Chapter 4 Chemical Foundations for Cells

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Chapter 4Chemical Foundations for Cells

• College Prep Biology
• Mr. Martino

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Introduction

• Certain chemicals enable organisms to function
  properly and are very useful
• Life is composed of matter anything that has
  mass and occupies space
• Matter is composed of elements substances that
  cannot be further broken down to other substances
• Approx. 92 elements are naturally occurring

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Introduction cont

• About 25 elements are essential to life
• C, H, O, N make up about 96.3 of humans
• Remaining 4 are considered trace elements
  essential to life, but only in minute quantities
  (lt 0.01)

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4.1 Atoms

• Each element consists of one kind of atom
  (invisible) the smallest unit of matter that
  still retains the properties of an element
• More than 100 subatomic particles but only 3
  important to us
• Proton (, nucleus p)
• Neutron (neutral, nucleus no)
• Electron (-, orbits nucleus e-)

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Atoms cont

• Atoms differ in number of subatomic particles
• Atomic number unique number of protons
  possessed by each element
• Neutral atoms have equal numbers of protons ()
  and electrons (-)
• Atomic mass sum of the number of protons and
  neutrons in the nucleus
• Protons and neutrons are almost identical in mass
• Electrons are much smaller approx. 1/2000 the
  mass of a proton
• Atomic weight same as atomic mass, but a whole
  number

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Isotopes

• Isotopes variant forms of elements that have a
  different number of neutrons
• Number of protons and electrons remain same
• Radioisotopes nuclei decay spontaneously -
  giving off particles and energy (E)
• 14C is radioactive

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4.2 Radioisotopes

• Have many uses since readily absorbed by cells
• can be monitored on film or by Geiger counter as
  tracers substances with a radioisotope
  attached
• 14CO2 to illustrate photosynthesis and other
  cellular processes
• PET Scanner shows organs and cancer

• Used to
• diagnose and treat AIDS, Alzheimers, arthritis,
  cancer, as well as other diseases of the brain,
  heart, lungs and bones
• Sterilize medical products
• Tissue grafts
• Medical research

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Radioisotopes cont

• Can also pose serious risks
• Uncontrolled exposure damages DNA
• Also can cause cancer
• Naturally occurring radon gas is very dangerous
• Found around uranium-bearing rocks

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Isotopes cont
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Isotopes cont

• 1 out of every 3 people admitted to hospital has
  a nuclear medical procedure for diagnosis or
  treatment using radioisotopes
• Nuclear medicine is 7-10 billion/year industry
• Isotopes sales are 100 million/year

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4.3 Bonding of Atoms

• Electron arrangement mainly determines how an
  atom behaves
• Distance from nucleus determines E
• The farther away, the E
• Electron shell (orbits) energy levels around
  the nucleus of an atom where electrons are found
• 1st 2 e-
• 2nd 8 e-
• 3rd 8 e-

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Electron Arrangement cont

• When outer shells are full the atoms are stable
  (inert)
• If not, they react readily
• Reactions enable them to fill their outer energy
  levels and become stable
• All atoms desire to become stable
• Chemical bonds when atoms either share or
  transfer electrons in order to become stable
• Compound substance containing two or more
  different elements in a fixed ratio (H2O)
• Mixture two or more elements intermingle in
  varying proportions no chemical reaction

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4.4 Ionic Bonds

• Ion an atom or molecule with an electrical
  charge resulting from the gain or loss of one or
  more electrons
• Ions of opposite charges attract each other and
  form an ionic bond
• ex Na Cl-

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Covalent Bonds

• Covalent bond strong chemical bond in which
  two or more atoms share one or more pairs of
  outer-shell electrons
• 2 or more atoms held together by covalent bonds
  form a molecule
• Ex. H2, O2, H2O
• Very strong bond
• Found in most organic compounds - sugars, fats
  and proteins

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Covalent Bonds cont

• Number of single covalent bonds an atom can form
  is equal to number of additional electrons
  needed
• H
• 1
• O
• 2
• N
• 3
• C
• 4

• Double bond forms when 2 pairs of electrons are
  shared
• O2
• O2 and H2 are molecules, but not compounds
• CH4 is a molecule AND a compound

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Chemical Reactions

• Chemical reaction process that rearranges
  matter determining the way it behaves and
  interacts
• 1st Law of Thermodynamics amount of matter and
  energy in the universe is constant they can be
  transferred and transformed - not destroyed
• In other words, equations must be balanced!
• 2 H2 O2 2 H2O
• reactants products

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Chemical Reactions cont

• E is needed to make break chemical bonds
• Activation energy the E required to start a
  chemical reaction
• 2 main types of chemical reactions
• 1. Exergonic more E is released than used and
  stored
• Ex. Burning wood

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Chemical Reactions cont

• 2. Endergonic more E is used and stored than
  is released
• Ex. Most cellular reactions
• Metabolism sum of all the reactions that occur
  within an organism

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4.4 Properties of Water

• Water comprises 70 95 of living organisms
• Water is electronegative attraction between
  shared electrons in a bond
• Greater the electronegativity, the more strongly
  an atom pulls electrons towards itself
• H2, O2, CH4 exert equal pull and are considered
  to be nonpolar

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Water cont

• Polar when an molecule is negative at one end
  and positive at the other because an element is
  pulling the electrons more
• Oxygen is one of the most electronegative
  elements
• Ex. H2O

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Water cont

• Polarity of water attracts other polar molecules
• Hydrophilic substances (water-loving) other
  polar molecules that are attracted to water
• Ex. Sugars
• Waters polarity repels nonpolar molecules
• Hydrophobic substances (water-fearing)
• Ex oils

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Hydrogen Bonding

• Waters polarity leads to hydrogen bonding
• H-bonds last only a few trillionths of a second
• Each H2O molecule can H-bond with as many as 4
  others
• Common in all 3 states of matter
• Allows for life on Earth

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Water is Cohesive

• Cohesion tendency for molecules to stick
  together
• Due to H-bonds
• Allows for capillary action
• Surface tension measure of how difficult it is
  to stretch or break the surface of a liquid
• Permits organisms to walk on water
• Unusually high in water

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Ice, Ice Baby

• Hydrogen bonds of ice are stable
• Each molecule is bonded to four others forming
  a crystal
• Causes the molecules to spread apart
• Ice is less dense than water
• Helps to maintain life

No, not him.this !
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Water Moderates Temperature

• Temperature measure of molecular motion
• High heat capacity takes a lot of E to
  temperature
• Helps organisms to maintain constant temp.
• Helps environment to moderate temp.
• High heat of vaporization takes a lot of E to
  cool and evaporate
• Heat is released when more H-bonds form, slowing
  the cooling process
• Evaporation also cools water left behind
  body temperature

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The Universal Solvent

• Solution homogeneous, liquid mixture of two
  or more substances
• Solute substance that is dissolved
• Solvent dissolving agent
• Water easily dissolves ions and polar molecules
  so, it is referred to as the universal solvent

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Universal Solvent cont

• Concentration amount of solute in a solvent
• Saturation solution cannot hold any more
  solvent
• When water is the solvent, results in - aqueous
  solution
• Polarity allows for waters tremendous solvent
  abilities universal solvent

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4.4 pH

• Sometimes the H2O molecules separate into ionsH
  and OH-
• Proper balance of ions is critical in organisms
• Acid compound that releases H in solution
• Ex. HCl
• Base compound that removes H from solution
  and releases OH-
• Ex. NaOH
• Salts release ions other than H and OH-
  in solution
• Strong acid strong base salt
• HCl NaOH NaCl H2O

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pH cont

• pH Scale describes how acidic or basic a
  solution is (potential hydrogen)
• Each point is a 10x
• 7 is neutral
• pH inside most living cells is neutral a change
  can be deadly

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pH cont

• Buffer resists change in pH by giving off or
  taking in H
• Metabolic rxns are sensitive to very slight
  shifts in pH
• Uncontrolled pH shifts in blood (pH 7.3 - 7.5)
  can cause a coma.

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pH Indicators

• Blue Litmus Paper
• Turns red in an acid
• Red Litmus Paper
• Turns Blue in a base
• pH Paper
• Changes color according to the color chart

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4.5 Acid Rain

• Acid precipitation rain or snow with pH below
  5.6
• Occurs mostly from sulfur and nitrogen oxides due
  to burning fossil fuels
• Over past 20 years, several American, Asian and
  European lakes have died as a result
• Eastern U.S. has experienced rain with pH as low
  as 2 3
• pH 1.7 fog has been recorded in Los Angeles

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Now, it is time to go study!!!!