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Concerning osmolarity and tonicity:
Understanding the difference between osmolarity and osmolality is essential to my understanding of osmosis.

Osmolarity descirbes the number of solute particles per litre of solution, whereas osmolality is the number of solute particles per kg of solvent. Most of the time in physiology this makes no practical difference.


L-amino-acids, but not D-amino-acids, are found in proteins.

Glycine doesn't have L- and D- forms, because it's R-group is H. That means that its central carbon atom doesnt have four groups attached to it.


ATP is an example of a nucleotide

A nucleotide is a base linked to a sugar to which one or more phosphates are attached. ATP contains the base adenine, the sugar ribose and three phosphates attached to the ribose at the 5' position.


In aerobic respiration, electrons of highly reduced food molecules (together with protons) finally attach to oxygen, and water is formed.

In eukaryotic cells, this occurs in the mitochondria, and some of the energy 'released' is saved in formation of ATP from ADP, a process referred to as 'oxidative phosphorylation'.


When 1 mol of glucose is completely catabolised, 6 mol of CO2 and 6 mol of H2O are formed.

Glucose(C6H12O6) is completely catabolised in oxygen to yield CO2 and H2O in these molar proportions.


The dissociation constant of an acid (Ka) is essentially another name for the equilibrium constant for the reaction in which the acid dissociates.

The dissociation constant (Ka) of an acid (HA) is indeed essentially the same as the equilibrium constant for the reaction in which the acid dissociates to produce H+ and A-.


Mitochondria are thought to have evolved from primitive eukaryotic cells.

The mitochondria of eukaryotic cells have many of the characteristics of prokaryotic cells. They are thought to have evolved from prokaryotic cells that invaded eukaryotic cells and were subsequently retained.


Both prokaryotic and some eukaryotic cells have a cell wall.

Most prokaryotic cells are surrounded by a rigid cell wall built of a complex of proteins and oligosaccharides. Plant cells are surrounded by a cell wall built of the polysaccharide cellulose. Animal cells lack a cell wall.


The mature red blood cell contains no genetic material, no organelles, and carries out no metabolic processes.

The mature red blood cell has no organelles and carries no genetic information. However, it is not biochemically inert. It must carry out metabolism, for example, to generate ATP necessary to maintain the structural integrity of its membrane.


Concerning osmolarity and tonicity:
A solution of 100 mMol NaCl and 100 mMol glucose has a higher water concentration than a solution of 200 mMol NaCl.

- As solute concentration goes up, the water concentration goes down. Assuming total dissociation of the ions, the first solution has a total osmolarity of 300 mOsm, whereas the second has a total osmolarity of 400 mOsm. The first solution therefore has a higher water concentration than the second.


Simple phospholipids contain a phosphodiester bond.

-The ‘head’ of simple phospholipids is formed by a phosphate group (phosphoric acid residue) that forms one ester link with one of the hydroxyl groups of glycerol, and another with an hydroxyl group-containing molecule, such as choline, ethanolamine or serine.


In a DNA double helix, adenine on one chain is linked by two hydrogen bonds to thymine on the other

-The purine adenine and the pyrimidine thymine are said to be specific complementary bases, as are the purine guanine and the pyrimidine cytosine (which are linked across the double helix by three hydrogen bonds).


Both NAD and FAD are formed from vitamins.

-Riboflavin andniacin are precursors of NAD and FAD respectively.


A process at equilibrium is said to be in a dynamic state.

-At equilibrium, the rate of conversion of A into B is equal to the rate of conversion of B into A (so, although there may be inter-conversion of A and B, there is no net gain (or loss) of either A or B). In contrast, if B is formed from A, and converted into C, then when the rate of formation of B from A equals the rate at which B is converted into C, then B is said to exist in a dynamic steady state. So a dynamic steady state is not the same as an equilibrium.


Three types of cytoskeletal elements found in eukaryotic cells are built of actin, tubulin and keratin proteins respectively.

-The three forms are microfilaments (actin), microtubules (tubulin) and intermediate filaments (several proteins, including keratin).


Regarding the different body compartments:
If body sodium intake exceeds sodium output, there will be an increase in intracellular fluid volume.

-Excessive intake over output will lead to an increased concentration of sodium in the extracellular fluid. The increased osmolarity will then cause an osmotic efflux of water from the intracellular fluid, causing a decrease in its volume.


Regarding the different body compartments: An increase in plasma urea concentration will cause haemolysis of erythrocytes in vivo.

-Although there will be an increase in osmolarity, urea is not an effective osmole and so it will not induce osmotic flux of water out of the erythrocytes. Instead urea will equilibrate across the cell membrane. In renal failure when uraemia occurs this does not cause haemolysis.


AZT is a nucleotide analogue.

-This drug, which inhibits replication of HIV, is a nucleoside analogue. It is taken up into cells, and phosphorylated (i.e. converted into a nucleotide). It is then incorporated into and inhibits further polymerisation of the DNA of the replicating virus.


‘ATP’ stands for adenine 5’-triphosphate.

-ATP stands for adenosine 5’-triphosphate. ‘Adenine’ is the name of a base. (It’s one of the five major bases found in nucleic acids.) ‘Adenosine’ is the name of the nucleoside that contains adenine linked to ribose. When a nucleoside is phosphorylated - that is, has one or more phosphates attached to it (as does ATP) - then it becomes a ‘nucleotide’.


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

-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.


Ribosomes of eukaryotic cells are made in the cytoplasm and transported to the nucleus.

-Eukaryotic ribosomal RNA is made in the nucleolus of the nucleus. Together with protein, it is assembled into ribosomal particles. These are then transported to the cytoplasm. Here, ribosomes function as sites of protein synthesis.