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Biological Molecules
Nutrients: Why do we need food?
Nutrients: Why do we need food?
Food is a source of energy & raw materials for organisms.
Food is required to:1. Provide energy for vital body activities2. Synthesize new protoplasm for cell
growth, repair, cell division3. Stay healthy
The longest time that anyone has ever lived without food or water is
18 days. An 18-year-old man in Austria was put into a police cell on 1st April 1979 and forgotten. When he was discovered on 18th April, he
was very close to death…
What was the longest time someone survived without food/water?
Learning objectives
By the end of this chapter, you will learn to: State roles of water in organisms. List chemical elements that make up
carbohydrates, proteins, fats State that large molecules are made
from smaller basic units Describe & carry out tests for starch,
reducing sugars, proteins and fats
Overview of topic
Water & Living Organisms Carbohydrates, Fats & Proteins Enzymes
Learning objectives: Water
By the end of the lesson, you should be able to:
State the roles of water in living organisms
Water
Water is essential to life. It can be found:
Within organisms Outside organisms
In ponds, lakes, seas, oceans
In cytoplasm of cells
In bloodIn intercellular spaces/
interstitial fluid
In vacuoles of cells
Water: Regulates temperature Regulates temperature in organisms
1. Cooling by evaporation of: sweat in animals water from leaves by transpiration Removal of latent heat of vaporization
from organism
2. Water in intercellular spaces, cytoplasm & blood absorbs heat produced by metabolic activities
Water has high heat capacity Temperature changes within water are
minimised Constant external
environment for cells & organisms
Water: Good solvent Good solvent for:
1. Metabolic waste, e.g. urea2. Gases, e.g. carbon dioxide & oxygen3. Nutrients from digestive tract, e.g. glucose4. Part of digestive juices, e.g. enzymes5. Part of protoplasm
Acts as a medium in which chemical reactions occur
Acts as a transport medium in: blood, lymphatic and excretory systems,
alimentary canal, xylem & phloem
Water: Provides support
Supports structures & organisms1. Maintains turgor pressure in plant cells
& keeps their shape2. Provides support (buoyancy) to
aquatic organisms
Turgor in plant cells
Recap: Water enters plant cells by osmosis, causing them to be firm and turgid.
Turgor pressure is important to keep plants upright
Water enters by osmosis
Water leaves by osmosis
Importance of turgor pressure in plants
Usually, for most substances…
Which state is denser, solid or liquid?
But, look at this beaker of ice & water.
Ice is less dense than water.
But, for water…
Ice is less dense than water. Ice forms insulating layer over water Prevents lakes from freezing upwards Ensures survival of aquatic organisms
in winter
Densityice<Densitywater: Ensures survival of aquatic organisms
Water: Lubrication
Helps in lubrication, e.g.
1. Mucus aids movement of food along digestive tract
2. Synovial fluid facilitates movement in joints
3. Pericardial fluid facilitates movement in heart
Water: Photosynthesis
Substrate for photosynthesis in plants
Water: Hydrolytic reactions
Substrate for certain reactions in animals, e.g. hydrolysis in digestion
+
C6H12O6 glucose (monosaccharide)
C6H12O6 glucose (monosaccharide)
H2O water
+
C12H22O11 maltose (disaccharide)
Water: Helps in fruit dispersal
Helps in dispersal of: certain fruits, e.g. coconut, nipah
Water: High surface tension & cohesion
Surface tension: Force of attraction between molecules on surface of liquid Allow many small organisms to settle
on water or skate over its surface
Cohesion: Force which causes molecules to stick together Important in transporting water
upwards in plant
Water Requirements Water is lost daily from the body:
during breathing (in expired air) in urine in faeces through sweating
Average amount required to replace that lost daily - 3 litres / 8 glasses
More water needed by: active people people with diseases, e.g. diabetes Those living in hot and dry climates
Summary: Roles of water in organisms
Role of water in organisms
Regulates temperature
Good solvent
Provides supportLubrication
Photosynthesis
Fruit dispersal
Survival of aquatic organisms in winter
Sweat Transpiration
In animals In plants Nutrients
Gases
Metabolic waste
Digestive juices
Protoplasm
Buoyancy Turgor pressure
Mucus in digestive tract
Synovial fluid in joints
In animals In plants
Pericardial fluid in heart
Learning objectives (achieved)
By now, you should be able to: State the roles of water in living
organisms
Overview of topic
Water & Living Organisms Carbohydrates, Fats & Proteins Enzymes
Learning objectives: Carbohydrates
By the end of the lesson, you should be able to:
List elements that make up carbohydrates
State that large molecules (glycogen) are synthesised from smaller basic units (glucose)
Describe and carry out tests for: starch (iodine solution) reducing sugars (Benedict’s solution)
Types of biological molecules
Carbohydrates
Proteins Fats Nuclei acids
Contain carbon, hydrogen & oxygen Hydrogen:Oxygen = 2:1 Chemical formula: Cn(H2O)m
Carbohydrates: Functions
Substrate for respiration Provide energy for cell activities
Form supporting structures E.g. plant cell walls
Form nuclei acids, e.g. DNA, RNA Synthesize lubricants
E.g. mucus: glycoprotein Synthesize nectar in some flowers
The world of carbohydrates
Carbohydrates
Polysaccharides (complex carbohydrates)
Disaccharides (double sugars)
Monosaccharides(single sugars)
Examples:1. Glucose2. Fructose
3. Galactose
Examples:1. Maltose 2. Lactose 3. Sucrose
Examples:1. Starch
2. Glycogen 3. Cellulose
Carbohydrates: Monosaccharides
Are carbohydrates that cannot be broken down into simpler forms
Common examples: Glucose
Found in all animals Fructose
Common in plants (e.g. fruits), but rare in animals
GalactoseFound in milk in mammals
C6H12O6 glucoseC6H12O6 fructose
Carbohydrates: Disaccharides Created when 2 monosaccharides
become linked through a condensation reaction
Examples: Glucose + glucose = Maltose (Germinating
seeds)
Glucose + galactose = Lactose (Milk) Glucose + fructose = Sucrose (Table sugar)
+
C6H12O6 glucose (monosaccharide)
C6H12O6 glucose (monosaccharide)
H2O water
+
C12H22O11 maltose (disaccharide)
Carbohydrates: Polysaccharides
Are long chains/polymers of monosaccharides
Most common carbohydrates in nature Examples:
Glycogen (Found in animals & fungi) Starch (Found in plants) Cellulose (Found in plants)
Carbohydrates: Polysaccharides: Starch
Polymer of glucose Energy reserve in plants Stored as starch granules in cytoplasm
Carbohydrates: Polysaccharides: Glycogen Polymer of glucose Primary store of carbohydrates in
animals Stored in liver & skeletal muscles of
vertebrate animals
Why are glycogen & starch used as storage materials?
Insoluble in water Osmotically inactive i.e. does not change
water potential in cells Large molecules
Cannot diffuse across cell membranes Easily hydrolysed to glucose when
needed for respiration Have compact shapes
Occupy less space than sum of individual molecules
Carbohydrates: Polysaccharides: Cellulose
Forms cell walls in plant cells to provide support
Cannot be digested in humans But is a valuable source of fibre
The purpose of food tests…
Given an unknown sample X, how do you find out what nutrient is present?
?
Different food tests that can be done:
Test for:
REDUCING SUGARS PROTEINS
FATS
Benedict’s test
Biuret test
Ethanol emulsion
test
STARCH
Iodine test
Carbohydrates: Polysaccharides: Iodine test for starch
Add a few drops of iodine solution to food sample
If iodine solution turns blue-black: Starch is present
If iodine solution remains yellowish-brown: Starch is absent
Different food tests that can be done:
Test for:
REDUCING SUGARS PROTEINS
FATS
Benedict’s test
Biuret test
Ethanol emulsion
test
STARCH
Iodine test
Test for carbohydrates: Reducing sugars
What are reducing sugars? Sugars with a free aldehyde or ketone group
that can reduce other substances e.g. all monosaccharides & some disaccharides
Carbohydrates
Polysaccharides (complex carbohydrates)
Disaccharides (double sugars)
Monosaccharides(single sugars)
e.g. glucose, fructose, galactose
e.g. maltose, sucrose, lactose
e.g. starch, glycogen, cellulose
Test for carbohydrates: Reducing sugars
To test for reducing sugars, carry out the Benedict’s test.1. Add 2 cm3 of Benedict’s solution to 2
cm3 of test solution.2. Shake well.3. Heat contents in boiling water bath for
5 min.
Test for carbohydrates (3): Reducing sugars
Results:
If Benedict’s solution remains clear blue, and no precipitate is formed, reducing sugar is absent
Benedict’s solution turns green OR Formation of a precipitate from yellow and orange to brick red Reducing sugar is present
Colour when there is a lot of reducing sugars
present
Colour when there is no
reducing sugar
Test for carbohydrates (2): Reducing sugars Which tube has the most reducing
sugars? Which tube has no reducing sugars?
Learning objectives: Carbohydrates
By now, you should be able to: List elements that make up
carbohydrates State that large molecules (glycogen)
are synthesised from smaller basic units (glucose)
Describe and carry out tests for: starch (iodine solution) reducing sugars (Benedict’s solution)
Biological Molecules
Proteins
Overview of topic
Water & Living Organisms Carbohydrates, proteins & fats Enzymes
Lesson objectives
By the end of this lesson, you should be able to:
State that proteins & polypeptides are synthesized from amino acids
State the test for proteins
Types of biological molecules
Carbohydrates
Proteins Fats Nuclei acids
Contain carbon, hydrogen, oxygen, nitrogen, phosphorus & sulphur
Roles of proteins in our bodies
Functions of proteins
Synthesis of new protoplasm, for growth & repair of worn-out body cells
Synthesis of enzymes and peptide hormones
Formation of antibodies to fight diseases
Structure of proteins Proteins are polymers of amino acids Amino acids are aligned in genetically
determined sequence Amount, type & arrangement of amino acids
affects protein properties
Amino acids ProteinPolypeptide
Denaturation of proteins
Under certain conditions, e.g. heat or change in pH, unique 3D shape of proteins can be changed Protein loses ability to function Protein is denatured
Heat or acids/alkalis
Different food tests that can be done:
Test for:
REDUCING SUGARS PROTEINS
FATS
Benedict’s test
Biuret test
Ethanol emulsion
test
STARCH
Iodine test
Test for proteins: Biuret test To test for proteins:
1. Add 2 cm3 of sodium hydroxide to 2 cm3 of sample in a test tube. Shake well.
2. Add copper(II) sulphate solution dropwise. Shake after each drop.
Step 1: 2cm3 of sodium hydroxide
2cm3 of sample
Step 2:Copper sulphate solution added dropwise
Blue solution turns violet Protein is present
Solution remains blue Protein is absent
Test for proteins: Biuret test
Copper ions react with peptide bonds in protein to give a violet coloration.
Blue solution Protein is absent
Violet coloration Protein is present
Lesson objectives
By now, you should be able to: State that proteins & polypeptides are
synthesized from amino acids State the test for proteins
Overview of topic
Water & Living Organisms Carbohydrates, Proteins & Fats Enzymes
Learning objectives
By the end of the lesson, you should be able to:
State that fats are made from glycerol and fatty acids
Describe and carry out test for fats (ethanol emulsion test)
Types of biological molecules
Contain carbon, hydrogen & oxygen Compared to carbohydrates, fats have
less O relative to H No fixed ratio for elements in fats
All fats are insoluble in water Can be animal fats or plant fats
Carbohydrates
Proteins Fats Nuclei acids
Glycerol Fatty acids waterFat
+ +
Fats
Fats are commonly used as a store of energy, especially by animals
Fats are made from fatty acids & glycerol in a condensation reaction
Functions of fats
Source & store of energy Insulating material Solvent for fat-soluble vitamins &
certain hormones Essential part of protoplasm (esp.
cell membranes) Sebum helps reduce water loss from
skin surface
Different food tests that can be done:
Test for:
REDUCING SUGARS
PROTEINS
FATS
Benedict’s test
Biuret test
Ethanol emulsion
test
STARCH
Iodine test
Test for fats: Ethanol emulsion test
To 2 cm3 of ethanol in a test tube, add 5 drops of test sample.
Shake well. Then add 2 cm3 of water. Shake well. If fats are present, a white emulsion
is seen. If fats are absent, no white emulsion
is seen.
Learning objectives (achieved)
By now, you should be able to: State roles of water in living organisms. List the chemical elements that make up:
Carbohydrates Proteins Fats
Learning objectives (achieved)
By now, you should be able to: Describe and carry out tests for:
1. Starch (Iodine solution)2. Reducing sugars (Benedict’s solution)3. Protein (Biuret test)4. Fats (Ethanol emulsion test)
State that large molecules are synthesised from smaller basic units:1. Glycogen is made from glucose2. Proteins are made from amino acids3. Fats are made from fatty acids & glycerol