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Meharry Biochem > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

where did live evolve

A

in water

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2
Q

T/F Organisms typically contain 40–50% water

A

False, Organisms typically contain 70–90% water

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3
Q

what is a critical determinant of the structure and function of proteins, nucleic
acids, and membranes

A

water

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4
Q

how many electron pairs are there around a oxygen atom in water

A

4

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5
Q

in which orbital are the 4 electron in in water

A

sp3

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6
Q

how many lone pairs are found on an oxygen molecule

A

2

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7
Q

what is the geometry of the water molecule

A

Water geometry is a distorted tetrahedron

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8
Q

what causes the net dipole on an oxygen atom

A

The electronegativity of the oxygen atom induces a net dipole moment

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9
Q

what contributes to waters ability to act as both an acid or a base

A

• Because of the dipole moment, water can serve as

both a hydrogen bond donor and acceptor

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10
Q

what kind of molecules do we typically see H bonding ?

A

• Typically involves two electronegative atoms (frequently

nitrogen and oxygen)

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11
Q

When are H bonds the strongest

A

Hydrogen bonds are strongest when the bonded molecules are
oriented to maximize electrostatic interaction
• Ideally the three atoms involved are in a line

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12
Q

T/F Water can serve as both – an H donor

– an H acceptor

A

True

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13
Q

What the maximum # of H bonds per molecule

A

4

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14
Q

Describe waters bp , surface tension and mp

A

Up to four H-bonds per water molecule gives water its
– anomalously high boiling point
– anomalously high melting point
– unusually large surface tension

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15
Q

Describe the lifetime of hydrogen bonding

A

Hydrogen bonding in water is cooperative and has a lifetime

of 1 to 20 picoseconds

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16
Q

Describe the difference in strength between an H bond and a covalent bond

A

Hydrogen bonds between neighboring molecules are longer and weaker
(20 kJ/mol) relative to the H–O covalent bonds (420 kJ/mol)

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17
Q

what is the bond angle of water

A

104.5

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18
Q

what kind of structure does ice form

A

a regular lattice

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19
Q

T/f a lattice structure has high enthalpy

A

false, • Hexagonal ice forms a regular lattice,

and thus has a low entropy

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20
Q

how many bonds does ice form

A

4

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21
Q

how many bonds does water from

A

3.4

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22
Q

how many bonds does vapor form

A

0

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23
Q

What allows ice to floar

A

the 4 H bonds form a crystal lattace structure which makes ice less dense than water, and thus ice floats on water

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24
Q

what kind of substances is water a good solvent for

A

Water is a good solvent for charged and polar

substances

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25
Q

what kind of substances is water a poor solvent for

A

Water is a poor solvent for nonpolar substances

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26
Q

is water a good solvent

amino acids and peptides

A

yes

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27
Q

is water a good solvent? – aromatic moieties

A

no

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28
Q

is water a good solvent? – carbohydrates

A

yes

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29
Q

is water a good solvent? – – small alcohols

A

yes

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30
Q

is water a good solvent?– nonpolar gases

A

no

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31
Q

is water a good solvent? – aliphatic chains

A

no

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32
Q

How can water dissolve salt

A

High dielectric constant reduces attraction
between oppositely charged ions in salt crystal; The NaCl crystal lattice is disrupted as water
molecules cluster about the Cl– and Na+
ions. The ionic charges are
partially neutralized, and the electrostatic attractions necessary for lattice
formation are weakened.

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33
Q

Does Entropy decrease or increase as ordered crystal lattice is dissolved

A

Entropy increases as ordered crystal lattice is dissolved

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34
Q

hemoglobin and myoglobin) are referred to as

A

• Some organisms have water-soluble carrier
proteins(hemoglobin and myoglobin) to
transport Oxygen.

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35
Q

is there sharing of electrons in non covalent interaction

A

no , Noncovalent interactions do not involve sharing a pair of electrons.

36
Q

what are the 4 types of non covalent interaction

A

ionic
hydrogen bonds
vander waals
hydrophobic effect

37
Q

what is an ionic bond

A

Electrostatic interactions between permanently charged

species, or between the ion and a permanent dipole

38
Q

what is a hydrogen bond

A

Electrostatic interactions between uncharged, but polar

molecules

39
Q

what is a van der waals interaction

A

– Weak interactions between all atoms, regardless of polarity
– Attractive (dispersion) and repulsive (steric) component

40
Q

Hydrophobic Effect

A

Complex phenomenon associated with the ordering of water

molecules around nonpolar substances

41
Q

T/f h bonds helps with binding of substrates to enzymes

A

True!

42
Q

T/f H bonds help with Binding of hormones to receptors

A

True

43
Q

T/f H bonds help with Matching of mRNA and tRNA

A

True

44
Q

In a H bond which atom is typically the acceptor

A

The

hydrogen acceptor is usually oxygen or nitrogen

45
Q

Does bulk water have high or low entropy?

A

high

46
Q

does water near a hydrophobic solute have high or low entropy

A

low

47
Q

do hydrophobic solutes have high or low solubility.

A

Low entropy is thermodynamically unfavorable, thus

hydrophobic solutes have low solubility

48
Q

Define the hydrophobic effect

A

Refers to the association or folding of nonpolar

molecules in the aqueous solution

49
Q

T/F hydrophobic effect contributes to protein folding
– protein-protein association
– formation of lipid micelles
– binding of steroid hormones to their receptors

A

True

50
Q

T/f the hydrophobic effect arises from some attractive

direct force between two nonpolar molecules

A

FALSE!! The hydrophobic effect does NOT arise because of some attractive
direct force between two nonpolar molecules

51
Q

does the water surrounding nonpolar solutes have high or low entropy

A

lower entropy

52
Q

T/F Nonpolar portions of a amphipathic molecule aggregate so that
fewer water molecules are ordered

A

True! The released water molecules will be more random and the
entropy increases
• All nonpolar groups are sequestered from water, and the released water molecules increase the entropy further

53
Q

which is more favored a cluster or lipid molecules or a micelle?

A

a micelle, because ALL of the hydrophobic groups are sequestered . n. By clustering together in micelles, the
fatty acid molecules expose the smallest possible hydrophobic surface area to the
water, and fewer water molecules are required in the shell of ordered water

54
Q

What force is this referring to : When two uncharged atoms are brought very close
together, their surrounding electron clouds influence
each other.

A

Van Der walls

55
Q

what are the 2 components of the van der wall interaction

A 
Attractive force (London dispersion) depends on the
polarizability

– Repulsive force (Steric repulsion) depends on the size of
atoms

56
Q

at longer distances does attraction of repulsion dominate in van der walls force

A

Attraction dominates at longer distances (typically

0.4–0.7 nm)

57
Q

at shorter distances does attraction or repulsion dominate

A

• Repulsion dominates at very short distances

58
Q

T/F van der walls forces are strong individually

A

false , they are Weak individually easily broken, reversible

59
Q

T/f van der walls force can happen between any 2 atoms

A

True! It is universal

and occur between any two atoms that are near each other

60
Q

what are the 3 colligative properties

A

Boiling point, melting point, and osmolarity

61
Q

do colligative properties depend on the nature of the solute

A

No! – Do not depend on the nature of the solute, just

the concentration

62
Q

what are the 4 non colligative properties

A

– Viscosity, surface tension, taste, and color

63
Q

Do colligative or non colligative properties depend on the nature of the solute

A

non colligative

64
Q

T/F cytoplasm of cells have high osmotic pressure

A

true

65
Q

Describe osmostic pressure

A

Osmotic pressure is measured as the force that must be applied to return the solution in the
tube to the level of that in the beaker.

66
Q

what is osmosis

A

movement of water

67
Q

a cell is in an isotonic environment . Describe what will occur

A

no net water movement

68
Q

a cell is in a hypertonic environment describe what will occur

A

water moves out of the cell and it shrinks

69
Q

a cell is in a hypotonic environment describe what will occur

A

water moves in, which causes cell to swell and burst

70
Q

are most water molecules ionized

A

no, Most water molecules remain un-ionized, thus pure water has
very low electrical conductivity
• The equilibrium is strongly to the left

71
Q

what does the extent of dissociation depend on for water

A

• Extent of dissociation depends on the temperature

72
Q

T/F protons from water typically exist freely in solution

A

false , Protons do not exist free in solution.

• They are immediately hydrated to form hydronium (oxonium) ions.

73
Q

what is the K eq for water

A

55.5 M

74
Q

T/F The pH and pOH must always add to 14

A

true

75
Q

T/F PH can be negative

A

True, pH can be negative ([H+] = 6 M)

76
Q

the ionic product of water is based on what concept

A

the ionic product of water

77
Q

T/F • Weak electrolytes dissociate only partially in water.

A

True ! They are more reluctant to give up their H

78
Q

The extent to which a substance dissociates is determined by what

A

Extent of dissociation is
determined by the acid
dissociation constant Ka

79
Q

If an acid is strong will it have a small or larger pka

A

small

80
Q

a conjugate acid-base pairs consist of what two things

A

Conjugate acid-base pairs consist of a proton

donor and a proton acceptor

81
Q

buffers are a mixture of what two things

A

Buffers are mixtures of weak acids and their anions (conjugate base)

82
Q

when the pH = pKa

(acid dissociation constant) what does this mean

A

At pH = pKa
(acid dissociation constant), there is a
50:50 mixture of conjugate acid and its conjugate
base

83
Q

At what point does a buffer lose its capacity

A

Buffering capacity is lost when the pH differs from

pKa by more than 1 pH unit

84
Q

what are the 3 buffer systems that we have in the body

A

phosphate, concentration in millimolar range
– bicarbonate, important for blood plasma
– histidine, efficient buffer at neutral pH

85
Q

if someone is hyperventilating will they experience acidosis of alklosis

A

alkalosis. They are breathing out too much co2, this means that the reaction will be pushed to the left ( to create more co2) which mean H+ concentration will decrease ( gets more basic)

86
Q

if someone is not exhaling enough would someone be more likely to experience alkalosis or acidosis

A

acidosis . This means there is excess co2 in the blood which will push the equation to the right , casuing H+ to increase.

Meharry Biochem (17 decks)

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