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Unit 1.1 MoleculesUnit 1.1 Molecules
Biology Department
Watford Girls Grammar School
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IntroductionFor 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
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WaterWater is a polar molecule It forms weak hydrogen bonds It remains a liquid over a wide
temperature rangeWater molecules stick to one another =
cohesion (surface tension)Water molecules stick to other
substances = adhesion (capillarity)
O
H
H
+
+-
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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 conductorWater is a good solvent
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Carbohydrates Contain the elements Carbon
Hydrogen & Oxygen There are 3 types:
Monosaccharides Disaccharides Polysaccharides
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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 C
C C
C
C
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IsomerismThey can exist as isomers:
& glucose OH
OH
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DisaccharidesFormed from two monosaccharidesJoined by a glycosidic bondA condensation reaction:
glucose + glucose maltose glucose + galactose lactose glucose + fructose sucrose
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Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
OH OH
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Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
OH OH
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Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
O
H2O
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Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
O
A disaccharide1,4 glycosidic bond
41
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PolysaccharidesPolymers formed from many
monosaccharidesThree important examples:
Starch Glycogen Cellulose
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Starch Insoluble store of glucose in plantsformed from two glucose polymers:
Amylose
-glucose
1,4 glycosidic bonds
Spiral structure
Amylopectin
-glucose
1,4 and some 1,6 glycosidic bonds
Branched structure
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Glycogen
Insoluble compact store of glucose in animals
-glucose units1,4 and 1,6
glycosidic bondsBranched structure
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CelluloseStructural polysaccharide
in plants-glucose1,4 glycosidic bondsH-bonds link adjacent
chains
O
O
O
O
O
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LipidsMade up of C, H and OCan exist as fats, oils and waxesThey are insoluble in waterThey are a good source of energy
(38kJ/g)They are poor conductors of heatMost fats & oils are triglycerides
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TriglyceridesFormed by esterification……a condensation reaction between 3
fatty acids and glycerol:
Glycerol
H
C
H C
C
H
H
H
H
O
O
O
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Fatty acidsCarboxyl group (-COOH) attached to a long non-polar
hydrocarbon chain (hydrophobic):
H
H
C
HH
C
H
H
C
HC
O
O
H
C
HH
C
H
H
C
H
H
C
H
H
A saturated fatty acid (no double bonds)
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HH
C
O
O
H
C
HH
C C
C C H
C
H
H
C
H
HA polyunsaturated fatty acid
C
O
O
H
C
HH
C
H
H
C
H
H
C
H
C
HH
C
H
H
C
H
H
A monounsaturated fatty acid
H H
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Esterification
H
C
H C
C
H
H
H
H
O
O
OC
O
O
H
C
HH
C
H
H
C
H
H
C
H
H
Glycerol Fatty acid
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Esterification
H
C
H C
C
H
H
H
H
O
O
OC
O
O
H
C
HH
C
H
H
C
H
H
C
H
H
Glycerol Fatty acid
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Esterification
H
C
H C
C
H
H
H
H
O
O
OC
O
O
H
C
HH
C
H
H
C
H
H
C
H
HGlycerol Fatty acid
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Esterification
H
C
H C
C
H
H
H
H
O
O
OC
O
O
H
C
HH
C
H
H
C
H
H
C
H
H
Ester bond
water
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EsterificationThis happens three times to form a
triglyceride:
glycerol fatty acids
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PhospholipidsOne fatty acid can be replaced
by a polar phosphate group:
glycerol Hydrophobic fatty acids
hydrophilicphosphate
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Functions of lipidsProtection of vital organsTo prevent evaporation in plants &
animalsTo insulate the bodyThey form the myelin sheath around
some neuronesAs a water source (respiration of lipids)As a component of cell membranes
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Proteins Made from C H O N & sometimes SLong chains of amino acidsProperties determined by the aa
sequence
Amino acids
H
CH
N C
HH
O
O
R
~20 aaGlycine R=HAlanine R=CH3
aminecarboxyl
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Peptide bonding
HC
HN C
HH
O
O
R
HC
HN C
HH
O
O
R
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Peptide bonding
HC
HN C
HH
O
O
R
HC
HN C
HH
O
O
R
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Peptide bonding
H
CH
N C
HH
O
O
R
HC
HN C
HH
O
O
R
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Peptide bonding
CH
N C
HH
OR
HC
HN C
H
HO
H
O
O
R
water
Peptide bond
A condensation reaction
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Peptide bonding
CH
N C
HH
OR
HC
HN C
H
O
O
R
A dipeptide
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Primary structureThe sequence of aa is know as the
primary structureThe aa chain is a polypeptide
Secondary structureH-bonding forms between the –COOH
and the -NH2 of adjacent aa
This results in the chains folding:
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Secondary structure
-helix -pleated sheet
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Tertiary structureBonding between R-groups
gives rise to a 3D shapeH-bonds =O HN-
Ionic bonds –NH3-COO-
Disulphide bridge
--CH2S-SCH2-
affected by temp & pH
affected by pH
affected by reducing agents
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Quaternary structureSome proteins have
more than one polypeptide chain
Each chain is held together in a precise structure
eg Haemoglobin
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Types of proteinsFibrous proteins
e.g. collagen Insoluble structural
Globular proteins e.g.enzymes Soluble 3D shape
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Functions of proteins Enzymes – Transport – Movement – Cell recognition – Channels – Structure – Hormones – Protection –
Amylase
Haemoglobin
Actin & myosin
Antigens
Membrane proteins
Collagen & keratin
Insulin
Antibodies
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Nucleic acidsDNA & RNAMade up of nucleotides:
phosphate
pentose sugar
base
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Nucleotides2 types of base:
Pyrimidines - Cytosine C Thymine T
Purines Adenine A Guanine G
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Complimentary base pairingAdenine will only bind with ThymineCytosine will only bind with Guanine
T C GA
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DNA structure
nucleotide
Condensation polymerisation of the deoxyribose nucleotides
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ReplicationDuring cell division the DNA must
replicateThe DNA double helix unwindsThe exposed bases bind to free floating
nucleotides in the nucleoplasmDNA polymerase binds the
complimentary nucleotidesReplication is
semiconservative
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The genetic codeThe sequence of nucleotide bases
forms a codeEach ‘code word’ has three letter – a
triplet codeEach codon codes for a specific amino
acid e.g: GGG = proline CGG = glycine ATG = tyrosine ACT = stop (no amino acid)
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Protein synthesisThe DNA codes for
proteinsA copy of DNA
(mRNA) is made in the nucleus (transcription)
The mRNA is used to make a protein (translation) in the cytoplasm
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TranscriptionThe DNA polymerase
unwinds the DNAFree nucleotides join
onto complimentary bases
RNA polymerase links adjacent nucleotides
The completed mRNA moves out of the nucleus
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Transcription
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Amino acid activation transferRNA:
tRNA binds onto a specific amino acid
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TranslationmRNA binds to a ribosome tRNA carries an amino acid to the
ribosome
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TranslationA second tRNA brings another aaThe two aa’s bindThe process repeats
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TranslationA polypeptide chain formsEventually a stop codon is reached
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The Human Genome Project A multinational project aimed at sequencing
the entire human genome Visit the Human Genome Web site:
www.ornl.gov/hgmis/project/about.html www.sanger.ac.uk
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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.
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Quiz 1. Which of the following is not an
important property of water
a) Its polar nature
b) Its low specific heat capacity
c) Its high latent heat of vaporisation
d) Its low density in solid form
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Quiz 2. The general formula for a
monosaccharide is:
a) (CH2O)n
b) (CHO)n
c) C(H2O)n
d) CnH2On
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Quiz 3. Sucrose is made up of
a) glucose + fructose
b) glucose + galactose
c) glucose + glucose
d) galactose + fructose
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Quiz 4. Amylopectin is made up of:
a) -1,4 glycosidic ondsb) -1,4 & -1,4 glycosidic bonds
c) -1,4 & 1,6 glycosidic ondsd) -1,4 & 1,6 glycosidic onds
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Quiz 5. Formation of a triglyceride does
NOT involve:
a) A condensation reaction
b) Esterification
c) Polymerisation
d) A reaction between 3 fatty acids & glycerol
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Quiz 6. The general formula of a saturated
fatty acid is:
a) CnH2nO2
b) Cn(H2O)n
c) (CH2O)n
d) (CH2)nO
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Quiz 7. Which of the following is not
responsible for a proteins tertiary structure
a) ionic bonding
b) covalent bonding
c) hydrogen bonding
d) disulphide bonding
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Quiz 8. Which of these is not an amino
acid:
a) alanine
b) cysteine
c) glycine
d) cytosine
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Quiz 9. Which process involves tRNA:
a) transciption
b) translation
c) DNA replication
d) gene mutation
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Quiz 10. The formation of RNA does not
involve:
a) ribose sugar
b) thymine
c) removal of water
d) phosphate