18 Questions
Which enzyme breaks down lactose in the intestinal mucosa?
Lactase
What are the final monosaccharides formed after the breakdown of sucrose?
Glucose and fructose
Where does glycolysis primarily occur in the cell?
Cytosol
Which molecule is generated from glycolysis that carries hydrogen to the respiratory chain?
NADH + H
In anaerobic glycolysis, what is the final product when pyruvate is converted?
Lactate
Which tissues are involved in the formation of lactic acid as a result of carbohydrate metabolism?
Skeletal muscle and brain
Which stage of obtaining energy from food involves the conversion of large molecules like proteins into small compounds like amino acids and glucose?
Stage 1
In most cell types, is the rate of glucose transport across the cell membrane a limiting factor for glucose metabolism?
No, it is not a limiting factor
Which tissue reflects blood glucose concentration and does not face limitations in glucose transport even at low blood sugar levels?
Erythrocytes
Which type of transporter regulates the transport of glucose into a myocyte and is influenced by insulin?
GLUT4
At what stage does the breakdown of carbohydrates typically begin?
In the mouth
Which stage involves the conversion of acetyl group of acetyl CoA to carbon dioxide and water through TCA cycle and respiratory chain?
Stage 3
What role does a-amylase play in breaking down polysaccharides?
Breaking down a-1,4 glycoside bonds by skipping a bond
Which enzyme secreted from the pancreas is very active in breaking down polysaccharides?
a-amylase
What happens when the activity of a-amylase stops?
2 glucose units remain at the end of the chain or the branch point
Which enzyme plays a role in breaking down the a1 ® 4 bond in carbohydrates?
a-glucosidase
What is the function of a-dextrinase in carbohydrate digestion?
Breaking down a-1,6 glycoside bonds
Where are other hydrolytic enzymes secreted for the completion of carbohydrate digestion?
Brushy edge of the small intestine mucosa
Study Notes
Stages of Obtaining Energy from Food
- There are three stages of obtaining energy from food:
- Stage 1: Converting large molecules (proteins and polysaccharides) into small compounds (amino acids and glucose)
- Stage 2: Converting small molecules into central simple compounds (mainly acetyl CoA)
- Stage 3: Converting acetyl group of acetyl CoA to carbon dioxide and water through TCA cycle and respiratory chain
Cellular Metabolism
- The rate of glucose transport across the cell membrane is not rate-limiting for glucose metabolism
- In most cell types, intracellular glucose concentration reflects blood glucose levels
- Erythrocyte is an example of a tissue in which glucose transport is not rate-limiting
Glucose Transport
- The glucose transport proteins (GLUT) have 12 transmembrane domains, but their properties differ from one tissue to another
- GLUT4 transports glucose into myocytes and is regulated by insulin
Digestion and Absorption of Carbohydrates
- Carbohydrate breakdown begins in the mouth
- Enzymes such as α-galactosidase and lactase break down lactose and sucrase breaks down sucrose in the intestinal mucosa
- Monosaccharides (glucose, galactose, and fructose) are formed from the breakdown of carbohydrates
Glycolysis
- Glycolysis is the principal metabolism route for glucose
- All enzymes involved in glycolysis are in the cytosol
- Glycolysis generates precursors for biosynthetic pathways in addition to providing ATP
- Glycolysis can be summarized as: C6H12O6 + 6H2O → 6CO2 + 6H2O + energy (heat-ATP-NADH)
Anaerobic and Aerobic Glycolysis
- In aerobic glycolysis, pyruvate enters the TCA cycle and is broken down to CO2 and H2O
- In anaerobic glycolysis, pyruvate is converted to lactate
- Anaerobic glycolysis occurs in cells without mitochondria
Lactate and Pyruvate
- Lactic acid is formed as a result of carbohydrate metabolism in tissues such as skeletal muscle, brain, RBC, renal medulla, and skin
- Blood lactate level depends on formation in these tissues and metabolism rates in the liver and kidney
Test your knowledge on the Introduction to Metabolism and Glycolysis as outlined in the book by Assist.Prof. Hadi Karimkhani. The quiz covers topics such as the stages of obtaining energy from food, the conversion of molecules, and the role of acetyl CoA in energy production.
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