2. 2
The chemicals of life
All living organisms are made up of chemical substances
Reactions between these substances keep the cytoplasm
(and the organism) alive. They are living processes.
The chemical substances described in the next series
of slides are carbohydrates, proteins and lipids.
3. 3
Carbohydrates
Carbohydrates contain the elements carbon, hydrogen
and oxygen
Familiar carbohydrates are sugar and starch
Glucose, fructose, maltose and sucrose are sugars
Glucose and fructose have the same formula, C6H12O6
Sucrose and maltose have the same formula, C12H22O11
Carbohydrates provide the main source of energy for
respiration in living organisms
4. 4
Glucose C H 6 12 O6
C HO C
HO C H C O
C C
HO C H
C C
H C OH
5 of the carbon atoms may
be arranged in a ring
H C OH
C H2OH
A glucose molecule as a This molecule is often represented
straight chain simply as a hexagon
5. Classification of sugars
• MONOSACCHARIDES: with a single carbon
ring.
- glucose and fructose
• DISACCHARIDES: 2 carbon rings.
- maltose (glucose – glucose)
- sucrose ( glucose – fructose)
• POLYSACCHARIDES:
- Glycogen (animal cells)
- Starch ( plant cells)
- Cellulose ( cell wall of plant cells)
6. 5
Other carbohydrates
2 molecules of glucose can sucrose is formed when
join together to form a a molecule of glucose and
molecule of maltose a molecule of fructose combine
Starch and cellulose are
formed from hundreds of
glucose molecules joined
maltose to form a long chain
part of a starch
molecule
7. 6
Proteins
Proteins are made up of carbon, hydrogen and oxygen
molecules but with the addition of nitrogen
-Carbohydrates are made up of glucose units.
-Proteins are made up of units called amino acids
-There are about 20 different amino acids. Examples are
glycine (Gly), alanine (Ala), valine (Val) and cysteine (Cyst)
-Proteins make up the structure of cells; cytoplasm,
nucleus cell membranes and enzymes, haemoglobin,
antibodies, hormones, fibrin.
8. Protein structure and shape 7
The way the amino acids join up, gives a protein molecule a
particular shape, which is different for every protein
Ser-Cyst-Val-Gly-Ser-Cyst Ala
Val
Val-Cyst-Ser-Ala-Ser-Cyst-Gly
Val- Cyst-Ala-Ala-Ser-Gly
This is a small, imaginary protein molecule showing how
it acquires a shape
High temperatures or certain chemicals can cause the
protein molecule to lose its shape and its properties.
9. Lipids 8
Lipids are fats and oils
They are made up from glycerol and fatty acids
Examples of fatty acids are stearic acid, oleic acid and
palmitic acid
H2 C O stearic acid
H C O oleic acid A simple lipid
H2 C O palmitic acid
glycerol fatty acids
10. FOOD TESTS
• Scientists often need to know wether or not
a particular type of molecule is present in a
solution.
• For e.g, a doctor might try to detect glucose
in a urine sample (if it is present suggests
the patient has diabetes)
• Simple chemical tests can be carried out on
biological solutions.
11. Test for lipids: The emulsion test
• Ethanol is added to the unknown solution,
and the mixture is gently shaken.
• The mixture is poured into a test tube
containing an equal volume of water.
• If a lipid is present, a milky- white
emulsion is formed.
14. 9
Salts and water
In addition to proteins, carbohydrates and lipids, cytoplasm
contains salts and water
Water makes up the bulk of cytoplasm
All the chemical reactions in cytoplasm take place in
solution, i.e. in water
Water itself takes part in many of these chemical reactions
Salts of sodium, potassium and calcium and many others
play an important part in these reactions
15. 29
Question 1
The correct formula for glucose is
(a) C12H22O11
(b) C5H10O5
(c) C4H8O4
(d) C6H12O6
16. 30
Question 2
Which is the most accurate description of a carbohydrate?
A carbohydrate contains
(a) carbon and oxygen
(b) carbon, oxygen and nitrogen
(c) carbon, hydrogen and oxygen
(d) carbon and hydrogen
17. 31
Question 3
When two molecules of glucose combine, they form
(a) maltose
(b) sucrose
(c) fructose
(d) ribose
18. 32
Question 4
Which is the most accurate description of a protein
Proteins contain
(a) carbon, hydrogen and oxygen
(b) carbon, hydrogen, oxygen and nitrogen
(c) carbon, hydrogen and nitrogen
(d) carbon, nitrogen and oxygen
19. 33
Question 5
Which statements are correct?
Proteins are present in
(a) cell membranes
(b) cell walls
(c) cytoplasm
(d) nucleus
20. 34
Question 6
High temperatures damage proteins by
(a) decomposing them
(b) changing their chemical composition
(c) changing their shape
(d) making them soluble
21. 35
Question 7
A protein is made up of a series of
(a) glucose units
(b) fatty acids
(c) amino acids
(d) carbohydrates
22. 36
Question 8
Lipids are made up of
(a) glycerol and amino acids
(b) glycerol and fatty acids
(c) protein and fatty acids
(d) starch and fatty acids
Editor's Notes
Glucose and fructose occur in fruits, e.g. grapes. Sucrose is the familiar table sugar and comes from sugar beet or sugar cane. Maltose is produced by germinating barley and is the sugar used in brewing beer. Note that the names of most sugars end in ‘-ose’.
Glucose and fructose have the same formula but differ in the way the hydrogen and oxygen atoms are distributed. Maltose and sucrose, with the same formulae, differ in a similar way. Starch is represented by a single long chain of up to 1000 glucose units but, in fact, the main component of starch is a branched chain
Most proteins are very large molecules, made up of hundreds of amino acids. Enzymes are proteins which carry out specific reactions in cells. They are more fully explained in slides 10-28
A protein which loses its shape is said to be denatured . This change cannot be reversed. Egg white is a protein (albumen). When it is heated it is denatured and changes from a clear, runny liquid to a white solid. This cannot be reversed. If an enzyme is denatured it can no longer carry out its normal function.
The fatty acids in a lipid may be all the same. In olive oil, for example, the fatty acid is oleic acid. Alternatively they may be different as shown in the slide.
In photosynthesis (see ‘How Plants Get Their Food’ ) water reacts with carbon dioxide to form glucose. 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2
