Biology Digestion, Enzymes, Metabolism & ATP Energy Reactions

Intracellular Digestion

Digestion that takes place inside the cell (found in plants and single-cell organisms).

Extracellular Digestion

Digestion that takes place outside cells (found in most animals).

Physical (Mechanical) Digestion

Physically breaking food into smaller pieces to increase surface area.

Chemical Digestion

Enzymes break food down into smaller molecules so they can be absorbed.

Mouth (Teeth & Saliva)

Teeth perform mechanical digestion; saliva softens food and contains salivary amylase which breaks starch down into maltose.

Epiglottis

A flap of tissue that blocks the trachea to prevent food and water from entering the airway.

Esophagus & Peristalsis

A tube with 2 layers of muscle connecting the pharynx to the stomach; uses peristalsis (wave-like contractions) to move food.

Stomach Mechanical Digestion

Composed of 3 layers of smooth muscle that contract to churn food.

Stomach Chemical Digestion

Gastric glands secrete mucus, hydrochloric acid (HCl), and pepsin.

Pepsin & Pepsinogen

Pepsin is the active protein-digesting enzyme, secreted in an inactive form called pepsinogen (activated by HCl).

Cardiac vs. Pyloric Sphincters

Cardiac sphincter is between esophagus and stomach; pyloric sphincter is between stomach and small intestine.

Liver Functions

Stores glycogen, detoxifies substances from blood, and secretes bile (not part of the digestive tract).

Bile

Mechanically breaks up large fat droplets into small droplets; stored in the gallbladder.

Pancreas Functions

Secretes pancreatic fluid (Trypsin, Amylase, Lipase, Nuclease) into the small intestine and neutralizes stomach acid.

Small Intestine Structure

Divided into duodenum, jejunum, ileum. Lined with villi containing blood vessels and lymph to absorb nutrients.

Small Intestine Enzymes

Trypsin (proteins), Amylase (carbs/starch), Lipase (fats), Nuclease (nucleic acids).

Large Intestine (Colon)

Reabsorbs water, absorbs vitamins produced by bacteria (like E. coli), and eliminates feces through the anus.

Metabolism

All the chemical activities and changes that take place continuously in a cell or organism.

Catalyst

A substance that speeds up chemical reactions; is not used up and is recycled.

Enzyme

A specialized protein catalyst in living cells that lowers activation energy.

Activation Energy

The energy required for a chemical reaction to begin.

Active Site

A small area of an enzyme's tertiary structure where the substrate binds.

Enzyme-Substrate Complex

The temporary union formed when a substrate fits into an enzyme's active site.

Noncompetitive Inhibition

A molecule attaches to an enzyme away from the active site, causing a shape change so the substrate can't bind.

Competitive Inhibition

A molecule other than the substrate blocks the active site, preventing the substrate from inserting.

Synthesis Reaction (Anabolic)

Building-up reactions that combine small molecules into larger ones; endothermic (requires free energy).

Decomposition Reaction (Catabolic)

Breaking-down reactions that break large molecules into smaller ones; exothermic (releases free energy).

Exothermic vs. Endothermic

Exothermic releases energy (products have lower potential energy); Endothermic absorbs energy.

Factors Affecting Reaction Speed

Reaction speed can be increased by increasing temperature or concentration.

ATP (Adenosine Triphosphate)

Chemical energy used to store and release energy; structured with adenine, ribose sugar, and 3 phosphates.

ATP Energy Release

Breaking the chemical bond between the 2nd and 3rd phosphate groups releases energy and forms ADP.

ATP Energy Storage

Forming a bond between the 2nd and 3rd phosphate groups stores energy and converts ADP to ATP.

Oxidation

The removal of electrons (usually with hydrogen), which releases free energy.

Reduction

The gaining of electrons, which stores or gains energy.