STEM Unit 1

covalent and ionic

occurs when valence electrons are shared by two atoms

The attraction of a particular atom for the electrons of a covalent bond is called its electronegativity.

occur when the electrons being shared are shared equally between the two atoms. Examples: O=O and H-H

This is the bond where one atom has a greater electronegativity than the other, resulting in an unequal sharing of electrons. This results in the region of the oxygen atom being slightly negative, whereas the regions about the hydrogen atoms are slightly positive.

It is a bond in which two atoms attract valence electrons so unequally that the more electronegative atom steals the electron away from the less electronegative atom.

Occurs because these ions will be either positively or negatively charged and will be attracted to each other by these opposite charges.

Hydrogen bonds are weak bonds that form between partial postive charged hydrogen atom of one molecule and the strongly electronegative oxygen or nitrogen of another molecule. Hydrogen bonds play a major role in the three-dimensional shape of proteins and nucleic acids.

These interactions are very weak, transient connections that are the result of asymmetrical distribution of electrons within a molecule. These weak interations contribute to the three-dimensional shape of molecules.

Hydrogen Bonds

Cohesion is the linking of like molecules. Think "water molecule joined to water molecule" and visualize a water strider walking on the top of a pond due to the surface tension that is the result of this property.

Is the clinging of one substance to another. Think "water molecule attactched to some other molecule." such as water droplets adhering to a glass windshield.

is the movement of water molecules up the very thin xylem tubes and their evaporation from the stomata in plants. The water molecules cling to each other by cohesion and to the walls of the xylem tubes by adhesion.

Specific heat is the amount of heat required to raise or lower the temperature of a substance by 1 degree Celcius. Relative to most other materials, the temperature of water changes less when a given amount of heat is lost or absorbed. This high specific heat makes the temperature of Earth's oceans relatively stable and able to support vast quantities of plant and animal life.

Bases have an excess of OH- ions, and pH above 7.0 [H+] < [OH-]

Buffers are substances that minimize changes in pH. They accept H+ from solution when they are in excess and donate H+ when they are depleted. Buffering compounds are essential in living tissues to minimize pH changes.

Carbonic acid is an important buffer in living systems. It moderates pH changes in blood plasma and the ocean.

All organic compounds contain carbon, and most also contain hydrogen.

- It has 4 valence electrons
- It can form up to 4 covalent bonds
- These can be single, double, or triple covalent bonds.
- It can form large molecules
- These molecules can be chains, ring-shaped, or branched.

Isomers are molecules that have the same molecular formula but differ in their arrangement of these atoms. These differences can result in molecules that vary in their biological activities. Ex: glucose and fructose.

Functional groups attached to the carbon skeleton have diverse properties. The behavior of organic molecules is dependent on the identity of their functional groups.

Alchohols such as ethanol, methanol; help dissolve molecules such as sugars

Carboxylic acids such as fatty acids and sugars; acidic properties because it tends to ionize; source of H+ ions

Ketones and aldehydes such as sugars

Ketones and aldehydes such as sugars

Amines such as amino acids

Organic phosphates, including ATP, DNA, and phospholipids

This group is found in some amino acids; forms disulfide bridges in proteins

Addition of methyl group affects expression of genes.

Carbohydrates include both simple sugars (glucose, fructose, galactose, etc.) and polymers such as starch made from these and other subunits. All carbo-
hydrates exist in a ratio of 1 carbon:2 hydrogen:1 oxygen or CH2O.

Monosaccharides are the monomers of carbohydrates. Examples: glucose (C6H12O6) and ribose (C5H10O5). Notice the 1:2:1 ratio discussed above.

Polysaccharides are polymers of monosaccharides. Examples: starch, cellulose, and glycogen.

Polymers are long chain molecules made of repeating subunits called monomers. Examples: Starch is a polymer composed of glucose monomers. Proteins are polymers composed of amino acid monomers.

Dehydration reactions create polymers from monomers. Two monomers are by removing one molecule of water. Example: C6H12O6 + C6H12O6 ➔ C12H22011 + H20.

Hydrolysis occurs when water is added to split large molecules. This occurs in the reverse of the above reaction.

Lipids are all hydrophobic. They aren't polymers because they are assembled from a variety of components. Ex: waxes, oilds, fats, and steroids

Fats are made up of a glycerol molecule and three fatty acid molecules.

Fatty acids include hydrocarbon chains of variable lengths. These chains are nonpolar and therefore hydrophobic.

- have no double bonds between carbons
- tend to pack solidly at room temperature
- are linked to cardiovascular disease
- are commonly produced by animals
Exmaples: butter and lard

- have some C=C (carbon double bonds); this results in kinks
- tend to be liquid at room temperature
- are commonly produced by animals
Examples: Corn oil and olive oil

- Energy Storage. Fats store twice as many calories per gram as carbohydrates.

- Protection of vital organs and insulation. In humans and other mammals, fat is stored in adipose cells.

Phospholipids make up cell membranes
They...

- have a hydrophillic (polar) head that included a phosphate group.
- have two fatty acid tails, which are hydrophobic.
- are arranged in a bilayer in forming the cell membrane

Steroids are made up of four rings that are fused together

- Cholesterol is a steroid. It is a common component of cell membranes
- Estrogen and testosterone are steroid horomones

Proteins are polymers made up of amino acid monomers

amino acids contain a central carbon bonded to carboxyl group at one end, an animo group at the other end, a hydrogen atom, and an R group.

Peptide bonds link amino acids. They are formed by dehydration synthesis between the animo and carboxyl groups of adjacent monomers.

Primary structure is the unique sequnece in which amino acids are joined.

refers to one of two three-dimensional shapes that are the result of hydrogen bonding between members of the polypeptide backbone (not the amino acid side chain)

tertiary structure results in a complex globular shape due to interactions between the side chains (R groups), such as hydrophobic interactions, van der Waals interactions, hydrogen bonds, and disulfide bridges.

A protein is denatured when it loses its shape and ability to function due to heat, a change in pH, or some other disturbance. Keep in mind: change the structure, change the function.

DNA and RNA are the two nucleic acids. Their monomers are nucleotides.

They are made up of three parts

- Nitrogenous base (adenine, thymine, cytosine, and guanine in DNA; adenine, uracil, cytosine, and guanine in RNA)
- Pentose (5-carbon) sugar (deoxyribose in DNA or ribose in RNA)
- Phosphate group