Chapter 2 - Chemical Basis of Life

Question 1

Is there water on Mars?

Answer 1

-gypsum found on Mars is best evidence that there was/is. So YES.

Question 2

How much does water content is in:

1) cells
2) earth
3) human body

Answer 2

1) 75%
2) 75%
3) 50-75%

Question 3

Is water a good solvent?

Answer 3

-can dissolve more substances than any other solvent (YES)

-

Question 4

Solvent
Solute
Solution

Answer 4

• what does the dissolving
• what is being dissolved
• the solute & the solvent

Question 5

Chemical Reactions

Answer 5

• occur when the reactants (starting materials) are converted into products (end materials)
• rxns that occur in cell occur readily in water

Question 6

When are atoms most stable?

Answer 6

When outermost electron shells are filled

Question 7

Molecule

Answer 7

consists of two or more atoms held together by chemical, or covalent, bonds

Question 8

Covalent Bonds

Answer 8

• occur between two atoms in a molecule that share electrons equally
• Covalent bonds can create partial negative charges on a molecule when the electrons are not shared equally

Question 9

Valence Electrons

Answer 9

electrons that participate in chemical bonds

Question 10

Hydrogen Bonds

Answer 10

-H atom covalently bonded to electroneg atom
-exist BETWEEN molecules
-The half life of each hydrogen bond is less than a nanosecond
-occur mostly btwn polar molecules
2-5 kcal/mole
-occurs btwn 2 strands of DNA
-form in solutions of a polar solute dissolved in the polar solvent

Question 11

Water is both cohesive yet fluid. Explain:

Answer 11

• “flickering crystal” model
• transient H bonds btwn water molecules
• makes it a good solvent bc of this

Question 12

Why is the boiling point of water high?

Answer 12

due to the number of hydrogen bonds that must break for boiling to occur.

Question 13

Which is less dense? Liquid or solid water

Answer 13

• Solid water less dense

- forms highly ordered crystalline lattice when frozen

Question 14

List the properties of water & briefly explain each: (5)

Answer 14

1) Heat storage- absorb heat when break, release heat when formed minimizing temp. changes
2) Ice formation- in ice crystal spaced far apart b/c of H bonding
3) High heat of vaporization- many H bonds need to break for evaporation
4) Cohesion- H bond hold water together
5) High polarity- attracted to ions & polar compounds

Question 15

Polar

Answer 15

molecules that have asymmetrical distribution of charge (or dipole)
-best example = water

Question 16

Nonpolar

Answer 16

molecules that lack electroneg atoms & strongly polarized bonds (molec made up of all C and H)

Question 17

Ionic bonds

Answer 17

• Molecules held together by electrostatic interactions (interactions between a positively and negatively charged atom)
• Na+Cl-, table salt is example
• known as salt bridges
• 3 kcal/mole

Question 18

Why is the strength of ionic bonds weak in cells?

Answer 18

-Bc of the presence of water

Question 19

Hydrophobic Interactions

Answer 19

molecules form weak bonds with each other (Van der Waals interactions) based on small electrostatic interactions
-not true bonds

Question 20

Van der Waals Force

Answer 20

form when 2 molecules w transitory dipoles are close & so they experience weak, attractive force which bonds them
- 01.-03 kcal/mole

Question 21

Acid

Answer 21

molecule that can donate a hydrogen atom

Question 22

Base

Answer 22

atom that can accept a hydrogen atom

Question 23

pH

Answer 23

= -log [H+]

-most biological processes are sensitive to the pH of a solution

Question 24

Buffered Solution

Answer 24

is one that can tolerate addition of acids or bases with very little change in the pH of the solution

Question 25

Water as a buffer?

Answer 25

-It can occur inside cells

Question 26

Amphoteric

Answer 26

- can be either acid or base | - ex. is water (weak acid, weak base)

Question 27

Why do non-polar (hydrophobic) molecules aggregate in a polar solvent?

Answer 27

to minimize surface contact with the polar solvent

Question 28

What is the chemical break up of life in %age?

Answer 28

``` ~70% water 30% chemicals: 15% proteins 6% RNA 4% ions, small molecules 2% phospholipids 2% polysaccharides ```

Question 29

Why is C the most important?

Answer 29

- 4 outer shell e-s allow it to bind to 4 other atoms (cov) - small nucleus of 6 protons 6 neutrons - can form single double triple bonds - is stable

Question 30

Go over common functional groups (7)

Answer 30

- methyl, hydroxyl, carboxyl | - amino, phosphate, carbonyl, sulfhydryl