Carbohydrates

Carbohydrates are broken down into subunits monosaccharides (1 subunit), oligosaccharides (multiple subunits), and polysaccharides (>20 subunits). 

 

Polysaccharides come in two forms: 

• Homopolysaccharides: one monosaccharide present 

• Heteropolysaccharides: many different monosaccharides present

 

These can both be branched or unbranched 

 

These differences lead to complex and simple carbohydrates: 

• ​Simple carbohydrates

  • Simple carbohydrates are either monosaccharides or disaccharides. They are broken down quickly leading to a rapid spike in blood sugar. Sources such as fruits, honey, and milk are natural foods with simple carbohydrates. Candy and soda have added sugars that are simple carbohydrates. ​

• Complex carbohydrates

  • Complex carbohydrates include many sugar units. They result in longer and steady raises in blood sugar. Sources include whole grains and vegetables. ​
     

Examples of carbohydrates: 

 

Starch and glycogen (occur in large granules or aggregates): 

• Starch: Starch is a mixture of two homopolysaccharides. Amylopectin is branched every 24-30 residues and is made of glucose. Amylose is an unbranched glucose chain. Together these make starch. 

• Glycogen: Glycogen is a homopolysaccharide made of just glucose. It has glucose monomers linked with branch points every 8-12 residues.

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Fuel source:

 

Carbohydrates are usually stored as glycogen for rapid release. They do not need carrier proteins and are highly soluble in aqueous solutions.

 

In our digestive system starch is broken down by amylase in the mouth and enzymes, maltose, lactose, and sucrose, break down the poly and disaccharides into monosaccharides in the small intestine. These are absorbed into the bloodstream and transported to the liver. Insulin helps cells absorb blood glucose where inside cells glycolysis occurs to break down glucose. When oxygen is present glucose is converted into pyruvate which produces electron carriers to produce ATP. When oxygen is not present glucose still releases small amounts of ATP, but is converted eventually into lactic acid (strenuous exercise). 

 

Structural Components: 

 

Our ECM (extracellular matrix) is the material found outside of cells. They create the strength, elasticity, and physical barrier for tissues. The main components are collagen, elastin, and proteoglycan aggregates. Tumor cells need to degrade the ECM first before they can spread throughout the body. 

 

Proteoglycans vs glycoproteins: 

 

Proteoglycans are proteins covalently attached to carbohydrates. 

 

Glycoproteins are 1 or more carbohydrate chains attached to a protein core. 

 

Cell signaling: 

 

Lectins: carbohydrate binding proteins that have high affinity for carbohydrates. They are involved in cell signaling and adhesion. 

 

Carbohydrate signaling molecules include: 

 

• Hormones (Insulin)

• Intracellular molecules (cAMP)

• Metabolic intermediates (G6P)

• Transporter molecules (GLUT4)