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Includes carbohydrates, proteins and fats structures and functions.
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Biological MoleculesBiological Molecules
Biology Department
IntroductionFor each of the following you should be
able to: Describe the properties Know the general formulae & structure Understand the role in animals & plants
•Carbohydrates
•Lipids
•Proteins
•Nucleic acids
Carbohydrates Contain the elements Carbon
Hydrogen & Oxygen There are 3 types:
Monosaccharides Disaccharides Polysaccharides
Monosaccharides
(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
IsomerismThey can exist as isomers:
& glucose OH
OH
DisaccharidesFormed from two monosaccharidesJoined by a glycosidic bondA condensation reaction:
glucose + glucose maltose glucose + galactose lactose glucose + fructose sucrose
Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
OH OH
Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
OH OH
Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
O
H2O
Condensation reaction
O
C C
C C
C
CO
C C
C C
C
C
O
A disaccharide1,4 glycosidic bond
41
PolysaccharidesPolymers formed from many
monosaccharidesThree important examples:
Starch Glycogen Cellulose
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
Glycogen
Insoluble compact store of glucose in animals
-glucose units1,4 and 1,6
glycosidic bondsBranched structure
CelluloseStructural polysaccharide
in plants-glucose1,4 glycosidic bondsH-bonds link adjacent
chains
O
O
O
O
O
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
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
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)
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
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
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
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
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
EsterificationThis happens three times to form a
triglyceride:
glycerol fatty acids
PhospholipidsOne fatty acid can be replaced
by a polar phosphate group:
glycerol Hydrophobic fatty acids
hydrophilicphosphate
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
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
Peptide bonding
HC
HN C
HH
O
O
R
HC
HN C
HH
O
O
R
Peptide bonding
HC
HN C
HH
O
O
R
HC
HN C
HH
O
O
R
Peptide bonding
H
CH
N C
HH
O
O
R
HC
HN C
HH
O
O
R
Peptide bonding
CH
N C
HH
OR
HC
HN C
H
HO
H
O
O
R
water
Peptide bond
A condensation reaction
Peptide bonding
CH
N C
HH
OR
HC
HN C
H
O
O
R
A dipeptide
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:
Secondary structure
-helix -pleated sheet
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
Quaternary structureSome proteins have
more than one polypeptide chain
Each chain is held together in a precise structure
eg Haemoglobin
Types of proteinsFibrous proteins
e.g. collagen Insoluble structural
Globular proteins e.g.enzymes Soluble 3D shape
Functions of proteins Enzymes – Transport – Movement – Cell recognition – Channels – Structure – Hormones – Protection –
Amylase
Haemoglobin
Actin & myosin
Antigens
Membrane proteins
Collagen & keratin
Insulin
Antibodies
Nucleic acidsDNA & RNAMade up of nucleotides:
phosphate
pentose sugar
base
Nucleotides2 types of base:
Pyrimidines - Cytosine C Thymine T
Purines Adenine A Guanine G
Complimentary base pairingAdenine will only bind with ThymineCytosine will only bind with Guanine
T C GA
DNA structure
nucleotide
Condensation polymerisation of the deoxyribose nucleotides
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
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)
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
TranscriptionThe DNA polymerase
unwinds the DNAFree nucleotides join
onto complimentary bases
RNA polymerase links adjacent nucleotides
The completed mRNA moves out of the nucleus
Transcription
Amino acid activation transferRNA:
tRNA binds onto a specific amino acid
TranslationmRNA binds to a ribosome tRNA carries an amino acid to the
ribosome
TranslationA second tRNA brings another aaThe two aa’s bindThe process repeats
TranslationA polypeptide chain formsEventually a stop codon is reached
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
Quiz 1. The general formula for a
monosaccharide is:
a) (CH2O)n
b) (CHO)n
c) C(H2O)n
d) CnH2On
Quiz 2. Sucrose is made up of
a) glucose + fructose
b) glucose + galactose
c) glucose + glucose
d) galactose + fructose
Quiz 3. 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
Quiz 4. Formation of a triglyceride does
NOT involve:
a) A condensation reaction
b) Esterification
c) Polymerisation
d) A reaction between 3 fatty acids & glycerol
Quiz 5. The general formula of a saturated
fatty acid is:
a) CnH2nO2
b) Cn(H2O)n
c) (CH2O)n
d) (CH2)nO
Quiz 6. Which of the following is not
responsible for a proteins tertiary structure
a) ionic bonding
b) covalent bonding
c) hydrogen bonding
d) disulphide bonding
Quiz 7. Which of these is not an amino
acid:
a) alanine
b) cysteine
c) glycine
d) cytosine
Quiz 8. Which process involves tRNA:
a) transciption
b) translation
c) DNA replication
d) gene mutation
Quiz 9. The formation of RNA does not
involve:
a) ribose sugar
b) thymine
c) removal of water
d) phosphate
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