Life at the Cellular Level 4

Question 1

What does water being a polar molecule allow it to do?

Answer 1

Bathe our cells

Dissolve and transport compounds

Allows compounds to move within and between our cells

Participate in chemical reactions

Dissipate heat

Question 2

Why is water polar?

Answer 2

Because O is more electronegative than H so it attracts the electrons of the covalent bond towards it causing partial charges

Question 3

What kind of bonds can water form due to being polar?

Answer 3

Hydrogen bonds

Question 4

What kind of molecules can form hydrogen bonds?

Answer 4

Any that contain electronegative atom bonded to H which is electropositive

Question 5

What do hydrogen bonds determine due to linking molecules in precise patterns in space?

Answer 5

3D structure

Question 6

Are bent or linear hydrogen bonds the strongest?

Answer 6

Linear

Question 7

Are molecules that can form hydrogen bonds water soluble or insoluble?

Answer 7

Water soluble

Question 8

What are some examples that can form hydrogen bonds?

Answer 8

Sugars

Alcohols

Aldehydes

Ketones

Compounds with N-H groups

Question 9

What happens when molecules with hydrogen bonds are dissolved in water?

Answer 9

Water-water hydrogen bonds and solute-solute hydrogen bonds are replaced with more energetically favourable solute-water hydrogen bonding

Question 10

Why are O₂ and CO₂ poorly water soluble?

Answer 10

O=O and O=C=O have no polarity

End molecules in the straight line are the same so no partial charge

Question 11

Why is O₂ carried by haemoglobin and CO₂ floats around as bicarbonate?

Answer 11

Because they are poorly water soluble

Question 12

Are charged molecules water soluble?

Answer 12

Yes, water forms ‘screens’ around each ion

Question 13

What is the hydrophobic effect?

Answer 13

Tendency of nonpolar substances to aggregate in an aqueous solution and exclude water molecules

Question 14

How do non polar molecules arrange themselves in water?

Answer 14

To minimise disruption of hydrogen bonding amount surrounding water molecules, because this is the most energetically favourable arrangement

Question 15

What does amphipathic mean?

Answer 15

Contains both hydrophobic and hydrophillic parts

Question 16

How do phospholipids minimise water-water hydrogen bonding?

Answer 16

By forming bilayers

Question 17

Why do proteins fold in on themselves?

Answer 17

So hydrophobic regions are on the inside and hydrophillic are on the outside, allowing them to be water soluble

Question 18

How are hydrophobic lipids transported in the blood?

Answer 18

In a chylomicron (phospholipid surface, triacylglycerols stored inside)

Question 19

How does water weakly dissociate?

Answer 19

H₂O ⇔ H⁺ + OH^-

Question 20

What does dissociate mean?

Answer 20

Molecule splits into smaller pieces

Question 21

What equation describes the equilbrium of water?

Question 22

Why can the equilbrium of water equation be expressed as this?

K_w = [H⁺][OH^-]

Answer 22

Because the concentration of H₂O is very high and essentially constant so it can be removed from the original equilbrium of water equation

Question 23

What is K_w known as?

Answer 23

The ionic product of water

Question 24

What is the value of K_w?

Answer 24

1x10^-14

The ratio of H⁺ and OH^- in pure water is 1:1 so:

[H⁺] = [OH^-] = 1x10^-7mol/L

Question 25

Why do we use the log to express the concentration of H⁺ in water?

Answer 25

Because the concentration is so small, we use the negative log to avoid negatives: -log[H⁺] = -log[OH^-] = 7 The negative log is appreciated to pH and pOH pH = pOH = 7

Question 26

Why does water have a neutral pH?

Answer 26

Because the concentration of H⁺ and OH^- is the same

Question 27

What is an acid?

Answer 27

A molecule capable of donating a proton pH \< 7 Greater concentration of H than OH

Question 28

What is a base?

Answer 28

Molecule capable of accepting a proton pH \> 7 Greater concentration of OH^- than H⁺

Question 29

What does an increase or decrease of 1pH represent?

Answer 29

A ten fold increase or decrease of [H⁺]

Question 30

What does pH + pOH equal?

Answer 30

pH + pOH = 14

Question 31

What is a strong acid/base, giving an example of each?

Answer 31

One which fully dissociates HCl is a strong acid NaOH is a strong base

Question 32

What is a weak acid/base, giving an example of each?

Answer 32

One which partly dissociates Lactic acid is a weak acid Ammonium hydroxide is a weak base

Question 33

What is a congugate acid?

Answer 33

Spieces after a base accepts a proton

Question 34

What is a congugate base?

Answer 34

Spieces after an acid donates a proton

Question 35

What makes up the conjugate acid/base pair?

Answer 35

A proton donor and the corresponding acceptor

Question 36

Does a strong or weak acid have a greater tendency to lose its proton?

Answer 36

The stronger an acid the greater its tendency go give up its proton HA⇔H⁺ + A^-

Question 37

The tendency of an acid to lose its proton is defined by what? What expression describes this?

Answer 37

The equilbrium constant (K_eq) or acid dissociated constant (K_a)

Question 38

What are pK_a values?

Answer 38

The negative log of K_a value pK_a = -logK_a

Question 39

What is a buffer?

Answer 39

Mixture of a weak acid and its conjugated base which can resist pH changes from the addition of an acid or base

Question 40

What two equilbriums are going on in a solution of a weak acid?

Answer 40

H₂O ⇔ H⁺ + OH^- HA ⇔ H⁺ + A^-

Question 41

What are the steps of a titration curve of a weak acid?

Answer 41

1. As NaOH is added the OH^- combines with free H⁺ to make H₂O 2. HA dissociates further to replace the lost H⁺ and maintain equilbrium 3. Process continues and more HA ionises to A^- 4. At midpoint pH = pK_a, beyond this HA continues to be used up until all of it is ionised to A^-

Question 42

What happens to the pH during the buffering region?

Answer 42

pH barely changes with a large input of an acid or base

Question 43

The Henderson-Hasselbalch equation relates the acid dissociation equiation to the bufffering ability of a week acid/conjugate base, what does this look like?

Question 44

What are important buffers in the body?

Answer 44

Phosphate Bicarbonate

Question 45

Why are buffers important in the body?

Answer 45

They maintian physiological pH when acids and bases are added