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Biological molecules

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by

Alvin Tay

on 16 March 2014

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Transcript of Biological molecules

BIOLOGICAL
MOLECULES

1. As a source of ENERGY...
Why do we need food?
2. For Growth, Repair or Replacement of worn and damgaed tissues...
3. To maintain HEALTH...
Food contains a store of
energy
called potential chemical energy
When digested food (eg. Glucose) is oxidised during respiration, the energy is released and used for
vital activities
to keep our body alive such as movement, heart beat and nerve impulses; and to maintain a
constant internal body temperature
.
Food provides the substances needed for synthesising new protoplasm, cells and tissues.
Food such as some vitamins and minerals, is required to prevent deficiency diseases.
Taking in useful substances is called feeding or
ingestion
7 types of NUTRIENTS
ORGANIC
INORGANIC
Carbohydrates
Fats
Proteins
Vitamins
Mineral Salts
Water
Dietary Fibre
Provide energy
Growth and Repair
Keep us healthy
70% of our body is water
Help form cytoplasm and nucleus
A
transport
reagent for digested food substances, excretory products and hormones
Helps in chemical reactions of an organism
Needed for hydrolytic reactions (
digestion
)
Helps to regulate body temperature
Water is best known solvent for both inorganic salts and many organic compounds
Food Tests
Iodine test for starch
Add
2 drops of iodine solution
onto any substance
Iodine solution changes from
yellow
to
blue-black
if starch is present.
Add 2cm3 Benedict’s solution
Red precipitate
Heat in water bath
About 2cm3 of test solution
The different colours indicate presence of reducing sugar in increasing amounts:
green ppt
for trace amount;
yellow ppt
for small amount,
orange ppt
for moderate amount and
brick-red ppt
for high amount
Blue – Green – Yellow - Red
Add 2cm3 Benedict’s solution to 2cm3 of test solution in a test tube.
Shake the mixture.
Put the test-tube in a beaker of boiling water for 5 minutes.
If reducing sugars are present, a brick-red precipitate will be formed.
Benedict’s Test for Reducing Sugars
Add
2cm3 of ethanol
to test solution.
Shake the mixture thoroughly
Add
2cm3 of water
to solution.
A
cloudy, white emulsion
is formed if fats are present.
Violet colour
Allow mixture to stand for 5min
Shake after each drop
Shake mixture thoroughly
Add 1% copper (II) sulphate solution drop by drop
Add 1cm3 of sodium hydroxide
Sample to be tested: in this case, Egg white (2cm3)
Biuret test for proteins
Ethanol emulsion test for fats
Oil droplet
2 layers of immiscible liquid
White emulsion
Add 2cm3 of water
Add 2cm3 of ethanol
Shake mixture thoroughly
Add
1cm3 of sodium hydroxide solution
to
2cm3
of test solution .
Shake well.
Add
1% copper (II) sulphate solution

drop by drop
, shaking after each drop.
Allow mixture to stand for
5 minutes
.
A
violet colouration
is formed if protein is present.
Quick check!
What do you add to test for starch?

What is the colour of the precipitate formed if reducing sugars are present?

What is the colour change you will observe if proteins are present?
Iodine solution
Brick-red precipitate
Blue to Violet
ENZYMES
These enzymes act like chemical ‘scissors’ to cut up large molecules into small molecules until they become small enough to pass through the cell membrane.
Enzymes are
biological catalysts
made of
proteins
.
They change the rate of chemical reactions without themselves being chemically changed at the end of the reaction.
No enzyme?
Biochemical reactions in the body will otherwise process
too slowly
to sustain life!
Digestive enzymes
are enzymes that help in digestion.
Different types of digestive enzymes break down different nutrients into smaller and soluble molecules during digestion.
Each enzyme is specific; it acts only on one type of food.
3 Main Types of
Digestive Enzymes!
Groups of enzymes that digest
carbohydrates.
Carbohydrases break down large carbohydrates into
simple sugars.
Groups of enzymes that digest
proteins.
Proteases break down large protein molecules into small
amino acid
molecules.
Groups of enzymes that digest
fats.
Lipase break down big fats molecules into small molecules called
glycerol
and
fatty acids.
Simple sugars, amino acids, fatty acids and glycerol are simple and soluble substances that are small enough to diffuse into the bloodstream.
Hence, nutrients can be absorbed and used by the body.
Carbohydrases
Proteases
Lipases
QUICK CHECK!
What are enzymes?

What is the product of protein digestion?

What is the product of carbohydrate digestion?

What are the products of fats digestion?
1.) Biological catalysts made of proteins
2.) They change the rate of chemical reactions without themselves being chemically changed at the end of the reaction
Amino acids
Simple sugars
Glycerol + Fatty Acids
'LOCK & KEY'
Hypothesis

Specific shape of an enzyme that binds the substrate
Substance on which an enzyme acts on i.e. the things we want to digest
Each enzyme has its
specific active site.
Each active site has a certain shape.
The specificity of an enzyme is due to its
three-dimensional shape.
The enzyme acts like a lock. The substrate acts like a key.
Only substrates with the
correct exact complementary shape
can fit into the enzyme like a ‘lock and key’ to form an
enzyme-substrate complex
.
The enzyme then acts on the substrates to form new products. The enzyme itself
does not
take part in the reaction.
The new product leaves the active sites.
The enzyme is now free to take part in another reaction.
Quick check
Identify the substrate, the enzyme and the products:
Amylase breaks down starch to form sugars
Protease breaks down protein in egg white to form amino acids
Lipases break down fats, to form fatty acids and glycerol
ENZYME ACTION
TEMPERATURE
pH
At low temperatures, enzymes are
inactive.
As temperature increases, its activity
increases
.
This is both the substrate and enzyme molecules gain
kinetic energy
and move about more rapidly, increasing the chance of collision between substrate and enzyme’s active site.
The enzyme is about twice as active for every
10 degree celsius
rise in temperature until the optimum temperature is reached.
Effect of temperature on enzymes
It is the temperature at which enzyme activity is
maximum
.
Enzyme works best and fastest at this temperature.
Different enzymes have different optimum temperatures (
30oC - 70oC
)
Most enzymes in our body work best at
37oC
(body temperature).
Optimum temperature
At high temperatures, enzyme activity
decreases.
Enzymes are
denatured
as they are protein molecules.
The enzyme
loses its unique shape
of its active site.
The active site is altered or lost.
Denaturation
is the
change in a three-dimensional structure
of an enzyme and loss in active site specific shape. This can be caused by heat or chemicals.
Hence, the enzyme loses its ability to function permanently.
Effect of temperature on enzymes
At high temp, enzyme is denatured
Enzymes are inactive
Increasing temp, increase enzyme activity
Most alkaline
Least alkaline
Least acidic
Most acidic
pH is a measure of how
acidic
or
alkaline
a solution is
What is pH?
Enzymes are affected by the acidity or alkalinity of the solution in which they act in.
Optimum pH is the pH at which enzyme activity is
maximum
.
Enzyme works best at this pH.
Different enzymes have different optimum pH.
Most enzymes work best in neutral conditions.
Extreme changes in pH may
denature
some enzymes.
Effect of pH on enzymes
Enzymes in the stomach

Enzymes in the small intestine

Enzymes in the mouth
Quick Check
Optimum pH: 2 (acidic conditions)
Optimum pH: 8 (alkaline conditions)
Optimum pH: 7 (neutral conditions)
Above optimum pH, decrease enzyme activity
Increasing pH, increase enzyme activity
Extremely LOW and HIGH pH reduces enzyme activity
pH of solutions can affect enzyme activity.
alvintaysl@gmail.com
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