Download An Introductory Overview of Cells, Chemical Bonds & Energy

Lecture no.4
An Introductory Overview of
Cells, Chemical Bonds & Energy
Part-II
BCH 361/ Section: xxxxx
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Lecture no.4
What We Will Be Covering-II?
 Covalent and non-covalent bonds.
 The four macromolecules and their building blocks
 Chemical reactions and delta G
 Coupling chemical reactions to ATP hydrolysis
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Chemical Hierarchy structure in living
cells
 Organization of molecules in cells:
1.
2.
3.
4.
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Atoms.
Small molecules.
Macromolecules.
Supramolecular aggregates.
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Lecture no.4
Organization is the key to the chemistry of life.
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Atoms
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 Each atom has a nucleus
(protons and neutrons) with
electrons orbiting it.
 H, C, O, and N make up 96.5%
weight of a living organism.
 Na, K, Cl, Ca, Fe, Zn are each
present at less than 1%.
 Two types of atomic interaction:
Covalent & Non-covalent Bonds.
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Atomic Interaction
Covalent
Bonds
Non-Covalent
Bonds
1
1
Hydrogen
Bonds
2
Polar
interaction
2
Non-polar
interaction
3
4
Ionic
interactions
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Van der
Waals
Hydrophobic
effects
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Hi, plz remember this regarding the
covalent bonds:
• It form the backbones of molecules.
• Electrons are shared between atoms.
• Single bonds allow rotation,
double bonds are rigid
 Molecules are covalently
bonded atoms, covalent bonds
result from sharing electrons
and depend on valence (C: +4,
N: -3, O: -2, H:+1).
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Nonpolar Hormones Pass Through Cell Membranes;
Polar Hormones Use Extracellular Receptor Proteins
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Covalent And Noncovalent Bonds Play Different Roles
In Maintaining Molecular Structure
 Covalent bonds assemble atoms
into molecules, but noncovalent
bonds determine the shape of large
molecules and the way in which
molecules interact with each other.
 Covalent bond = approx. 350
kJ/mol and difficult to break,
Noncovalent bond = 1- 30 kJ/mol
and readily reversible by thermal
movement or interactions with
other molecules.
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Hydrogen Bonds In Biomolecules
Hydrogen has a low electronegativity
(it has only one proton to attract
electrons with).
 Oxygen and nitrogen are highly
electronegative.
When there is a bond between O and
H, or N and H, the molecule forms a
dipole -- the O or N will become δ(hydrogen bond acceptor), and the H
will become δ+ (hydrogen bond donor).
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Hydrogen Bonds Hold The
DNA Double Helix Together
Lecture no.4
 An AT pair has 2 H bonds,
while a CG pair has 3 H bonds.
 The helix is harder to unwind
in a CG-rich region than in an
AT-rich region.
 H-bonds play pivotal roles in
different aspects of the central
dogma of MB DNA.
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Noncovalent Bonds Influence Molecular
Structure--Hydrophobic Interactions
 Lipids form micelles, in
which the hydrophilic groups
line the outside of the micelle
and the hydrophobic groups
cluster inside it, away from the
water.
 The first stage of lipid
digestion involves breaking up
huge globs of fat into smaller
globs and micelles
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 They determine the shape of macromolecules (i.e. the double
stranded helical shape of DNA is determined by hydrogen bonds
between complementary base pairs A-T and G-C).
 They produce reversible self-assembly of pre-synthesized
subunits into specific structures (i.e. membrane lipid bi-layer,
protein "polymers" like microtubules).
 They determine the specificity of most molecular interactions
(i.e. enzyme substrate specificity and catalysis).
 Molecules or supramolecular aggregates denature (unfold)
upon environmental changes (pH, temperature, or ionic
strength) which affect the strengths of weak bonds.
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Disrupting Noncovalent Bonding
Causes Sickle-Cell Anemia
 Hemoglobin is a heterotetramer2 alpha globin chains plus 2 betaglobin chains.
 Glutamic acid (negative charge)
is replaced by valine (uncharged) in
the beta-globin polypeptide.
 If beta-globin shape changes,
hemoglobin's solubility decreases,
hemoglobin precipitates into rodlike aggregates in red blood cells.
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Hemoglobin aggregation causes sickling of the red blood cell, and the
aggregates punctures the cell when it gets squeezed through capillaries
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The Molecules of Life
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 Cells are 70% water,
nearly
30%
carbon
compounds.
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All living things are made up of four classes of large
biological molecules: carbohydrates, lipids, proteins, and
nucleic acids.
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Overview: The Molecules of Life
• Concept 1: Macromolecules are polymers, built from
monomers.
• Concept 2: Carbohydrates serve as fuel and building
material.
• Concept 3: Lipids are a diverse group of hydrophobic
molecules.
• Concept 4: Proteins include a diversity of structures,
resulting in a wide range of functions.
• Concept 5: Nucleic acids store, transmit, and help express
hereditary information
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Monosaccharide
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 The simplest carbohydrates form.
 It serve as a major fuel for cells and
raw material for building molecules
 Polysaccharides, polymers composed
of many sugar building blocks.
 Monosaccharides are classified by:
 The location of the carbonyl group
(as aldose or ketose).
 The number of carbons in the carbon
skeleton.
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Lipids
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 Lipids are the one class of large
biological molecules that do not form
polymers.
 The unifying feature of lipids is
having little or no affinity for water.
 Lipids are hydrophobic because they
consist mostly of hydrocarbons,
which form nonpolar covalent bond.
 The most biologically important lipids
are fats, phospholipids, and steroids.
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Amino acids
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 Subunits of proteins.
 20 major types of amino
acids.
 Side groups of amino acids
dictate protein structure
(non-polar,
polar,
and
charged subgroups).
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Nucleotides
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 Made up of 5 carbon sugar,
phosphate & nitrogenous base
(adenine, cytosine, thymosine,
guanine, Uracil).
 Subunits of DNA and RNA.
 ATP - the main energy source.
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Summary
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The Adenosine triphosphate (ATP)
 Adenosine-5'-triphosphate (ATP) is a multifunctional
nucleotide used in cells as a coenzyme.
 ATP transports chemical energy within cells.
 ATP is produced by phosphorylation and cellular
respiration and used by enzymes and structural proteins in
many cellular processes, including:
• Metabolism, synthesis, and active transport.
• Roles in cell structure and locomotion.
• Cell signaling.
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The phosphoryl groups, starting with the group closest to
the ribose, are referred to as the (α), (β), and (γ) phosphates.
ATP
molecule as it exists in the intact cell is highly
charged at pH 7, the three phosphate groups are completely
ionized (4 negative charges) near the linear phosphate
structure.
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Metabolic processes that use ATP as an energy
source convert it back into its precursors.
 ATP is therefore continuously recycled in
organisms.
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Ionization in biological systems
 ATP has several negatively-
charged groups in neutral
solution, it can chelate metals
with very high affinity.
 ATP forms stable complexes
with certain divalent cations
as Mg2+. Most of ATP in the
cell present as Mg2+-complex
Mg2+.
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Gibbs Free Energy (G)
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Energy released Energy supplied
 Gibbs Free Energy (G)
The energy associated with a chemical reaction that can be
used to do work.
• Reactions can also be classified as:
exergenic (G < 0) or endergenic (G > 0).
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Product
Energy
must be
supplied.
Reactant
Reactant
Energy is
released.
Product
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Lecture no.4
• Example:
 the phosphorylation of glucose to glucose 6-phosphate:
Glucose + phosphate
G-6 phosphate
ΔG°' = +3.3 kcal/mol (unfavorable)
 Consider the hydrolysis of ATP:
ATP
ADP + Pi
Δ G°' = - 7.3 kcal/mol (favorable)
 Summing these reactions together:
ATP + glucose
ADP + G- 6-phosphate
Δ G°' = +3.3 + (-7.3) = -4kcal/mol (still favorable)
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Lecture no.4
The energy released in the formation of
noncovalent bonds is on the order of 1-5 kcal
per mol
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Lecture no.4
Time to relax ...
Later we will start with the
main part of the course
“Nucleic acids”..
Good luck
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