Today’s video is on carbohydrates, especially focused for healthcare students. My website, science with susanna.com has the blank drawing to accompany this video as well as practice materials to quiz yourself.

Carbohydrates are biomolecules that always contain carbon, hydrogen, and oxygen. Polysaccharides are built from monosaccharides.

The monomers of large carbohydrate molecules are the monosaccharide simple sugar carbohydrates, most notably glucose. Dextrose is the term used for glucose in the purified form administered in IVs or other medical settings. The two other main 6 carbon monosaccharides are fructose and galactose.

Disaccharides are two simple sugar monosaccharides put together. Sucrose is one glucose and one fructose. Lactose and maltose are the two other wellknown disaccharides.

Polysaccharides, the very large biomolecules that are built with many many simple sugars. Plant starch is digestible by the enzyme amylase. Amylase breaks down complex carbohydrates such as starch into many many individual molecules of glucose.

Animals store their carbohydrates as long branching chains called glycogen. We can store limited quantities of glycogen in our liver and our muscle cells.

Plant cellulose is highly structured polysaccharide, and it makes up all plant cell walls. This is completely indigestible for us. Cellulose provides us with insoluble dietary fiber.

Peptidoglycan, which is actually a combination of carbohydrate and proteins makes up bacterial cell walls. Protein crosslinks hold together many layers of simple sugars.

Glucose is what we measure when we test for blood glucose or blood sugar. The ideal range in the blood remains quite steady, even between meals. As people lose metabolic flexibility or become prediabetic, they may vary more and more widely from the ideal range of between 70 120mg/dL.

Hyperglycemia literally means too much sugar in the blood. It is most commonly seen when people damage their metabolism and begin to develop Type II diabetes. Hypoglycemia is the opposite problem, not enough sugar in the blood. It is most commonly seen in diabetics that inject more insulin than they needed. As we’ll see in a moment, insulin lowers blood sugar. Normoglycemia means normal amounts of sugar in the blood.

Now, in order for the polar glucose molecules to pass through the cell membranes and enter cells, the protein hormone insulin binds to insulin receptors on cells. These receptors then stimulate glucose channels to be inserted into the cell membrane; the polar glucose molecules can then passively enter the cells through these glucose channels, moving down their concentration gradient.

Insulin allows glucose to enter cells. Thus, insulin decreases blood sugar.

Once inside the cell, glucose is broken down in the cytoplasm in the process of glycolysis, into 2 3carbon molecules called pyruvate. Pyruvate enters the mitochondria, where complete breakdown of the carbon molecules is finished with many enzymatic reactions of the Citric Acid Cycle. The electron transport chain, on this inner mitochondrial membrane, then generates ATP energy for cellular activities. Glucose is a key source of ATP production for many cells.

Glycoproteins are really neat molecules that are part protein, and part sugar. They serve to identify a cell as part of you, or not! Think of them as ID tags. An antigen is the name we give to glycoproteins that provoke an immune response. The spike protein of SarsCoV2 is a glycoprotein, for example.

The liver monitors blood glucose levels in the blood glucose is absorbed from the intestine, and immediately enters the liver through the hepatic portal vein. The liver allows just the right amount (ideally about 100mg/dL) to exit the liver and return to the circulation through the hepatic vein. The liver modifies carbohydrates by storing or releasing glucose in order to keep blood sugar steady.

If excess glucose was in the meal, then the liver stores the excess glucose as glycogen in a process that is called glycogenesis. Once the glycogen stores are maxed out, the liver must store additional excess glucose and all excess fructose as triglycerides; we call this lipogenesis. Once the liver stores too much fat, inflammation can begin in the liver, leading to nonalcoholic fatty liver disease, a disease that was virtually unheard of 50 years ago but has become very common.

In between meals, glycogen stores can be broken down via glycogenolysis, releasing glucose into the blood so hypoglycemia doesn’t occur. Given enough hours between meals, the liver can also start breaking down triglycerides by performing lipolysis. The liver is even capable of building new glucose molecules from amino acids in a process called gluconeogenesis.

Now spend a few minutes reviewing this information, make sure you understand it reasonably well, and then use my Quizlet flashcards to practice and review! See you in the next video!