Metabolism Of Carbohydrates And Formation Of ATP Flashcards
What’s the role of insulin in glucose absorption?
There isn’t enough glucose that can be absorbed into cells in the absence of insulin.
- the rate of glucose utilization depends on rate of insulin secretion from the pancreas
- once in the cell, glucose is phosphorylated so it can diffuse out
- only cells that have phosphatase (liver, renal tubular, intestinal epithelium) can reverse this reaction
What happens to glucose once its absorbed into a cell?
If can be immediately used as an energy source or stored as glycogen
- all cells can make glycogen but liver and muscles have the largest capacity
What’s glycogenolysis and how does it get initiated?
Glycogenolysis = break down of glycogen into glucose molecules by breaking the phosphate bond on each branch
- requires the enzyme phosphorylase, which is activated by epinephrine and glucagon
- these hormones increase the formation of cAMP which sets the cascade that leads ton activation of the phosphorylase
Describe how energy is released during the glycolytic pathway.
Equivalent in energy: 1 mole of glucose = 38 moles of ATP
- but only 2 moles of ATP is formed per mole of glucose –> 57% of energy is lost as heat
- in glycolysis, glucose is split to form 2 pyruvate
- pyruvate forms Acetyl CoA, which releases 2 CO2 and 4 H+
- the 4H+ is later oxidized via oxidative phosphorylation to form 4 molecules of ATP
- the acetyl portion of acetyl CoA enters the citric acid cycle in the mitochondria –> degrades to CO2 and H+
- the H+ later oxidized, releasing energy to form ATP
- each molecules of glucose = 2 ATP
Describe the chemiosmotic mechanism.
- located in the mitochondria
- leads to oxidative phosphorylation
- hydrogen atoms are converted to hydrogen ions and e-
- e- forms with dissolved O2 to make hydroxyl ion
- hydrogen + hydroxyl ion = water
- the e- enters electron transport chain
- its shuttle from one receptor to another (ex. flavoprotein, iron sulfide proteins, ubiquinone, and cytochrome B, C1 C, A, and A3), until it reach cytochrome A3
- cytochrome A3 = cytochrome oxidase –> by giving up 2 e-, it can form water
How does the e- transport chain produce ATP?
The e- transport chain creates a large H+ gradient / electrical potential difference
- H+ flow into the mitochondria via ATP synthetase –> turning ADP to ATP
- for every 2H+ , up to 3 ATP is made
What’s the net yield of ATP in
a. glycolysis
b. citric acid cycle
c. oxidative phosphorylation
a. glycolysis: 2 ATP (needed 2 to make 4)
c. citric acid cycle: 2 ATP
c. oxidative phosphorylation: 34 ATP
Which enzyme has allosteric control over glucose conversion to ATP?
phosphofructokinase
- it forms fructose-1,6-diphosphate, the initiating step in glycolysis
- inactive when there is plenty of ATP, activated with increased # of ADP
Is anaerobic glycolysis an efficient process?
no, only 3% of the energy is harvested in the form of ATP
How is the formation of lactic acid beneficial in anaerobic glycoysis?
The end product of glycolysis = pyruvate and NADH
- combined with lactic dehydrogenase, forms lactic acid and NAD+
- a build up of pyruvate and NADH would inhibit further glycolytic processes
- the lactic acid freely diffuses out of the cell into the extracellular space, therefore, glycolysis can continue on
Describe the pentose phosphate pathway in glucose/ATP metabolism.
Up to 30% in liver and fat cells, ATP is not produced via glycolysis or the citric acid cycle
- with each turn, the pentose phosphate cycle takes 1 carbon from the glucose molecule to make CO2 and H+
- the H+ is eventually used in the oxidative phosphorylation to make ATPH
How can glucose be made from amino acids and the glycerol portion of fatty acids?
- via gluconeogenesis
- stimulated when there is low carb and decreased blood sugar
- ~ 60% of amino acids in the body can be easily turned into carbohydrates
