9. Energy Metabolism Flashcards
What is the difference between anabolism and catabolism?
- 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
Which part of the mitochondria does each part of metabolism occur?
Where does Kreb’s cycle and electron transport chain occur in the mitochondria?
- 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.
What does food energy refer to?
Food energy refers to energy derived from sunlight via photosynthesis in plants and stored in the chemical bonds of carbohydrates, protein and lipids.
How is anabolism and catabolism seen in fat storage reactions?
What are enzymes and coenzymes?
- 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.
What are coupled reactions?
- 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
How does a coenzyme help the catalysis of a reaction?
- 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.
Where does the energy released from catabolic reactions go to?
- 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.
How does ATP allow energy transfer?
What happens in glycolysis?
- 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.
What happens when pyruvate is converted to acetyl CoA?
- 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.
What is the Cori cycle?
- 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.
Why is lactic acid production important for glycolysis?
- 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.
What happens in aerobic metabolism stage 3 (tca cycle)?
- 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).
Why is actual yield of ATP less than theoretical in aerobic metabolism?
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.
What is NAD high energy electron carrier?
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
What is FAD molecule electron carrier?
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.
What happens to acetyl-CoA if its not need to produce energy?
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.
What is the role of glycerol in lipid metabolism?
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)
How does gluconeogenesis convert fat molecule to carbohydrate?
- 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.
What is the role of NAD in glycerol metabolsim?
- 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
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.
What does glucogenic and ketogenic mean?
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
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.
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.
What happens to excess carbs fat and protein when a person overeats?
How are ketone bodies formed?
What is a standard drink defined as?
A standard drink is defined as containing 10 g pure ethanol.
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.
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.
