Metabolism 1/2 (handout p. 1-20) Flashcards
(42 cards)
Describe metabolism and its two contrasting processes.
refers to the chemical changes that convert foodstuffs into usable forms of energy and complex biological molecules
Catabolism – breakdown of more complex organic molecules into simpler biological molecules and the release of energy through ATP.
Anabolism – assembly of simpler substances to form new and more complex molecules, which requires the use of ATP and energy.
Describe the formation of ATP and the formation of ADP.
Adenosine triphosphate (ATP) (see above) is a crucial component of metabolism. ATP contains three phosphates held together by high-energy bonds.
Adenosine diphosphate (ADP) is formed
when the third phosphate is cleaved from ATP. Energy is released, which can then drive anabolic
reactions, as well as other reactions in the body (i.e. membrane transport).
Inversely, energy is
needed to add the third phosphate group to ADP in order to form ATP. Therefore, the synthesis of
ATP is an energetically unfavorable phosphorylation reaction in which a phosphate group is added
to ADP. When required, ATP gives up its energy packet though its energetically favorable hydrolysis to ADP and inorganic phosphate.
What do oxidation reactions result in?
Oxidation reactions result in the loss of electron from an atom, as occurs during the addition of
oxygen to a molecule or when hydrogen is removed.
What is reduction?
Reduction is the addition of electron to an atom, as occurs during the addition of hydrogen to a molecule or the removal of oxygen from it.
What are the most important electron carriers? What purpose do they serve?
How do they differ from each other?
NAD+ (nicotinamide adenine dinucleotide) and the closely related NADP+ (nicotinamide adenine
dinucleotide phosphate) are the most important electron carriers.
NADP+ has an additional
phosphate group on the 2’ position of the ribose ring that carries the adenine moiety. NAD+ and
NADP+ are needed as an oxidizing agent.
NADH= reduced form of NAD+ NADPH= reduced form of NADP+
Give an overview metabolism starting with mono, di and polysaccharides.
P 8 on h/o
What is the primary function of acetyl-CoA
Where is it generated? What is it a major source of?
What gives rise to acetyl-CoA?
key molecule, which is used in many biochemical reactions in carbohydrate, protein and lipid metabolism. The primary function of acetyl-CoA is to convey the carbon atoms within the acetyl group to the citric acid cycle (a.k.a Tricarboxylic acid cycle or Krebs
cycle) to be oxidized for energy production.
Acetyl-CoA is generated in the mitochondrial matrix
and is a major source of useful metabolic energy.
It is important to note that all metabolic components (carbohydrates, lipids, proteins) can give rise to
acetyl-CoA, making it a “common fuel” that can enter the CAC and give rise to energy production
through ATP.
What are the fates of Acetyl-CoA?
4 fates of paths of usage
p 9 h/o
1) The primary fate is to oxidize acetyl groups in CAC for energy generation. Note: this is a
combustion reaction, and the products are ATP, H20, CO2.
2) Lipogenesis – formation of fatty acids. These fatty acids can then go through esterification to form Triacylglycerol (a.k.a, triacylglyceride, TAG).
3) Ketogenesis – formation of ketone bodies.
4) Cholesterologenesis – formations of cholesterol, which can then be synthesized into steroids.
Involves the transfer of acetyl units in the cytosol. Therefore, Acetyl-CoA is also a precursor of cholesterol, which is then a precursor of steroids.
Where does the conversion of pyruvate to acetyl CoA take place?
matrix of mitochondria
Why does dietary balance determine whether we gain or lose weight?
All components of metabolism (carbs, proteins, fats) can give rise to the synthesis
and storage of fat by first converting into Acetyl CoA. Therefore, the consumption of calories from all components can lead to the formation of fat. This is why the dietary balance determines whether we gain or lose weight.
Describe the storage and catabolism of dietary carbohydrates.
How are carbohydrates primarily metabolized?
What happens to fructose and galactose?
What happens to excess carbohydrates?
How is glycogen stored? Where are the largest stores?
- Carbohydrates are metabolized primarily via glucose.
- Fructose and galactose are converted to intermediates in the same glycolysis pathway.
- Excess carbohydrates are stored in glycogen.
- There is a limit to how much glycogen we can store.
In the liver, glycogen is stored to be used as glucose by the rest of the body later on.
The liver and skeletal/heart muscle have the largest stores.
Most cells have some storage of glycogen
p 10
Describe the storage and catabolism of dietary fatty acids.
How do fatty acids form acetyl-CoA?
If they don’t form Acetyl-CoA what do they form instead?
- Fatty acids go through beta-oxidation in the mitochondria to form acetyl-CoA
Therefore, only cells that have mitochondria can have beta-oxidation
- Otherwise, they form triacylglycerols, which are stored in adipose tissue.
The breakdown of TAGs into fatty acids is triggered by a hormonal signal.
Fatty acids are then released.
Describe the storage and catabolism of dietary proteins.
How are amino acids metabolized? What is produced during this process?
How are amino acids stored?
Amino acids can be metabolized to either Acetyl CoA or an intermediate in the citric acid cycle.
This leads to the production of ammonia, which can be toxic at high levels.
- Amino acids are store as proteins.
p11
The preferred fuels are not the same in all cell types.
Describe: liver adipose tissue skeletal muscle at rest skeletal muscle exertion heart muscle fatty acids brain fed state brain starvation
liver- fatty acids, glucose, aa
adipose tissue- fatty acids
skeletal muscle at rest: fatty acids
skeletal muscle exertion: glucose
heart muscle- fatty acids
brain fed state: glucose
brain starvation: ketone bodies/glucose
The liver expends energy during fasting through the access of fatty acids to make glucose.
The heart will use everything, but it has a preference for fatty acids.
Describe the brain’s need for glucose during fed state.
During the fed state, the brain has an absolute need for glucose. If it does not have access
to glucose, nerve cells die in a very short period of time. Therefore, the driving force for the
coordination of metabolism is to provide the normal range of glucose levels for the brain.
In the fasted state, what happens in adipose tissue?
In the fasted state, what occurs in the liver? How is ATP acquired for gluconeogenesis?
In the fasted state (after 3 days of starvation), low blood insulin levels cause the activation of
lipolysis in the adipose tissue, raising the blood levels of fatty acids. These fatty acids are used in preference to glucose by many tissues.
In the fasted state, fatty acid oxidation (beta-oxidation) in the
liver provides most of the ATP needed for gluconeogenesis.
The small amounts of Acetyl CoA generated by fatty acid oxidation in the liver are completely oxidized to form ketone bodies by the
liver mitochondria.
Ketones bodies are released in the blood and are a source of energy for many tissues. The brain starts to use ketone bodies as an alternative fuel when ketone body levels in the blood are high enough. This is caused by an up-regulation of a transporter that gets ketone into the
brain. It is important to note, however, that the brain will never lose its requirement for glucose
During fasting, the small amounts of Acetyl CoA
generated by fatty acid oxidation in the liver are completely oxidized to form ketone bodies by the
liver mitochondria. What are the ketone bodies used for? Where?
Ketones bodies are released in the blood and are a source of energy for many tissues. The brain starts to use ketone bodies as an alternative fuel when ketone body levels in the
blood are high enough. This is caused by an up-regulation of a transporter that gets ketone into the
brain. It is important to note, however, that the brain will never lose its requirement for glucose.
How are small portions of protein stored?
How are carbohydrates and proteins stored?
How are fats stored?
Small portions of protein can be stored as energy.
Carbohydrates and proteins are stored in a hydrated state.
Fats are stored in anhydrous state.
Give the number of kcal per gram of carbohydrates, proteins, and fat.
p 13
Describe the following major dietary carbohydrates and the food source they are found in, enzyme, and linkage.
amylose sucrose lactose fructose glucose
starch maltose trehalose raffinose cellulose
amylose- potatoes rice corn bread
sucrose- table sugar, desserts
lactose- milk, milk products
fructose- fruit, honey
glucose- fruit, honey, grapes
starch- (mixture of amylose and amylopectin)
maltose- barely
trehalose- young mushroom
raffinose- leguminous seeds
cellulose- “fiber” in plant foods, not digestible by humans, forms the bulk of the feces
p 14 to check linkages/enzymes!
Describe starch. What is it? What kind of linkages? How is it broken down?
Is pancreatic or salivary amylase more important for digestion?
Starch- most carbohydrates come in as starch, which (as shown) is a polymer composed entirely of
glucose. Starch has a mixture of alpha 1-4 and alpha 1-6 linkages that are broken down by amylase
in the saliva and pancreas. Pancreatic amylase is secreted in large excess relative to starch intake and
is more important for digestion than the salivary enzyme.
What are the major disaccharides? Where are they found?
Discuss sucrase and lactase. Which is found in greater concentration?
Where is final hydrolysis of di and oligosaccharides carried out?
What happens to saccharides that are not hydrolyzed by alpha amylase or intestinal surface enzymes? Where do they end up?
the major disaccharides are sucrose (glucose and fructose) and lactose (galactose
and glucose).
Disaccharidases, found in the brush border of the small intestine, break these down.
Two examples are sucrase and lactase. Sucrase is generally found in great excess. Lactase is
generally in lower concentrations.
Final hydrolysis of di- and oligosaccharides is carried out by
enzymes on the luminal surface of small intestinal epithelial cells.
Saccharides that are not
hydrolyzed by alpha-amylase and/or intestinal surface enzymes cannot be absorbed; therefore they reach
the lower tract of the intestine, which from the lower ileum on contains Bacteria.
Describe lactose intolerance. How might it develop?
What happens in lactose intolerance. Where? What clinical symptoms may manifest?
Lactose intolerance is a genetically determined (can also be caused by environmental factors,
physiological decline due to ageing, or damage to the mucosa) characteristic that results in a deficiency in lactase enzyme production. Over 30 million people are lactose intolerant in the United States alone, and the disorder is particularly prevalent in African American, Asian, and Hispanic populations.
Due to a decreased amount of intestinal lactase, dietary lactose is not sufficiently hydrolyzed
or absorbed. It remains in the intestine, where it causes osmosis of water into the intestine. In
addition, intestinal bacteria metabolize the lactose to produce lactic acid and mixtures of hydrogen,
carbon dioxide, and methane gas. The result is bloating, flatulence, and diarrhea, all of which can be avoided simply by eliminating milk and milk products from the diet.
What produces the lactase enzyme? Where is this gene found? What causes congenital lactase deficiency?
How is this gene affected in lactose intolerance in adults?
The LCT gene is expressed by intestinal epithelia cells and produces the lactase enzyme. At least nine mutations in this gene cause congenital lactase deficiency (congenital alactasia) starting at infancy. These mutations can cause changes in the enzyme’s secondary structure or truncate it abnormally. In adults, lactose intolerance is cause by gradually decreasing activity of the LCT gene.
