chapter 2 chemistry of life mader, sylvia s. human biology. 13 th edition. mcgraw-hill, 2014
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Chapter 2
Chemistry of Life
Mader, Sylvia S. Human Biology. 13th Edition. McGraw-Hill, 2014.
Points to ponder
• How are living things organized from atoms to molecules?
• What is pH and how is it important to living organisms?• What are the four macromolecules found in living
organisms?• What are the structure (subunits) and function of these 4
macromolecules?• How are proteins organized and how is their shape
important to their function?• How are DNA similar and how are they different?
Building blocks from large to small
• Matter is anything that has weight and takes up space
• Elements are the basic building blocks of matter that cannot be broken down by chemical means
• Atoms are the smallest units of an element that retain the element’s physical and chemical properties. These bond together to form molecules
• 90% of the human body is composed of 4 elements– Carbon, nitrogen, oxygen, and hydrogen
2.1 From atoms to molecules
Atoms• Atom symbol • Atomic mass
– Quantity of matter– Protons & Neutrons
• = 1 mass unit
– Electrons• = 0 mass units
• Atomic number– # of protons– When electrically neutral:
• # protons = # electrons
2.1 From atoms to molecules
Subatomic particles of atoms
• Neutrons have a neutral charge
• Protons are positively charged
• Neutrons and protons make up the nucleus
• Electrons are electrically charged and orbit around the nucleus
2.1 From atoms to molecules
Isotopes
• 2 or more elements with equal numbers of protons but different numbers of neutrons
Electron shell
p+ p+
p+n
n
n
e e e
(a) Hydrogen-1(electron-shell model)
(b) Hydrogen-2 deuterium
(c) Hydrogen-3, tritium
Isotopes• Radioactive isotopes
– Unstable isotopes break down/decay and release energy in the form of rays and subatomic particles
• Low Levels of Radiation– Useful in dating old objects,
imaging body organs and tissues through x-rays and killing cancer cells
• High Levels of Radiation– Harmful by damaging cells and
DNA and/or causing cancer
2.1 From atoms to molecules
Radiation therapy• Radiation therapy works by damaging the DNA of cells. • The damage is caused by a photon, electron, proton, neutron,
or ion beam directly or indirectly ionizing the atoms which make up the DNA chain.
• Cells have mechanisms for repairing DNA damage, breaking the DNA on both strands proves to be the most significant technique in modifying cell characteristics.
• Cancer cells generally are undifferentiated and stem cell-like, they reproduce more, and have a diminished ability to repair sub-lethal damage compared to most healthy differentiated cells.
• The DNA damage is inherited through cell division, accumulating damage to the cancer cells, causing them to die or reproduce more slowly.
Molecules:
• Are made of atoms that are bonded together
• Can be made of the same atom or different atoms
• If atoms are different = compound
2.1 From atoms to molecules
Chemical Bonds• Ionic bonds:
– attraction between cations (+) and anions (-)
• Covalent bonds: – strong electron bonds– Non polar covalent bonds: equal sharing of
electrons– Polar covalent bonds: unequal sharing of
electrons
• Hydrogen bonds: – weak polar bonds
Ionic Bonds
Figure 2–3a
- Atoms donate or take on electrons- Results in a stable outer shell- Occurs between particles that are charged (ions)
Covalent bonds:• Atoms in this type of bond share electrons• Results in a stable outer shell
2.1 From atoms to molecules
Covalent Bond
Hydrogen(H2)
Oxygen(O2)
CarbonDioxide
(CO2)
NitricOxide(NO)
MoleculeElectron-Shell Model and
Structural Formula
H–H
O=O
N=O
O=C=O
Free Radicals:Ion or molecule that contain unpaired electrons in the outermost shell. - Extremely Reactive -Typically enter into destructive reactions -Damage/destroy vital compounds
What are the properties of water?1. Liquid at room temperature due to hydrogen bonds2. Liquid water does not change temperature quickly
– Good temperature buffer since it absorbs heat3. High heat of vaporization
– Prevents body from overheating4. Frozen water is less dense than liquid water
– Ice acts as an insulator to prevent water below from freezing
5. Molecules of water cling together– Allow dissolved and suspended molecules to be evenly
distributed throughout a system• Example: Blood is 92% water and transports oxygen and nutrients to the body organs and removes wastes and CO2
6. A solvent for polar (charged) molecules – facilitates chemical reactions
7. Makes up 60-70% of the total body weight
What bond holds water molecules together?
• Hydrogen bonds occur between a hydrogen in a covalent bond anda negatively charged atom
• These are relatively weak bonds
2.2 Water and living things
Acids and bases
• Acids are substances that dissociate and release hydrogen (H+) atoms
• Bases are substances that take up hydrogen atoms or release
hydroxide (OH-) ions
2.2 Water and living things
What is the pH scale?
• A measure of hydrogen ion concentration
• Working scale is between 0 and 14 – 7 = neutral pH
• A pH below 7 is acidic
• A pH above 7 is basic
• The concentration of ions between each whole number is a factor of 10
2.2 Water and living things
pH Scale
Figure 2–9
• Has an inverse relationship with H+ concentration: – more H+ ions mean lower pH, less H+ ions
mean higher pH
Looking at the pH scale2.2 Water and living things
pH Scale• pH of body fluids measures free H+ ions in solution• Excess H+ ions (low pH): Acidosis
– damages cells and tissues– alters proteins– interferes with normal physiological functions
• Excess OH— ions (high pH): Alkalosis – Uncontrollable and sustained skeletal muscle
contractions
• Buffers prevent pH changes:– Chemicals or combinations of chemicals that take up
excess H+ or OH-
– Example: In blood H+ + HCO3- H2CO3
OH- + H2CO3 HCO3- + H2O
Organic and Inorganic Molecules
• Organic: – molecules based on carbon and hydrogen
• Inorganic: – molecules not based on carbon and hydrogen
What organic molecules are found in living organisms?
• 1. Carbohydrates
• 2. Lipids
• 3. Proteins
• 4. Nucleic acids
2.3 Molecules of life
Making and breaking down organic molecules
• Dehydration reaction – the removal of water that allows subunits to link together into larger molecules
• Hydrolysis reaction – the addition of water that breaks larger molecules into their subunits
2.3 Molecules of life
How do we build and break down organic molecules?
2.3 Molecules of life
1. What are carbohydrates?
• Made of subunits called monosaccharides
• Made of C, H and O in which the H and O atoms are in a 2:1 ratio
• Function as short and long-term energy storage
• Found as simple and complex forms
2.4 Carbohydrates
What are simple carbohydrates?
• Monosaccharide – 1 carbon ring as found in glucose
• Disaccharide – 2 carbon rings asfound in maltose– 2 glucose molecules
2.4 Carbohydrates
What are complex carbohydrates?
• Polysaccharides made of many carbon rings
• Glycogen is the storage form of glucose in animals– Insulin promotes the
storage of glucose as glycogen
• Starch is the storage form of glucose in plants
2.4 Carbohydrates
Carbohydrate Functions
Table 2–5
PolysaccharidesGlycogen: made and stored in muscle cellsCellulose: structural component of plants -Ruminant Animals: Cattle, sheep, and deerCattle, sheep, and deer
The Ruminant StomachRuminant stomach is polygastric: four compartments
-Rumen -Reticulum
-Abomasum -Omasum
RumenOccupies 80% of the stomach
Muscular PillarContract to mix feed
Digest starch and fibersMicrobes produce VFA’s
Lined with Papillae
pH of 5.8-7.0Provide a suitable environment for bacteria and protozoa
2. What are lipids?
• Molecules that do not dissolve in water
• Used as energy molecules
• Found in cell membranes
• Found as fats and oils, phospholipids and steroids
2.5 Lipids
How are fats and oils different?
• Fats• Usually animal origin• Solid at room temperature• Function as long-term energy storage, insulation from
heat loss and cushion for organs
• Oils• Usually plant origin• Liquid at room temperature
2.5 Lipids
Fatty Acids• Carboxyl group -COOH
– Hydrophilic
• Hydrocarbon tail:– Hydrophobic– Longer tail = lower solubility
• Saturated vs. Unsaturated– Saturated: solid at room temp.
• Cause solid plaques in arteries resulting in cardiovascular disease• Butter
– Unsaturated: liquid at room temp.• Healthier• Cooking oils and margarines
• Trans-Fatty Acids: semi-solid– Partially hydrogenated
Figure 2–13
The structure of a Fat Molecule
• A glycerol molecule and 3 fatty acid tails• Fat molecule = triglyceride
2.5 Lipids
Phospholipids and GlycolipidsCombination Lipids
Figure 2–17a, b
Diglyceride
Cell Membranes are Composed of these lipids
Hydrophilic
Hydrophobic
Phospholipids Vs. GlycolipidsCombination Lipids
Figure 2–17c
Understanding fats when reading a nutrition label
• Recommendation for total amount of fat for a 2,000 calorie diet is 65g
• Be sure to know how many servings there are
• A % DV of 5% or less is low and 20% or more is high
• Try to stay away from trans fats
• Would you eat the food on the right? Why or why not?
2.5 Lipids
What are steroids?
• A lipid
• Structure is four fused carbon rings
• Examples are cholesterol and sex hormones
2.5 Lipids
3. Protein
• Proteins are the most abundant and important organic molecules
• Basic elements: – carbon (C), hydrogen (H), oxygen (O), and
nitrogen (N)
• Basic building blocks: – 20 amino acids
Protein Functions
• 7 major protein functions:– support: structural proteins– movement: contractile proteins– transport: transport proteins– buffering: regulation of pH– metabolic regulation: enzymes– coordination and control: hormones– defense: antibodies
Proteins
• Proteins: – control anatomical structure and physiological
function– determine cell shape and tissue properties– perform almost all cell functions
Amino Acid Structure
1. central carbon
2. hydrogen
3. amino group (—NH2)
4. carboxylic acid group (—COOH)
5. variable side chain or R group
Figure 2-18
What do amino acids look like?2.6 Proteins
Peptide Bond
• A dehydration synthesis between:– amino group of 1
amino acid– and the carboxylic acid
group of another amino acid
– producing a peptide
What are the four levels of protein organization?
• Primary – linear order of amino acids
• Secondary – localized folding into pleated sheets and helices
• Tertiary – the 3-D shape of the entire protein in space
• Quaternary – combination of more than one polypeptide
• All proteins have primary, secondary and tertiary structure, while only a few have quaternary structure
2.6 Proteins
Figure 2–20a
Primary Structure
• Polypeptide:– Linear sequence of amino acids
• How many amino acids were bound together• What order they are bound
Secondary Structure
Figure 2–20b
• Hydrogen bonds form spirals or pleats
Figure 2–20c
Tertiary Structure
• Secondary structure folds into a unique shape
• Global coiling or folding due to R group interaction
Quaternary Structure
Figure 2–20d
• Final protein shape: – several tertiary structures together
Shape and Function
• Protein function is based on shape
• Shape is based on sequence of amino acids
• Denaturation: – loss of shape and function due to heat or pH
4. What are nucleic acids?
• Made of nucleotide subunits
• Function in the cell to make proteins
• Includes DNA and RNA – DNA deoxyribonucleic acid– RNA ribonucleic acid
2.7 Nucleic acids
DNA and RNA
DNA• Determines inherited characteristics• Directs protein synthesis• Controls enzyme production• Controls metabolismRNA• Codes intermediate steps in protein
synthesis
KEY CONCEPT
• DNA in the cell nucleus contains the information needed to construct all of the proteins in the body
Nucleotides
• Are the building blocks of DNA
• Have 3 molecular parts: – sugar (deoxyribose)– phosphate group– nitrogenous base (A, G, T, C)
What are the 3 parts of a nucleotide?
2.7 Nucleic acids
The Bases
Figure 2–22b, c
RNA and DNA
• RNA: – a single strand
• DNA: – a double helix joined at bases by hydrogen
bonds
Protein Synthesis:Three forms of RNA
• messenger RNA (mRNA)– Protein blueprint or instructions
• transfer RNA (tRNA)– Carry amino acids to the place where proteins
are being synthesized
• ribosomal RNA (rRNA)– Forms the site of protein synthesis in the cell
• Factory = ribosomes
Summary of DNA and RNA structural differences?
• DNA– Sugar is deoxyribose– Bases include A, T, C
and G– Double stranded
• RNA– Sugar is ribose– Bases include A, U, C
and G– Single stranded
2.7 Nucleic acids
Figure 2–24
ATP: An Energy Carrier
Adenosine triphosphate (ATP): – Adenine + ribose + 3 phosphate groups (tri=3)
• Chemical energy stored in phosphate bonds
Summary of the macromolecules
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