18 Questions
What is the general formula for carbohydrates?
CnH2nOn
What type of derivatives can carbohydrates be?
Aldehyde and ketone
What is one of the important functions of carbohydrates in the body?
Preventing blood clots
What is the name of the pathway where glucose is converted into energy?
Glycolysis
What are ABO blood markers made up of?
Carbohydrates
What is the name of the process by which glucose is absorbed into the bloodstream?
Absorption
What is the primary function of pancreatic bicarbonate in the small intestine?
Neutralizing the acidic pH of the stomach contents
What type of glucose transporters are responsible for glucose absorption in the kidney?
Na+-dependent glucose transporters (SGLT 2)
What is the product of glycolysis in the absence of oxygen?
Two lactate molecules
Where does glycolysis occur in the cell?
Cell cytoplasm
What is the consequence of SGLT 1 deficiency in the small intestine?
Glucose is left unabsorbed and is excreted in feces
What is the primary function of glucose transport proteins in the small intestine?
Transporting glucose across the absorptive cell membrane
What is the primary characteristic that distinguishes monosaccharides from other types of carbohydrates?
They cannot be further hydrolyzed.
What is the result of the spontaneous reaction between the aldehyde or ketone group and the alcohol groups on the downstream carbon in an aqueous solution of monosaccharides?
Formation of a ring structure.
What is the minimum number of carbon atoms required for a monosaccharide to be classified as a triose?
3
Which of the following types of carbohydrates is composed of more than 10 monosaccharide units per molecule?
Polysaccharides
What is the term used to describe a carbon atom that has four different atoms or groups of atoms bonded to it?
Chiral carbon
Which of the following monosaccharides is an exception to the rule that all monosaccharides contain at least one asymmetrical carbon atom?
Dihydroxyacetone
Study Notes
Classification of Carbohydrates
- Carbohydrates can be classified into three types based on the number of sugar units:
- Monosaccharides: simplest form of sugars, which cannot be further hydrolyzed
- Disaccharides: consist of two monosaccharide units joined together by glycosidic linkage
- Oligosaccharides: 2-10 monosaccharide units linked together
- Polysaccharides: higher polymers of carbohydrates, containing > 10 monosaccharide units per molecule
Monosaccharides
- Monosaccharides contain the elements carbon, hydrogen, and oxygen, and have the general formula Cn(H2O)n, where n ≥ 3
- Monosaccharides cannot be broken down (non-hydrolysable) to smaller carbohydrates
- Classification of monosaccharides is based on:
- Number of carbon atoms: trioses to heptoses
- Functional groups: aldehyde (-CHO) or ketose group (-C=O)
- Cyclic structure of monosaccharides:
- In aqueous solution, the aldehyde or ketone group spontaneously reacts with alcohol groups on the downstream carbon to form ring structures
- New chiral carbon or anomeric center is formed
- Chirality:
- A carbon atom that has four different atoms or groups of atoms bonded to it is called a chiral carbon atom or chiral center
- All monosaccharides contain at least one asymmetrical (chiral) carbon atom and are therefore optically active, except dihydroxyacetone
Importance of Carbohydrates
- Carbohydrates are the major source of energy
- Precursors for many organic compounds (fats, amino acids)
- Constitute an important part of free nucleotides
- Prevent blood clots
- Carbohydrate polymers lubricate skeletal joints
- Carbohydrates are found on the surface of cells, participate in recognition and adhesion between cells
- ABO blood markers found on red blood cells are made up of carbohydrates
Digestion, Absorption, and Transport of Carbohydrates
- Carbohydrate digestion in the small intestine:
- Food bolus enters into the duodenum, exposed to pancreatic juice, containing pancreatic bicarbonate and pancreatic amylase
- Absorption of carbohydrates:
- Monosaccharides are almost completely absorbed from the small intestine
- Two types of glucose transport: Na+-dependent glucose transporters and facilitative glucose transporters
- Two mechanisms of glucose absorption: active absorption and facilitated absorption
Glucose Transport Proteins
- Glucose enters absorptive cells by binding to transport proteins that bind glucose on one side and release it on the opposite side
- Two types of glucose transport proteins:
- Na+-dependent glucose transporters (SGLT 1 and SGLT 2)
- Facilitative glucose transporters
Glycolysis
- Glycolysis is a cascade of reactions that converts glucose into:
- Two pyruvate molecules
- Two lactate molecules (mitochondria/O2 not available)
- Glycolysis can run independent of mitochondria/O2, it is mainly called anaerobic oxidation of glucose
- Intracellular site and tissue distribution: Glycolysis occurs in the cell cytoplasm of all tissues of the body
Learn about the process of carbohydrate digestion in the small intestine, including the role of pancreatic juice and enzymes, and the mechanisms of glucose absorption. Understand the different types of glucose transporters and how they facilitate the absorption of monosaccharides.
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