogen during glycogenesis?

A

Glycogen synthase

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14
Q

What physiological condition stimulates glycogenesis?

A

When blood glucose levels are high, insulin secretion activates glycogen synthase which converts glucose into glycogen

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15
Q

Where in the body is glucose stored as glycogen?

A

Hepatocytes
Skeletal muscle cells

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16
Q

What is glycogenolysis?

A

Glycogenolysis is the breakdown of glycogen into glucose

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17
Q

What is the enzyme which converts glycogen back into glucose during glucogenolysis?

A

Glucose-6-phosphatase

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18
Q

What physiological condition stimulates glyocgenolysis?

A

When blood glucose levels are low, glucagon secretion activates glucose-6-phosphatase which converts glycogen back into glucose

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19
Q

Why do only the glycogen stores in the liver undergo glycogenolysis and contribute to blood glucose levels?

A

Liver cells have the enzyme glucose-6-phosphatase whereas skeletal muscle cells do not and thus the glycogen stores within these muscle cells can only be used as an energy source for the muscle itself and do not contribute to the blood glucose levels

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20
Q

What physiological condition stimulates fatty acid synthesis from glucose?

A

When blood glucose levels are high, insulin secretion stimulates excess glucose to be converted into fatty acids and stored as triacylglycerols (TAGs)

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21
Q

Where in the body are fatty acids stored as triacylglycerols (TAGs)?

A

Hepatocytes
Adipose cells

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22
Q

Where within the cell does fatty acid synthesis occur?

A

Fatty acid synthesis occurs within the cytoplasm of the cell

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23
Q

Describe the process of the fatty acid synthesis pathway

A
  1. Within the cytoplasm, glycolysis converts glucose into pyruvate which passes into the mitochondria
  2. Within the mitochondria, pyruvate is converted into acetyl CoA
  3. Acetyl CoA undergoes a condensation reaction with oxaloacetate to produce citrate which enters the citric acid cycle
  4. Citrate can cross the mitochondrial membrane back into the cytoplasm where it is broken down into acetyl CoA and oxalocaetate
  5. Acetyl CoA undergoes fatty acid synthesis in the cytoplasm and is stored as triacylglycerols (TAGs) in liver and adipose cells
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24
Q

Where in the digestive tract does the majority of lipid digestion occur?

A

Lipid digestion occurs predominately within the small intestine by the actions of pancreatic lipase

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25
Q

Other than pancreatic lipase, what are the other enzymes involved in lipid digestion?

A

Lingual lipase
Gastric lipase
Lipoprotein lipase

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26
Q

What is the role of bile salts in lipid digestion?

A

Bile salts mediate emulsification of lipids

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27
Q

Describe the process of lipid emulsification and why it is so important for lipid digestion

A

Lipids are hydrophobic molecules and thus clump together in the small intestine to form fat droplets. Small intestinal motility breaks down these fat droplets and mixes them with bile, coating them in bile salts, forming lipoprotein complexes, prevent the lipids from re-clumping and to increase the surface area of the lipids for enzymatic digestion

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28
Q

What is the structure of lipoprotein complexes?

A

Lipoprotein complexes have a central hydrophobic core containing triacylglycerols (TAGs) and cholesterol. This hydrophobic core is surrounded by hydrophilic membrane consisting of phospholipids and free cholesterol

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29
Q

What are the specific lipoprotein complexes formed within the small intestine?

A

Chylomicrons

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30
Q

What are the four steps of triacyglycerol (TAG) digestion?

A
  1. Triacyglycerol (TAG) partial digestion in the small intestinal lumen
  2. Triacyglycerol (TAG) resynthesis in the enterocytes
  3. Triacyglycerol (TAG) transport to target cells
  4. Triacyglycerol (TAG) hydrolysis
31
Q

Describe the process of triacyglycerol (TAG) partial digestion in the small intestinal lumen

A

Colipase enzyme anchors pancreatic lipase to the surface of the chylomicrons, allowing pancreatic lipase to partially digest the triacyglycerols (TAGs) through gaps in the chylomicrons. This partial digestion breaks down the triacyglycerols (TAGs) in fatty acids and a monoacyl glycerol which diffuse into the enterocytes

32
Q

Describe the process of triacyglycerol (TAG) resynthesis in the enterocytes

A

Fatty acids and monoacyl glycerol are resynthesised into triacyglycerols (TAGs) within the enterocytes and repackaged into chylomicrons

33
Q

Describe the process of triacyglycerol (TAG) transport to target cells

A

Chylomicrons in the enterocytes undergo exocytosis into the lymphatic system and then into the bloodstream to target cells

34
Q

Where in the body are lipoprotein lipases found?

A

Luminal surface of capillaries
Cardiac muscle cells
Skeletal muscle cells
Adipose cells

35
Q

Describe the process of triacyglycerol (TAG) hydrolysis

A

Lipoprotein lipases hydrolyse the triacyglycerols (TAGs) within the chylomicrons into fatty acids and glycerol which can diffuse into target cells

36
Q

What happens to the chylomicron remnant after triacyglycerol (TAG) hydrolysis?

A

The chylomicron remnant still contains cholesterol so is transported to and taken up by the liver where the cholesterol is released

37
Q

Which physiological condition stimulates fatty acid metabolism?

A

When blood glucose levels are low, glucagon secretion stimulates fatty acid metabolism

38
Q

Where in the cell does fatty acid metabolism occur?

A

Fatty acid metabolism occurs within the matrix of the mitochondria

39
Q

What are the three steps of fatty acid metabolism?

A
  1. Entry into mitochondria
  2. Beta oxidation
  3. Acetyl CoA oxidation
40
Q

How do short chain fatty acids enter the mitochondria for fatty acid metabolism?

A

Short chain fatty acids diffuse into the mitochondria for fatty acid metabolism

41
Q

How do long chain fatty acids enter the mitochondria for fatty acid metabolism?

A

Long chain fatty acids require a carnitine shuttle to enter the mitochondria for fatty acid metabolism

42
Q

Describe how the Carnitine shuttle transfers long chain fatty acids into the mitochondria

A
  1. Acyl CoA synthase activates fatty acids in the cytoplasm, causing them to react with coenzyme A to form fatty acid CoA
  2. The CoA of the fatty acid CoA is exchanged for carnitine, forming fatty acid carnitine
  3. Fatty acid carnitine can pass through the mitochondrial membrane via carnitine palmitoyl transferase I (CPT I)
  4. In the mitochondria, fatty acid carnitine is reversed to fatty acid CoA by carnitine palmitoyl transferase II (CPT II)
43
Q

Describe the beta oxidation step of fatty acid metabolism

A

Within the mitochondria, each beta oxidation cycle releases two carbons from the acetyl CoA until the whole fatty acid is released as acetyl CoA

44
Q

Describe the Acetyl CoA oxidation step of fatty acid metabolism

A

The Acetyl CoA released from the fatty acid chain enters the citric acid cycle and undergoes oxidative phosphorylation to produce ATP

45
Q

What is the theoretical yield of ATP from one round of beta oxidation in fatty acid metabolism?

A

The theoretical yield is 17 ATP

46
Q

In which cell types are fatty acids resynthesised for storage as triacyglyerols (TAGs)?

A

Fatty acids are resynthesised for storage as triacyglyerols (TAGs) in adipose cells

47
Q

Where in the body is hormone sensitive lipase found?

A

Hormone sensitive lipase is found within adipose cells

48
Q

What is the function of hormone sensitive lipase?

A

When blood glucose levels are high, insulin secretion stimulates hormone sensitive lipase to cleave triacyglyerols stored in adipose cells into fatty acids and glycerol so they can be used as a source of energy

49
Q

What is ketogenesis?

A

Ketogenesis is the production of ketone bodies when fatty acids are metabolised to excess

50
Q

Where in the body does ketogenesis occur?

A

Ketogenesis occurs in the liver

51
Q

What are the three ketone bodies?

A

Hydroxybutyrate
Acetoacetate
Acetone

52
Q

What are the three physiological conditions that stimulate ketogenesis?

A

Fasting
Starvation
Carbohydrate restricted diet

53
Q

Why does insufficient dietary carbohydrates lead to ketone body formation?

A

If there are insufficient carbohydrates, this will stimulate intense gluconeogenesis to increase glucose production. Gluconeogenesis removes oxaloacetate from the citric acid cycle, preventing acetyl CoA from entering the citric acid cycle and becoming ATP so instead is converted into ketone bodies in the liver

54
Q

Which enzyme mediates the conversion of ketone bodies back into Acetyl CoA for ATP production?

A

CoA transferase

55
Q

Which two cell types cannot utilise ketone bodies as an energy source?

A

Erythrocytes: no mitochondria
Liver cells: no CoA transferase enzyme

56
Q

What is ketosis?

A

Ketosis is the excess accumulation of ketone bodies

57
Q

What is ketoacidosis?

A

Ketoacidosis is the pathological state of uncontrolled ketone body production leading to metabolic acidosis

58
Q

What is the main cause of ketoacidosis?

A

Insulin deficiency (type one diabetes)

59
Q

Where in the digestive tract does the majority of protein digestion occur?

A

Protein digestion occurs predominately in the stomach due to the actions of pepsin

60
Q

What are the three steps of protein digestion?

A
  1. Protein digestion in the stomach
  2. Protein digestion in the small intestine
  3. Amino acid absorption into the small intestinal wall and into the bloodstream
61
Q

Describe the process of protein digestion within the stomach

A

Distention of the stomach due to bolus entry stimulates G-cells in the gastric mucosa to secrete gastrin. Gastrin stimulates chief cells to secrete pepsinogen and parietal cells to secrete HCL. HCL activates pepsinogen to form pepsin which cleaves the peptide bonds between the amino acids making up proteins

62
Q

Describe the process of protein digestion in the small intestine

A

The pancreas secretes proenzymes into the small intestine which when activated, will cleave the peptide bonds between the amino acids making up proteins

63
Q

What are the two main proenzymes secreted by the pancreas into the small intestine to digest proteins?

A

Trypsinogen
Chymotripsinogen

64
Q

What activates trypsinogen?

A

Trypsinogen is activated by enteropepsinogen to form trypsin

65
Q

What activates chymotrypsinogen?

A

Chymotrypsinogen is activated by trypsin to form trypsinogen

66
Q

Describe the absorption of amino acids into the small intestinal wall and the bloodstream

A

Amino acids are absorbed into the enterocytes and into the bloodstream via diffusion or transport proteins and travel to the liver and the kidneys

67
Q

Where does catabolism of amino acids occur?

A

Catabolism of amino acids occurs in the liver

68
Q

What are the two steps that amino acids have to undergo in amino acid catabolism?

A

Removal of the amino group
Breakdown of the carbon skeleton

69
Q

What are the two reactions that occur to remove the amino group from the amino acid?

A

Transamination reaction
Deamination reaction

70
Q

Describe the transamination reaction involved in amino acid catabolism

A

Transamination reaction is the transfer of an amino group from the amino acid to an acceptor molecule

71
Q

What is the most common acceptor molecule seen in transamination reactions?

A

Ketoglutarate

72
Q

Describe the deamination reaction involved in amino acid catabolism

A

Deamination reaction is the removal of the amino group from the acceptor molecule in the form of ammonium by the glutamate dehydrogenase enzyme. Ammonium is then directed to the urea cycle

73
Q

What is the difference between glucogenic amino acids and ketogenic amino acids?

A

Glucogenic amino acids: carbon skeletons enter gluconeogenesis to produce glucose

Ketogenic amino acids: carbon skeletons are converted into ketone bodies

74
Q

What are the only two exclusively ketogenic amino acids?

A

Leucine
Lysine

MODULE 3 - Gastrointestinal System (17 decks)

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