Carbohydrate Metabolism and Regulation

Where is energy found in carbohydrate molecules?

within the chemical bonds (bigger molecules = more energy)

What are monosaccharides and what are some common examples?

• single sugar molecules that cannot be broken down into simpler forms

• examples:

  • glucose, fructose, galactose, ribose, and deoxyribose

What is the disaccharide called when glucose and glucose are combined?

maltose

What is the disaccharide called when glucose and galactose are combined?

lactose

What is the disaccharide called when glucose and fructose are combined?

sucrose

polysaccharides

• large sugar molecules

• can be exogenous (obtained in the diet) or endogenous (produced by the body)

• used for energy storage and cell structure

• starch, glycogen, or cellulose (fiber)

What are the 6 main steps of carbohydrate metabolism? (exogenous)

1. polysaccharides are ingested

2. salivary amylase and pancreatic amylase break down the polysaccharides into disaccharides and monosaccharides (glucose, fructose, or galactose)

3. intestinal enzymes (maltase, lactase, and sucrase) digest the disaccharides into monosaccharides

4. intestinal mucosa —> hepatic portal vein —> liver

5. in the liver, all monos other than glucose are converted to glucose

6. glucose is used in one of 4 ways

What are the 4 ways/pathways in which glucose can be used?

• glycolysis

  • glucose is broken down immediately for cellular energy (NOW)

• glycogen

  • polysaccharide energy storage for later use

• triglycerides

  • used for long-term energy

• keto acids/amino acids/proteins

  • used for energy production and building blocks

What are the 2 metabolism pathways in glycolysis?

• Embden-Meyerhoff pathway

  • net gain = 2 ATP

• pentose phosphate pathway

  • net gain = 1 NADPH

glycogenesis

the process of converting glucose to glycogen in the liver

glycogenolysis

• the breaking down of glycogen for energy NOW

• when glycogen is broken down into glucose, glycolysis provides energy for our tissues

• used to regulate blood sugar throughout the day between meals

What happens if the body does not have any glycogen to break down for energy?

• gluconeogenesis occurs

  • creating glucose from non-carbohydrate precursors

  • amino acids, glycerol, and lactate is converted to glucose

  • occurs in the liver

When carbs are ingested and are converted to monosaccharides, how do they provide the body energy?

• monosaccharides enter the circulatory system

  • glucose can go directly to peripheral tissues for energy

  • fructose or galactose go to the liver and are converted to glucose, then reenter circulation

• excess glucose is converted into triglycerides for future energy needs

What is the purpose of insulin?

to lower blood sugar levels by promoting the uptake of glucose into our cells

Where is insulin produced?

the beta cells of the pancreas

How is insulin different than other related hormones?

insulin is the only hypoglycemic hormone, it effectively inhibits glycogenolysis and gluconeogenesis

glucagon

is a hormone produced by the alpha cells of the pancreas that increases blood sugar for immediate energy needs, inhibits glucose storage