Nutrition in Man

3 types of nutrients

FATS

CARBOHYDRATES

PROTEINS

Function: main source of energy for the body

disaccharides (contains 2 monosaccharides)

monosaccharides (all are reducing sugars)

made up of carbon, hydrogen and oxygen

polysaccharides (long chains of monosaccharides linked by glycosidic bands)

glucose

fructose

galactose

glucose + glucose = maltose (reducing sugar)

fructose + glucose = sucrose

galactose + glucose = lactose (reducng sugar

starch

glycogen

cellulose

reducing sugar: any sugar that is capable of acting as a reducing agent, gives a brick-red precipitate when boiled with Benedict's solution

highly branched of glucose molecules

branched chains of glucose molecules

Function: energy storage in plants, stored in storage organs

Function: energy storage in animals, stored in liver and muscle tissues

made up of carbon, hydrogen, oxygen and nitrogen

amino acids link up to form polypeptides

Functions: structural support, speed up chemical reactions (enzymes),growth and repair of worn-out tissues

made up of carbon, hydrogen and oxygen

found in plants

cannot be digested by the human body, acts as fiber to bind waste and is passed out

linear chain of glucose molecules

functions: connects cells to form tissues, controls shape of plant cells ; helps plant to remain stiff and strong, structural support

contains twice as much energy than carbohydrates (gram for gram)

functions: source and store of energy, insulating material ; prevents heat loss, cushions vital organs, essential part of cell membranes, a way to reduce water loss from skin surface

(aka triglyceride) can be broken into glycerol and (3) fatty acids

saturated: solids at room temperature
unsaturated: liquids at room temperature

can be denatured by:
1.heating 2.changes in acidity or alkalinity

bonds between polypeptide chains cause the chain to fold and form proteins

How to test for presence of nutrients

Benedict's for reducing sugars: - blue mixture forms a brick red precipitate ; reducing sugar is present - mixture remains blue ; reducing sugar is absent

Iodine for starch - yellow brown mixture turns blue black ; starch is present - mixture remains yellow brown ; starch is absent

Ethanol emulsion for fats - clear mixture forms a white emulsion ; fat is present - mixture remains clear, fat is absent

Buiret test for proteins - blue mixture turns violet ; protein is present - mixture remains blue ; protein is absent

Physical digestion : mechanical break-up of food into smaller particles - usually by the action of chewing in mouth and peristalsis in stomach Chemical digestion : breakdown of large molecules of proteins, starch and fats into small soluble molecules (involves reactions catalyzed by enzymes)

catalyst (meaning): a substance that alters or speeds up a chemical reaction without itself being changed at the end of the reaction ; enzyme

what is an enzyme?

is a protein

functions as a biological catalyst

alters or speeds up chemical reactions

remains unchanged at the end of the reaction

characteristics of enzymes:

  • speed up chemical reactions
  • required in minute amounts
  • specific in action due to its three-dimensional shape

building up of complex substances

break down of complex sunstances

enzyme > substrate > product

  • amylase > starch > maltose
  • maltase > maltose > glucose
  • protease > protein ; polypeptide > amino acids
  • lipase > fat > glycerol + fatty acids

factors affecting rate of reaction: temperature, pH, concentration of enzyme, substrate

'lock and key' hypothesis

an enzyme has a specific 3-D shape which contains an active site

only substrate with a 3-D shape complementary to that of the active site of the enzyme can fit into the enzyme and form an enzyme-substrate complex

chemical reactions will occur and the substrate is converted into products

the products detach from the active site ; the enzyme remains unchanged at the end of the reaction

the change in 3-D shape of an enzyme or an protein is known as denaturation

denaturation can be caused by: high temperatures relative to opimum, chemicals such as acids and alkalis

when an enzyme is denatured, there is a loss of shape of its active site

the substrate can no longer fit into the active site to form an enzyme-substrate complex. Thus, no reaction can take place

at low temperatures, the enzymes are inactive. the KE is low. Hence, chances of the substrate molecules colliding with enzymes are very low.

as temperature rises, the enzyme activity increases. the temperature rise increases the KE of molecules, increasing the chance of a collision which increases the rate of formation of an enzyme-substrate complex

the temperature and pH at which the rate of enzyme reaction is the highest is called the optimum temp/pH.

beyond the optimum temperature, the enzyme activity decreases as the high temperature breaks the bond within the enzyme and changes its 3-D shape. The active site is lost and the enzyme is denatured

pH is the measure of the acidity/alkalinity of a solution

enzymes work in a very narrow band of pH values

extreme pH denatures enzymes. the acid or alkaline environment will break the bonds that hold the enzymes in its specific shape.

shape of the active site is changed, the substrate cannot fit and no product is formed

'lock': enzyme, 'key': substrate

Ingestion: taking in of nutrients by eating or drinking

Digestion: breaking large insoluble molecules into small soluble molecules that can dissolve into the bloodstream

Absorption: taking up of small soluble substances into body cells

Egestion: the removal of undigested waste through the anus

Digestive system

Alimentary canal

Accessory organs (food doesn't pass through)

Liver

Pancreas

Gall bladder

Mouth

Oesophagus

Stomach

Small intestine

colon (LI)

rectum (LI)

anus (LI)

physical digestion: increases surface area to volume ratio
eg. chewing, peristalsis,emulsification

chemical digestion: higher surface are, enzyme digests faster

Peristalsis

refers to the rhythmic,wave-like contractions ; enables food to be mixed with digestive juices and travel down the gut

requires the action if antagonistic muscles (pair of muscles with opposing movements)

Inner circular and outer longitudinal muscles in the wall of the gut are antagonistic muscles

increases SA:VR of boli ; more exposed to digestive juices

Circular muscles: 1.(in front of bolus: relax) 2.(behind bolus: contract)

carbohydrase: enzymes that break down carbohydrates (eg. amylase,maltase,cellulose)

one side: food is squeezed out, other side: expands

Longitudinal muscles: 1.(in front of bolus: contract) 2.(behind bolus: relax)

  1. wall of gut dilates, allowing food to enter the lumen
  1. wall of gut constricts, pushing food forward

food is broken down when squeezed upon

salivary amylase in saliva chemically digests starch starch into maltose ; digestion starts

physical digestion ; chewing

saliva is mixed with food by tongue which softens it

tongue rolls food into boli

food passes down by peristalsis and enters the stomach

peristalsis mixes food with gastric juice ; a dilute solution of hydrochloric acid and pepsin (protease)

hydrochloric acid denatures salivary amylase > environment is acidic, unsuitable environment for salivary amylase > no starch digestion

stores bile temporarily

releases bile into small intestine

produces bile which emulsifies fats into smaller fat droplets ; physical digestion. Increases SA:VR for lipase to chemically digest it efficiently (bile is not an enzyme)

produces pancreatic juice which contains digestive enzymes (eg. amylase, protease, lipase and trypsin)

HA an acidic medium (optimum pH) for action of pepsin and kills micro-organisms in food

pepsin (protease): protein > polypeptides

the partially digested food is liquefied : forming chyme

stores feces/waste

acid provides an ideal environment for the enzyme to work in and kill bacteria

protease breaks down proteins into polypeptides