AS Biology

1
AS Biology

• Biological molecules

2
OBJECTIVES

• All should be able to describe the structure of
  a water molecule,the H bonds that hold them
  together and understand this is responsible for
  its unusual properties. Be able to describe some
  of the properties of water and link some to its
  structure and importance to living organisms
• Some may be able to take this a stage further
  and give detailed explanations of how the H bonds
  in water control the properties that are so
  important for living organisms

3


Unit 2 Module 1 Biological molecules
l
4
structural proteins
transport protein
water
DNA
Proteins
enzymes
nucleic acids
RNA
Unit 2 Module 1 Biological molecules
phospholipids
carbohydrates
saccharides
lipids
triglycerides
polysaccharides
cholesterol
structural
storage
5
(No Transcript)
6
The Elements of life

• 92 naturally occurring elements
• The atoms of only 16 are commonly found in living
  organisms
• 4 account for 99 of the atoms found in living
  organisms,these are in order of abundance
• H hydrogen
• C carbon
• O oxygen
• N nitrogen
• This is because living organisms are made up of
  organic molecules
• Others are calcium(Ca),iron(Fe),potassium(K),sodiu
  m(Na), chlorine(Cl),sulphur(S) magnesium(Mg)

7
Bonding

• Atoms are joined together to make molecules and
  compounds
• This is done by chemical bonds
• Most of the molecules making up living organisms
  have atoms joined by covalent bonds
• Covalent bonds are shown by lines.They can be
  single,double or treble.They are formed by
  sharing electrons

Glycine an amino acid
8
Covalent bonding

• Carbon always has 4 covalent bonds with other
  atoms. Terrestrial life forms are carbon based.
  This multiple bonding allows carbon to be a
  framework atom
• All the biological molecules we will learn about
  use carbon as a framework atom.
• Other bonds formed are Oxygen 2 ,hydrogen 1
  nitrogen 3

ethanol
ethene
9
Covalent bonding

10
The building blocks of life

• Living organisms are mainly made up of
  macromolecules (giant molecules)
• These are polymers made up of many smaller
  monomers by a process called polymerisation
• The main macromolecules are
• Polysaccharides
• Nucleic acids
• Proteins (polypeptides)
• Lipids (fats)

11
The Building Blocks of life

• MONOMER POLYMER

Organic base, sugar phosphate
Amino acids
Fatty acids glycerol
monosaccharide
nucleotides
Nucleic acids
polysaccharide
lipids
proteins
12
Carbohydrates

• All contain the elements carbon, hydrogen
  oxygen
• The name comes from hydrated carbon!
• For every carbon atom there is a water
• General formula for carbohydrate is
  
• Cn(H2O)n
• Q. Fructose has 6 carbons, what is it formula?
  What about ribose which is a pentose sugar?
• There are 2 types of carbohydrate
• 1. Simple sugars Monosaccharide Disaccharides
• 2. Polysaccharides

13
Simple sugars Monosaccharides

• Sugars all end in -ose
• White,crystalline substances,dissolve easily in
  water to give sweet solutions.
• Single sugar molecule mono one
• General formula (C H2O)n where n is the number
  of carbon atoms
• So if 6 carbon atoms(a hexose sugar) the
  molecular formula is C6H12O6
• What about pentose sugars(C5) or triose
  sugars(C3)?

14
Glucose

• Most important and widespread monosaccharide.
• Hexose sugar
• The 6 carbons are numbered
• FunctionTransported around in the blood and used
  in cells as a source of energy in respiration.
  The energy is released in the form of ATP

Structural formula
1
2
3
4
5
6
Molecular formula C6H12O6
15
The ring form of glucose

• The chain of carbons in hexose(and pentose)
  sugars is long enough to close up and form a more
  stable ring structure
• Carbon atom 1 joins to the oxygen on carbon atom 5

16
Glucose isomers

• The new OH formed in the reaction can be above
  the ring - ß glucose or below - a glucose
• These are isomers-two forms of the same chemical.

17
Triose,pentose hexose sugars
18
Roles of monosaccharides in living organisms

• A source of energy for respiration.
• Due to large number of C-H bonds which when
  broken release a lot of energy
• This energy is used to make ATP(adenine
  triphosphate) from ADP(adenine diphosphate)
• Also used as building blocks to make larger
  molecules for example
• Deoxyribose(pentose) used to make DNA
• Ribose used to make RNA and ATP
• Glucose makes up starch,cellulose and glycogen.

19
Disaccharide formation

• Two glucose molecules are held close together by
  an enzyme.
• Water is lost and a 1-4 glycosidic bond(link)
  formed .
• This is a condensation reaction
• The new molecule is a disaccharide - maltose

20
A disaccharide - maltose
1-4 glycosidic link
21
Common Disaccharides
22
Hydrolysis of maltose by enzyme maltase
23
Chemical test for saccharides(sugars)

• Reducing Sugars
• Heat the sugar solution with an equal volume of
  blue benedict's solution for 2-3 minutes at about
  90C
• A positive result is a brick red precipitate
• Benedicts solution contains blue Cu2 ions, the
  sugar reduces this to the insoluble brick red Cu
  compound
• Cu2 Cu

Electron From sugar
24
Non reducing sugar test

• Some sugars are non reducing.
• They do not reduce benedict's solution
• One example is sucrose, it must be
  hydrolysed(broken-down by adding water) to form
  glucose and fructose
• This can be done by heating with a few drops of
  acid at 90C for a few minutes. Then neutralising
  the solution with an equal amount of sodium
  hydroxide solution
• You will then get a positive result when
  repeating the benedict's test

25
Sugar Type of saccharide? Result of benedicts test for reducing sugar Result of non-reducing sugar test Reducing or non-reducing sugar?
lactose
fructose
glucose
sucrose
maltose
26
Quantitative Estimation of glucose concentration
in a solution
Glucose solution() Weight of precipitate (g) Light Transmission of filtrate ()
0
0.01
0.05
0.1
0.5
1
27
Sugars homework

• a. Glyceraldehyde C3 Triose
• Ribose C5 Pentose
• Glucose Fructose C6 Hexose
• b. Glucose is an aldose sugar H-CO is on
  C1
• c.

28
d
29

• e alpha glucose OH below the ring
• beta glucose OH above ring
• f
  alpha galactose

30
Polysaccharide- Structure Function

• Polysaccharides are polymers made up of
  monosaccharide subunits
• The polymers can be many thousand monosaccharides
  making macromolecules
• Most important are starch,glycogen cellulose
• All are polymers of glucose
• They are insoluble in water and do not taste
  sweet.

31
Starch

• Made up of a mixture of two macromolecules
• Amylose (20) and amylopectin (80)

32
Amylose

• Amylose is formed by condensation of a long chain
  of a glucose using 1a 4 glycosidic bonds

33
Amylose a helix

• The 1a 4 glycosidic links in amylose mean the
  glucose monomers are at a slight angle to each
  other
• This causes a helix to form
• This is stabilised by hydrogen bonds

34
Amylopectin

• Branching chains of a glucose
• Branches about once every 25 glucose
• Branches formed by 1-6 glycosidic bonds
• The branching structure gives many ends to
  attach new glucose or to remove it. So it is
  ideal for storing glucose

35
Starch Role in living organisms

• Starch is a store of glucose in plants
• Plants cannot store sugars as this would increase
  the osmotic potential (low water potential) of
  the cells,the solution inside the cells would be
  too concentrated.
• This would lead to .
• Starch is insoluble and has no osmotic effect

36
Starch Grains

• In plants starch is stored as starch grains
• These are most often found in chloroplasts or in
  specialised plant structures such as seeds or
  tubers eg potatoes
• The helical shape of amylose means it can be
  packed tightly

37
Chemical test for Starch

• Add iodine solution to the material
• Iodine solution is orange brown
• A blue black colour is produced on contact with
  starch
• This is because the iodine molecules fit into the
  amylose helix giving the colour

38
Glycogen

• Starch is not found in animal cells
• Glycogen is used to store glucose in animal cells
• It is very similar to amylopectin but more
  branched
• It branches every 8-10 glucoses,again giving
  plenty of ends to add extra glucose
• It forms granules which can be seen in muscle
  liver cells

39
Cellulose

• Cellulose makes up plant cell walls
• It is a structural polysaccharide
• It is made up of ß glucose where OH is above the
  ring
• In order to form a glycosidic bond the other
  glucose must be upside down.
• The bond formed is a ß1-4 glycosidic bond

40
Cellulose cross links

• Cellulose cannot form a helix
• It exists in long chains
• Chains lie side by side and hydrogen bonds form
  between them
• These form between adjacent glucose molecules and
  between the chains.

41

• This gives the cellulose molecule great
  mechanical strength
• They are insoluble,tough,durable and slightly
  elastic, ideal structural components
• 60-70 chains are strongly linked together to form
  bundles called microfibrils
• Microfibrils are held together in fibres
• Fibres make up the plant cell wall

42
Structure of cellulose
43

• Cellulose fibres are laid down in layers to form
  the cell wall
• Fibres are at right angles to increase strength
• Other molecules help cross linking
• Older cell walls are reinforced with lignin
• A glue like matrix(pectins) is laid down in
  between the fibres to increase strength
• Similar to reinforced concrete

44
Cellulose structure function

• High tensile strength of cellulose fibres means
  they are difficult to break if pulled at both
  ends
• Allows the cell to withstand the pressure caused
  when water enters by osmosis.
• Gives plant cells strength and rigidity
• Provides support
• Despite strength they are freely permeable
• Even though cellulose contains glucose it cannot
  be digested by most animals as they do not have
  the required enzyme cellulase

45
Other structural polysaccharides

• Chitin
• Exoskletons of arthropods
• Peptidoglycan
• Cell wall of bacterial cells

46
(No Transcript)
47
(No Transcript)
48
Lipids

• This group contains a wide range of molecules
  ranging from fats,oils,phospholipids,waxes
  steroids
• They all contain the elements C,H O
• Normally much less O
• The most widespread are TRIGLYCERIDES also known
  as fats or oils

49
Triglyceride structure

• Made up of 3 FATTY ACID molecules
• And 1 GLYCEROL molecule

50
Fatty Acid structure

• Stearic acid an example of a saturated fatty
  acid.
• All the carbon atoms in the tail are
  full,saturated with hydrogen

Can also be written as CH3(CH2)16COOH
51

• The COOH group is called a CARBOXYLIC ACID group
• The long tail of the molecule is called a
  HYDROCARBON TAIL
• This hydrocarbon chain will not dissolve in water
  it is said to be non-polar or hydrophobic(water
  hating)

52

• The carboxylic acid group is polar or
  hydrophilic(water loving)

53
Unsaturated Fatty Acids

• These fatty acids contain a double bond
• It causes a kink in the tail
• These fatty acids melt more easily
• One double bond is monounsaturated
• More than one are called polyunsaturated

54
Glycerol structure

• Glycerol is a type of alcohol with 3 alcohol
  groups.

55
Forming a triglyceride

• When glycerol combines with a fatty acid it forms
  a glyceride
• When it combines with 3 fatty acids it is a
  triglyceride
• They combine in a condensation reaction, losing
  water
• Forming an ester link

56
Properties

• Triglycerides are insoluble in water, they are
  non-polar molecules
• The more unsaturated fatty acids the lower the
  melting point making these oils at room
  temperature, normally found in plants
• Animal fats have a higher melting point and are
  generally solid at room temperature due to
  saturated fatty acids

57
Roles of triglycerides

• ENERGY RESERVES- high number of C-H bonds so
  much more energy content than carbohydrate-so you
  need to store less to get the same energy
• In humans stored around organs and under the skin

58

• Stored in adipose tissue

59

• Under the skin it is also INSULATION eg blubber
  in sea mammals
• It can also produce metabolic water when used in
  respiration by desert animals such as camels
• Insoluble so no osmotic effect

60
Phospholipids

• In this molecule the glycerol has two fatty acids
  attached
• On the 3rd carbon is a phosphate group

61
Phospholipid examples
62
Phospholipid properties and roles

• These molecules have a hydrophobic tail and
  hydrophilic head
• They form the membranes of living cells

63
Cholesterol

• Not formed from fatty acids and glycerol
• 4 carbon based rings
• Small hydrophobic molecule
• Found between phospholipid tails in membranes
• Controls membrane fluidity and mechanical strength

64
Excess cholesterol

• Many cells make cholesterol from saturated fats
• Especially liver cells
• Excess can be deposited in artery walls
• Causing atherosclerosis

65

• Excess cholesterol is removed in bile
• It can form gallstones in the gall bladder

66
Steroid hormones

• These are made from cholesterol and include

67
Chemical test for Lipids

• Emulsion test
• Add ethanol to the suspect material and mix well
  (any fat will dissolve in the alcohol)
• Filter off the ethanol
• pour the ethanol into water
• A milky emulsion will form if fat was present(fat
  can no longer dissolve and forms small droplets

68
Proteins(Polypeptides)

• Proteins make up more than 50 of the dry mass of
  cells
• They have many important functions
• All proteins are made up of amino acids
• Functions of proteins

69
active transport
channel protein
Respiration/ photosynthesis
complex
intracellular (metabolic)
glycoprotein
enzymes
membrane
Extracellular (digestive)
Albumin/ globulin
globular
blood
transport
antibodies
haemoglobin
Proteins in living organisms
hormones
collagen
fibrous
contractile
structural
elastin
blood
Fibrinogen (fibrin)
Actin/myosin (muscles)
keratin
70















Proteins in living organisms









71
Amino Acid Structure

• NH2 is the a amine or amino group
• COOH is the carboxylic acid group
• The R group or amino acid side chain varies.
• There are 20 different R groups found in nature
  so giving 20 different naturally occuring amino
  acids

72

• The 20 naturally occurring amino acids R groups

73
(No Transcript)
74
Amino Acids
75
The Peptide Bond

• Amino acids are joined together by a peptide bond
• Two amino acids joined form a dipeptide

76
Peptide bond formation
77
Polypeptide formation

• Adding more amino acids to the chain forms a
  polypeptide
• In cells this occurs in ribosomes
• A protein molecule may contain many hundred AAs
  and sometimes more than one polypeptide chain

78
Protein Primary structure

• The sequence of the amino acids in the
  polypeptide is known as its primary structure
• A protein of several hundred amino acids has a
  huge number of possible primary structures
• A change in one of the AAs can completely alter
  the properties of the protein

79
Protein- Secondary Structure

• This is when parts of the polypeptide chain
  becomes twisted or folded
• There are 2 main types of 2 structure
• ? helix
• ? pleated sheet

80
Polypeptide a helix

• Proteins form this stable helix due to hydrogen
  bonding
• This takes place between CO of one A.A
• And the N-H of the A.A 4 places ahead

81
Polypeptide - ß Pleated Sheet

• This looser, straighter shape is also formed by H
  bonds.
• This time between CO and N-H of adjacent chains

82

• Proteins may contain both of these secondary
  structures
• They are easily disrupted by heat changes in pH

83
Biological molecules chemical tests

• Reducing Sugars
• Heat the sugar solution with an equal volume of
  blue benedict's solution for 2-3 minutes at about
  90C
• A positive result is a brick red precipitate
• Non reducing sugar (sucrose)
• Collect some filtrate from the reducing sugar
  test
• Add a few drops of acid and heat in a water bath
  for a few minutes
• Neutralise with an equal amount of sodium
  hydroxide solution
• Repeat the benedicts test, a brick red ppt is a
  positive result
• Starch
• Add orange brown iodine solution to the material
• A blue black colour is produced on contact with
  starch
• Protein
• Biuret reagent is made by combining equal amounts
  of Sodium Hydroxide and Copper Sulphate
• Add biuret reagent to the suspect food or add
  some dilute sodium hydroxide solution and mix
  followed by a little dilute copper sulphate
  solution.
• The copper ions interact with the amino groups in
  the protein to give PURPLE colour for a positive
  result
• If the solution stays BLUE this is a negative
  result

84
Food Testing

• Starch
• Add orange brown iodine solution to the material
• A blue black colour is produced on contact with
  starch
• Protein
• Biuret reagent is made by combining equal amounts
  of Sodium Hydroxide and Copper Sulphate
• Add biuret reagent to the suspect food or add
  some dilute sodium hydroxide solution and mix
  followed by a little dilute copper sulphate
  solution.
• The copper ions interact with the amino groups in
  the protein to give PURPLE colour for a positive
  result
• If the solution stays BLUE this is a negative
  result