Case 5- Carbohydrate Metabolism Flashcards
How Glucose enters the cell
By facilitated diffusion through transporters GLUT1-14. The number of transporters increase with insulin. GLUT1 is involves in glucose uptake in RBC. GLUT2 is in the liver and kidney. GLUT3 is in the neurons. GLUT4 is found in adipose tissue and skeletal muscle. A Na+ and glucose cotransporter (SGLT) is used in the intestine.
Where does Glycolysis occur
In the cytoplasm
The role of Glycolysis in different tissues
In the liver and adipose tissue the main function is to produce precursors for fat (triglyceride) synthesis. Skeletal muscles will produce ATP
What is NADH and FADH
Electron carriers
End products of aerobic Glycolysis
For each glucose molecules you get 2 Pyruvate molecules, 2 ATP molecules and 2 NADH molecules.
End products of anaerobic Glycolysis
For each glucose molecules you get 2 Pyruvate molecules, 2 ATP molecules and 2 NADH molecules.
Why does anaerobic glycolysis take place
When you have low O2, no mitochondria and low pH
Step 1 of Aerobic respiration
Energy investment (2 ATP molecules are used) this creates 2 ADP molecules and energy.
1) The phosphate from one ATP molecules converts Glucose into Glucose-6-phosphate.
2) This is then converted into Fructose-6-phosphate.
3) This is phosphorylated by another ATP molecule into Fructose 1,6-bisphosphate.
4) This is then converted into either two Glyceraldehyde-3-phosphate molecules or two Dihydroxyacetone (DHAP) molecules which can then be converted into 2 Glyceraldehyde-3-phosphate molecules. These end products are composed of 3 carbons whilst Glucose is composed of 6.
Ste 2 of aerobic respiration
Energy generation, 4 ATP molecules and 2NADH molecules are produced.
1) The 2 molecules of Glyceraldehyde-3-phosphate are converted into 2 molecules of 1,3-bis-phosphoglycerate by oxidising 2 molecules of NAD+ to form 2 molecules of NADH.
2) This is converted into 2 molecules of 3-phosphoglycerate by phosphorylating 2 ADP molecules to form 2 ATP molecules.
3) This is converted into 2 molecules of 2-phosphoglycerate
4) Which is converted into 2 molecules of 2-phosphoenolpyruvate.
5) This is finally converted into two Pyruvate molecules by phosphorylating two ADP molecules. All the molecules are 3 carbon intermediates, so one glucose molecule produces two Pyruvate molecules.
Substrate level phosphorylation
The transfer of phosphate from one molecule to another
Anaerobic Glycolysis
The Pyruvate is converted into lactate using the NADH produced earlier, ATP is still produced but not as much. Occurs in red blood cells and exercising cells. Lactate is converted to glucose in the liver but this requires ATP.
ATP
Used to provide energy for cellular processes
How is insulin released
It is secreted by beta cells of the islets of Langerhans in the Pancreas
How energy is generated from food
Metabolism coverts high energy products (fats, carbohydrates and proteins) into low energy products (CO2 and H2O). By oxidising these high energy products you generate a lot of electrons which can be used to generate ATP through substrate level phosphorylation. Energy stores can also be oxidised.
Oxidation
Removing electrons
Metabolism
The chemical processes by which cells produce the substances and energy needed to sustain life
Catabolism
Catabolic pathways are degradative pathways. They produce chemical energy from the break down of energy rich fuel molecules.
Anabolism
Anabolic pathways are bio-synthetic pathways, they combine small molecules to produce complex molecules using energy from ATP
The 3 stages of metabolism
Stage 1- Hydrolyses of complex molecules into building blocks. For example= carbohydrates to monosaccharides.
Stage 2= Conversion of building blocks into Acetyl CoA by oxidation.
Stage 3= Oxidation of acetyl CoA to produce ATP.
How is glycolysis controlled
The irreversible reactions are controlled by enzymes and the reversible reactions depend on the conditions of the cells. When energy is high glycolysis is inhibited, because in the liver their main function is to produce triglyceride Glycolysis will proceed when energy levels are high.
Hexokinase
Catalyse the first reaction of Glycolysis - (Glucose →Glucose-6-Phosphate). The enzyme used in all tissues but the liver. High affinity for glucose (Low Km Glucose), binds to Glucose even when there is a low concentration. Low Vmax Glucose, slow reaction. Inhibited by Glucose-6-phosphate (cell energy levels are high). Works more efficiently when glucose concentrations are low.
Glucokinase
Catalyse the first reaction of Glycolysis - (Glucose →Glucose-6-Phosphate), used in the liver. Low affinity for glucose (High Km Glucose). High Vmax Glucose. Stimulated by Glucose (Feed forward). Not inhibited by G6P, glycolysis proceeds even when cell energy levels are high. Works more efficiently when Glucose concentrations are high.
Phosphofructokinase 1 (PFK1)
Catalyses the third reaction of Glycolysis - (Fructose-6-P → Fructose-1,6-BP)
Most important regulatory enzyme of glycolysis it is the rate limiting step. Allosterically inhibited by ATP (cell energy levels high) and stimulated by AMP (cell energy levels low). Most potent allosteric activator of PFK1 is Fructose 2,6-bisphosphate, it activates PFK1 even when ATP levels are high. Stimulated by insulin
Pyruvate kinase
Catalyses the final reaction of Glycolysis - (Phosphoenolpyruvate → Pyruvate). It is used in the liver and is activated by Fructose-1,6-BP. The activity of PFK1 and Pyruvate kinase are linked.
