Transcript Understanding Our Environment

The Nature of Life
Chapter 2
Outline

Attributes of Living Organisms

Chemical and Physical Bases of Life
• The Elements: Units of Matter
• Molecules
• Valence, Bonds and Ions
• Acids, Bases and Salts
• Energy
• Chemical Components of Cells
• Monomers and Polymers
–
–
–
–
Carbohydrates
Lipids
Proteins
Nucleic Acids
Attributes of Living Organisms

Composition and Structure
• Cells - structural units of organisms
–
Cytoplasm - interior cell matrix
o Nucleus - houses genetic material (DNA)
suspended in cytoplasm
–
Cell Wall - bounds cytoplasm
Attributes of Living Organisms

Growth
• Increase in mass accompanied by an increase in
volume

–
Results from production of new cells and
includes variation in form
–
Controlled by genetic make up and
environment
Reproduction
•
Production of offspring
–
Offspring always resemble parents
Attributes of Living Organisms

Response to Stimuli
• Plants respond to stimuli
• What types of stimuli do plants respond to?
Light, gravity, injury, temperature
Attributes of Living Organisms

Metabolism
• Collective product of all biochemical reactions in
an organism
–
Respiration - energy release
–
Photosynthesis - energy harnessing
–
Digestion - conversion of large insoluble food
molecules to smaller soluble molecules
–
Assimilation - conversion of raw materials into
cell substances
Attributes of Living Organisms

Movement
• Occurs at all levels of organization
–
Usually slow and imperceptible
–
Mostly related to growth phenomena
–
Cytoplasmic streaming = movement at cellular
level
Attributes of Living Organisms

Complexity of Organization
• Molecules organized into compartments,
membranes and other structures within cells
• Arrangements of molecules highly structured and
complex

Environmental Adaptation
• Living organisms respond to their environment
• Natural selection adapts organisms to their
environment
Chemical and Physical Bases of Life
The Elements: Units of Matter

Matter
• Three states: solid, liquid, gas
• Occupies space
• Has mass
• Composed of elements
Chemical and Physical Bases of Life
The Elements: Units of Matter

Atoms - smallest stable
subdivision of element
• Nucleus - center of an atom
–
Protons - positively charged
particles
–
Neutrons - neutral particles
Model of an
oxygen atom
Chemical and Physical Bases of Life
The Elements: Units of Matter
• Atomic Number - number of protons
–
Cannot change within an element
• Atomic Mass - combined number of protons and
neutrons
Chemical and Physical Bases of Life
The Elements: Units of Matter

Electrons - negative electric charges circling
nucleus
• Paths of electrons guided by protons
• Orbitals - volume of space where electron occurs
90% of time
Models of
orbitals
Chemical and Physical Bases of Life
The Elements: Units of Matter

Electron’s distance from
nucleus depends on
energy level
• Electron Shells
–
Energy levels of atom
–
Associated with orbitals
–
Outermost shell
determines atom’s
reactivity
Energy levels of electrons
Chemical and Physical Bases of Life
The Elements: Units of Matter

Isotope - form of element varying in number
of neutrons and atomic weight
• Radioactive isotopes unstable and spontaneously
split into smaller parts, releasing great amounts of
energy.
Oxygen
isotopes
Chemical and Physical Bases of Life
Molecules

Compound - two or more elements united in
definite ratio by chemical bonds

Molecule - two or more atoms bound
together
• Smallest independently existing particle of a
compound or element
• In constant motion
Chemical and Physical Bases of Life
Molecules

Random collisions between molecules
capable of sharing electrons are basis for all
chemical reactions
• Often results in formation of new molecules
• Usually controlled by specific enzymes (catalyst)
–
Catalyst - speeds up reaction without being
used up in reaction
Chemical and Physical Bases of Life
Molecules

To form a water molecule: two hydrogen
atoms attach to an oxygen atom
• Electrons shared and form electron cloud
–
Gives molecule asymmetrical shape
• Asymmetrical shape and unequal sharing of
electrons make it polar
Water molecule
Chemical and Physical Bases of Life
Molecules

Water molecules form
cohesive network
• Cohesion - attraction of
similar molecules
–
Capillary movement in
plants
• Adhesion - attraction of
dissimilar molecules
Cohesion of water
molecules
Chemical and Physical Bases of Life
Valence, Bonds, and Ions

Valence - combining capacity of atom or ion
based on electron number

Bonds - forces that form molecules by
attracting and holding atoms together
• Number of electrons in atom’s outermost orbital
determines number of chemical bonds formed
• Formed by losing, gaining or sharing electrons
• What are the 3 types of bonds?
covalent bonds, ionic bonds and hydrogen bonds
Chemical and Physical Bases of Life
Valence, Bonds, and Ions

Covalent Bonds
• Form when two atoms share pair of electrons
• Nonpolar - electrons
shared equally
• Polar - electrons
shared unequally
(like water)
Covalent bond between
two oxygen atoms
Chemical and Physical Bases of Life
Valence, Bonds, and Ions

Ionic Bonds
• Electrons in outermost orbital removed from one
atom and transferred to another atom.
–
Ions - formed when molecules lose or gain electrons
• Form when oppositely charged ions come into
contact
Chemical and Physical Bases of Life
Valence, Bonds, and Ions

Hydrogen Bonds
• Form from attraction between positively charged
hydrogen atoms in polar molecules and
negatively charged atoms in other polar
molecules
–
Only have 7–10% strength of covalent bonds
Chemical and Physical Bases of Life
Acids and Bases

Acids - chemicals that release hydrogen
atoms (H+) when dissolved in water

Bases (alkaline compounds) - compounds
that release hydroxyl ions (OH-) when
dissolved in water.
Chemical and Physical Bases of Life
Acids and Bases
• pH scale represents measurement of H+ ion
concentration
7
=
Neutral (H+ and OH- are same
concentration)
<7
=
Acidic (lower number = higher
acidity)
>7
=
Alkaline (higher number = higher
alkalinity)
Chemical and Physical Bases of Life
Energy

Energy - capacity to perform work

Thermodynamics - study of energy and its
conversions from one form to another
• First Law: Energy is constant. It cannot be
gained or lost, only converted from one form to
another.
• Second Law: When energy is converted to
another form, it flows from a high energy state to
a low energy state and releases energy during
the conversion.
Chemical and Physical Bases of Life
Energy

Forms of energy include kinetic and
potential energy
• Potential Energy - capacity to do work owing to
position or state of particle

Where are electrons with the least potential
energy located? The most potential energy?
the inner shell; the outermost shell
Chemical and Physical Bases of Life
Chemical Components of Cells

Living substance of cells includes
cytoplasm and structures within it

About 96% of cell composed of carbon,
hydrogen, oxygen, and nitrogen

Simple molecules and ions converted to
large, complex molecules through cell
metabolism
Chemical and Physical Bases of Life
Monomers and Polymers

Polymers (macromolecules) - “many units”
• Formed when two or more small units called
monomers (“single units”) bond together

Bonding between monomers occurs by
dehydration synthesis reactions
• Dehydration synthesis - Removal of water in the
formation of a bond
Chemical and Physical Bases of Life
Monomers and Polymers

Bonds between monomers broken by
hydrolysis
• Hydrolysis - occurs when hydrogen becomes
attached to one monomer and hydroxyl group to
the other
• Energy is released, may be stored temporarily or
used in manufacture or renewal of cell
components

Polymers include carbohydrates, lipids,
proteins, and nucleic acids.
Carbohydrates

Carbohydrates - most abundant
organic compounds in nature
• Contain carbon, hydrogen and
oxygen in ratio of CH2O
• 3 basic kinds of carbohydrates:
monosaccharides, disaccharides,
and polysaccharides.

Monosaccharides - simple
sugars with backbones of 3-7
C (glucose and fructose)
Carbohydrates

Disaccharides - 2 monosaccharides
bonded together (sucrose)

Polysaccharides - several to many
monosaccharides bonded together
• Can be in long branched or unbranched
chains, or in coils of monosaccharides
–
Starch = coils of glucose molecules
o main carbohydrate reserve of plants
–
Cellulose = unbranched chain of glucose
molecules
o main structural polymer in plant cell walls
Lipids

Lipids - fatty or oily substances mostly
insoluble in water (fats and oils)
• Typically store twice energy as carbohydrates
• Long term energy reserves and structural
components of cells
• Contain C, H, and O, but have proportionately
less O than carbohydrates
Lipids

Fats and oils produced from one glycerol
molecule and three fatty acid molecules
• Most fatty acids consist of chain with 16–18 C
–
Saturated - H
attached to every
available bonding site
on C of fatty acid, and
with no double bonds
–
Unsaturated - with
fewer H and with at
least one double bond
between C atoms
Structure of a
fat molecule
Lipids

Waxes - lipids consisting of long-chain fatty
acids bonded to long chain alcohol, instead
of glycerol
• Surfaces of leaves and stems

Phospholipids - constructed like fats, but one
fatty acid usually replaced by phosphate
group
• Important components of membranes
Proteins, Polypeptides, and Amino Acids

Proteins regulate chemical reactions in cells,
usually very large and consist of one or more
polypeptide chains
• Polypeptides - composed of chains of amino acids
–
–
Amino acid composed of:
o Amino group (-NH2)
o Carboxyl group (-COOH)
o R group - can vary from
one hydrogen to a
complex ring
R groups distinctive for each
of 20 amino acids
Structure of amino
acid, glycine
Proteins, Polypeptides, and Amino Acids

Polypeptide Structure
• Primary Structure
–
Sequence of amino
acids fastened
together by peptide
bonds
• Secondary Structure
–
Formation of alpha
helix or pleated
sheets due to
hydrogen bonding
Proteins, Polypeptides, and Amino Acids

Polypeptide Structure
• Tertiary Structure
–
Coiling or folding
maintained by
interactions among R
groups
• Quaternary Structure
–
Association of more
than one polypeptide
to form single
functional protein
Storage Proteins

Some plant food-storage organs store small
amounts of proteins as well as large
amounts of carbohydrates
• Ex. potato tubers and onion bulbs

Seeds contain proportionately larger
amounts of proteins in addition to
complement of carbohydrates
• Get used during germination and during seedling
development
• Important sources of nutrition for humans and
animals
Enzymes

Enzymes - large, complex proteins
functioning as organic catalysts under
specific conditions
• Break bonds and allow new bonds to form,
facilitating chemical reactions
• Increase reaction rates
• Lower the energy of activation
–
Energy of activation - minimal amount of
energy needed to cause molecules to react
with one another
Enzymes

Enzymes temporarily
bond with substrate
• Substrate fits into
active site of enzyme
• Reaction occurs
rapidly and products
released
• Enzyme remains
unchanged and
capable of catalyzing
another reaction
Mode of action of an enzyme
Nucleic Acids

Nucleic acids - very large, complex polymers
• Vital to internal communication and cell
functioning
• What are the two types?
–
Deoxyribonucleic Acid (DNA)
–
Ribonucleic Acid (RNA)
Nucleotide structure

DNA - double helix of repeating subunits of 4
kinds of nucleotides
• Nucleotides composed of nitrogenous base, five-
C sugar and phosphate
Nucleic Acids

DNA contains genes encoding information
determining form and structure of organism

Can be passed from generation to generation
without change

RNA differs from DNA in its sugar and one of
its nucleotide components

Occurs as single strand and involved in
protein synthesis
Outline

Attributes of Living Organisms

Chemical and Physical Bases of Life
• The Elements: Units of Matter
• Molecules
• Valence, Bonds and Ions
• Acids, Bases and Salts
• Energy
• Chemical Components of Cells
• Monomers and Polymers
–
–
–
–
Carbohydrates
Lipids
Proteins
Nucleic Acids