Chemistry of Life

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Lecture Outline

2.1 Basic Chemistry

o Matter – anything that takes up space

o States of matter• Solid• Liquid• Gas

Basic Chemistry

o Elements – basic substances that make up matter

o Four elements that make up >90% of the human body

• Carbon (C)• Nitrogen (N)• Oxygen (O)• Hydrogen (H)

Basic Chemistry

o Atoms• Smallest unit of an element that has

chemical and physical properties of that element

• Smallest unit to enter into chemical reactions

• Structure Central nucleus Outer shells (energy levels)

Basic Chemistry

Subatomic particlesoIn nucleus

• Protons – positive charge

• Neutrons – no chargeoIn shells

• Electrons – negative charge

• Innermost shell can have 2 electrons

• Outer shells can have up to 8 electrons

• Number of electrons in outer shell determines the chemical properties of an atom

Basic Chemistry

o Atomic number• Number of protons in the nucleus• Denoted as a subscript to the lower

left of the atomic symbol

o Atomic weight• Number of protons plus the number of

neutrons• Denoted as a superscript to the upper

left of the atomic symbol

Basic Chemistry

o Mole• Measurement for the number of

atoms or molecules of a compound• Avogadro’s number 6.02 x 10 23

• Based on the number of atoms in exactly 12 grams of carbon atoms

Basic Chemistry

o Isotopes• Variations of one type of atom• Differ in number of neutrons

o Radioactive isotopes• Unstable isotopes that break down over

time• Releases detectable energy• Low levels of radiation can be used as

tracers• High levels of radiation can be harmful to

cells, but can also be useful

Basic Chemistry

o Molecules – form when atoms bond to each other

o Compounds – formed when atoms of different elements bond

Basic Chemistry

o Ionic bonds• Created by electrical attraction between

ions• Ions form when an atom gains or loses

electrons in its outer energy level to become stable

Positive ion—has lost electrons; indicated by superscript positive sign(s), as in Na+

Negative ion—has gained electrons; indicated by superscript negative sign(s), as in Cl–

• Can dissociate (separates into ions) when dissolved in water and are then referred to as electrolytes.

Basic Chemistry

o Covalent bonds• Created when atoms share electrons• Atoms can share more than one pair

of electrons Double bonds – atoms share two pairs of

electrons Triple bonds – atoms share three pairs of

electrons between them

• Polar covalent bonds result when there is an unequal sharing of electrons between atoms

2.2 Water, Acids, and Bases

o Water• Most abundant molecule in living

organisms• Is an inorganic molecule (does not

contain carbon atoms)• Is a polar molecule

Oxygen has a slight negative charge (δ-) Hydrogen atoms have a slight positive

charge (δ+) Attraction between slightly positive

hydrogen atoms and slightly positive oxygen atom results in hydrogen bonds

Water, Acids, and Bases

• Properties of Water1. Water is a solvent (liquid into which ions

are dissolved) Facilitates chemical reactions Molecules that dissolve in water are said to be

hydrophilic (water-loving) Molecules that do not dissolve easily in water

are said to be hydrophobic (water fearing)

Water, Acids, and Bases

2. Water molecules are cohesive and adhesive

Water molecules cling together (cohesion) because of hydrogen bonding

Water molecules cling to other substances (adhesion)

Water flows freely, allowing it to distribute evenly

Allows for transport

Water, Acids, and Bases

3. Water has a high specific heat capacity and a high heat of vaporization

Specific heat capacity is the amount of energy needed to change an object’s temperature by 1C

Heat of vaporization is the amount of energy needed to turn water into steam

Both allow for thermoregulation body temperature

Water, Acids, and Bases

o Acids and Bases• When water molecules break up, an

equal number of hydrogen ions (H+) and hydroxide ions (OH-) are released

• Acids are substances that release hydrogen ions (H+)

• Bases are substances that release hydroxide ions (OH-)

Water, Acids, and Bases

o Salt• A salt is an electrolyte formed when

an acid and a base are combined.• Water also forms.

• HCl + NaOH → NaCl + H2O

Water, Acids, and Bases

• pH Scale Used to indicate the acidity and basicity

(alkalinity) of a solution pH 7 is neutral (an equal number of

hydrogen ions and hydroxide ions are released)

pH above 7 is a base (more hydroxide ions are released than hydrogen ions)

pH below 7 is an acid (more hydrogen ions are released than hydroxide ions)

Water, Acids, and Bases

• pH of body fluids Normal pH of blood is 7.4 Acidosis – blood pH less than 7.35 Alkalosis – blood pH greater than 7.45 Blood pH needs to be maintained within a

narrow range Respiratory and urinary systems Buffers (chemicals that take up excess

hydrogen or hydroxide ions) Carbonic acid and bicarbonate ions

Water, Acids, and Bases

• Electrolytes Substances that release ions when put

into water The balance of electrolytes in the blood

affects the functioning of vital organs

2.3 Molecules of Life

o Four categories of molecules are unique to cells (called macromolecules)

• Carbohydrates• Lipids• Proteins• Nucleic acids

o Synthesis of macromolecules involves a dehydration reaction

o Breakdown of macromolecules involves a hydrolysis reaction

2.4 Carbohydrates

o The ratio of hydrogen (H) atoms to oxygen (O) atoms is approximately 2:1

o Function for quick, short-term cellular energy

Carbohydrates

o Simple carbohydrates• Low number of carbon atoms (3-7)• Monosaccharides

Glucose Fructose – found in fruits Galactose – found in milk

• Disaccharides Two monosaccharides joined together Sucrose (table sugar) – formed when

glucose joins with fructose Lactose – formed when glucose joins with

galactose

Carbohydrates

o Complex carbohydrates• Contain many glucose

(monosaccharide) units• Starch – storage form of glucose in

plants• Glycogen – storage form of glucose in

animals• Cellulose

Found in plant cell walls Humans are unable to digest (passes

through digestive tract as fiber)

2.5 Lipids

o Contain more energy per gram than other biological molecules

o Some function as long-term energy storage in organisms

o Do not dissolve in water o Consist mostly of carbon and

hydrogen atoms; contain few oxygen atoms

Lipids

o Fats and Oils• Formed when one glycerol molecule

reacts with three fatty acid molecules• Fats

Usually of animal origin Solid at room temperature Used for long-term energy storage,

insulation, and cushioning

• Oils Usually of plant origin Liquid at room temperature

Lipids

• Emulsification – cause fats to mix with water

• Saturated and Unsaturated Fatty Acids

Fatty acid (carbon-hydrogen chain ending with an acidic group –COOH

Saturated fatty acids have only single covalent bonds; lard and butter are examples

Unsaturated fatty acids have double bonds between carbon atoms wherever fewer than two hydrogens are bonded to a carbon atom; vegetable oils

Lipids

o Phospholipids• Contain a

phosphate group• Have a hydrophilic

head and hydrophobic tails

• Form backbone of cellular membranes

Lipids

o Steroids• Structure consists of four fused

carbon rings with attached functional groups

• Cholesterol Structural component of animal cell

membrane Precursor of several other steroids

2.6 Proteins

o Function of proteins• Fibrous structural proteins• Hormones• Muscle contraction• Transport• Protection• Enzymes

Proteins

o Structure of proteins• Made of amino acid subunits

Amino group Acid group R (Remainder) group – differentiates

amino acids

• Dipeptide – two amino acids joined together

• Polypeptide – three or more amino acids joined together

Proteins

• Amino acids joined together by a peptide bond

• Secondary structure – due to hydrogen bonding that may occur in a polypeptide

• Tertiary structure results from bonding between R groups

• Quaternary structure – arrangement of individual polypeptides in a protein containing more than one polypeptide

• Denaturation – irreversible change in the normal shape of a protein due to extremes in heat and pH

Proteins

o Enzymatic Reactions• Metabolism - sum of all chemical

reactions that occur in a cell• Enzymes (protein catalysts that

enable metabolic reactions) Named for their substrate(s) The shape of the active site determines

specificity of enzyme Many require cofactors that assist an

enzyme

Proteins

• Types of Reactions Synthesis Reactions

Two or more reactants combine Require energy Dehydration synthesis

Degradation (Decomposition) Reactions Larger, more complex molecule breaks down

into smaller, simpler products Hydrolysis reactions

Replacement (Exchange) Reactions – involve both degradation and synthesis

2.7 Nucleic Acids

o Huge macromolecules composed of nucleotides

o Nucleotides composed of 3 subunit molecules:

• A phosphate• A pentose sugar• A nitrogen-containing base

o Two classes of nucleic acids• DNA• RNA

Nucleic Acids

o Two classes of nucleic acids• DNA

Make up genes Contain pentose sugar deoxyribose Nitrogen-containing bases

Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Usually double stranded

Nucleic Acids

• RNA Intermediary in process of protein

synthesis Contain pentose sugar ribose The nitrogen-containing base uracil (U)

replaces thymine Usually single stranded

Nucleic Acids

o ATP (Adenosine Triphosphate)• Primary energy carrier in cells• Cells break down glucose and convert

released energy into ATP• Used when cellular reactions require energy• Breakdown of ATP results in one molecule of

ADP (adenosine diphosphate) and one molecule of inorganic phosphate

• ATP is rebuilt by the addition of inorganic phosphate to ADP

• One glucose molecule can build 36 ATP molecules