chemistry - chemical basis of life - power point
TRANSCRIPT
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Lectures by Tom Chen
The Chemical Basis of LifeThe Chemical Basis of Life
Atoms, elements, compounds, & molecules
How molecules interact
Water is essential for life
Acids, bases and salts
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Chemicals play many more roles in life
– Making up our bodies, those of other organisms, and the physical environment
ELEMENTS, ATOMS, AND MOLECULES
2.1 Living organisms are composed of about 25 chemical elements
• About 25 different chemical elements
– Are essential to life
• Trace elements
– Are essential to life, but occur in minute amounts
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Atom: A unit of matter, the smallest unit of an element.
Element: A substance composed of atoms having an identical number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.
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Carbon, hydrogen, oxygen, and nitrogen Make up the bulk of living matter
Table 2.1
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2.2: Trace elements are common additives to food and water
• Dietary deficiencies in trace elements– Can cause various physiological
conditions
Figure 2.2A
Figure 2.2B
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2.3 Elements can combine to form compounds• Chemical elements
– Combine in fixed ratios to form compounds
Sodium Chlorine Sodium Chloride
Figure 2.3
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Subatomic Particles
• An atom is made up of protons and neutrons
Located in a central nucleus
• The nucleus is surrounded by electrons
• Arranged in electron shells
Figure 2.4A
+
+
– –
+
–
2
2
2
Protons
Neutrons
Electrons
Massnumber = 4
++
2e–
Electroncloud
Nucleus
2.4 Atoms consist of protons, neutrons, and electrons
• Atom: The smallest particle of matter that still retains the properties of an element
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Differences in Elements
• Atoms of each element
– Are distinguished by a specific number of protons
Figure 2.4B
+
–
6
6
6
Protons
Neutrons
Electrons
Massnumber = 12
+ +
6e–
Nucleus
Electroncloud
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Isotopes The number of neutrons in an atom may vary
• Variant forms of an element are called isotopes • Some isotopes are radioactive
Table 2.4
2.5 Radioactive isotopes can help or harm us
• Radioactive isotopes are useful as tracers
- For monitoring the fate of atoms in living organisms
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Medical Diagnosis
• Radioactive tracers are often used for diagnosis
- In combination with sophisticated imaging instruments
Figure 2.5A Figure 2.5B
Basic Research
• Biologists often use radioactive tracers
- To follow molecules as they undergo chemical changes in an organism
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How brain function is studied now?PET, CAT, MRI, etc.
Music Appreciation
Hearing, speaking, seeing, thinking about words
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2.6 Electron arrangement determines the chemical properties of an atom
• Electrons in an atom
– Are arranged in shells, which may contain different numbers of electrons
Hydrogen (H)Atomic number = 1
Electron
Carbon (C)Atomic number = 6
Nitrogen (N)Atomic number = 7
Oxygen (O)Atomic number = 8
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Figure 2.6
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Atoms whose shells are not full, tend to interact with other atoms and gain, lose, or share electrons. These interactions form chemical bonds
Types of chemical bonds:
1. Ionic bond
2. Covalent bond
3. Hydrogen bond
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Ionic bonds are attractions between ions of opposite charge
• When atoms gain or lose electrons
– Charged atoms called ions are created
Transfer of electron
NaSodium atom
ClChlorine atom Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
Na Cl ClNa
+ ––
–
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Covalent bonds join atoms into molecules through electron sharing
• In covalent bonds, two atoms share one or more pairs of outer shell electrons, forming molecules
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Sharing of electrons may be EQUAL or UNEQUAL
• A molecule is nonpolar
– When its covalently bonded atoms share electrons equally
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• In a polar molecule
– Electrons are shared unequally between atoms, creating a polar covalent bond
(–) (–)
(+) (+)
O
HH
Figure 2.9
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Hydrogen
bond (+)
(+)
H
H(+)
(+)
(–)
(–)
(–)(–)
O
Hydrogen bonds are weak bonds important in the chemistry of life
• The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules
Hydrogen bonding occurs in other biologically important compounds such as proteins and DNA.
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Used in food preparation
Used for hygienic purposes
Can be used for recreation
Supplies body with essential
minerals
Helps in maintaining homeostasis
Source of oxygen
Surrounds ¾ of the Earth’s surface
Serves as habitat for
aquatic organisms
Makes up almost 70% of human’s
body
Source of energy e.g
hydroelectric power plants
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Essential Minerals
•are inorganic substances that exist naturally on and in the earth
•14 minerals that have been shown by research to be essential to human health are: calcium, chromium, copper, fluorine, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, sodium and zinc
• “Essential” because they comprise human tissue
•Good sources of essential minerals include fruits, vegetables, meats, nuts, beans and dairy products.
• Varying amounts of minerals can be obtained from WATER
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Importance of minerals in body
• crucial to the growth and production of bones, teeth, hair, blood, nerves, skin, vitamins, enzymes and hormones
•For healthy functioning of nerve transmission
• blood circulation
•cellular integrity
• energy production and muscle contraction
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Water is the solvent of life
• Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions
+
–
–
–
–
–
–
–
–
––
++
+
++
Na+
+
Na+
Cl–
Ion insolution Salt
crystal
Cl–
WATER’S LIFE-SUPPORTING PROPERTIES
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WATER’S LIFE-SUPPORTING PROPERTIES
Hydrogen bonds make liquid water cohesive
• Due to hydrogen bonding
– Water molecules can move from a plant’s roots to its leaves by adhesion
• Insects can walk on water due to surface tension
– Created by cohesive water molecules
Figure 2.11
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Water’s hydrogen bonds regulate temperature
• Water’s ability to store heat (high heat capacity)
– Moderates body temperature and climate
• It takes a lot of energy to disrupt hydrogen bonds
- So water is able to absorb a great deal of heat energy without a large increase in temperature
• As water cools
- A slight drop in temperature releases a large amount of heat
WATER’S LIFE-SUPPORTING PROPERTIES
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Figure 2.12
Water has high heat of vaporization
A water molecule takes energy with it when it evaporates
• Leading to evaporative cooling
WATER’S LIFE-SUPPORTING PROPERTIES
Storm Turns Focus to Global Warming
Is the rash of powerful Atlantic storms in recent years a symptom of global warming?some scientists have maintained that the rise in mean global temperatures over the last half a century — a well-documented trend widely linked to human activities such as the burning of fossil fuels — will inevitably have an effect on storms.
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Liquid waterHydrogen bonds
constantly break and re-form
IceHydrogen bonds are stable
Hydrogen bond
Ice is less dense than liquid water
• Hydrogen bonds hold molecules in ice farther apart than in liquid water
• Ice is therefore less dense than liquid water which causes it to float
• Floating ice protects lakes and oceans from freezing solid
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Living organisms are sensitive to acidic and basic conditions
Acid = An ionic compound that releases H+ ions in solution
Base = An ionic compound that accepts H+ ions or produces OH- ions in solution
• Acidity is measured on the pH scale from 0 (most acidic) to 14 (most basic or alkaline)
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The pH scale
Basic solution
Oven cleaner
Acidic solution
Neutral solution
pH scale
0
1
2
3
4
5
6
7
8
9
10
11
12
Lemon juice, gastric juice
Grapefruit juice, soft drink
Tomato juice
Human urine
Pure waterHuman blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Incr
easi
ngly
AC
IDIC
(Hig
her
conc
entr
atio
n of
H+)
NEUTRAL[H+]=[OH–]
H+ H+
H+OH– H+
H+ H+
OH– H+ H+
OH–
OH–
H+ H+OH–
OH– OH–
H+ H+H+
OH–
OH–
OH– OH–
OH–OH– H+
Incr
easi
ngly
BA
SIC
(Low
er c
once
ntra
tion
of H
+)
OH–
H+
14
13
Figure 2.15
• The pH of most cells
Is kept close to 7 (neutral) by buffers
• Buffers are substances that resist pH change
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Acid precipitation threatens the environment
• Some ecosystems are threatened by acid precipitation
• Acid precipitation is formed when air pollutants from burning fossil fuels
– Combine with water vapor in the air to form sulfuric and nitric acids
– Can kill trees and damage buildings
Figure AFigure B
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Salts
Are formed when an acid and a base react with one another neutralizing the concentration of H+ ions
the process is called neutralization
Acid Base Salt
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1. Life processes occur in neutral pH.
2. Acids, bases and salts when dissolved in water serve as electrolytes.
3. Salts are abundant in our body in the form of different body fluids like sweat and tears.
Importance of acids, bases and salts in living organisms
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Electrolytes
•are the elements necessary for electrochemical activity in our body.
•Water (H20) – and the three minerals sodium, potassium and chloride are all necessary for the transmission of electrical impulses between cells
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CHEMICAL REACTIONS
2.17 Chemical reactions change the composition of matter• In a chemical reaction
- Reactants interact, atoms rearrange, and products result
2 H2O2 2 H2O
Figure 2.17A
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This is the general equation for photosynthesis—the process of capturing sunlight energy and converting it to chemical energy. Which of the following are the reactants of this reaction?
A. C6H12O6 and O2.
B. CO2 and H2O.