9. Energy Metabolism Flashcards
1
Q
What is the difference between anabolism and catabolism?
A
- The breakdown of energy containing molecules is termed catabolism
- The synthesis of fat and other molecules from breakdown of products when energy surplus occurs in called anabolism
2
Q
Which part of the mitochondria does each part of metabolism occur?
A
3
Q
Where does Kreb’s cycle and electron transport chain occur in the mitochondria?
A
- Reactions of the TCA cycle are often called Krebs cycle and occur in fluid of the mitochondria.
- Final stage of energy release occurs on the internal walls of mitochondria. Protein structures of the ETC are found here.
4
Q
What does food energy refer to?
A
Food energy refers to energy derived from sunlight via photosynthesis in plants and stored in the chemical bonds of carbohydrates, protein and lipids.
5
Q
How is anabolism and catabolism seen in fat storage reactions?
A
6
Q
What are enzymes and coenzymes?
A
- Enzymes are protein molecules that facilitate rapid chemical reactions without being changed themselves and are able to be used over and over acting as catalysts.
- Each enzyme requires a coenzyme, a small organic molecule that binds to and assists the enzyme.
7
Q
What are coupled reactions?
A
- Some reactions in energy metabolism are coupled reactions. Energy released from breakdown of one compound is used to create a bond in a new compound.
- However the energy released from macronutrient breakdown has to be captured in ATP molecules first, then transferred to another reaction
8
Q
How does a coenzyme help the catalysis of a reaction?
A
- The coenzyme is usually made up of a B group vitamin (light red) with other chemical components (dark red) attached.
- This coenzyme complex now fits neatly into the much larger protein enzyme molecule making it active.
- The entire unit is now ready to catalyze a chemical reaction, either catabolic or anabolic. Once the reaction occurs, the enzyme-coenzyme unit is reused many times over.
9
Q
Where does the energy released from catabolic reactions go to?
A
- Energy released from catabolic reactions (breakdown of molecules) is captured by ‘go between’ molecules that transfer energy to other compounds for anabolic reactions later in time or at a different location.
- Some energy is lost in the process and escapes as heat
- These ‘go between’ compounds are referred to as ‘high energy compounds’ or ‘common energy currency’. The most important is adenosine triphosphate (ATP).
- ATP contains adenosine, ribose and 3 phosphate groups, which have high energy bonds capable of storing energy and releasing it easily at a later stage when needed.
10
Q
How does ATP allow energy transfer?
A
11
Q
What happens in glycolysis?
A
- First stage in cellular respiration of glucose is the formation of pyruvate that involves a number of metabolic steps, each with their own enzyme
- This process is called glycolysis and results in the formation of two pyruvate molecules from each glucose. This process yields a small amount of energy, so is not considered efficient.
- This process of glycolysis occurs in the cytoplasm where there is little oxygen, so the process is anaerobic.
12
Q
What happens when pyruvate is converted to acetyl CoA?
A
- The second step in carbohydrate metabolism involves the movement of pyruvate into the mitochondria and conversion of the pyruvate into acetyl-CoA (with the release of Carbon dioxide CO2).
- This step is not reversible. Glucose can be reformed from pyruvate while still in the cytoplasm but not from acetyl-CoA once in the mitochondria.
13
Q
A
14
Q
What is the Cori cycle?
A
- During extreme exertion O2 is inadequately supplied to the mitochondria and pyruvate is converted to lactic acid rather than entering the mitochondria.
- Relaxation allows the blood to clear lactic acid to the liver where it is reconverted back to glucose.
- This glucose is then available to be returned to cells for glycolysis.
15
Q
Why is lactic acid production important for glycolysis?
A
- A critical aspect of lactate (lactic acid) production is NAD regeneration for glycolysis (shown on next slide)
- Lactic acid formation generates a little energy, but the liver uses energy to reconvert lactic acid to glucose.
16
Q
What happens in aerobic metabolism stage 3 (tca cycle)?
A
- Acetyl-CoA enters the TCA cycle where it is metabolised in an aerobic environment (O2) to yield a series of compounds, liberating carbon dioxide (CO2) at certain stages along with hydrogen atoms (taken up by NAD to produce NADH*). These Hydrogens possess high energy electrons from the chemical bonds of nutrient molecules.
- Each glucose molecule that entered glycolysis will yield another 2 ATP in the TCA cycle and up to 34 more in the Electron Transport Chain (ETC).
17
Q
Why is actual yield of ATP less than theoretical in aerobic metabolism?
A
Although there is a theoretical yield of 38 ATP molecules per glucose during cellular respiration, such conditions are generally not realized because of losses such as the cost of moving pyruvate (from glycolysis), phosphate, and ADP (substrates for ATP synthesis) into the mitochondria. All are actively transported using carriers that utilize energy.
18
Q
What is NAD high energy electron carrier?
A
The high energy electrons are carried from the TCA Cycle (mitochondrial fluid) to the Electron Transport Chain (ETC) located on the inner mitochondrial membranes, by coenzyme carrier molecules such as NAD (NADH) and FAD (FADH2) molecules
19
Q
What is FAD molecule electron carrier?
A
A second carrier coenzyme is FAD (FADH2), based on the B group vitamin riboflavin. FAD can pick up two Hydrogens with high energy electrons and carry them from the TCA to the ETC.
20
Q
What happens to acetyl-CoA if its not need to produce energy?
A
If energy is not required to be produced, acetyl-CoA does not enter the TCA cycle. Instead multiple acetyl-CoA molecules are joined to form fatty acid molecules, which are linked to a glycerol molecule to form a triglyceride fat molecule, this will be transported to and stored in adipocyte cells.
21
Q
What is the role of glycerol in lipid metabolism?
A
Glycerol, is a 3 carbon compound and easily converted to pyruvate in the cytoplasm. The pyruvate can enter the mitochondria and form acetyl- CoA and be metabolised for energy or be converted to glucose via gluconeogenesis (gluco/neo/genesis)
22
Q
How are fatty acids from lipids broken down as part of the stage of metabolism?
A
- Fatty acids from lipids are broken down into 2 carbon segments and enter the mitochondria where they are converted to acetyl- CoA directly and metabolised for energy through the TCA cycle and ETC.
- If energy is not required, the acetyl-CoA units are rejoined to form fatty acids for storage fat .
23
Q
How does gluconeogenesis convert fat molecule to carbohydrate?
A
- Pyruvate in cytoplasm can be reconverted to glucose by a reverse glycolysis pathway, “gluconeogenesis”
- Hence part of the fat molecule (glycerol) can be converted into a carbohydrate.
24
Q
What is the role of NAD in glycerol metabolsim?
A
- NAD coenzyme molecules collect Hydrogens with high energy electrons from reactions attaching CoA to acetyl (2 carbon) groups.
- The NADH produced (NAD) then travel from cytoplasm into the mitochondria and on to the ETC to release energy.
- Glycerol can enter glycolysis in the cytoplasm. Hence it can be converted to pyruvate and eventually acetyl CoA in the mitochondria. Or it can undergo gluconeogenesis and be converted to glucose
25
What happens in protein metabolism?
* If constituent amino acids from dietary protein are used to make human proteins, then no breakdown of amino acids is necessary.
* If amino acids are to be used for energy they must be broken down first and the nitrogen group removed.
* The cleavage of the amino (nitrogen) group from amino acids creates a problem for the body, in that the ammonia formed is toxic and must be efficiently removed from the body.
26
What does glucogenic and ketogenic mean?
27
Which amino acids are glucogenic and which ketogenic?
* Which amino acids are glucogenic versus ketogenic is a complex and confusing area.
* Generally any amino acid that can be converted to glucose is glucogenic.
* Those that enter the metabolic pathway via pyruvate in the cytoplasm are clearly glucogenic as they can undergo gluconeogenesis to form glucose.
* Some others that enter as acetyl CoA or a TCA Cycle intermediary can also form glucose by other pathways. If they cannot they are termed ketogenic
28
How does fat storage occur?
* Both the glucogenic and ketogenic amino acids can be converted to storage fat if eaten in excess of bodily protein and energy needs.
* Pyruvate from glucogenic amino acids can be converted to acetyl-CoA and used to make fatty acids in the same way that acetyl-CoA from ketogenic amino acids are used to produce fatty acids
* Fatty acids are then linked to glycerol to produce triglycerides for storage. Thus high protein diets can build fat as well as muscle
* Similarly excess carbohydrate and fat itself can be converted to storage body fat.
29
How does glucose fuel brain function?
* Glucogenic amino acids can also be used to fuel the central nervous system (CNS) activity via glucose formation from pyruvate (gluconeogenesis), whereas dietary fatty acids are unable to do this.
* Thus dietary protein will maintain brain function better than fat.
30
How can high protein diet cause toxicity?
* In the case of a high protein diet, nitrogen may be a problem. Due to increased urea there is greater water loss in the urine. Also the liver can only make a certain amount of urea per day (MRUS).
* Ammonia from proteins above the level that can be dealt with (liver production of urea) will lead to a toxic effect
31
How is pyruvate added into the Kreb's cycle?
Acetyl CoA is the primary substrate for the TCA Cycle, however to stop the cycle running down, some pyruvate is added directly from the cytoplasm into the mitochondria to form oxaloacetate, the last compound in the cycle. This then joins with acetyl CoA to perpetuate the reactions.
32
What happens to electrons in the electron transport chain?
* Electrons pass along the ETC attached to hydrogen atoms, giving up a little of their energy at each protein in the chain.
* At the end of the chain the electrons have low energy levels. In this state the Hydrogens carrying them react readily with oxygen to form water.
* Final products of the ETC are energy in the form of ATP as well as H2O molecules.
33
In early evolutionary times how was energy excess from food stored?
* When food was available in abundance we ate as much as we could and stored the extra energy.
* Some energy was stored as glycogen, mainly in the liver and a little in muscle tissue.
* Most energy excess from food however was stored as fat, mainly within fat cells (adipocytes) and some within general body cells such as muscl
34
What happens to excess carbs fat and protein when a person overeats?
35
During fasting conditions what becomes an energy source for the brain?
* However if a period of food shortage or fasting continues as in the past, using stored fat alone is not enough as fatty acids cannot make glucose, and glucose is needed for brain and nervous system functioning.
* Other cells can efficiently breakdown fatty acids from fat reserves as an energy source, but the brain and nerve cells (and red blood cells) cannot.
* Glucogenic amino acids from proteins in muscle and organ tissue will be broken down for glucose production to allow the brain and CNS to keep functioning. This can be done for some time (days - weeks).
* Glucose from protein eventually becomes limited and brain and CNS must use a further adaptation humans developed, and that is the use of ketone bodies from fat for their energy needs (note: ketogenic amino acids can also produce ketone bodies). This phase overlaps with the previous phase and can extend life for several weeks.
36
37
38
When does the shift to ketosis occur?
* Once glycogen storage is exhausted another glucose source is needed. Protein (body tissues) can be converted to glucose initially (glucogenic amino acids only)
* – Shift to ketosis: Ketones are produced when glucose becomes less available.
* – Ketones can cross the blood – brain barrier and are produced from fatty acids and ketogenic amino acids
* Production of ketones is termed ketosis, which will cause a suppression of the appetite and slowing of metabolism (BMR).
39
How are ketone bodies formed?
40
What is a standard drink defined as?
A standard drink is defined as containing 10 g pure ethanol.
41
What are the three stages of liver deterioration due to alcohol?
* Alcohol abuse can cause fatty liver and is the first stage of liver deterioration.
* Fibrosis is the second stage.
* Cirrhosis is the most advanced stage of liver deterioration.
42
How does alcohol metabolism impact other metabolism?
* Although alcohol contains available energy (29kJ/g), its metabolism is handled differently in the body, compared with the three macronutrients.
* Alcohol metabolism interferes with the metabolism of the other macronutrients and impairs health and nutrition.
* Although alcohol contains energy (29kJ/g), the energy it releases is largely converted to fat in the liver.
* It also causes energy from the macronutrients to be converted to fat due to its high demand for NAD molecules, thus fewer are available for the normal TCA cycle function.
43
What happens when there is insufficient NAD due to alcohol metabolsim?
* If NAD is insufficient for TCA cycle activity, the macronutrient molecules being broken down to acetyl-CoA have to be converted to fat.
* As the coenzyme NAD is based on the niacin molecule, people with high alcohol intake have a higher demand for niacin in their diet.
44
How is high alcohol intake linked to thiamine demand in the diet?
* High alcohol intake has also been observed to cause Wernicke–Korsakoff syndrome, through severe thiamine deficiency due to alcohols interference with thiamine uptake by the GI tract. Hence high alcohol intake also results in a higher demand for thiamine in the diet.
* NOTE: Thiamine forms a critical coenzyme (thiamine pyrophosphate [TPP]) involved in glucose metabolism and in the TCA Cycle
45
How does alcohol metabolism in the liver impact TCA cycle?
* When NAD becomes limited due to excessive use in metabolising alcohol, the TCA cycle slows and energy output decreases.
* Because the acetyl CoA formed (from alcohol itself + 3 macronutrients) cannot all be metabolised in the TCA Cycle, it must exit the mitochondria as fatty acids and form fat.
* Some remains in the liver causing fatty liver disease and some is carried away to be stored in adipocytes around the body.
46
Where in the energy metabolism pathway does alcohol remove NAD?
* The energy metabolism pathway showing where alcohol has the potential to disturb the normal functioning by removing NAD coenzyme molecules needed for transferring H atoms with high energy electrons to the ETC.
