The Digestive System

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Many of the molecules we eat are polymers. Polymers are big, insoluble molecules that need to be broken down into smaller, soluble molecules so they can be absorbed and assimilated by the body

Carbohydrates are monosaccharides made of carbon, hydrogen and oxygen.

Proteins are amino acids made of carbon, hydrogen, oxygen and nitrogen.

Digestive enzymes catalyse the hydrolysis reactions that break down big molecules into smaller ones:

  • Salivary glands: amylase hydrolyses starch into maltose
  • Pancreas: amylase hydrolyses starch into maltose
  • Small intersine: maltase hydrolyses maltose into glucose. sucrase hydrolyses sucrose into glucose and fructose. lactase hydrolyses lactose into glucose and galactose.

Structure of the digestive system

  • Mouth: teeth, saliva
  • Oesophagus: transports food to stomach using muscle contractions. Mucus lubricates walls
  • Stomach: walls produce gastric juice that contains hydrochloric acid, pepsin and mucus to break down food.
  • Small intestine: pancreatic juice neautralises the acidity. Glucose and small molecules are absorbed through villi via diffusion, facilitated diffusion and active transport.
  • Large intestine: absorbs water, salts and minerals. Folded wall for absorption.
  • Rectum: stores faeces 

Amino acid structure:

                R

                 l        

    H2N ---- C ---- COOH

                 I

                H

Condensation reactions link amino acids together with peptide bongs to form polypeptides.

Condensation reactions link monosaccharides together using glycosidic bonds.

Primary structure: sequence of amino acids in the polypeptide chain

Secondary structure: polypeptide chain doesn't remain flat and straight. Hydrogen bonds form between the amino acids in the chain. This makes it automatically coild into an alpha helix or folded into a beta pleated sheet.

Tertiary structure: coiled or folded chain of amino acids is coiled and folded futher. More bonds form between different parts of the polypeptide chain. 

Quarternary structure: final 3D structure. Made of several polypeptide chains help together by bonds. 

Protein shape and function

A protein's shape determines its function.

Enzymes: spherical shape due to tight folding of the polypeptide chaincs. Soluble.

Antibodies: made up of 2 light (short) polypeptide chains and 2…

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