1. Biology Department Watford Girls Grammar School
Unit 1.1 Molecules
Biology Department
Watford Girls Grammar School

2. Introduction For each of the following you should be able to:
Describe the properties
Know the general formulae & structure
Understand the role in animals & plants
Water
Carbohydrates
Lipids
Proteins
Nucleic acids

3. Water - Water is a polar molecule It forms weak hydrogen bonds+ O - H +
Water is a polar molecule
It forms weak hydrogen bonds
It remains a liquid over a wide temperature range
Water molecules stick to one another = cohesion (surface tension)
Water molecules stick to other substances = adhesion (capillarity)

4. Water
It has a high specific heat capacity – so water can maintain a reasonably constant temperature (homeostasis)
It has a high latent heat of vaporisation – so animals use water to cool themselves
It is less dense as a solid (ice)…
… and ice is a poor conductor
Water is a good solvent

5. Carbohydrates Contain the elements Carbon Hydrogen & Oxygen
There are 3 types:
Monosaccharides
Disaccharides
Polysaccharides

6. Monosacharides (CH2O)n If n=3, triose (glyceraldehyde)
If n=5, pentose (fructose, ribose)
If n=6, hexose (glucose, galactose)
Monosaccharides are used for
Energy
Building blocks O C

7. Isomerism
They can exist as isomers:
 &  glucose OH   OH

8. Disaccharides Formed from two monosaccharides
Joined by a glycosidic bond
A condensation reaction:
glucose + glucose  maltose
glucose + galactose  lactose
glucose + fructose  sucrose

9. Condensation reactionOH OH

10. Condensation reactionOH OH

11. Condensation reaction
H2O

12. Condensation reaction1 4 O
A disaccharide
1,4 glycosidic bond

13. Polysaccharides Polymers formed from many monosaccharides
Three important examples:
Starch
Glycogen
Cellulose

14. Starch Insoluble store of glucose in plants formed from two glucose polymers:
Amylose
-glucose
1,4 glycosidic bonds
Spiral structure
Amylopectin
-glucose
1,4 and some 1,6 glycosidic bonds
Branched structure

15. Glycogen Insoluble compact store of glucose in animals -glucose units
1,4 and 1,6 glycosidic bonds
Branched structure

16. Cellulose Structural polysaccharide in plants -glucose
1,4 glycosidic bonds
H-bonds link adjacent chains

17. Lipids Made up of C, H and O Can exist as fats, oils and waxes
They are insoluble in water
They are a good source of energy (38kJ/g)
They are poor conductors of heat
Most fats & oils are triglycerides

18. Triglycerides Formed by esterification…
…a condensation reaction between 3 fatty acids and glycerol: H C O
Glycerol

19. Fatty acids Carboxyl group (-COOH)
attached to a long non-polar hydrocarbon chain (hydrophobic): C O H H C H C H C H
A saturated fatty acid (no double bonds)

20. A monounsaturated fatty acidH C H H C H C O C H C H C H C C O H H
A monounsaturated fatty acid H C H H H C O C C H C H C C C O H H H
A polyunsaturated fatty acid

21. Esterification H C O C O H
Fatty acid
Glycerol

22. Esterification H C O C O H
Fatty acid
Glycerol

23. Esterification Fatty acid Glycerol C O H H C O H C H H C H O H C H C C

24. Esterification Ester bond water C O H H C O H C H H C H O H C H C C C

25. Esterification This happens three times to form a triglyceride:
glycerol
fatty acids

26. Phospholipids One fatty acid can be replaced
by a polar phosphate group:
hydrophilic
phosphate
glycerol
Hydrophobic fatty acids

27. Functions of lipids Protection of vital organs
To prevent evaporation in plants & animals
To insulate the body
They form the myelin sheath around some neurones
As a water source (respiration of lipids)
As a component of cell membranes

28. Proteins Amino acids Made from C H O N & sometimes S
Long chains of amino acids
Properties determined by the aa sequence
Amino acids H C N O R
~20 aa
Glycine R=H
Alanine R=CH3
amine
carboxyl

29. Peptide bonding H C N O R H C N O R

30. Peptide bonding H C N O R H C N O R

31. Peptide bonding R R O O H H N C C N C C H O H H H H H O

32. Peptide bonding R R O O H H N C C N C C H O H H H Peptide bond H O
A condensation reaction
water

33. Peptide bonding C H N O R R O N C C O H H H
A dipeptide

34. Primary structure Secondary structure
The sequence of aa is know as the primary structure
The aa chain is a polypeptide
Secondary structure
H-bonding forms between the –COOH and the -NH2 of adjacent aa
This results in the chains folding:

35. Secondary structure
-helix
-pleated sheet

36. Tertiary structure Bonding between R-groups gives rise to a 3D shape
H-bonds =O HN-
Ionic bonds –NH3-COO-
Disulphide bridge
--CH2S-SCH2-
affected by temp & pH
affected by pH
affected by reducing agents

37. Quaternary structure
Some proteins have more than one polypeptide chain
Each chain is held together in a precise structure
eg Haemoglobin

38. Types of proteins Fibrous proteins Globular proteins e.g. collagen
Insoluble
structural
Globular proteins
e.g.enzymes
Soluble
3D shape

39. Functions of proteins Enzymes – Transport – Movement –
Cell recognition –
Channels –
Structure –
Hormones –
Protection –
Amylase
Haemoglobin
Actin & myosin
Antigens
Membrane proteins
Collagen & keratin
Insulin
Antibodies

40. Nucleic acids DNA & RNA Made up of nucleotides: phosphate base
pentose sugar

41. Nucleotides 2 types of base: Pyrimidines - Purines Cytosine C
Thymine T
Purines
Adenine A
Guanine G

42. Complimentary base pairing
Adenine will only bind with Thymine
Cytosine will only bind with Guanine T A C G

43. DNA structure nucleotide Condensation polymerisation of the
deoxyribose nucleotides

44. Replication During cell division the DNA must replicate
The DNA double helix unwinds
The exposed bases bind to free floating nucleotides in the nucleoplasm
DNA polymerase binds the complimentary nucleotides
Replication is
semiconservative

45. The genetic code The sequence of nucleotide bases forms a code
Each ‘code word’ has three letter – a triplet code
Each codon codes for a specific amino acid e.g:
GGG = proline
CGG = glycine
ATG = tyrosine
ACT = stop (no amino acid)

46. Protein synthesis The DNA codes for proteins
A copy of DNA (mRNA) is made in the nucleus (transcription)
The mRNA is used to make a protein (translation) in the cytoplasm

47. Transcription The DNA polymerase unwinds the DNA
Free nucleotides join onto complimentary bases
RNA polymerase links adjacent nucleotides
The completed mRNA moves out of the nucleus

48. Transcription

49. Amino acid activation transferRNA:
tRNA binds onto a specific amino acid

50. Translation mRNA binds to a ribosome
tRNA carries an amino acid to the ribosome

51. Translation A second tRNA brings another aa The two aa’s bind
The process repeats

52. Translation A polypeptide chain forms
Eventually a stop codon is reached

53. The Human Genome Project
A multinational project aimed at sequencing the entire human genome
Visit the Human Genome Web site:

54. Acknowledgements
Animated cell models used by kind permission of The Virtual Cell website:
Feel free to use this presentation for educational non-profit making purposes.

55. Quiz 1. Which of the following is not an important property of water
Its polar nature
Its low specific heat capacity
Its high latent heat of vaporisation
Its low density in solid form

56. Quiz 2. The general formula for a monosaccharide is: (CH2O)n (CHO)n
CnH2On

57. Quiz 3. Sucrose is made up of glucose + fructose glucose + galactose
glucose + glucose
galactose + fructose

58. Quiz 4. Amylopectin is made up of: -1,4 glycosidic bonds

59. Quiz 5. Formation of a triglyceride does NOT involve:
A condensation reaction
Esterification
Polymerisation
A reaction between 3 fatty acids & glycerol

60. Quiz 6. The general formula of a saturated fatty acid is: CnH2nO2
Cn(H2O)n
(CH2O)n
(CH2)nO

61. Quiz
7. Which of the following is not responsible for a proteins tertiary structure
ionic bonding
covalent bonding
hydrogen bonding
disulphide bonding

62. Quiz 8. Which of these is not an amino acid: alanine cysteine glycine
cytosine

63. Quiz 9. Which process involves tRNA: transciption translation
DNA replication
gene mutation

64. Quiz 10. The formation of RNA does not involve: ribose sugar thymine
removal of water
phosphate