4.1 Carbohydrate Metabolism Flashcards
Using organic chem, explain the four types of dietary carbohydrates
- Sugars (one molecule)
- Oligosaccharides (a few sugars together)
- Starches (many sugars)
- Fibre (so many sugars it can’t be broken)
What are the two main sites of storage of glycogen in the body (which is larger?)
- Skeletal muscle (larger)
- Liver
What is the first step of carbohydrate metabolism called? Where does it occur in the cell, and what are the products/reactants?
- Glycolysis
- Occurs in cytoplasm
- Glucose is broken down into two pyruvate molecules
Why is oxygen important in ATP formation?
- The final step of ATP formation is oxidative phosphorylation
- This involves the electron transport chain, where electrons are passed between molecules, creating an electrochemical gradient
- Through a process known as chemiosmosis (whereby ions move across a semipermeable membrane), this energy gradient is used to convert ADP to ATP
- Oxygen is the final acceptor of electrons, enabling the transport chain to function, and therefore allowing ATP to be formed
What are the three broad steps of carbohydrate metabolism (from glucose onward)?
- Glycolysis (glucose split into pyruvate)
- Citric acid cycle (produces ATP, FADH2, and NADH)
- Oxidative Phosphorylation (incl. ETC)
Explain where the electron transport chain occurs, and how it allows ATP to be formed. Where do the electrons end up?
- NADH and FADH2 donate electrons
- These electrons move between proteins in the inner mitochondrial membrane, each with a higher affinity for electrons than the past.
- In this process, a proton gradient is created, with more protons within the intermembranous space than the mitochrondrial cytoplasm
- The protons move back into the mitochondria through a channel known as ATP synthase, which harnesses the energy of this chemiosmosis to convert ADP into ATP
Which two coenzymes are important for ATP production? Why?
- NADH and FADH2
- Produced in the citric acid cycle, and important because they donate their electrons to the ETC
Outline the process by which glucose is converted into fat. Where does this occur in the body?
- Glucose is converted into pyruvate, and then into Acetyl-CoA
- In the cytoplasm, this acetyl-coa is converted into fatty acids
- These are then esterified with glycerol into TAGs
- These TAGs can then be stored in areas such as the liver or adipose tissue
Put simply: why can’t fatty acids be converted into carbohydrates?
Because Acetyl-CoA cannot be converted into pyruvate. This is a one-way rxn that only occurs when glucose is converted into fatty acids.
Describe the location of carbohydrate absorption in the GI tract (and the form they’re absorbed as)
- Absorbed in the small intestine
- Absorbed as monosaccharides
What are the three disaccharides? Therefore, what are the four enzymes involved in carbohydrate metabolism?
- Amylase breaks down starch into disaccharides
- Each is broken down by its own enzyme: maltose = maltase, sucrose = sucrase, lactose = lactase
Where in the cell does the citric acid cycle occur? What is its purpose?
- Occurs in the mitochondria
- Converts Acetyl-CoA into coenzymes (FADH2 and NADH), and produces a relatively small amount of energy as well
- These coenzymes will later donate electrons into the ETC, driving ATP synthase
True or false: glycolysis is aerobic
False. Anaerobic.
How many steps in the citric acid cycle?
8 (shitrick acid is werry lucky)
Explain the importance of the citric acid cycle. What goes into the mitochondria vs the CA cycle? Why is it called the citric acid cycle?
- Citric acid cycle is important for producing energy, and the coenzymes that later drive the ETC
- Pyruvate goes into the mitochondria, where it is converted to Acetyl-CoA, which is then the first reactant in the cycle
- Called the citric acid cycle because the Acetyl group from Acetyl-CoA is added to oxaloacetate in the first step, forming citric acid
