Understanding Carbohydrates - AP Biology

Carbohydrates, such as glucose and fructose, are primarily used in metabolic pathways to provide energy for the cell. Glucose is the first reactant necessary for driving glycolysis and subsequent cellular respiration in the cell, with the goal of producing ATP.

Proteins and enzymes serve to catalyze reactions. Nucleic acids store genetic material. Lipids form the membranes that surround and protect organelles.

Starch and glycogen have alpha glycosidic bonds between each glucose molecule. Humans can digest starch and glycogen because humans possess alpha amylase, which breaks these alpha linkages.

Cellulose contains beta glycosidic bonds, which can be digested by beta amylase. Since humans do not possess beta amylase protein, they are unable to digest cellulose.

Starch and cellulose are polysaccharides that are found in plants and glycogen is found in human liver. All three polysaccharides are made from glucose, a monosaccharide.

Polymers are built up from monomers. Polymers are placed into different classes based on the different natures of the monomers that make up their structure.

Carbohydrates have an empirical formula of . The most common types of carbohydrates are pentoses (5-carbon carbohydrates) and hexoses (6-carbon carbohydrates). All 6-carbon carbohydrates share the molecular formula .

Glucose, galactose, and mannose are all hexoses. The only difference between these three carbohydrates is their relative orientation of hydroxyl groups on the carbons.

Ribose is a pentose, and has a different molecular formula. Remember that all nucleic acids contain 5-carbon rings.

Recall that glucagon promotes the breakdown of glycogen to glucose, whereas insulin promotes formation of glycogen from glucose molecules. Both hormones function to regulate glucose levels. You can eliminate choices with galactose because glycogen is made up of glucose, not galactose.

You can also eliminate the answer choice that suggests that glycogen is stored in the pancreas. The pancreas releases the hormones insulin and glucagon, but it doesn’t store glycogen. The glycogen is actually stored in the liver. Increased levels of insulin increase the amount of glycogen stored in the liver.

Glucose is the main source of energy in the human body. It is a six carbon sugar that, when fully oxidized, can yield as many as 36 ATP. The brain in the human body uses glucose exclusively, though other parts of the body are capable of metabolizing other sugars. When complex sugars are ingested, they are broken down and converted by various enzymes to produce glucose. The glucose then enters into glycolysis to generate cellular energy.

Glycolysis occurs within the cytosol of the cell, during both aerobic and anaerobic respiration. Glycolysis is the first step to generate energy from the breakdown of carbohydrates.

Glycolysis does not involve the breakdown of proteins or fatty acids. Fermentation can be used to regenerate NAD+, with a byproduct of lactic acid or ethanol, during anaerobic respiration. Glycolysis will occur simultaneous to fermentation, but will also occur during healthy aerobic respiration.

Enzymes are proteins, which are composed of amino acids. Biomolecules are made of polymers. The monomers in nucleic acids are nucleotides. The monomers in carbohydrates are monosaccharides. Lipids are biomolecules, but their structure does not follow as clear of a pattern as the other three. Depending on the textbook, we may consider fatty acids, or hydrocarbons as "monomers" of lipids. There is some ambiguity with lipids because their structures are diverse and are not always chains of repeating subunits.

Carbohydrates and proteins are polymers (a long chain molecule generally composed of repeating single units), but glucose and lipids are not polymers (though glucose has the ability to polymerize). Proteins are polymers of amino acids. Carbohydrates are polymers of sugar monomers or monosaccharides. Lactose is a disaccharide or two sugar monomers connected.

Polymers are broken down into monomers via hydrolysis. Hydrolysis is the reverse of a condensation synthesis reaction. In hydrolysis, adding water molecules breaks the bonds between monomers. In this reaction polymers are broken down when the hydrogen of the water molecules attaches to one monomer and the hydroxyl attaches the next monomer.

is the base molecular formula for carbohydrates. Carbohydrates vary based on multiples of this formula (i.e. is the formula for glucose).

is the molecular formula for glucose. Most carbohydrates such as glucose and sucrose have a molecular formula that is a multiple of .

A glycosidic linkage is defined as a covalent bond created by a dehydration reaction between two monosaccharides. The resulting product is called a disaccharide.

Energy is stored in the form of glucose. Cells, in turn, tap into glucose reserves to fuel cellular respiration. The carbon in glucose also serves as raw materials for the synthesis of other molecules such as amino acids.

When two monosaccharides connected together by a glycosidic linkage into a single unit, the product is called a disaccharide. Strings of monosaccharides linked together are called polysaccharides.

Starch is a storage polysaccharide in plants. It is a polymer consisting solely of glucose. Glucose is a source of fuel for cells; therefore, starch is stored for energy.

Starch is a storage polysaccharide in plants. It is a polymer consisting solely of glucose. Glucose is a source of fuel for cells; therefore, starch is stored for energy.

Glycogen is a polysaccharide used as energy storage in animals. Glycogen is a polymer made up of glucose units and undergoes hydrolysis to release glucose when demand for sugar increases.

The polysaccharide cellulose is a major component of plant cell walls. Similar to starch, cellulose is made up of glucose though the linkages in the polymers are different.