#10 What I Learned Today

Professionalism and Ethics I

The focus of today's lecture was to look at the characteristics of a profession, and the professionals committed to it. A profession was defined as job that needs someone who possess esoteric but useful knowledge and skills, based on specialized training or education of exceptional duration and difficulty. Some characteristics of a profession include:

• special/advanced education
• identifiable membership
• strong service orientation
• autonomy of practice
• self-regulating
• adherence to a code of ethics

A professional is a person who belongs to a learned profession, and is an expert at his or her work. Some characteristics of a professional include:

• selfless
• compassionate
• competent
• good communicator
• evidence-based
• ethical
• patient advocate
• responsible
  

Biochemistry

We continued our lecture on carbohydrate metabolism by looking at some other metabolic pathways, aside from the pentose phosphate pathway. These included the metabolic pathways for fructose, galactose, and mannose. We finished off by looking at the synthesis, branching, and debranching of glycogen.

Fructose is not the preferred substrate for sugars entering a cell (as glucose is), and can get across cell membranes via two different enzymatic pathways. Fructo-hexokinase can convert fructose to fructose-6-P, which is the product of the reversible pentose phosphate pathway. The second enzyme, fructo-kinase, converts fructose to fructose-1-P. Since this molecule cannot enter the pentose phosphate pathway, it gets but by aldolase B to get glyceraldehyde (which is an intermediate in the PP pathway!).

Galactose is processed through a isoenergetic transfer. The enzyme galactokinase puts a phosphate on galatctose to form galactose-1-P. It is useless to a cell in this form, so it is further converted. An activated form of glucose called UDPG (has a glucose-1-P 'tail') reacts with galactose-1-P, and transfers/switches the glucose-1-P tail with the galactose-1-P. The molecule then converts the galactose-1-P to glucose-1-P, and the UDPG molecule is taken back in order to start the process up again.

Mannose metabolic pathway will be described later.

With high levels of glucose-6-P ina cell, you get an increase in osmotic pressure as water tends to flow into the cell, which can eventually lead to its lysis. Thus, the cell prevents this by storing glucose-6-P as a glycogen polymer, by these steps:

• glucose-6-P is converted to glucose-1-P by phosphoglucomutase
• since the addition of glucose-1-P is not thermodynamically favoured, it is transformed by UTP (a high phosphate anolog of ATP)
• the glucose-1-P is then added to the Carbon-4 on the glycogen chain
• a PPi product is released, which ensures that the reaction will not be reversed

The glycogen chain has two ends: a reducing end, which is a 'free' carbon-1 (which is actually connected to a tyrosine residue on the protein glycogenin), and a non-reducing end, which is the last glucose molecule which has a free hydroxyl group at Carbon-4.

You also tend to see lots of branching in the glycogen polymers, in order to become more compact through alpha-1,6 branching. A 1,4-alpha-glucan branching enzyme separates an alpha-1,4 chain and moves it over to an alpha-1,6 branch.

Branching is reversed by a process called glycogenolysis, which involves three specific enzymes. Phosphorylase cleaves the alpha-1,4 bond with inorganic phosphate at the terminal end of a chain. This process requires the cofactor pyridoxal. Glucan transferases then transfers three glucose residues from one branch to another, leaving just the lsat sugar with an alpha-1,6 bond. A debranching enzyme then hydrolyzes the alpha-1,6 bond and at this point the branch has been fully removed.