3 pain processes: Digestion, Absorption (taking molecules into body) and Assimilation (absorbed molecules incorporated into body tissues). 2 stages of digestion:
1. Physical breakdown:
- Large food into smaller by structures such as teeth or stomach muscles.
- Makes ingestion possible.
- Provides large surface area for chemicals.
2. Chemical digestion:
- Conversion of large, complex, insoluble molecules into smaller, soluble ones.
- Carried out by enzymes functioning by hydrolysis.
- Carbohydrases - carbohydrates into monosaccharides in the s. intestine.
- Lipases - lipids into glycerol and fatty acids in the s. intestine.
- Proteases - proteins into amino acids in the stomach/s. intestine.
- Amylase - starch into glucose and maltose in the mouth/s.intestine.
- They're absorbed into the blood and re-built into larger molecules for tissues.
Major Parts of the Digestive System.
- Oesophagus - transports food from mouth to stomach.
- Stomach - is a muscular sac producing enzymes. It stores and digests.
- S. intestine - is a long muscular tube to further digest by enzymes. Uses villi.
- L. intestine - absorbs water from secretion of digestive glands. Food thickens to form faeces.
- Rectum - the final part of the intestine, faeces is stored and removed by egestion.
- Salivary glands - pass secretions to mouth. Includes amylase.
- Pancreas - is a gland to secretes pancreatic juices (protease, lipase and amylase).
- Mouth - uses tongue to move food, saliva lubricates and teeth for breakdown.
- Liver - bile breaks down fats. It processes food from s. intestine, breaks down toxins and converts ammonia to urea.
- Gall bladder - bile breaks down fats and neutralises acids.
- Bile duct - carriers bile secreted by liver.
Emulsification - making 2 substances that would not normally mix, mix.
Emmisable - 2 substances that won't mix.
Carbohydrates - Monosaccharides.
- Monomer - individual organic molecule that makes up part of a larger 1.
- Polymer - is a long chain of monomers.
- Hydrolysis - adding water to break a bond.
- Condensation - removing water to make a bond.
- In carbohydrates, the basic monomer is a sugar (saccharide).
- MONOSACCHARIDES are sweet tasting and soluble.
- General formula = (CH2O)n.
- Glucose + glucose = maltose.
- Glucose + fructose = sucrose.
- Glucose + galactose = lactose.
- When monosaccharides join water is removed: condensation reaction making glycosidic bonds.
- Many combined monosaccharide molecules.
- Insoluble so good for storage and some structual support in plants.
- E.g. starch.
- Reducing Sugars - BENEDICT'S TEST.
- All monosaccharides and some disaccharides are reducing sugars. This means they donate electrons to/reduce another chemical.
- Add Benedict's reagent to food and heat gently.
- Blue, green, yellow, orange, red (semi-quantitative).
- Non-Reducing Sugars - BENEDICT'S TEST.
- No change with Benedict's.
- Add HCl to food and heat to hydrolyse disaccharide.
- Add sodium hydrogencarbonate to neutralise HCl, check it's alkaline.
- Re-test with Benedict's and heat.
- Test for Starch - IODINE.
- Add iodine and shake.
- Yellow to blue/black.
- Test for Proteins - BIURET TEST.
- Detects peptide bonds.
- Add sodium hydroxide and few drops of dilute copper sulfate and mix.
- Blue to purple.
- Uses many enzymes as they're specific and converts molecules to monomers.
- Enzymes produced in different places due to different optimum pH's.
- Amylase hydrolyses alternate glycosidic bonds to produce disaccharide maltose, the hydrolysed into monosaccharide alpha-glucose by maltase.
- Food chewed so larger surface area: Salivary amylase + food = maltose.
- Food moves to stomach, acid denatures amylase. Then to s. intestine and mixed with pancreatic juices: pancreatic amylase + starch = maltose.
- Epithelial lining produces maltase: maltase + maltose = alpha-glucose.
- Mineral/alkaline salts maintain neutral pH in mouth and s. intestine.
- Sucrose- found inside cells so teeth required to get it, epithelium of s. intetsine produce sucrase: sucrase + single glycosidic bond = glucose + fructose.
- Lactose - sugar found in milk. Lactase in s. intestine hydrolyses glycosidic bond between glucose and galactose (some people intolerant as have no lactase).
Amino Acids, Peptide Bonds and Protein Function.
Amino acids - basic monomer units. They combine to form a polymer - polypeptide which combine to form proteins. They have an amino group (NH2), a carboxyl group (C=OOH) and a R group which is unique.
Peptide bonds- amino acid monomers form dipeptides. Bonds form between C of 1 and N of another by condensation.
Proteins have 2 basic shapes:
1. Fibrous proteins - have structural functions e.g. collagen.
2. Globular proteins - have metabolic functions e.g. enzymes.
Fibrous proteins form long chains that run parallel and are linked by cross-bridges so are very stable.
Structure of Proteins/Polypeptides.
- Polymerisation - joining of amino acid monomers through condensation to form polypeptide.
- 20 amino acids in any sequence.
- Determines shape which is very specific to the function
- Linked amino acids have -NH and -C=O groups on either side of bond. H is positive and O is negative so form hydrogen bonds.
- Polypeptide twists into 3D coil called alpha-helix
- A-helices further twist and fold to form unique structure.
- Maintained by disulphide, ionic(between carboxyl and amino groups and broken by pH change) and hydrogen (numerous and weak) bonds
- Large proteins have complex molecules with individual linked polypeptide chains
These are globular (dissolve in water) proteins that are catalysts. They have a specific shape with an active site (functional part).
For reactions to take place naturally: molecules must collide with enough energy to alter atom arrangement; energy particles must be less than substrate ones; an initial boost of energy is needed to start the reaction - activation energy.
The molecules that act on enzymes are substrates, these form an enzyme-substrate complex. The substrate is held in the active site by temporary bonds between some amino acids of enzyme and groups of substrate.
Lock and Key Model - enzyme is rigid with active site complementary to substrate. They fit exactly as have a specific shape.
Induced Fit Model - when a substrate binds with an enzyme it induces changes in enzyme's shape i.e. enzyme flexible. As it changes shape the strain on the substrate distorts a bond and so lowers activation energy needed to break it.
Factors Affecting Enzymes.
- Reactions measured by: formation of products and disappearance of substrate.
- Increased kinetic energy so collide more often, therefore enzyme and substrate come together more often.
- If too high hydrogen and other bonds break, altering active site and slowing reaction (45 degrees).
- Denaturation - enzyme so disrupted it stops working (60 degrees).
- Body at 37 degrees otherwise additional energy would be needed to
- maintain higher temp, other proteins may denature and illnesses that further increase temp would denature enzymes.
- Change from optimum reduces effectiveness until denatured.
- Alters charges on amino acids of active site so no complex can form.
- Causes bonds in tertiary structure to break, altering shapes and denaturing.
- SUBSTRATE CONCENTRATION:
- Rate of reaction proportional to amount of substrate added.
- If concentration low enzymes have limited number to collide with.
- When all active sites used, more addition will have no affect.
Inhibitors - interfere with functioning of active site so reduce activity. Reversible inhibitors make temporary attachments to the active site, there are 2 types:
1. Competitive Inhibitors:
- Similar shape to substrate so occupy active site: enzyme-inhibitor complex.
- Inhibitor and substrate compete for active site.
- At high sub. concns inhibitor has little effect. At low ones the rate is lower.
- Eventually, all substrate molecules occupy an active site, the greater the inhibitor concentration the longer it takes.
2. Non-competitive Inhibitors:
- Attach to site other than active one as have no structural similarity to substrate.
- Alters shape of active site so substrate can't bind and enzyme cannot function.
- An increase in substrate concentration does not decrease effect of inhibitor.
End-product inhibition - a product acts as a non-competitive inhibitor on earlier enzyme.