Quiz 1 true or false

Question 1

Regarding the different body compartments:

Water is easily able to cross most cell membranes.

Answer 1

TRUE
-How else would you get the movements of water caused by the joy of osmosis? Though the phosholipid bilayer is relatively impermeable to water, it also contains membrane proteins, called aquaporins, that form channels through which water can diffuse.

Question 2

The major non-penetrating solutes in the intracellular fluid are potassium ions.

Answer 2

TRUE
-The action of the Na/K-ATPas concentrates potassium ions inside the cell. They can actually leak out of cell through specific potassium selective channels, however the Na/K-ATPase just pumps the potassium ions back in again so it is as though they never left. They therefore behave like a non-penetrating solute.

Question 3

The central carbon (a-carbon) of an amino-acid is referred to as ‘an asymmetric centre’.

Answer 3

TRUE
-Another name that is sometimes used is ‘chiral centre’. This means that the carbon has four different groups attached to it. They can be arranged relative to one another in two distinctly different ways in space that are not inter-convertible without breaking and reforming covalent bonds. These different configurations are the L- and D- forms (or isomers) of the amino-acid.

Question 4

Biosynthetic reactions are referred to as amphibolic processes.

Answer 4

FALSE
-They are called anabolic processes. ‘Amphibolic’ means both anabolic and catabolic. Later in the course you will meet a process (the citric acid cycle) that is sometimes regarded as being amphibolic.

Question 5

The three atoms involved in a hydrogen bond lie in a straight line.

Answer 5

TRUE
-The hydrogen atom and the two electronegative atoms on either side of it interact most stably when they lie in a straight line. This contributes, for example, to the specific complementarity seen in the base-pairing of the DNA double helix.

Question 6

A buffer containing a weak acid that has a pKa of 8 works well around pH 8.

Answer 6

TRUE
-Buffers work best when the molar concentrations of HA (the weak acid of the buffer) and of A- (its conjugate base) are about equal. When they are equal, the Henderson-Hasselbalch equation (pH = pKa + log10 [A-]/[HA]) says that pH = (pKa + log101) = (pKa + 0) = pKa.

Question 7

If pOH = 7 then [H+] = 107 mol/L.

Answer 7

FALSE
-If pOH = 7, then pH = (14 - 7) = 7.
So -log10 [H+] = 7 and log10 [H+] = -7.
So [H+] = antilog10(-7) = 10-7 mol/L (not 107 mol/L).

Question 8

The ion product of water is defined as [H+] x [OH-].

Answer 8

TRUE
-In other words, it is the product of multiplying the concentrations of the two ions of water together - hence ‘ion product’. It is essentially unchanging under most conditions, and equal to 1 x 10-14 (mol/L)2.

Question 9

The Golgi apparatus is a specialised form of lysosome.

Answer 9

FALSE
-The Golgi apparatus is a series of stacks of flattened membranous sacs. Proteins formed in the endoplasmic reticulum are passed to the Golgi apparatus, where they are collected, modified and distributed to various parts of the cell. In particular, many are passed from the Golgi apparatus into secretory vesicles that discharge their contents to the outside of the cell. The lysosome is a membrane-bound vesicle concerned with the degradation of many biomolecules as part of their ‘turnover’.