Metabolism & major metabolic pathways Flashcards
(137 cards)
1
Q
What is digestion?
A
Digestion is the process of breaking food down into molecules small enough to absorb
2
Q
What is the purpose of mechanical digestion?
A
Chewing or grinding, increases the surface area of food
3
Q
What is the purpose of chemical digestion?
A
Chemical digestion splits food into small molecules that can pass through membranes; these are used to build larger molecules
4
Q
In chemical digestion, what does the process of enzymatic hydrolysis
A
It splits bonds in molecules with the addition of water
5
Q
What chemical digestion occurs in the human digestive system?
A
1) Carbohydrate Digestion
2) Protein Digestion
3) Nucleic Acid Digestion
4) Fat Digestion
6
Q
How are carbohydrates digested in the Oral cavity, Pharynx and Esophagus?
A
Polysaccharides such as starch and glycogen are broken down by salivary amylase into smaller polysaccharides or maltose
7
Q
Are carbohydrates broken down in the stomach?
A
No, Ph is too high
8
Q
How are carbohydrates broken down in the small intestine
A
1) Pancreatic amylases break down the smaller polysaccharides into disaccharides (that weren’t broken down)
2) The disaccharides (from oral cavtity) are then broken down by enzymes from inestinal epithelium into monosaccharides
9
Q
How are proteins digested in the stomach?
A
Proteins are digested by pepsin into small polypeptides
10
Q
How are proteins digested in the small intestine?
A
1) Small polypeptides are digested by pancreatic trypsin and chrymotrypsin into smaller polypeptides and then finally by pancreatic carboxypeptidase into small peptides
2) Then, the small peptides are digested into amino acids by dipeptidases, carboxypeptidase and aminopeptidase
11
Q
Are nucleic acids digested in the oral cavity, pharynx and esophagus?
A
No
12
Q
Are proteins digested in the oral cavity, pharynx and esophagus?
A
No
13
Q
Are nucleic acids digested in the stomach?
A
No
14
Q
How are nucleic acids digested in the small intestine?
A
1) DNA and RNA is digested into nucleiotides by pancreatic nucleases
2) Nucleotides are converted to nucleotidases which is then digested into nitrogenous bases, sugars and phosphates by nucleosidases and phosphatases
15
Q
Are fats digested in the oral cavity, pharynx and esophagus?
A
No
16
Q
Are fats digested in the stomach?
A
No
17
Q
How are fats digested in the small intestine?
A
Fat (triglycerides) are converted to glycerol, fatty acids and monoglycerides by pancreatic lipase
18
Q
What does over nourishment cause?
A
obesity, which results from excessive intake of food energy with the excess stored as fat
19
Q
Why is obesity bad for you?
A
Obesity contributes to type 2 diabetes, cancer of the colon and breasts, heart attacks, and strokes
20
Q
What helps regulate body weight?
A
Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain
i. Ghrelin
ii. Insulin and PYY
iii. Leptin
21
Q
How does ghrelin help regulate body weight?
A
A hormone secreted by the stomach wall, triggers feelings of hunger before meals
22
Q
How does insulin and PYY help regulate body weight?
A
Insulin from the pancreas and PYY, a hormone secreted by the small intestine after meals, both suppress appetite
23
Q
How does leptin help regulate body weight?
A
Produced by adipose (fat) tissue, also suppresses appetite and plays a role in regulating body fat levels
24
Q
How does the small intestine have a huge surface area?
A
Due to villi and microvilli that are exposed to the intestinal lumen (The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption)
25
What is the imprortance of digestion?
It allows materials needed to process the food to be localised in a single place eg, teeth in mouth
Prevents each cell having to contain a full range of digestive enzymes
26
What is ingestion?
It's the taking in of food into the alimentary canal eg, putting food in your mouth
27
Why is digestion essential for absorption?
If food isn't broken down, chemicals in food would not pass from digestive system into body tissues
28
What is absorption?
Soluble food is passed from cells into bloodstream
29
What is egestion?
It's the removal of unabsorbed and undigested material from the digestive system through anus
30
What is the function of villi?
It increases the surface area for either digestion or absorption
31
Where are the villus found?
Lining of duodenum and Ileum
32
What are the adaptions of the small intestine for absorption?
Very long
Numerous villi
Walls of villi are one cell thick
Rich blood supply to carry away water soluble products
Each villus has lymph supply [lacteal] to carry away fats
33
The body stores energy-rich molecules that are not immediately needed, how is it stored?
In humans, excess energy is first stored in the liver and muscle cells in a polymer called glycogen, which is a branched chain form of glucose
34
What is the purpose of the body storing energy-rich molecules?
When fewer calories are taken in than expended, the human body expends liver glycogen first, then muscle glycogen and fat and subsequently proteins
35
What happens to the excess energy when glycogen stores become full?
When glycogen stores become full, excess energy is stored in fat in adipose cells in the form of triglycerides.
36
What allows tryglyceride to make multiple oxidations possible?
Are highly reduced molecules
37
What makes tryglycerides compact?
They are anhydrous (exclude water)
38
Which tissue fuel provides fuel for the longest to shortest, in order
Fat, Body Protein, Muscle Glycogen, Liver Glycogen, Blood/Extracellular Glucose
39
What is the fate of carbohydrates in the body (in the “non-fasting” state)
Carbohydrates are broken down into glucose by various enzymes.
Some glucose is used immediately, but the majority enters the blood stream triggering insulin release and the uptake of glucose into cells. Excess glucose is stored as glycogen in liver and muscle.
40
What is the fate of proteins in the body (in the “non-fasting” state)
Proteins are broken down into individual amino acids and used in body cells to form new proteins or to join the amino acid pool.
Amino acids that are in excess of the body's needs are converted by liver enzymes into keto acids and urea. Keto acids may be used as sources of energy, converted into glucose, or stored as fat. Urea is excreted from the body in sweat and urine.
41
What is the fate of Fats in the body? (in the “non-fasting” state)
Fats are digested in the small intestine, and packaged into lipoproteins.
Excess fat is stored as droplets in fat cells. When fats are used as an energy source, they are broken down in cellular mitochondria through b-oxidation.
42
What is the fate of Carbohydrates, fats and proteins in the body (in the fasting state)
Carbohydrate, fats and protein are metabolized in separate processes into a common product called acetyl-CoA.
Acetyl-CoA is a major metabolic pathways player, and is an important part of the process which creates the energy molecule called ATP (adenosine triphosphate) in the mitochondria.
43
What is the function of the hormone glucagon?
It is released and it triggers the release of glycogen and fatty acids to fuel the body until the next meal arrives.
44
What occurs approximately 2-4 hours after a meal?
Blood glucose concentration drops to normal baseline levels and a fasting state begins. This drop in blood sugar causes insulin levels to also decline. Another hormone, glucagon, is released and it triggers the release of glycogen and fatty acids to fuel the body until the next meal arrives.
45
If you skip lunch, what will your body begin to do?
When you skip lunch, your glucose levels are low – you release hormone glucagon and it enters blood stream and acts on target cells in liver. It breaks glycogen to glucose, glucose is released and blood glucose levels increase
46
What happens to your metabolism in the “starvation” state?
The stored glycogen in the liver and muscles is exhausted, insulin levels drop and the body ramps up its access to stored fat.
As fatty acids flow into the blood stream, the liver takes the excess fats and more ketone bodies through ketosis.
The muscles continue to burn fatty acids, but decrease their use of ketones. The ketone bodies then build up in the blood stream to a level at which the brain begins to oxidize them for fuel. As the brain uses the ketones, it needs less glucose, so the liver decreases the rate of gluconeogenesis.
47
As the brain uses the ketones, it needs less glucose, so the liver decreases the rate of gluconeogenesis, how does this help to preserve muscle tissue?
This helps preserve muscle tissue as the body doesn't need to break down the amino acids to convert them to glucose.
48
How can the body survive for long periods without eating?
Due to the ability to metabolise ketones, the human body can survive for long periods without eating.
49
Where are the hormones glucagon and insulin both produced and what cells produce them?
Islets of the pancreas
Alpha cells -glucagon,
Beta cells(most abundant) - make insulin
50
What are alpha cells?
Alpha cells (more commonly alpha-cells or α-cells) are endocrine cells in the pancreatic islets of the pancreas.
51
Degeneration of the beta cells is the main cause of what?
type I (insulin-dependent) diabetes mellitus
52
The synthesis and breakdown of glycogen is central to what?
Maintaining metabolic balance
53
What regulates the breakdown of glycogen into glucose?
Insulin and glucagon
54
What is the site for glucose homeostasis?
The liver
55
What stimulates glycogen synthesis?
A carbohydrate-rich meal raises insulin levels, which triggers the synthesis of glycogen.
56
What stimulates the break down of glycogen?
Low blood sugar causes glucagon to stimulate the breakdown of glycogen and release glucose
57
What is glycogen?
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage, representing the main storage form of glucose in the body.
58
What are the two types of alpha linkage found in glycogen?
a-1,4 and a-1,6-glycosidic bond
59
What are alpha linkages?
When a compound with alpha confirmation links with another compound with alpha confirmation, the linkage is alpha linkage
60
Where is the glycogen in humans stored?
The liver and skeletal muscle.
61
How is the liver and skeletal muscle able to hold a large amount of glycogen?
Due to the large weight of muscle (however this glycogen is not available to the rest of the body)
62
What is the function of the liver glycogen stores?
To maintain glucose homeostasis
63
What do the liver cells use glycogen for?
To control glucose levels.
64
What makes glucose useful that differs from fats and amino acids in terms of energy
Glucose is useful for shorts bursts of energy without using oxygen. This differs from the breakdown of fats and amino acids which requires oxygen
65
What is the key enzyme in glycogen breakdown?
Glycogen phosphorylase is the key enzyme in glycogen breakdown i.e. control point.
66
What is the key enzyme in glycogen synthesis?
The primary, regulated enzyme in glycogenesis is glycogen synthase
67
What is Glycogenolysis?
process by which glycogen, the primary carbohydrate stored in the liver and muscle cells of animals, is broken down into glucose to provide immediate energy and to maintain blood glucose levels during fasting.
68
Describe Glycogenolysis
In humans, excess energy is first stored in the liver and muscle cells in a polymer called glycogen, which is a branched chain form of glucose. Low blood sugar causes you to release the hormone glucagon and it enters blood stream and acts on target cells in liver. It breaks glycogen to glucose, glucose is released and blood glucose levels increase.
This drop in blood sugar causes insulin levels to also decline.
Once glucose is trapped in cells as glucose-6-phosphate, it can be converted to glucose-1-phosphate, which is then added to glycogen chains by two repetitive reactions.
Glycogen phosphorylase is the key enzyme in glycogen breakdown i.e. control point
69
What is Gluconeogenesis?
The formation of glucose, allows the production of glucose from non-sugar molecules.
70
What are the major non-carbohydrate precursors which may be used for the formation of glucose?
Lactate, pyruvate, glycerol and amino acids
71
What are the major non-carbohydrate precursors which may be used for the formation of glucose?
Lactate, pyruvate, glycerol and amino acids
72
In mammals, where does glucogenesis principally occur?
The liver, kidney, intestine, and muscle.
73
```
What major non-carbohydrate precursos does the
a) liver
b)kindey
c) intestines
use for the formation of glucose
```
Liver - lactate, glycerol, and glucogenic amino acids (especially alanine)
Kidney - lactate, glutamine and glycerol.
Intestine - glutamine and glycerol.
74
The liver can use both glycogenolysis and gluconeogenesis to produce glucose, whereas the kidney only uses gluconeogenesis, why?
After a meal, the liver shifts to glycogen synthesis, whereas the kidney increases gluconeogenesis. (ask)
75
Gluconeogenesis is not the reverse of glycolysis, why?
Glycolysis is an exergonic process whereas gluconeogeneis is endergonic. Seven of the steps in glycolysis steps are at equilibrium. However, steps 1, 3 and 10 are exergonic and cannot be reverse.
76
Does gluconeogenesis and Glycolysis occur at the same time?
Liver can be performing gluconeogenesis (say, from a protein meal) while at the same time skeletal muscle can be performing glycolysis during a brief burst of contraction (maybe a sprint). Due to the reciprocal nature and control of these pathways, they should not be running simultaneously in the same cell.
77
Where does Glucogenesis begin and how?
Gluconeogenesis begins in the mitochondria with the formation of oxaloacetate by the carboxylation of pyruvate.
78
What does Glucogenesis require and how is it catalysed?
This reaction also requires one molecule of ATP, and is catalyzed by pyruvate carboxylase. This enzyme is stimulated by high levels of acetyl-CoA (produced in β-oxidation in the liver) and inhibited by high levels of ADP and glucose.
79
To export oxaloacetate to the cytosol from the mitochondria, what has to occur?
To export oxaloacetate to the cytosol from the mitochondria, it has to be reduced to malate using NADH. In the cytosol, malate is again oxidized back to oxaloacetate using NAD+, where the remaining steps of gluconeogenesis take place.
Oxaloacetate is decarboxylated and then phosphorylated to form phosphoenolpyruvate using the enzyme PEPCK. A molecule of GTP is hydrolyzed to GDP during this reaction.
A molecule of GTP is hydrolyzed to GDP during this reaction.
80
Oxaloacetate is decarboxylated and then phosphorylated to form phosphoenolpyruvate using what enzyme?
The enzyme PEPCK
81
Describe Gluconeogenesis
Gluconeogenesis begins in the mitochondria with the formation of oxaloacetate by the carboxylation of pyruvate. This reaction also requires one molecule of ATP, and is catalyzed by pyruvate carboxylase. This enzyme is stimulated by high levels of acetyl-CoA (produced in β-oxidation in the liver) and inhibited by high levels of ADP and glucose.
To export oxaloacetate to the cytosol from the mitochondria, it has to be reduced to malate using NADH (not shown). In the cytosol, malate is again oxidized back to oxaloacetate using NAD+, where the remaining steps of gluconeogenesis take place.
Oxaloacetate is decarboxylated and then phosphorylated to form phosphoenolpyruvate using the enzyme PEPCK. A molecule of GTP is hydrolyzed to GDP during this reaction.
The next several steps in the reaction are at equilibrium and are the same as in glycolysis, except reversed.
Fructose 1,6-bisphosphatase converts fructose 1,6-bisphosphate (F1,6BP) to fructose 6-phosphate (F6P), using one water molecule and releasing one phosphate
In both glycolysis and gluconeogensis, this reaction is the rate-limiting step and is highly regulated by allostery. F2,6BP, AMP and Citrate all act to control this step.
The final reaction of gluconeogenesis, the formation of glucose, occurs in the lumen of the endoplasmic reticulum, where glucose-6-phosphate is hydrolyzed by glucose-6-phosphatase to produce glucose and release an inorganic phosphate i.e. again it is not a simple reversal of glycolysis.
Glucose is shuttled into the cytoplasm by glucose transporters located in the endoplasmic reticulum's membrane.
82
What does the enzyme Fructose 1,6-biphosphate convert?
Fructose 1,6-bisphosphatase converts fructose 1,6-bisphosphate (F1,6BP) to fructose 6-phosphate (F6P), using one water molecule and releasing one phosphate
83
In both glycolysis and gluconeogensis, the equilibrium reaction is highly regulated, how?
Highly regulated by allostery. F2,6BP, AMP and Citrate all act to control this step.
84
In both glycolysis and gluconeogensis, the equilibrium reaction is highly regulated, how?
Highly regulated by allostery. F2,6BP, AMP and Citrate all act to control this step.
85
Describe the final reaction of gluconeogenesis
The final reaction of gluconeogenesis, the formation of glucose, occurs in the lumen of the endoplasmic reticulum, where glucose-6-phosphate is hydrolyzed by glucose-6-phosphatase to produce glucose and release an inorganic phosphate i.e. again it is not a simple reversal of glycolysis.
Glucose is shuttled into the cytoplasm by glucose transporters located in the endoplasmic reticulum's membrane.
86
Describe glucose-6-phosphate in gluconeogensis
Glucose-6-phosphate is formed from fructose 6-phosphate by phosphoglucoisomerase (the reverse of step 2 in glycolysis).
Glucose-6-phosphate can be used in other metabolic pathways or dephosphorylated to free glucose by glucose-6-phosphatase.
Whereas free glucose can easily diffuse in and out of the cell, the phosphorylated form (glucose-6-phosphate) is locked in the cell, a mechanism by which intracellular glucose levels are controlled by cells.
87
How are fats broken down in the gut?
In the lumen of the gut triglycerides aggregate into fat globules as a consequence of the aqueous environment i.e. they are hydrophobic
The liver produces bile salts (cholesterol like molecules that are amphipathic meaning they are both hydrophilic and hydrophobic), that are stored in the gall bladder
The bile salts break down the fat globules so that the triglycerides can be accessed
The pancreases secretes lipases to breakdown fats into monoacylglycerols and fatty acids that can now be absorbed by epithelial cells of the gut.
88
In the lumen of the gut triglycerides aggregate into fat globules, why?
As a consequence of the aqueous environment (they are hydrophobic)
89
What actually breaks down the fat globules and triglycerides in the gut? [Digestion and absorption of fats]
The bile salts break down the fat globules so that the triglycerides can be accessed
The pancreases secretes lipases to breakdown fats into monoacylglycerols and fatty acids that can now be absorbed by epithelial cells of the gut.
90
Explain the uptake of fats by epithelial cells [Digestion and absorption of fats]
Epithelial cells absorb fatty acids and monoglycerides and then recombine them back into triglycerides
These fats are coated with phospholipids, cholesterol, and proteins to form water-soluble chylomicrons
Chylomicrons are transported into a lacteal, a lymphatic vessel in each villus
Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart
91
In the uptake of fats by epithelial cells, where are chylomicrons are transported into
A lacteal, a lymphatic vessel in each villus
92
What are chylomicrons and what do they arise from?
They are fats coated with phospholipids, cholesterol, and proteins and is water-soluble. Chylomicrons arise solely from the intestine, and contain 90% triglyceride primarily of dietary origin and other phospholipids, cholesterol, and fat soluble vitamins and are coated with a layer of apolipoprotein (apo A and B types).
93
Where do the lymphatic vessels deliver chylomicron-containing lymph?
Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart
94
What is a lacteal?
A lymphatic vessel in each villus
95
How are the tryglicerides transported to adipose and muscle cells
Predominately triglycerides are stored in fat cells (adipose cells) as fat globules in the cytoplasm.
Muscle cells also store triglycerides but for ATP production
In the gut, the triglycerides are placed into carrier particles called Chylomicrons
The chylomicrons bind to the membranes of fat and muscle cells and then are again broken down to the fatty acids and monoglycerides
They are then reformed back into fat globules to function as high energy stores
96
Where are tryglycerides stored?
Triglycerides are stored in fat cells (adipose cells) as fat globules in the cytoplasm.
97
Describe the digestion of fats
- In the lumen of the gut triglycerides aggregate into fat globules as a consequence of the aqueous environment i.e. they are hydrophobic
- The liver produces bile salts (cholesterol like molecules that are amphipathic meaning they are both hydrophilic and hydrophobic), that are stored in the gall bladder
- The bile salts break down the fat globules so that the triglycerides can be accessed
- The pancreases secretes lipases to breakdown fats into monoacylglycerols and fatty acids that can now be absorbed by epithelial cells of the gut.
98
What happens to triglycerides when the body needs energy?
When the body needs energy, adipose cells mobilise the triglycerides into free fatty acids and glycerol, which are released into the blood.
99
What is serum albumin?
Serum albumin is found in human blood. It is the most abundant protein in human blood plasma.
100
What are Chylomicrons?
Chylomicrons are lipoprotein particles that consist of triglycerides, phospholipids, cholesterol, and proteins.
101
Describe the absorption of fats
- Epithelial cells absorb fatty acids and monoglycerides and then recombine them back into triglycerides. These fats are coated with phospholipids, cholesterol, and proteins to form water-soluble chylomicrons
- Chylomicrons are transported into a lacteal, a lymphatic vessel in each villus
- Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart
Predominately triglycerides are stored in fat cells (adipose cells) as fat globules in the cytoplasm.
In the gut, the triglycerides are placed into carrier particles called Chylomicrons
- The chylomicrons bind to the membranes of fat and muscle cells and then are again broken down to the fatty acids and monoglycerides
-They are then reformed back into fat globules to function as high energy stores
102
Do muscle cells store triglycerides?
Yes, but for ATP production
103
What cells absorb fatty acids and monoglycerides and then recombine them back into triglycerides?
Epithelial cells
104
Where are triglycerides stored predominantly?
Triglycerides are stored in fat cells (adipose cells) as fat globules in the cytoplasm.
105
What breaks down the fat globules so that the triglycerides can be accessed
Bile salts
106
In the breakdown of FAs they must be activated by the addition of ______ and replaced by ______, why?
Coenzyme A (CoA), which is then exchanged for a Carnithine molecule so that the FA can pass across the mitochondrial membrane
107
Describe fatty acid breakdown
i. A hydrogen is extracted and a double bond is created
ii. A hydroxyl group is added to the double bond giving an alcohol
iii. The alcohol group is oxidised to carbonyl group, a ketone
iv. CoA cleaves the activated FA, removing 2 carbons and generating Acetyl-CoA
108
Are FA breakdown and synthesis the reverse of eachtother and why?
Yes, the inverse steps oxidation vs reduction
109
Where does fatty acid synthesis and breakdown occur?
Fatty acid synthesis occurs in the cytoplasm in contrast to β-oxidation which occurs in the mitochondria
110
What is fatty acid breakdown?
Fatty acid degradation is the process in which fatty acids are broken down into their metabolites, in the end generating acetyl-CoA, the entry molecule for the citric acid cycle, the main energy supply of animals.
111
Is FA breakdown oxidation or reduction?
FA breakdown is an oxidative process that consists of 4 steps. (known as β-oxidation)
112
Is FA breakdown cyclic or not?
It is a cyclic process that is repeated.
113
To facilitate FA breakdown what is added?
A CoA molecule is added (i.e. activation) making more reactive.
114
Is fatty acid synthesis oxidation or reduction and what sort of conditions does it require?
FA synthesis is a reduction process and occurs under conditions where energy supply is large
115
Is β-oxidation catabolic or anabolic?
Catabolic
116
What is fatty acid synthesis?
Fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases
117
What is added for fatty acid synthesis?
An activated Malonyl-CoA unit and Acetyl-CoA is added.
118
How is fatty acid synthesis regulated?
Acetyl-CoA carboxylase is the point of regulation in saturated straight-chain fatty acid synthesis, and is subject to both phosphorylation and allosteric regulation.
119
What is Malonyl-CoA and what is it's function?
Malonyl-CoA is a key inhibitor of FA oxidation and contols the switch between fatty acid synthesis and oxidation.
Malonyl CoA inhibits the enzyme carnitine palmitoyltransferase 1 (CPT1) thereby stopping FAs from entering the mitochondria
120
What is the first step of fatty acid synthesis?
Release of fatty acids from Adipose cells
- Adipose cells mobilise the triglycerides into free fatty acids and glycerol in response to glucagon or adrenaline
- The FAs are released into the blood
- Serum albumin picks up the FAs and brings them to target cells
121
Describe stage two of fatty acid synthesis
Uptake and activation of fatty acids
- In the cytoplasms of the target cells the FA must be activated (enzyme) and taken up into the mitochondrial of the cell to undergo b-oxidation. This process breaks them down to Acety-CoA molecules that can be fed into the citric acid cycle, generating ATP
- Firstly, an enzyme on the outer membrane of the mitochondria called Fatty Acyl CoA synthetase activates the fatty acid by forming a thioester bond between the sulphur atom on CoA and the carboxyl carbon of the FA.
- The enzyme catalyses this reaction in two steps
i. An AMP molecule is transferred onto the fatty acid with the release of pyrophosphate.The hydrolysis of pyrophosphate to inorganic phosphate provides the driving force for the reaction
ii. A CoA molecule is attached to the FA displacing the AMP molecule
122
An enzyme on the membrane of the mitochodria activates the fatty acid, what is this enzyme and how does it do so?
An enzyme on the outer membrane of the mitochondria called Fatty Acyl CoA synthetase activates the fatty acid by forming a thioester bond between the sulphur atom on CoA and the carboxyl carbon of the FA.
i. An AMP molecule is transferred onto the fatty acid with the release of pyrophosphate.The hydrolysis of pyrophosphate to inorganic phosphate provides the driving force for the reaction
ii. A CoA molecule is attached to the FA displacing the AMP molecule
123
How are fatty acids activated?
Fatty acids are activated by reaction with CoA to form fatty acyl CoA. (The reaction normally occurs in the endoplasmic reticulum or the outer mitochondrial membrane.) This is an ATP-requiring reaction, yielding AMP and pyrophosphate (PPi).
124
Describe stage 3 of fatty acid synthesis
Translocation of fatty acids into the mitochondrial matrix
- For the oxidation of FAs to occur they must be transported from the cytoplasm to the inner mitochondrial space.
- Following activation of a long-chain fatty acid to a FA-CoA, the CoA is exchanged for carnithine by the enzyme carnithine palmityltransferase 1 (CPT-1).
- The FA-carnithine molecule is then transported to the inside of the mitochondrion through the action of the Carnithine AcylCarnithine Translocase (CACT) where a reversal exchange takes place through the action of CPT-2.
- Once inside the mitochondrion the FA-CoA can serve as a substrate for the β-oxidation machinery, which we discussed in an earlier slide
125
For the oxidation of FAs to occur they must be transported from the cytoplasm to where and how?
The inner mitochondrial space through the action of the Carnithine AcylCarnithine Translocase (CACT) where a reversal exchange takes place through the action of CPT-2.
126
What is stage 4 of fatty acid synthesis?
Actual synthesis itself
- To build FAs Acetyl-CoA is needed, which comes from the matrix of the mitochondria.
- Fatty acid synthesis takes place in the cytosol of the cell. Therefore need to move Acetyl-CoA into the cytoplasm.
- Citrate synthase converts oxaloacetate to citrate and transports it across the membrane
- When ATP is high in the mitochondria it inhibits the CAA enzyme isocitrate dehydrogenase thereby increasing the citrate levels
- Citrate is not used in FA synthesis it is recycled back to oxaloacetate
- The enzyme malate dehydrogenase converts oxaloacetate to malate via malate dehydrogenase using a molecule of NADH than can subsequently by converted to pyruvate and moved back into the mitochondria
- Malate enzyme generates the NADPH that will be used in fatty acid synthesis
127
To build Fatty acids, what is needed?
FAs Acetyl-CoA is needed, which comes from the matrix of the mitochondria.
128
What promotes fatty acid synthesis?
When ATP is high in the mitochondria it inhibits the CAA enzyme isocitrate dehydrogenase thereby increasing the citrate levels. Citrate is not used in FA synthesis it is recycled back to oxaloacetate
129
In humans, the first opportunity for ingested food to undergo enzymatic hydrolysis is in the _____.
a) mouth
b) stomach
c) liver
d) small intestine
e) large intestine
a) mouth
130
What is Enzymatic hydrolysis?
Enzymatic hydrolysis is a process in which enzymes facilitate the cleavage of bonds in molecules with the addition of the elements of water. It plays an important role in the digestion of food.
131
Increased appetite is the typical result of increased levels in the blood of _____.
a) leptin
b) PYY
c) ghrelin
d) insulin
e) secretin
C) Ghrelin is released in greater quantities by an empty, shrunken stomach than by a full stomach.
Leptin (a), PYY (b), and insulin (d) are associated with satiety, not hunger. Secretin (e) is not linked to appetite regulation.
132
The bile salts function in fat digestion by _____.
a) hydrolyzing fat molecules to glycerol and fatty acids
b) separating individual fat molecules from each other
c) dissolving fats in water
d) dispersing big droplets of fats to small droplets
e) triggering the secretion of pancreatic lipase
D) When fat globules enter the small intestine, they are mixed with water and bile salts. Bile salts coat smaller fat globules, emulsifying them. Options b and c do not occur in water.
133
A fatty acid absorbed into an intestinal cell _____.
a) is hydrolyzed to smaller fragments
b) enters a lacteal vessel as a carbohydrate
c) becomes part of a chylomicron
d) is bound to bile salts
e) exits the cell to directly enter the blood
C) Fats are insoluble in water, and fat droplets are too large to pass through the membranes of capillaries, so chylomicrons enter the lacteal vessels of the lymph system.
134
Glucagon, a pancreatic hormone, functions to _____.
a) stimulate hunger
b) inhibit activity in the small intestine
c) increase fat storage in fat cells
d) reduce glucose levels in the blood
e) stimulate the liver to release glucose
e)
135
Increased glucose levels in blood, after a meal, trigger _____.
a) glucagon release from the pancreas
b) insulin release from the pancreas
c) secretin release from the duodenum
d) cholecystokinin release from the pancreas
e) activation of amylase in the blood
b) The main response to high blood glucose is release of pancreatic insulin, triggering its target cells to take up the excess glucose. Glucagon secretion will be reduced during this time. Secretin and cholecystokinin are digestive hormones, not related to blood glucose levels. Amylase is a digestive enzyme mainly in saliva, not in the blood.
136
In which of the following structures does absorption of water, vitamin K, and salt occur?
a) large intestine
b) small intestine
c) liver
d) stomach
e) pancreas
A) The final absorption of those three key elements occurs in the large intestine. This is why treatment of diarrhea, which is watered-down stool from rapid expulsion of food from the body, includes replenishing water, sodium, and potassium immediately.
137
Which statement about glycolysis is true?
a) It splits water.
b) It produces FADH2.
c) It occurs in the cytosol.
d) It makes the most ATP compared to the other steps in the breakdown of glucose.
e) It splits lipids.
C)
