2.1 Energy Production with Carbohydrates Flashcards
(12 cards)
What is the general structure & function of carbohydrates?
mono (3-9 carbons), di (2 units), oligo (3-12), polysaccharide (10-1000).
sucrose = glucose + fructose
lactose = glucose + galactose
maltose = glucose x2
starch (plants), glycogen (animals)
How are carbohydrates digested and absorbed?
- Salivary amylase (starch/glycogen –> dextrins)
- Pancreatic amylase in ileum (dextrins –> monosaccharides)
- ileum (dissacharidases - bound to brush border of ileum - lactase, sucrase, isomaltase - a1-6 bonds, pancreatic amylase a1-4 bonds)
- secondary active transport of 2Na+ and monosaccharide through sodium-dependent glucose transporter 1.
- Passive transport of glucose into blood from epithelial cell. Uses GLUT2.
- Na/K pump.
Explain why cellulose is not digested in the gastrointestinal tract?
cellulose contains beta 1-4 glycosidic bond.
humans don’t have enzymes to digest these bonds.
Explain the biochemical basis of lactose intolerance?
lactase activity declines after infancy.
lactase remains high for some in adulthood - lactase persistence phenotype.
primary lactase deficiency: only in adults. absence of lactase persistance allele.
secondary lactase deficiency: caused by injury to ileum (gastroenteritis, crohn’s disease, coeliac disease, ulcerative colitis). adults & infants. Reversible.
congenital lactase deficiency: rare - autosomal recessive defect in lactase gene. Cannot digest any breast milk.
Describe the glucose depency of some tissues?
Red blood cells, neutrophils, kidney medulla (inner most cells) & lens of the eye.
CNS prefers glucose –> takes time to adapt to other fuel stores.
Due to lack of mitochondria or other factors.
Describe the key features and functions of glycolysis?
Overview of Catabolism:
1. Polymer –> Monomer
2. Oxidisation - releases some NADH/ATP.
3. Krebs cycle (TCA) –> releases more NADH/FADH2 + GTP.
4. Oxidative phosphorylation - reducing power converted to ATP.
Glycolysis in the cytosol.
Functions:
- oxidisation of glucose
- produce NADH
- net gain of 2 ATP per glucose from ADP
- provide biosynthetic precursors for amino acids and nucleotides.
Features
- occurs in all tisses
- exergonic, oxidising the glucose
- irreversible, due to several steps having very negative delta Gs.
- can operate anaerobically by adding LDH.
Many steps allows for energy conservation, versality with interlinking other pathways and allows for control.
What types of glucose transporters are there?
Glucose via faciliated diffusion through:
GLUT1: fetal tissues, adult RBCs, blood-brain barrier.
GLUT2: kidney, liver, pancreatic beta cells, small intestine.
GLUT3: Neurones, placenta.
GLUT4: Adipose tissue, striated muscle (INSULIN REGULATED).
GLUT5: Spermatazoa, intestine.
Glycolysis Stage 1 - What enzyme is required to convert glucose to glucose-6-phosphate? Give both the normal enzyme and alternative enzyme used in the liver.
Hexokinase in regular tissues.
Glucokinase in the liver.
- makes glucose negatively charged, so is locked in the cell as it cannot pass back through the plasma membrane.
- increases the glucose reactivity, priming it for subsequent steps.
- uses 2 molecules of ATP per glucose, producing 4 ATP with net gain of 2 ATP.
Glycolysis Stage 3 - What enzyme is required to convert fructose-6-phosphate to fructose-1,6-bisphosphate? Uses a molecule of ATP.
Phosphofructokinase-1
- commits the glucose to metabolism via glycolysis.
Glycolysis Stage 10 - What enzyme is needed to convert phosphoenolpyruvate to pyruvate? Produces a molecule of ATP and occurs twice per glucose molecule.
Pyruvate kinase.
- substrate level phosphorylation.
What is the importance of 2,3-bisphosphoglycerate?
Intermediate produced from a step in glycolysis.
Only produced in RBCs.
Regulator of haemoglobin affinity - promoting dissociation of oxygen molecules.
Enzyme is bisphoglycerate mutase.
What is the importance of glycerol 3-phophate?
Dihydroxyacetone phosphate (DHAP) is converted to glycerol phosphate by glycerol-3-phosphate dehydrogenase.
Needed for triglyceride and phospholipid synthesis.
Produced in adipose and liver tissue.
