Carbohydrates Flashcards

Question

feeder pathways for glycolysis

Answer 1

Glucose molecules are cleaved from glycogen and starch by glycogen phosphorylase. o yielding glucose-1-phosphate o uses inorganic phosphate as phosphate source Disaccharides are hydrolyzed. o lactose: glucose and galactose o sucrose: glucose and fructose o Monosaccharides fructose, galactose, and mannose enter glycolysis at different points. if a molecule can be converted into a glycolytic intermediate it can enter glycolysis and produce energy

Answer 2

Central pathway: 1st part of glycolysis. Glucose converted into glyceraldehyde 3-phosphate. Glucose 1-phospahte from breakdown of starch, enzyme converts into glucose 6-phospahte. From then on, glucose processed in glycolytic cycle. Galactose can be rearranged to glucose 1-phosphate. Sucrose converted to glucose or fructose.

Answer 3

Three possible catabolic fates of the pyruvate formed in glycolysis pyruvate --> lactate (anaerobic) pyruvate --> acetyl-CoA --> CO2 + H2O (aerobic) pyruvate --> ethanol + 2CO2 (anaerobic)

Answer 4

Generation of energy (ATP) without consuming oxygen or NAD+ No net change in oxidation state of the sugars Reduction of pyruvate to another product Regenerates NAD+ for further glycolysis under anaerobic conditions

Answer 5

Reduction of pyruvate to lactate, reversible During strenuous exercise, lactate builds up in the muscle, (generally less than 1 minute) Acidification of muscle prevents its continuous strenuous work. Lactate can be transported to the liver and converted to glucose there. Requires a recovery time o high amount of oxygen consumption to fuel gluconeogenesis o restores muscle glycogen stores Acidification – significant change in pH – interferes with the chemical processes in muscle contraction. - Large –ve ΔG'˚ so favourable reaction NAD+ within cytosol, is available for glycolysis to continue occurring. - Main function is to recycle NADH – keeps glycolysis going (diagram below)

Answer 6

Opposing pathways that are both thermodynamically favourable o operate in opposite direction o end product of one is the starting compound of the other Reversible reactions are used by both pathways. Irreversible reaction of glycolysis must be bypassed in gluconeogenesis. o no ATP generated during gluconeogenesis (uses ATP) o different enzymes in the different pathways o differentially regulated to prevent a futile cycle processes highly regulated, glyc has 3 points and GNG regulated at the 3 points going back the other way. Occur at different points (counterproductive to occur at same time glycolysis: occurs mainly in muscle and brain gluconeogenesis: occurs mainly in liver

Answer 7

1. pyruvate carboxylase: pyruvate --> oxaloacetate 2. phosphoenolpyruvate carboxykinase: oxaloacetate --> PEP 3. fructose bisphosphatase-1: fructose 1,6-bisphosphate --> fructose 6-phosphate 4. glucose 6-phosphatase: glucose 6-phosphate --> glucose

Answer 8

2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O --> Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ “Costs” 4 ATP, 2 GTP, and 2 NADH Physiologically necessary: Brain, nervous system, and red blood cells generate ATP ONLY from glucose. Allows generation of glucose when glycogen stores are depleted: o during starvation o during vigorous exercise o can generate glucose from amino acids, lactate, glycerol but not fatty acids **(expensive from an energy/ATP point of view)

Answer 9

animals can produce glucose from sugars or proteins sugars: pyruvate, lactate or oxaloacetete protein: AA converted to Krebs cycle intermediates animals cannot produce glucose from FA - produce of FA degradation is acetyl CoA - can't have net conversion of acetylCoA to oxaloacetate

Answer 10

alternate use for glucose, how body generates ribose sugar (for DNA and RNA) and NADPH, pentose phosphates can be regenerated into glucose-6-phosphate, which requires no ATP. glucose-6-phosphate --> ribose-5-phosphate - utilised to synthesise nucleotides (important precursor) - NADHPH is main e- carrier The main products are NADPH and ribose 5-phosphate. - NADPH is an electron donor. o reductive biosynthesis of fatty acids and steroids o repair of oxidative damage -Ribose-5-phosphate is a biosynthetic precursor of nucleotides. o used in DNA and RNA synthesis o or synthesis of some coenzymes

Answer 11

biochemical reactions in the living cell - metabolism, organised into metabolic pathways purpose: extraction of energy, storage of fuels, synthesise of important building blocks, elimination of waste

Answer 12

flow of metabolites through pathways is regulated in order to maintain homeostasis. metabolite levels can be altered very rapidly to inc/dec glycolysis during/after action or to inc capacity of glujconeogeneis after successful action

Answer 13

products of metabolic pathways directly or indirectly inhibit their own biosynthetic pathways eg: high ATP synthesise inhibits the glycolysis step that prevents glucose degradation

Answer 14

- [reactants] vs [products] - activity of catalyst - [enzyme] - rate of translation vs rate of degradation - intrinsic activity of enzyme - substrate, effectors, phosphorylations state [effectors] - allosteric regulators, competing substrates, ph, Ionic environment temperature

Answer 15

The rate is more sensitive to concentration at low concentrations. o Chemical kinetics: Frequency of substrate meeting the enzyme matters. The rate becomes insensitive at high substrate concentrations. o The enzyme is nearly saturated with substrate.

Answer 16

Phosphorylation is catalyzed by protein kinases. Dephosphorylation is catalyzed by protein phosphatases, or can be spontaneous. Typically, proteins are phosphorylated on the hydroxyl groups of Ser, Thr, or Tyr.

Answer 17

Binding of regulatory protein subunits affects specificity enzymes recognise several target proteins, its specificity provided by the regulatory subunit. Each of several regulatory subunits fits the scaffold containing the catalytic subunit, and each regulatory subunit creates its unique substrate binding site.

Answer 18

10% decrease in [ATP] can greatly affect the activity of ATP utilizing enzymes. 10% decrease in [ATP] leads to a dramatic increase in [AMP]. - AMP can be a potent allosteric regulator. ATP and AMP (adenosine monophosphate) can both be allosteric effectors

Answer 19

converts glucose --> glucose-6-phosphate has a high affinity for glucose inhibition: inc FA and its product (-ve feedback) - important because ATP used in this step, prefer to use glycogen to produce product so HK is inhibited to spare blood glucose and ATP

Answer 20

fructose-6-phosphate --> fructose1,6biphosphate key rate limiting step activation: inc fructoste-6-phospahte, inc ADP, inc AMP inhibition: inc H+, inc citrate, inc ATP

Answer 21

phosphoenolpyruvate --> pyruvate activation: inc fructose-1,6-biphosphate inhibition: inc ATP, alanine

Answer 22

pyruvate --> oxaloacetate activation: inc acetyl CoA inhibition: ADP replenishing Krebs cycle intermediates in the mitochondrial matrix.

Answer 23

oxaloacetate --> phosphoenolpyruvate activation: n/a inhibition: ADP

Answer 24

fructose 1,6 bisphosphate --> fructose-6-phosphate activation: citrate inhibition: AMP, fructose-2,6-biphosphate

Answer 25

also known as G6Pase hydrolyzes glucose 6-phosphate glucose-6-phosphate --> glucose + Pi