15 March 2007

Biochemistry Revisited

I thought I would spend a bit of an essay discussing the nuts and bolts of Biochemistry. This class is usually taken along with Gross Anatomy and thus it can be a problem for some students.

My prevaling theme in all medical school classes is to keep up with the material. I cannot emphasize this more because good medical students find themselves failing because something (illness, family illness, emergency) interferes with their studies and they fall far enough behind and are unable to catch up or keep up. Biochemistry can be one of the most "unforgiving" courses if you fall behind. This class ranks right up there with Gross Anatomy in terms of volume of subject matter. It is vitally important that you do everything that you can, not to fall behind. If you do fall behind, you must catch up the very next weekend. Again, weekends are catch up days so don't use weekdays to catch up. Go immediately to where the class is and keep moving until Saturday.

Biochemisty is the "chemistry " of large molecules. These molecules are proteins, lipids, carbohydrates and nucleic acids. Since you are dealing with chemistry, you have to remember the subject matter of chemistry. This includes polar versus nonpolar, molecular shape, molecular funtion and chemical reactions. Most of the biomolecules are composed of carbon, hydrogen, oxygen and nitrogen and thus you need to be fairly familiar with the chemistry and characteristics of these elements. You also need to be familiar with the effects of water, pH and electronegativity. Throw in some enzyme kinetics and some equilibrium chemistry and you have the basis of biochemistry. The rest is application of the above characteristics and principles.

Biochemistry is NOT organic chemistry though we are a "carbon-based" life form. You need to understand carbon in terms of its covalent bonding and simularity in electronegativity when it is hooked to hydrogen but get rid of sp3, sp2 and sp1 bonding, free radicals and all of those synthetic schemes that you memorized in organic chemistry. In biochemistry, you are studying how reactions take place not why these reactions take place. They are already there but you have to put them together. Most of the reaction pathways in biochemistry involve hydrolysis, dehydration, hydration, oxidataion and reduction. You also need to know enzyme catalysis and you will be largely set.

Carbohydrates are polyhydroxy (poly alcohol) aldehydes and ketones. Amino acids have the amino and carboxyl characteristics (weak acid and base) and nucleic acids are based on their sequences, formation and degration. Lipids are non-polar and thus have the simpliest chemistry and function. That's the essence of the biomolecules.

Now all of these biomolecules have pathways, locations and functions. You can sit down and rote memorize the pathways but it is far more effective to ask yourself, "What are the substrates of these pathways?" "Where is the pathway located?" "Why does the body need this pathway?" and finally "What are the products of this pathway?" From that lauching pad, you can look at the individual reactions and enzyme characteristices (oxidation, reduction, hydrolysis, hydration, dehydration) and figure out where the regulation points are found. "Is the body building up a macromolecule?" or "Is the body tearing down a macromolecule for storage, ATP production or production of reducing equivalents?".

Other subjects of biochemistry are signal transduction pathways, hormones and functional characteristics of important molecules like hemoglobin, collagen and elastin. You will also study post translational modifications of proteins and how these relate to their function. Always remember to link structure with function when you are studying macromolecules. Think about glycogen and its function as a storage form of glucose. Glycogen is made up of multiple molecules of glucose and thus the pathway for its formation and degradation is going to involve glucose molecules. You need to know where other sugars feed into this pathway (where they feed into glucose metabolism), etc. You need to know where glycogen is stored (muscle and liver) and what the regulatory points of glycogen synthesis and degradation are. After that, you can look at the individual reactions of glycogen synthesis and glycogen storage in relation to the regulatory points of each pathway.

Bottom line for biochemistry is that you need to see the "big" picture and fill in the details. Never lose complete sight of the ultimate reason why you are studying the details. This is why my method of scanning the syllabus at the beginning of the semester (gives you an overview of how the course is organized), pre-viewing the next days lecture and reviewing the previous day's lecture before you study and learn the present lecture is very important. Again, you have to organize the material so that you can learn it efficiently.

Finally, a good review book like Harvy & Champe's Biochemistry is good to have but it cannot be the major source of your study. The best use of this book (also known commonly as Lippincott's Biochemistry) can help you summarize things or put things together but cannot substitute for your class notes or text book. Review books do reviews and you cannot "review" what you have not "learned " in the first place. Don't make a major mistake of believing that you can memorize a review book and that is what you will need to do well in your coursework. Review books can be good adjuncts to study but cannot replace your text, syllabus and notes. You can use your review book as a means of pre-viewing your lecture but your syllabus and the objectives that it contains are you guides in mastery of the material.

There are loads of new terms that will be introduced to you in your medical biochemistry course. You do not need to have taken undergraduate or graduate biochemistry before medical school. If you have throughly mastered your undergraduate pre-med chemistry coursework (that is general chemistry and organic chemistry), you have more than enough tools to master medical biochemistry. Do not fall into the trap of taking an undergraduate biochemistry or graduate biochemistry course unless you have plenty of time to master these courses or a passionate interest in the subject matter. If your medical school requires undergraduate/graduate biochemistry, then you have to take the course to meet a pre-req but most medical students are able to do well and pass this course without a previous biochemistry course. Also, most organic chemistry texts contain a very nice introduction to biochemistry that will get you on your way.

Do not fear Biochemistry because like the rest of medical school, its mastery depends more on organization and diligent mastery. In that first week (as soon as you get the syllabus in hand), start making out your study schedule. Never go to class unprepared (you can at least skim the syllabus) meaning that you know what the important points of the lecture will be and you know what is in the book so you are not trying to listen to the lecture cold. Don't forget to review the previous lecture (you have already studied and learned it at this point) before you tackle study and learning of the present lecture. A review book is an adjunct to your lecture material and not a substitute. Use a review book to review and supplement your class lectures if you like.


Anonymous said...

Love the blog. Please write about your experiences with physiology. I'm a first year struggling with the subject and need all the advice I can get. Thanks!

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