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1

Mass Number

number of protons + neutrons

2

Atomic Number

number of protons

3

Covalent Bond

- Made of 2 electrons
- Those 2 electrons are shared (i.e. one electron comes from each atom)
- Atoms can form bonds until their outermost shell is filled

4

Polar Covalent Bonds in water molecules

electrons are not shared equally (O is more electronegative than H), so partial charges exist on the O and H atoms

5

Increasing positive electrical charge in nucleus

H < C < N < O < F

6

Hydrogen Bond

A hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen (H) atom, covalently bound to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F)

7

Meniscus

forms where water meets a solid surface,
as a result of two forces.
Adhesion: Water
molecules that adhere
to the glass resist the
downward pull of
cohesion
Cohesion: Water
molecules at the
surface experience a
net downward pull
from hydrogen bonds
with water molecules
below

8

High Surface Tension

Property of Water
- Because of surface
tension, light objects
do not fall through the
water’s surface

9

Ice

Water molecules form a crystal lattice.

10

Liquid water

- No crystal lattice forms.
- Denser than ice. As a result,
ice floats.

11

Ionic Bond

- Electrostatic attraction between positive and negative charge
- Forms ions

12

Hydrophilic

Water loving
a) Polar molecules and ions dissolve readily in water
- partial negative and positive charges of water interact with the positive and negative ions
ex. salt dissolved in water, ions separate then dissolve

13

Hydrophobic

Water Fearing
b) Nonpolar molecules do not dissolve in water.
cannot interact with water, so they stay away
ex. Water and oil

14

Hydrophobic interaction

Water forces nonpolar molecules together, because doingso minimizes their disruptive effects on the hydrogen-bonded water network
- important for protein folding

15

Van der Waals interaction

Nonpolar molecules are also attracted to each other via relatively weak attractions called van der Waals forces (transient dipoles).

16

Bond Energy

Amount of energy needed to separate two bonded or interacting atoms under physiological conditions

17

Chemical bonds in order of strength in biology

Covalent > H bond > Ionic Bond > Hydrophobic interaction > LDF

18

Chemical Reactions

A chemical reaction can be written as an equation. The equation must balance because matter is neither created nor destroyed.

19

Molarity

A 1 molar (1 M) solution is one mole of a compound dissolved in water to make one liter.
Example: One mole of NaCl is the atomic weight of Na (23) plus the atomic weight of Cl (35.5), or 58.5, in grams. When 58.5 grams of NaCl are dissolved in water to make one liter, the solution is 1 molar.

20

Mole

- amount of a substance in grams whose weight is equal to its molecular weight.

21

Acids

release/donate H+ ions in solution.
If the reaction (dissociation) is complete, it is a strong acid, such as HCl.
The carboxyl group (—COOH) is common in biological compounds. It functions as a weak acid because it dissociates partially and reversibly
—COOH —COO– + H+

22

Bases

- accept H+ in solution (release OH–). (takes protons from water)
- NaOH ionizes completely to Na+ and OH–. The OH– absorbs H+ to form water. It is a strong base.
- The amino group (—NH2) is an important part of many biological compounds; it functions as a weak base by partially and reversibly accepting H+:
—NH2 + H+ —(NH3)+

23

pH

defined as the negative logarithm of the H+ concentration in moles/liter
1 (very acidic) -14 (very basic)
7- neutral (water)