Lecture 2

OrR

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?

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

The Biological Hierarchy

The study of life can be divides into different level of biological organization

Life, Chemistry and Water

•Biology is a multidisciplinary science

•Living organisms are subject to basic laws of physics and chemistry

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

Is oxygen an element or a compound? What about iron? Water? Carbon di oxide?

Sodium (Na) Chlorine (Cl)Table Salt

Sodium Chloride(NaCl)

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

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

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

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)

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

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

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

Covalent Bonds

• Principle form to hold atoms together

• based on sharing electrons

• very strong

•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

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

Chirality characteristics of covalent bond

Carbon can make 4 COVALENT bonds comes out as tetrahedron

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

Sharing of electron

C-C or C-H equal sharing (non-polar bond)

N-H, O-H unequal sharing (polar bond)

Electronegativity

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.

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.

The polarity of water molecules results in hydrogen bonding

Ionic BondingIonic Bonding

Sodium chloride (table salt)

is an example of ionic

bonding, that is, electron

transfer among atoms or

redox reaction.

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.

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

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

Summary: From Atoms to Molecules

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.

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

Diffusion

Diffusion

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

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

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

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.

MOVEMENT OF WATER WHEN A MEMBRANE SEPARATES EQUAL AND UNEQUAL SOLUTIONS OF A NONPENETRATING SOLUTE

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.