What are carbohydrates made up of? What is its simplest form? What is the general formula, and their names respectively? What does it consist of? What are the two specific names of the group they consist of?
- made up of carbon and water
- monosaccharides
- (CH2O)n, where n >/= 3, 3 (triose); 4 (tetrose); 5 (pentose); 6 (hexose)
- consist of a carbon chain with a number of hydroxyl groups (-OH) and either one aldehyde (C double bond O, H) group or ketone group (C double bond O)
- aldose and ketose
What is the common characteristic of monosaccharides? Give examples of monosaccharides. What is the special arrangement of monosaccharides?
- hexose (C6H12O6)
- glucose, fructose and galactose
- owing to the presence of asymmetric carbons forming stereoisomers which are with same structural formula but different spatial orientation of atoms
What are disaccharides formed by? List out the three equations. How does it form? How to identify ๐ผ and ๐ฝ ?
- formed by 2 monosaccharides
- glucose + glucose –> maltose
glucose + fructose –> sucrose
glucose + galactose –> lactose - aldehyde group on anomeric carbon of one monosaccharide reacts with the hydroxyl group of another monosaccharide to form glycosidic bond (๐ผ or ๐ฝ with removal of water)
- ๐ผ is with OH below the ring and ๐ฝ is with OH above the ring
What are polysaccharides? What are the types of polysaccharides and their respective example? What are the major functions? What are the respective examples?
- long chain of monosaccharides joined together
- linear (starch and cellulose) and branched (glycogen)
- important storage and structural components
- major storage polysaccharides are glycogen in animals and starch in plants
- cellulose is a structural polysaccharide in plant cell walls to maintain integrity and cell shape
What is glycolysis? Where does glycolysis take place? What substances are required? What products are produced? What are the functions of glycolysis? What is the overall equation of glycolysis?
-breakdown of glucose
- takes place in the cytosol
- breakdown of 1 glucose –> 2 pyruvate and a net gain of 2 ATP and 2 NADH
- generation of ATP
=> directly from glycolysis
=> indirectly from feeding substrates into citric acid cycle and oxidative phosphorylation (pyruvate generates ATP in citric acid cycle and NADH generates ATP in oxidative phosphorylation)
- provide precursors for other biosynthetic pathways (eg. acetyl CoA is derived from pyruvate in the presence of O2 which act as an intermediate switching from carbohydrate metabolism into fat metabolism)
- 1 glucose + 2 inorganic phosphate + 2 NAD + 2 ADP –> 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
What are the first and last steps of glycolysis? What is their respective phase and reaction name?
- (preparatory phase) (1st priming reaction) glucose is irreversibly phosphorylated by ATP to form glucose 6-P catalysed by hexokinase
- (payoff phase) (2nd ATP-forming reaction) pyruvate kinase catalyses the irreversibly transfer of phosphate group from phosphoenolpyruvate (PEP) to ADP to form ATP and pyruvate (all times 2)
What are the fates of pyruvate in aerobic and anaerobic conditions? What is the corresponding word equation?
- aerobic condition:
=> Pyruvate is converted to acetyl Coenzyme A (acetyl CoA) by pyruvate dehydrogenase, provides material for the citric acid cycle
Eq: pyruvate + NAD + CoA –> acetyl CoA + NADH + CO2 - anaerobic condition:
=> in mammalian muscle: pyruvate is converted into lactate (lactic acid) by lactate dehydrogenase
Eq: pyruvate + NADH + H+ –> lactate + NAD
=> in yeast: pyruvate is converted into ethanol by pyruvate decarboxylase and alcohol dehydrogenase
Eq: pyruvate + H+ –> acetaldehyde + CO2
acetaldehyde + NADH + H+ –> ethanol + NAD
What is the hormonal regulation of glycolysis after meals and during starvation?
- regulated by insulin and glucagon released by the pancreas
- after meal:
=> blood glucose increases, insulin increases and glucagon decreases
=> increases the amount of glucokinase, phosphofructokinase and pyruvate kinase in the liver –> increases glycolysis and the breakdown of glucose - during starvation
=> insulin decreases and glucagon increases
=> decreases glycolytic enzymes and increases gluconeogenic enzymes including glucose 6-phosphatase and fructose 1,6-phosphatase
What is gluconeogenesis? What is actual the process? What is the importance of gluconeogenesis? What is the location of the process?
- synthesise glucose from non-carbohydrate precursors (eg. lactate, pyruvate, amino acids and glycerol)
- reversal of glycolysis
- to maintain blood glucose levels during starvation or vigorous exercise
- occurs mainly in the liver
What is the gluconeogenic pathway? What is the special thing about it? Describe them in detail. What does it require in the whole process?
- essentially a reversal of glycolysis
- 7 reaction steps are reversible so they are common in both pathways
- 4 unique steps
=> carboxylation of pyruvate to form OAA by pyruvate carboxylase
=> decarboxylation and phosphorylation of OAA to PEP by PEP carboxykinase
=> dephosphorylation of fructose 1,6-bis-P to form fructose 6-P by fructose 1,6-phosphatase
=> dephosphorylation of glucose 6-P to form glucose by glucose 6-Phosphatase - 4 ATP and 2 GTP are required
What are the substrates for gluconeogenesis? How do they come from?
- glycerol
=> from hydrolysis of triacylglycerols in fat tissue
=> phosphorylated and oxidised to dihydroxyacetone phosphate (DHAP), an intermediate in glycolysis - lactate
=> from Cori cycle
=> glucose in blood –> lactate in muscle –> lactate in blood –> lactate in liver –> glucose in liver –> glucose in blood - ๐ผ - ketoacids (eg. pyruvate)
=> derived from the metabolism of some amino acids (eg. alanine and glycine)
What is the general function of the citric acid cycle? What material will also be used in the cycle? Where does the cycle take place? What are the products produced? What are the three major reactions?
- oxidise pyruvate from glycolysis to CO2 and H2O, forming ATP and precursors for many other biosynthetic pathways
- acetyl CoA from fatty acid metabolism and amino acid degradation products are also oxidised
- occurs in the mitochondrial matrix in eukaryotes and cytosol in prokaryotes
- oxidation of one acetyl CoA yields 12 ATP (after oxidative phosphorylation)
=> 3 NADH –> 3 NAD (9 ATP)
1 FADH2 –> 1 FAD (2 ATP)
1 GDP + Pi –> 1 GTP (1 ATP) - oxidation of pyruvate into acetyl CoA
=> Pyruvate dehydrogenase oxidises pyruvate to form acetyl CoA and CO2 - oxidation of acetyl CoA
=> 8 intermediates
=> production of 3 NADH, 1 FADH2 and some CO2 - oxidation of NADH and FADH2
=> NADH and FADH2 produced are re-oxidised to synthesise ATP by oxidative phosphorylation
What is oxidative phosphorylation? How are the electrons being transported? How is chemiosmosis prepared and what will happen during the process? What are the products from each substrate?
- oxidation of NADH and FADH2 from the citric acid cycle by electron transport chain to synthesise ATP
- electrons are transported from complex I to IV via 2 small electron carriers coenzyme Q (CoQ) and cytochrome C (Cyt c) in the inner mitochondrial membrane
- energy released by the electron transport –> pump H+ out to the inter membrane space –> H+ gradient
- H+ flow back into the mitochondrial matrix through ATP synthase –> ATP production
- 3 NADH –> 9 ATPs
- FADH2 –> 2 ATPs
What is the number of ATP molecules generated from the oxidation of one glucose molecule?
- glycolysis = 2 ATP + 6 ATP = 8 ATP (6 ATP from 2 NADH)
- 1 glucose –> 2 pyruvate –> 2 acetyl CoA with the release of 2 NADH –> 6 ATP
- citric acid –> 12@each acetyl CoA (24 in total)
=> 3 NADH –> 9 ATP
=> 1 FADH2 –> 2 ATP
=> 1 GTP –> 1 GTP - total= 8 + 6 + 24 = 38 ATP
Where is the glycogen stored? What are they stored as? What is the function of glycogenolysis? What will happen with different levels of blood glucose respectively?
- stored mainly in the liver and skeletal muscle as an energy reserve
- stored as glycogen granules in the cytosol with enzymes for synthesis and degradation
- provides energy for muscle contraction and maintains blood glucose levels
- high blood glucose level –> glycogenesis
- low blood glucose level –> glycogenolysis
What is the process of glycogenesis and glycogenolysis?
Refer to notes p.5
