Biochemistry and the
Organization of Cells
Chapter 1
Levels of Structural Organization in the
Human Body
Why is study of Biochemistry
important?
• Biochemistry describes life processes
• Multidisciplinary nature allows it use other
sciences to answer questions about molecular
nature of life processes
• Some biomolecules act in multiple ways and
some take part in specific series of reactions
• More complex cells are found in larger
organisms than simpler organisms
How is Biochemistry related to
Organic Chemistry?
• Organic Chemistry is study of compounds of
carbon and hydrogen and their derivatives
• Biomolecules are made up of carbon
• Many carbon compounds are not found in any
organism
• Biomolecules of life can be synthesized in
laboratories (synthesis of urea from
ammonium cyanate by Friedrich Wohler in
1828)
• Functional group: an atom or group of atoms that
shows characteristic physical and chemical properties
What makes biomolecules special?
• Biomolecules have important functional groups
• Emphases of functional groups differ in Organic
chemistry (alkyl halides and acyl chlorides) and in
Biochemistry (carbonyl groups, hydroxyl groups,
carboxyl groups, amines, amides and esters).
• Derivatives of phosphoric acid such as esters and
anhydrides are also important (in Biochemistry)
• ATP contains both ester and anhydride linked by
phosphoric acid (in Biochemistry) (figure 1.2)
How and when did the Earth come to be?
• Big bang theory explains the origin of earth – formed
from matter
• Due to explosion (released Hydrogen, Helium and
some Lithium), temperature of Universe raised to (15
billion K)
• Decrease in temperature led to formation of stars and
planets
• Rest of chemical elements i) by thermonuclear
reactions that take place in stars, ii) in explosions of
stars, iii) by the action of cosmic rays outside the stars
How did elements arise from stars?
• Age of earth – 4 to 5 billion years ago
• Second generation of stars formed from
supernovas – led to formation of sun
• Atmosphere of earth is always been debated
• Existence of Co2 from 3.8 billion years
• N2 in atmosphere – source for formation of
proteins and nucleic acids
How were biomolecules likely to have
formed on the early earth?
• Miller-Urey experiment
• Occurred in earth’s early
ocean
• Occurred on early earth’s
clay particles
• Simple compounds can react
(polymerize) abiotically to
produce biologically
important components of
proteins and nucleic acids
Formation of biomolecules on early
earth
HCN present in nucleic acids and HCHO present in sugars
Biomolecules
• Living cells include very large molecules, such as
proteins, nucleic acids, polysaccharides, and lipids
– these biomolecules are polymers (Greek: poly + meros,
many + parts)
– they are derived from monomers (Greek: mono + meros,
single + part)
--amino acids --> proteins
--nucleotides --> nucleic acids
--monosaccharides --> polysaccharides
--glycerol and 3 fatty acids --> lipids
Informational Macromolecules
How is cellular activity determined?
• Enzymes: a class of proteins that are biocatalysts
– the catalytic effectiveness of a given enzyme depends on its
amino acid sequence
• Genetic code: the relationship between the
nucleotide sequence in nucleic acids and the amino
acid sequence in proteins
Which came first – the catalysts or the
hereditary molecules?
• Cellular activity depends upon presence of
catalysts and its synthesis by genetic code
• Discovery of enzyme ‘Ribozyme’ – RNA
• RNA has both catalytic and genetic coding
properties
• Life originated from RNA
• Peptide bond formation is catalyzed by RNA
portions of Ribosome
Stages in the Evolution of Self-replicating RNA
Molecules
Vital importance of a cell membrane in
origin of life
Assignment 1
• Write down the structure and
function of all organelles in
eukaryotes.
Differences between prokaryotes and
eukaryotes
• Prokaryotes – before
nucleus and absence of
membrane bound
organelles
• DNA is present in
nuclear region and not
separate from the cell
• Plasma membrane is
present surrounding the
cell
• Eukaryotes – true
nucleus and presence of
membrane bound
organelles
• DNA is well defined
Differences between prokaryotes and
eukaryotes
• Mitochondria is absent and
enzymes for oxidative
reactions are located on
plasma membrane
• Endoplasmic reticulum is
absent
• Ribosomes are found freely
floating in cytosol
• Chloroplasts are absent.
Photosynthesis takes place
in chromatophores which
are extensions of plasma
membranes
• Plasma membrane is present
surrounding the cell
• Mitochondria is present
• Endoplasmic reticulum is
present
• Ribosomes are bound to
Endoplasmic reticulum
• Chloroplasts present in
plants and absent in animals
Some more points
• Polysaccharide cellulose present in prokaryotic
and eukaryotic cell walls (plant cells only)
• Some protists and all animal cells lack cell
walls and chloroplasts
• Three important organelles – nucleus,
mitochondria and chloroplast – separated from
rest of the cell by double membrane
• Mitochondria and chloroplasts contain DNAcarry out transcription and protein synthesis
Five Kingdom classification of living
organisms
• Prokaryotes
• Kingdom: Monera
• Bacteria and Cyanobacteria
are members
• Unicellular
• Eukaryotes
• Kingdom: Protists, Fungi,
Plants and Animals
• Unicellular protists are
Euglena, Volvox, Amoeba
and Paramecium
• Multicellular protists are
algae
• Fungi, plants and animals
are multicellular
• Fungi like yeasts and molds
are unicellular
Three Kingdom classification of living
organisms
• Bacteria and Archaea form prokaryotes
• Eukarya forms eukaryotes
• Bacteria (true bacteria) and Archaea (early
bacteria) have different biochemical features –
molecular structure of cell walls, membranes
and some types of RNA
• Archaebacteria live in extreme environments –
extremophiles – Methanogens, Halophiles and
Thermoacidophiles
Did symbiosis play a role in development
of eukaryotes?
• Theory of Endosymbiosis
• Proposal that eukaryotic
organelles evolved through
a symbiotic relationship
• One cell engulfed a second
cell and a symbiotic
relationship developed
• Mitochondria and
chloroplasts are thought to
have evolved this way
Evidence for Endosymbiosis
Mitochondria and chloroplasts:
-have 2 membranes
-possess DNA and ribosomes
-are about the size of a prokaryotic cell
-divide by a process similar to bacteria
What is thermodynamics?
• Sun is ultimate source of energy on earth
• Energy released or absorbed can be measured
in Biochemistry
• Energy is converted from one form to another
• Thermodynamics deals with changes in
energy that determine whether a process will
take place
• Spontaneous reactions will take place without
outside intervention
How can we predict what reactions
will happen in living cells?
• Spontaneity of reaction at a given
temperature and pressure is decided by
changes in free energy (ΔG)
• ΔG is negative, ΔG<0, spontaneous
reaction, energy will be released
• ΔG is positive, ΔG>0, reaction is not
spontaneous, energy will be required
• ΔG=0, reaction is in equilibrium
Is life thermodynamically possible?
Free energy: the energy available to do
work
-denoted by the symbol G (Gibb’s free
energy)
enthalpy: energy contained in a molecule’s
chemical bonds
free energy = enthalpy – (entropy x temp.)
G = H - TS
Laws of Thermodynamics
First Law of Thermodynamics – energy cannot
be created or destroyed
-energy can only be converted from one form
to another
For example:
sunlight energy
chemical energy
photosynthesis
Is life thermodynamically possible?
• In spontaneous reactions entropy of universe is
always increasing
• Living organisms (local decreases) can reduce
entropy with an increase in entropy of
surroundings
Laws of Thermodynamics
Second Law of Thermodynamics: disorder
is more likely than order
entropy: disorder in the universe
The 2nd Law of Thermodynamics states that
entropy is always increasing.
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