Transcript CHAPTER 2 The Chemistry of Living Things

CHAPTER 2
The Chemistry of
Living Things
All Matter Consists of Elements Made of
Atoms
“atom” means “can’t be cut” by Greeks 2500
years ago.
Atoms, the smallest functional unit of an element,
consist of:
Slide 2.1
Atoms are made of
• Protons: positive charge, in nucleus, are heavy,
“p+”
• Neutrons: no charge, in nucleus, are heavy, “n0”
• Electrons: negative charge, outside nucleus
“electron cloud”, very light (1/1840 of a proton or
neutron), “e-”
Charges in an Atom
• The + charge on a proton is equal to the - charge
on an electron.
• Atoms are neutral (have no overall charge)
• Therefore, the # of protons = # electrons in an
atom.
Atomic number
• determines the identity of the atom.
• It tells us the number of protons in the atom.
• It also tells us the number of electrons (b/c an atom is
neutral in charge.)
• Ex: atomic number of carbon, C = 6
• Question: how many protons? How many electrons?
How many neutrons?
Slide 2.2
Isotopes
• The number of neutrons can vary from atom to
atom in an element.
• Atoms of the same element w/different #s of
neutrons are called ISOTOPES.
• In order to know how many neutrons in an atom
you must be told.
• The mass number tells you how much mass the
atom has.
• Since p+ and n0 are the heavy parts, the mass # tells
you the # of p+’s + n0’s.
QUESTION: If the mass number of a
carbon atom is 14,
• How many protons?
• How many electrons?
• How many neutrons?
• LET’S PRACTICE!
• Whiteboard
• Marker
• Paper towel
BONDING: Atoms Combine to Form Molecules
• Joining atoms requires energy
• Energy is the capacity to do work
• Stored energy = potential energy
• Energy in motion, doing work = kinetic energy
• Electrons have potential energy
• Shells = the energy levels of electrons
• Orbitals describe the probable location of an electron
.
Slide 2.3
Three Types of Chemical Bonds
Table 2.1
Slide 2.4
Ionic Bonds
Written NaCl NOT Na-Cl
Elements of Living Organisms
Table 2.2
Slide 2.5
Life Depends on Water
• Water molecules are polar (they have slight
electrical charges)
o The biological solvent-ex: K+ for muscle
contraction
o Hydrogen bonds make it expand when frozen
• Water is liquid at body temperature
• Water can absorb and hold heat energy
o Water helps regulate body temperature
o Has high heat of evaporation
Slide 2.6
Hydrogen bonds (dotted lines)
Oxygen slightly
–ve charge
Hydrogen
slightly +ve
Water Keeps Ions in Solution
Figure 2.8
Slide 2.8
The Importance of Hydrogen Ions
• Acids are proton (hydrogen ion) donors, bases
accept hydrogen ions
• pH Scale = a logarithmic scale of the hydrogen ion
concentration
(going from a pH of 2 to 4 is a change of 2 numbers=
102, so pH 4 is 100 times less acidic than pH 2
• Buffers: minimize pH change
• Carbonic acid and bicarbonate act as one of
body’s most important buffer pairs
Slide 2.9
The pH Scale
Figure 2.10
Slide 2.10
The Organic Molecules of Living
Organisms
Carbon, the building block of living things:
• Comprises 18% of body by weight
• Forms four covalent bonds
• Can form single or double bonds
• Can build micro- or macromolecules
Slide 2.11
Carbon Can Bond in Many Ways
Figure 2.12
Slide 2.12
Making and Breaking Biological
Macromolecules: Dehydration Synthesis
and Hydrolysis
Figure 2.13
Slide 2.13
Dehydration Synthesis is the Reverse of
Hydrolysis
• Dehydration synthesis
• Removes equivalent of a water molecule to link
molecular units
• Requires energy (Process of ANABOLISM)
• Hydrolysis
• Adds the equivalent of a water molecule to break
apart macromolecules
• Releases energy (Process of CATABOLISM)
Slide 2.14
Carbohydrates are Composed of
Monosaccharides
Figure 2.14
Slide 2.15
Carbohydrates are Used for Energy and
Structural Support
• Oligosaccharides: short chains of
monosaccharides
• Disaccharides: sucrose, fructose, lactose
• Polysaccharides: thousands of monosaccarides
joined in chains and branches
• Starch: made in plants; stores energy
• Glycogen: made in animals; stores energy
• Cellulose: undigestible polysaccharide made in plants
for structural support
Slide 2.16
Lipids: Insoluble in Water
• Triglycerides: energy storage molecules
• Fatty acids: saturated and unsaturated
• Phospholipids: cell membranes
• Steroids: carbon-based ring structures
• Cholesterol: used in making estrogen and
testosterone
Slide 2.17
Unsaturated
triglyceride
Steroids (type of
lipid)
Proteins: Complex Structures Contructed
of Amino Acids
• Structure
• Primary: amino acid sequence
• Secondary: describes chain’s orientation in space;
e.g., alpha helix, beta sheet
• Tertiary: describes three-dimensional shape created
by disulfide and hydrogen bonds
• Creates polar and nonpolar areas in molecule
• Quarternary: describes proteins in which two or
more tertiary protein chains are associated
Slide 2.18
Hemoglobin (4 protein
strands held together)
Enzyme Function
Enzymes:
• are proteins
• function as catalysts
• facilitate chemical reactions
The functional shape of an enzyme is dependent on:
• temperature of reaction medium
• pH
• ion concentration
• presence of inhibitors
Slide 2.19
Enzyme Action
Structure and Function of Nucleic Acids
• Functions
• Store genetic information
• Provide information used in making proteins
• Structure
• Nucleotides consist of a phosphate group, a sugar,
and a nitrogenous base
• DNA structure is a double helix: two associated
strands of nucleic acids
• RNA is a single-stranded molecule
Slide 2.20
Structure of DNA and RNA
• DNA: double-stranded
• Sugar: deoxyribose
• Nitrogenous bases: adenine, thymine, cytosine,
guanine
• Pairing: adenine-thymine and cytosine-guanine
• RNA: single-stranded
• Sugar: ribose
• Nitrogenous bases: adenine, uracil, cytosine, guanine
• Pairing: adenine-uracil, cytosine-guanine
.
Slide 2.21
DNA nucleotides
RNA structure
Structure and Function of Adenosine
Triphosphate (ATP)
Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.
Figure 2.25
Slide 2.22