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Chapter 3
Molecular Components of
Cells
Molecular Components of Cells
 Chemical composition
 C, H, N, O and small amount of other elements
 Molecular building blocks




Lipids
Carbohydrates
Proteins
Nucleic acid
• DNA (deoxyribonucleic acid)
• RNA (ribonucleic acid)
Atoms, Ions, and Molecules
 Atoms




Smallest piece of an recognizable element
Nucleus (proton + neutron) + electron
Same number of protons and electrons : no charge
Biologically important atoms:
• C, H, O, N : > 99% of cell mass
• S, P, Na, K, Ca, Cl
 Ions
 Electrically charged atoms
 Biological importance: electrical impulse, ion balance
• Ca2+, Na+, K+, Cl-
 Molecules
 Generated from chemical bonding of atoms
Energetics and Carbon Flow
Subunits of Biological Molecules
Class of Molecules Examples
Repeating Unit
Lipid
Fats, oils
Glycerol, fatty acid
Carbohydrate
Sugars, starch,
cellulose
Simple sugars
Nucleic acid
DNA, RNA
Nucleotide
Proteins
Enzymes
Amino acids
Chemical composition of living cells
Table. Overall Macromolecular Composition of an
Average Cell of E. coli
Percentage of
Macromolecules
Different kinds of molecules
total dry weight
Protein
55.0
RNA
20.5
1050
rRNA
16.7
3
tRNA
3.0
60
mRNA
0.8
400
DNA
3.1
1
Lipid
9.1
4
Lipopolysaccharide
3.4
1
Peptidoglycan
2.5
1
Glycogen
2.5
1
Soluble pool
3.9
Media elemental composition
Element
Chemical forms
%(Dry
cell Wt)
Carbon
Glc, malate, AA, acetate, YE, peptone
50
Nitrogen
N2, Inorganic & organic nitrogen cpds
14
Oxygen
O2, H2O, organic cpds
20
Hydrogen
H2O, organic cpds
8
Phosphorous
PO4-3
3
Sulfur
H2S, SO4-2
1
Potassium
K salts
1
Magnesium
Mg2+ salts
0.5
Sodium
NaCl and Na+ salts
1
Calcium
CaSO4 and Ca2+ salts
0.5
Iron
FeS or Fe2+ and Fe3+ salts
0.2
Defined vs. Complex media
Complex media for E.coli
MM media for B. megatrium
Component
Amount
Function of
component
Compone Amount
nt
sucrose
10.0 g
C and energy
source
Glucose
15g
K2HPO4
2.5 g
pH buffer; P
and K source
Yeast
Extract
5g
KH2PO4
2.5 g
pH buffer; P
and K source
Peptone
5g
(NH4)2HPO4
1.0 g
pH buffer; N
and P source
KH2PO4
2g
Distilled
H2O
1000mL
Mg++
MgSO4 7H2O
0.20 g
S and
source
FeSO4 7H2O
0.01 g
Fe++ source
MnSO4 7H2O
0.007 g
Mn++ Source
water
985 ml
pH 7.0
pH 7
Function
Comparison of amino acid compositions
in cell
Various mammalian cell
Amino Acids (1997) 13:379-391
1
Lipids
2
Carbohydrates
3
4
Proteins
Nucleic acids
Lipids
 Characteristics
 Water insolubility
 Diverse structures
 Functions
 Energy storage : high energy C-H, C-C bonds
• Fats : fatty acid + glycerol
 Components of biological membrane
• Phospholipids
• Cholesterol
 Signals
• Steroid hormones
 Enzyme cofactors
• Vitamins
Fats
 Structure
 Glycerol + 3 fatty acids linked
by ester linkage
 Function
 Energy storage
 Other names
 Triacylglycerol, triglycerides,
neutral fats
 Oil : liquid at room
temperature
Fatty Acids
 Saturated fatty acids
 Tight packing  High melting point
 Solid at room temperature
 Unsaturated fatty acids
 More than one cis-double bond  Low melting point
 Lliquid at room temperature
Phospholipids
 Structure
 Glycerol backbone
 two fatty acids (hydrophobic)+ phosphate (hydrophilic)
 Additional small polar molecules bound to phosphate group
 Function
 Major component of cellular membrane
Sterols
 Structure
 Cyclic hydrocarbon compounds
 Planar and rigid rings
• 3 with C6 and 1 with C5
 Cholesterol
 Component of animal cell membranes
• Decrease membrane fluidity
 Starting material for steroid hormones and bile synthesis
Vitamins
 Vitamin A, D, E, K
Vitamin A
(retinol)
Vitamin D2
1
Lipids
2
Carbohydrates
3
Proteins
4
Nucleic acids
Carbohydrates
 Structure
 Polyhydroxy aldehydes or ketones
 C:H:O = 1:2:1
 Classes of carbohydrates
 Simple sugars (monosaccharide)
• 3 to 7 carbons
• Aldose: aldehyde group, e.g) glucose, galactose
• Ketose: ketone , e.g) fructose
 Disaccharides
• Simple sugars linked by glycosidic bond
– Sucrose: glucose (a1↔2b) fructose
– Lactose : galactose (b14) glucose
– Maltose : glucose (a1  4) glucose
 Oligosaccharides
 Polysaccharides
Cyclic Structure of Monosaccharides
 Formation of cyclic
structure
 Monosaccharides with 5
or more carbons
Carbohydrates
OH
2
1
1
CH2OH
Glc (a1↔2b)Fru
Gal (b14)Glc
Carbohydrates
 Polysaccharide
 Starch, Glycogen, cellulose from glucose
 Agar, carrageenan (thickener)
Cellulose
b-1,4 glycosidic linkage
Starch,
glycogen
a-1,6 glycosidic
linkage
a-1,4 glycosidic linkage
Starch
Glycogen
Roles of Carbohydrates I
 Carbohydrates in energy metabolism
 Plant
• Glucose synthesis by photosynthesis
6CO2 + 6H2O + energy  C6H12O6 + 6O2
• Starch for energy storage
• cellulose for structural compound
 Animals
• Intake glucose from food
• Glycogen for energy storage
Roles of Carbohydrates II
 Carbohydrates in molecular recognition
 Cellular recognition, cell signaling, cell adhesion
 e.g. blood typing : sugar chains in the membrane of RBC
1
Lipids
2
Carbphydrates
3
Proteins
4
Nucleic acids
Proteins
 Roles of proteins
 Most of the cellular functions
• Enzymes : chemical reactions
• Receptors : signal transduction
• Antibody : recognition of foreign molecules and trigger
immune responses
• Transporters : e.g. hemoglobin for oxygen
• Structural proteins : keratin (hair and nails), actin and myosin
(muscle)
 Diversity of organism
• Due to diversity in organization of proteins within an
organism
Proteins
 Amino acids
 Building blocks of proteins
 Hydrophilic backbone + 20
side chains
 Polypeptide
 Amino acid chains linked by
peptide bond
 Three-dimensional
structure
 Determines protein function
 Determined by amino acid
sequence
1
Lipids
2
Carbphydrates
3
4
4
Proteins
Nucleic acids
Nucleic acids
 Nucleotides
 Building blocks of nucleic acids
 2’(deoxy)ribose + phosphate group
+ 4 bases
 Bases: adenine (A), guanine (G),
cytosine (C), thymine (T)
o
 Terminology
 Base
 Nucleoside : sugar + base
 Nucleotide : sugar + base +
phosphate
o
Primary Structure : Nucleotides
Base
Nucleoside
Nucleotide
Adenine
Adenosine
Adenylate
Guanine
Guanosine
Guanylate
Cytosine
Cytidine
Cytidylate
Thymine (D)
Thymidine
Thymidylate
Uracil (R)
Uridine
Uridylate
Purine
Pyrimidine
H
2’-Deoxyribose
RNA
DNA
Nucleotide Chains
 Linkage of 5’ carbon to 3’ carbon through
phosphodiester bond
Base Pairing
 C=G, T=A : hydrogen
bonding
 Complementary base pairs
 Antipararallel strand in DNA
molecule
DNA Double Helix
Chromosome
 Tightly packed complex of DNA and histone proteins
DNA Replication
 Synthesis of a complementary strand using the other strand as a
template
 DNA polymerase
Expression of Genetic Information
Replication
DNA
Transcription
mRNA
Translation
Protein
Differences Between DNA and RNA
Properties
DNA
RNA
Chemical
Deoxyribose
ribose
Tymine
Uracil
Double strand
Single strand
Structural
Balanced growth
  max 
 Monod Equation
 Substrate-limited growth
 Exponential phase in
Semi-log plot: slope =
S 

 Ks  S 
max