Enzymes and Digestion
The Oesophagus- carries food from the mouth to the stomach.
- Adapted for transport- made up of a thick muscular wall
- Peristalsis- wave of movement to pass the food down the oesophagus.
The Stomach- muscular sac that produces enzymes.
- Stores and digests food
- glands that secrete enzymes to digest proteins (pepsin/pepsinogen)
- other glands secretes mucus- stops stomach being digested by enzymes.
The Small Intestines- long muscular tube
- Enzymes that are produced by its walls and glands that pour secretions into it.
- Inner walls folded into villi- increases SA.
- SA further increased by microvilli on epithelium of cells of each villus.
- Rate of absorption increased- from lumen to cells to bloodstream.
The Large Instestine- absorbs water
- food becomes drier and thicker and forms faeces.
Enzymes and Digestion
- where the faeces is stored before being removed via the 'bum' (egestion)
The Salivary Glands-
- Pass secretions via a duct in the mouth.
- Secretions contain amylase: breaks down starch into maltose.
- Produces pancreatic juice- contains proteases, lipases and amylase
What is digestion?
- The teeth breaks down large insoluble molecules into smaller soluble ones.
- This creates a larger SA for chemical digestion.
- Food churned by muscles in the stomach (peristalsis)
- Hydrolysis- splits up molecules by adding water to the chemical bonds that hold it together.
- Carbohydrases- break down carbohydrates into monosacharrides.
- Lipases- break down lipids into glycerol and fatty acids.
- Proteases- break down proteins into amino acids
Once these molecules have been broken down they travel through the small intestine in a thick liquid called chyme where they are absorbed into the blood---> they get carried to different parts of the body where they are built up again and associated into body tissues (ASSIMILATION)
- The general formula of a monosaccharide is (CH2O)n
Testing for Reducing Sugars
- Reduction- molecules gain electrons
- A reducing sugar is a molecule that can donate their electrons to another chemical (Benedicts reagent (copper sulphate))
- When sugar heated with Benedict's reagent--> forms an insoluble red precipitate of copper oxide
- When monosaccharides join a glycosidic bond is formed in a condensation reaction
- Test for non-reducing sugars (disaccharides):
- first step is same for testing reducing sugars
- If colour change doesn't occur, add HCL (hydrolyses disaccharide) to food sample
- add sodium hydrogencarbonate (neutralises HCL)
- If non-reducing sugar present reagent will turn orange-brown- polymers been broken down into monomers.
- polysaccharides are insoluble- suitable for storageTest for starch:
- add iodine solution to food sample
- presence of starch indicated by blue-black colouration.
- Amylase( found in the salivary glands and the pancreatic juice of the pancreas) break down(hydrolyse) the alternate glycosidic bonds of starch into maltose.
- Maltose is then hydrolysed into alpha glucose by MALTASE, which is found in the lining of the intestine.
- Food is chewed by the teeth in the mouth= SA of food increased (food broken down into smaller pieces)
- Saliva mixes w/ food- salivary amylase hydrolyses any starch found in food to maltose.
- Mineral salts keep the pH at around neutral (which is optimum working conditions for salivary amylase)
- Food swallowed--> enters stomach (which is acidic--> denatures salivary amylase= stops the hydrolysis of starch.
- Peristalsis in the stomach churns food up further= SA ↑ of food for chemical digestion (chyme)
- Chyme passed into S.Intestine where pancreatic juices containing pancreatic amylase hydrolyses any remaining starch into maltose.
- Muscles in the instesine move food along the S.Intestine (peristalsis)
- Epithelial lining produces MALTASE→ hydrolyses maltose in α-glucose→absorbed into epithelial cells of S.Intestine→Assimilation.
- Sucrose usually contained in cells of food
- Released by chewing in the mouth
- Passes through stomach into S.Intestines
- Epithelial lining produces enzyme SUCRASE→ hydrolyses glycosidic bond between fructose and α-glucose.
- Epithelial lining in the S.Intestine produces LACTASE→ hydrolyses glycosidic bond to break down lactose into galactose and glucose.
- undigested lactose reaches L.Intestines where microorganisms break it down into smaller, soluble molecules and large volume of gas→ Ψ ↓= Ψ potential gradient created= causes water to move out of cells into lumen of intestines= smelly diarrhoea (eww)
- This can be solved by drinking milk with enzyme lactase in it or taking foods rich in calcium.
Structure of an Amino Acid
- Amino acids are the basic monomer units which combine to make the polymer, polypeptide.
- Polypeptides combine to form proteins
- Every amino acid has a central carbon:
- amino group (-NH2)
- carboxy group (-COOH)
- R group- variety of chemical groups- each A.A has a different R group
The formation of a peptide bond
- The -OH from the carboxyl group and the -H from the amino group are removed (makes water during a condensation reaction) to form a new peptide bond between the carbon atom of one A.A and nitrogen of the other A.A.
- Can be broken down by hydrolysis.
The primary structure of a protein
- Many A.A can be joined together in a process called polymerisation
- Polypeptide chains are formed from the binding of hundreds of A.A's
- The sequence of these chains is called the PRIMARY STRUCTURE
- The primary structure determines the shape of the protein- so a single change in an amino acid in the chain could cause the shape of the protein to change→proteins will function less well.
The secondary structure of proteins
- H of amino group has a overall +ve charge
- O of the carboxyl group has a overall -ve charge
- These two groups readily form HYDROGEN BONDS
- Causes polypeptide chain to be twisted into a 3-D shape: α-helix or ß-pleated sheets.
Tertiary structure of proteins
- α-helices can be folded even more to give a more complex and unique 3-D shape/structure of each protein.
- Maintained by:
- Disulfide bonds- strong, not easily broken down
- Ionic bonds- formed between carboxyl and amino groups not involved in making peptide bonds. Weaker, easily broken by changes in pH.
- Hydrogen bonds- weak, but there are lots of them.
- Hydrophobic interactions
Quartenary structure of proteins
- Large proteins formed containing numerous individual polypeptide chains that are linked in various ways (haemoglobin)
- There may be a prosthetic group, which is a non-protein (ferrous group) associated with the molecules.
Test for proteins
- The Biuret test- detects peptide bonds;
- add sodium hydroxide to sample solution at room temp.
- add copper sulphate solution and mix gently
- purple colouration indicated presence of peptide bonds, hence a protein--- if no protein present, solution stays a blue colour.
Enzymes as catalysts
- The reactant molecules must collide with energy to break it down.
- The product molecules have to have lower energy than the reactants.
- ACTIVATION ENERGY- minimum energy required for a reaction to take place.
- Enzymes lower the Ea→ allows reactions to take place at a lower temperature= reactions can take place at body temperature.
- Active site- only functional part of the tertiary structure of an enzyme
- This is made up of relatively small numbers of amino acids.
- Substrate binds to active site of enzyme to form an ENZYME-SUBSTRATE COMPLEX- which is held together by bonds formed by various amino acids.
- The key (substrate) has a specific shape that fits only a single lock (enzyme)
- scientists observed that other molecules can bind to sites of the enzyme other than the active site which could change the shape of the active site- so the structure can't be rigid like a lock and key, it has to be flexible
- INDUCED FIT MODEL
- The enzyme changes its shape to fit the shape of the substrate- the enzyme is flexible and can mould its way around the substrate (like the way a glove moulds around the hand).
- As the enzyme changes shape it puts a strain on substrate molecules-- this distorts a certain bond and lowers the Ea needed to break the bond.
- It is a better explanation:
- it shows how other molecules can affect enzyme activity
- how the Ea is lowered.
Effect on temperature on enzyme action
- ↑ in temperature= more kinetic energy in molecules= molecules move more rapidly and collide more often= ↑ E-S complexes= rate of reaction ↑.
- ↑ temp.= hydrogen bonds begin to break= enzyme structure changes shape= substrate bind less easily = ↓ rate of reaction.
- ↑↑↑ temp.= enzymes to denature= permanent change= enzymes can't function again
Effect of pH on enzyme action
- A change in pH alters the charges on the amino acids that makes up the active site= substrate can no longer become attached to active site= E-S complexes can't be formed.
- Could cause bonds that maintain tertiary structure to break= enzyme changes shape= substrate no longer fits= enzyme denatured.
Effects of substrate concentration on the rate of
- at a low substrate concentration- there are too few substrate molecules to bind the the active sites of the enzymes= rate of reaction is half of the maximum
- intermediate substrate concentration- all active sites are occupied, maximum rate of reaction is formed.
- high substrate concentration- addition of more substrate molecules has no effect on the rate of enzyme action because all E-S complexes have been formed.
- Similar molecular shape that of the substrate.
- It occupies active site of enzyme= compete for active site with original substrate.
- If substrate concentration ↑= effect of inhibitor ↓
- Inhibitor not permenantly bound to active site so when it leaves another molecule can take its place.
- Eventually all substrate molecules will occupy active site of the enzyme but it's the concentration of the inhibitor molecules that determine how long that will take.
- Attach themselve to a site other than the active site.
- Alters the shape of the active site of the enzyme.
- Substrate molecules can no longer occupy the active site- enzyme cannot function.
- ↑ in substrate concentration doesn't reduce the effect of the inhibitor.