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Lecture 2
OrR
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Overview: Inquiring About the World of life
Evolution is the process of change that has transformed life on Earth.
Biology is the scientific study of life
Biologist ask questions such as:
How does a single cell develop into an organism?
How does the human brain work?
How do living things interact in communities?
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Evolution, the Overarching Theme of Biology
•Evolution makes sense of everything we know about living organisms
•Organisms living on Earth are modified descendents of common ancestors
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The Biological Hierarchy
The study of life can be divides into different level of biological organization
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Life, Chemistry and Water
•Biology is a multidisciplinary science
•Living organisms are subject to basic laws of physics and chemistry
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Organisms are composed of matter
Matter – anything that takes up space and has massMass measures the quantity of matter in an object and is defined by:
Volume is how much space it takes upDensity measure concentration of matter
•Matter is made up of elements
•An element is a substance that cannot be broken down to other substances by chemical reactions
•A compound is a substance consisting of two or more elements in a fixed ratio.
•A compound has characteristics different from those of its elements
Matter, Elements & compounds
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Is oxygen an element or a compound? What about iron? Water? Carbon di oxide?
Sodium (Na) Chlorine (Cl)Table Salt
Sodium Chloride(NaCl)
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Essential Elements of Life
• About 25 of the 92 elements are essential of life
• Carbon (C), hydrogen (H), oxygen (O), and nitrogen make up 96% of living matter.
• Most of the remaining consist of calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl) and magnesium (Mg).
• Trace elements are those required by an organism in minute quantities. Example: selenium, Zinc
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Atomic Structure
•Each elements consists of one type of atom
• Each atom consists of an atomic nucleus surrounded by fast moving, negatively charged electrons
• Atomic nuclei contain positively charged protons – the number of protons (atomic number) identifies an element
• The nuclei of all atoms (except hydrogen) also contain uncharged neutrons
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Isotopes • Makes atomic number not as simple as it may seem
Protons and Neutrons in the nucleusNeutrons can vary independently of the number of protonsNeutrons add weight to the atom
• Isotopes have the same number of protons, different number of neutrons
ISOTOPES OF CARBON
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Isotopes in Research
• Radioisotopes decay can be used to estimate the age of organic material, rocks, or fossils that contain them.
• Isotopes are used in biological research as tracers
• Radioisotopes such as 14C, 32P, and 25S• Stable, nonradioactive isotopes such as 15N
(heavy nitrogen)
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123I can be used to visualize the thyroid gland
•Scans of human thyroid glands after 123I was injected into the blood stream
•Radioactive iodine becomes concentrated in the thyroid gland
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Chemical Bonds and Chemical Reactions
• Atoms of reactive elements tend to combine into molecules by forming chemical bonds
• The four most important chemical linkages in biological molecules are ionic bonds, covalent bonds, hydrogen bonds and van der Waals forces.
• Chemical reactions occur when atoms or molecules interact to form new chemical bonds or break old ones
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Chemical Bonds and Chemical Reactions
Forces:
1. Covalent bonds2. Hydrogen bonds3. Ionic bonds4. van der Waals bonds5. Hydrogen bonds
Macromolecules
1. Carbohydrate2. Proteins3. Nucleic acids4. Lipids
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Covalent Bonds
• Principle form to hold atoms together
• based on sharing electrons
• very strong
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•to break a C-C bond require 83 kcal/mole
• the bond cant be break with any physiological condition
• The bond can only be bend, stretch or rotate
• Enzymes: Biological catalysts that enable specific bonds to be broken or formed under physiological conditions
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Types of covalent bonds:
Single bonds C-C
Double bonds C=C
Triple bonds C=C
Strongerunsaturated
saturated
rotate
Can’t rotate
Other molecules:
Oxygen molecule O=O
Nitrogen molecule N=N
Nitrogen is strong molecule, cant be broken by any organism, but by bacteria which produce enzyme name nitrogenase
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Chirality characteristics of covalent bond
Carbon can make 4 COVALENT bonds comes out as tetrahedron
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Chirality characteristics of covalent bond
Mirror image
Molecules are known as Optical isomer
Important concept: At molecular level much of biology relies on interaction of complementary 3d surfaces
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Sharing of electron
C-C or C-H equal sharing (non-polar bond)
N-H, O-H unequal sharing (polar bond)
Electronegativity
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Two Types of Covalent Bonds• Nonpolar Covalent Bond
– The atoms participating in the bond are sharing electrons equally.
There is no difference in charge between the two ends of such
bonds.
• Polar Covalent Bond
– Atoms participating in the bonds do not share electrons equally.
– One atom pulls the electrons a little more toward its "end" of the
bond, so that atom bears a slightly negative charge. The atom at
the other end of the bond bears a slightly positive charge.
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Polar Covalent BondPolar Covalent BondPolarity occurs when atoms electrons unequally due to differences in electronegativities. This is seen in water (H2O).
More electronegative atoms tend to pull electrons toward them creating a polar molecule.
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The polarity of water molecules results in hydrogen bonding
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Ionic BondingIonic Bonding
Sodium chloride (table salt)
is an example of ionic
bonding, that is, electron
transfer among atoms or
redox reaction.
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IonizationIonization
Molecules formed by ionic bonding breakup (ionization) when dissolved in water (solvent), producing separate positive (cation) and negative (anion) ions.
These ions conduct electricity and thus called electrolytes.
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Hydrogen Bonds
• A hydrogen bond is a weak attraction between a hydrogen atom
and another atom taking part in a separate polar covalent bond
• Like ionic bonds, hydrogen bonds form by the mutual attraction
of opposite charges.
• Unlike ionic bonds, hydrogen bonds do not make molecules out of
atoms, so they are not chemical bonds
• Hydrogen bonds form and break much more easily
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Hydrogen BondHydrogen Bond
Hydrogen bonding is formed between the partially positive (hydrogen) end of a polar molecule and the negative end of another (e.g. O2 or N2).
Example : Water molecules
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Summary: From Atoms to Molecules
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Water: The Molecule That Supports All of Life
• Water is the biological solvent on Earth
• All living organisms require water more than any other substance
• Most cells are surrounded by water, and cells themselves are about 70-95% water
• The abundance of water is the main reason the Earth is habitable.
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Water
• Water: Polar covalent bonds gives water its unique
properties that make life possible
• Water is an excellent solvent
– Hydrophilic substances
– Hydrophobic substances
• Water is stable in high temperature
– Why ice floats on water
• Water has cohesive properties
• Water evaporates
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Diffusion
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Diffusion
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OSMOSIS• Osmosis is the net diffusion of water down its
own concentration gradient• Water molecules can readily permeate the plasma
membrane • Slower Process• Aquaporins• One molecule of solute can displace one molecule of water
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Osmosis when pure water is separated from a solution containing a nonpenetrating solute.The net diffusion of water down its concentration gradient through a
selectively permeable membrane is known as osmosis
OSMOSIS
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MOVEMENT OF WATER AND SOLUTE WHEN A MEMBRANE SEPARATES UNEQUAL SOLUTIONS OF A PENETRATING SOLUTE
Solutes that can penetrate the plasma membrane do not contribute to osmotic
differences between the ICF and ECF and do not affect cell volume (although before
equilibrium is achieved, transient changes in volume may occur as a result of differing
rates of diffusion of water and the solute across the membrane
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Tonicity
• The effect of a solution on the osmotic movement of H20.
• The tonicity of a solution has no units and is a reflection of its
concentration of nonpenetrating solutes relative to the cell’s
concentration of nonpenetrating solutes• Isotonic
– Equal tension to plasma.– RBCs will not gain or lose H20.
• Hypotonic: – Osmotically active solutes in a lower osmolality and osmotic pressure than
plasma.– RBC will hemolyse.
• Hypertonic:– Osmotically active solutes in a higher osmolality and osmotic pressure than
plasma.– RBC will crenate.
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MOVEMENT OF WATER WHEN A MEMBRANE SEPARATES EQUAL AND UNEQUAL SOLUTIONS OF A NONPENETRATING SOLUTE
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Acids and Bases
• What is pH
• Acids: Fossil fuel, N2 containing fertilizers,
Acid rain
• Bases
• Buffers
• Hydrogen ions contribute to pH. Acids release
hydrogen ions in water; bases accept them. Salts
release ions other than H+ and OH-.
• Buffers keep the pH of body fluids stable. They are
part of homeostasis.