chapter 2 the chemistry of living things. slide 2.1 “atom” means “can’t be cut” by greeks...
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CHAPTER 2
The Chemistry of Living Things
Slide 2.1
“atom” means “can’t be cut” by Greeks 2500 years ago.
Atoms, the smallest functional unit of an element, consist of:
All Matter Consists of Elements Made of Atoms
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.
Slide 2.2
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?
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, – mass # = # 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
Atomic Mass Units
• Atoms are weighed in a.m.u.• 1 a.m.u. is based on the mass of a Carbon-12
atom. – it has 6 p+ and 6 n0, – 1 a.m.u = 1/12 the mass of a carbon-12 atom.
IONS
• Electrons are in constant motion around the nucleus.
• e-s in the highest occupied level are called valence e-s.
• Some atoms lose or gain electrons in their valence level.
IONS
• When they do this, they get a charge.– If you lose an electron, the ion has a ___ charge– If you gain an electron, the ion has a ___ charge
ATOM v. ION
• ATOM – has no charge• ION- has a charge (b/c e-s have been lost OR
gained)
Slide 2.3.
BONDING: Atoms Combine to Form Molecules
• Atoms want a stable arrangement
• For most atoms this is 8 e-s in the valence level (for small guys, it’s 2 in the valence)
• There are 2 ways to get the e-’s you need.ShareGain/lose
Table 2.1Slide 2.4
Three Types of Chemical Bonds
Written NaCl NOT Na-Cl
Ionic Bonds
Elements of Living Organisms
Table 2.2Slide 2.5
Life Depends on Water• Water molecules are polar (they have slight
electrical charges, like little magnets)o Biological solvent-ex: K+ for muscle contractiono Hydrogen bonds make it expand when frozen
(animals in lakes can survive winter)oWater is liquid at body temperatureoWater can absorb and hold heat energyoWater helps regulate body temperature
Slide 2.6
Hydrogen bonds (dotted lines)
a.k.a. van der Waals forces
Oxygen slightly –ve charge
Hydrogen slightly +ve
Properties of Water (b/c of hydrogen bonding)
• Cohesion- attraction between molecules of the same substance. (water-water attraction)
Examples– Drops of water– Surface tension (Fig 2-8 p 41 of text)
Properties of Water (b/c of hydrogen bonding)
• Adhesion-attraction btwn molecules of different substances (water-other substance attraction)
Examples– Capillary action-water drawn up a tube– “Meniscus”= the curve shape water has when in a
tube
Water forms Important Mixtures
• Solutions
• when a substance dissolves in water• Ex: Salt-water.
• NaCl is pulled apart into IONS by the water.
Figure 2.8Slide 2.8
Water Keeps Ions in Solution
Water forms Important Mixtures(cont.)
• Suspensions
• Material does NOT dissolve, but separates into small pieces that remain floating
• Ex: blood w/red blood cells
ACIDS & BASES
• Water can form ions too!
• H2O H+ + OH-
• When by itself, water makes equal amounts of H+ + OH-
ACIDS & BASES (cont.)
• Some things cause water to release many H+ ions. These are acids.
• Some things cause water to release many OH- ions. These are bases.
• pH is a measure of the H+ concentration in a solution.
Figure 2.10Slide 2.10
The pH Scale
BUFFERS
(DON’T WRITE THIS) Remember homeostasis?
WRITE THIS:• All living things need to maintain a stable pH.– Humans need a pH between 6.5 & 7.5– Otherwise, chemical reactions get messed up.
• They do this through buffers: weak acids or bases that prevent sharp, sudden changes in pH– Ex: ______ for an upset stomach. It absorbs extra H+ ions.
(Section 3): Carbon “Organic” Compounds
• Why is carbon so special?• Carbon has 4 valence electrons, • Allows it to bond to many other things at
once.
• Pix of organic compounds important to living things
Carbon, the building block of living things:
• Is 18% of human body by weight
• Forms four covalent bonds
• Can form single or double bonds
• Can build micro- or macromolecules (big chains)
Slide 2.11
Section 3: Carbon (Organic) Compounds of Living Organisms
Figure 2.12Slide 2.12
Carbon Can Bond in Many Ways
Figure 2.14Slide 2.15
1: Carbohydrates MADE OF: C, H, O
FUNCTION: energy & structure
1. Sugars: short chains of
• Monosaccharides- 1 sugar ring
Ex: glucose, galactose
• Disaccharides-2 attached sugar rings
Ex: sucrose, fructose, lactose
2. Polysaccharides: thousands of monosaccharides 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
Types of Carbohydrates
Lipids: Insoluble in Water
TYPES OF LIPIDS• Triglycerides: energy storage molecules– Fatty acids: saturated and unsaturated
• Phospholipids: cell membranes
• Steroids: carbon-based ring structures– Cholesterol: used in making estrogen and
testosteroneSlide 2.17
2: LipidsMade of: C,H,(O)
Function: energy storage, waterproof coverings
Unsaturated triglyceride
Steroids (type of lipid)
• Made of: C,H, O, N
• Function: building materials, enzymes
• Structure• Made of monomers called amino acids
• The instructions for building proteins are in DNA
Slide 2.18
Proteins: Complex Structures Contructed of Amino Acids
Hemoglobin (4 protein strands held together)
Enzyme FunctionEnzymes:– are proteins– function as catalysts (something that speeds up
chem rxns)– facilitate chemical reactions
• Lower the activation energy (energy required to start a rxn.)
The function of an enzyme is dependent on:– temperature – 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
Figure 2.25Slide 2.22Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.
Structure and Function of Adenosine Triphosphate (ATP)
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