DIVERSITY OF BIOMOLECULES

Introduction:  The human body is made up of chemicals, cells, tissues, body organs and the systems, all in the increasing order of complexity.  More than 99% of the human body is composed of 6 elements namely; oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus.  Human body is composed of about 60% water, 15% proteins, 15% lipids, 2% carbohydrates and 8% minerals.  It is also surprising to know that out of these molecules, more than 90% contains Carbon as on of the atoms associated, making Carbon one of the most abundant atom on Earth in both animals and plants.  These molecules of life interact in different fashions to make life moving and duplicating.  In some my previous discussions, I have been talking about the molecules of inheritance and there is a great deal of knowledge about DNA and RNA as the parent molecules as you can read about them in the embedded links.

Structural makeup and organization:  Molecular structures in organisms are built from 30 small precursors, sometimes called the alphabet of biochemistry.  These are 20 amino acids, 2 purines, 3 pyrimidines, sugars (glucose and ribose), palmitate, glycerol and choline.  In living organisms the biomolecules are ordered into a hierarchy of increasing molecular complexity.  These biomolecules are covalently linked to each other to form macromolecules of the cell, for example glucose to glycogen, amino acids to proteins, and many others.

Major complex biomolecules are Proteins, Polysaccharides, Lipids and Nucleic acids.  The macromolecules associate with each other by noncovalent forces to form supramolecular systems, such as ribosomes, lipoproteins.  Finally, at the highest level of organisation in the hierarchy of cell structure, various supramolecular complexes are further assembled into cell organelle.  In prokaryotes such as bacteria, these macromolecules are seen in a homogeneous matrix; but in eukaryotic cells or higher organisms, the cytoplasm contains various subcellular organelles.

RELATED;

1.  PROTEINS  

2.  ENZYMES

3.  AMINO ACIDS

4.  DNA, THE GENETIC MATERIAL

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PENICILLINS

 

Objectives of the topic; By the end of this topic, the medical student/reader/ will be able to;

1.  Explain the mechanism of action and drug class of penicillins

2.  Briefly describe the sub classes of penicillins

3.  Mention some of the most common side effects of penicillins

Introduction:  The penicillins share features of chemical properties, mechanism of action, pharmacological aspects, and immunologic characteristics such as reactions and hypersensitivity with cephalosporins, monobactams, carbapenems, and β-lactamase inhibitors.  

Classification:  These group of drugs are named β-lactam antibiotics basing on their chemical structure.  

Penicillins can be assigned to one of three groups as described in the following discussion.  Within each of these groups are compounds that are relatively stable to gastric acid and suitable for oral administration because that means they will not be deactivated in the stomach.  These include drugs such as penicillin V, dicloxacillin, and amoxicillin.

Penicillins such as, penicillin G:  These have greatest activity against gram-positive organisms, gram-negative cocci, and non-β-lactamase producing anaerobes.  However, they have little activity against gram-negative rods, and they are susceptible to hydrolysis by β-lactamases.

Antistaphylococcal penicillins such as, nafcillin:  These penicillins are resistant to staphylococcal β-lactamases. They are active against staphylococci and streptococci but not against enterococci, anaerobic bacteria, and gram-negative cocci and rods.

Extended-spectrum penicillins:  These include ampicillin and the antipseudomonal penicillins.  These drugs retain the antibacterial spectrum of penicillin and have improved activity against gram-negative organisms.  Like penicillin, however, they are relatively susceptible to hydrolysis by β-lactamases.

Microbial Resistance to penicillins: Resistance to penicillins and other β-lactams is due to one of four general mechanisms:  

(1) Inactivation of antibiotic by β-lactamase.  

(2) Modification of target PBPs.  

(3) Impaired penetration of drug to target PBPs, and  

(4) Efflux.  

Beta-lactamase production is the most common mechanism of resistance. Hundreds of different β-lactamases have been identified.

RELATED;

1.  CEPHALOSPORINS

2.  PHARMACOLOGY AND THERAPEUTICS

REFERENCES

EXCHANGE OF GASES

 

INTRODUCTION: There are two sites of exchange of oxygen and carbon dioxide: the lungs and the tissues of the body. The exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries is called external respiration. This term may be a bit confusing at first, because we often think of “external” as being outside the body. In this case, however, “external” means the exchange that involves air from the external environment, though the exchange takes place within the lungs. Internal respiration is the exchange of gases between the blood in the systemic capillaries and the tissue fluid (cells) of the body.

COMPOSITION OF ATMOSPHERIC AIR: The air we inhale is approximately 21% oxygen and 0.04% carbon dioxide. Although most (78%) of the atmosphere is nitrogen, this gas is not physiologically available to us, and we simply exhale it. This exhaled air also contains about 16% oxygen and 4.5% carbon dioxide, so it is apparent that some oxygen is retained within the body and the carbon dioxide produced by cells is exhaled. OXYGEN: CARBON DIOXIDE

DIFFUSION OF GASES AND THE ROLE OF PARTIAL PRESSURES: Within the body, a gas will diffuse from an area of greater concentration to an area of lesser concentration. The concentration of each gas in a particular site lets say alveolar air, pulmonary blood, and so on, is expressed in a value called partial pressure. The partial pressure of a gas, measured in mmHg, is the pressure it exerts within a mixture of gases, whether the mixture is actually in a gaseous state or is in a liquid such as blood. Because partial pressure reflects concentration, a gas will diffuse from an area of higher partial pressure to an area of lower partial pressure. The air in the alveoli has a high PO2 and a low PCO2. The blood in the pulmonary capillaries, which has just come from the body, has a low PO2 and a high PCO2. Therefore, in external respiration, oxygen diffuses from the air in the alveoli to the blood, and carbon dioxide diffuses from the blood to the air in the alveoli. The blood that returns to the heart now has a high PO2 and a low PCO2 and is pumped by the left ventricle into systemic circulation. CHAMBERAND CIRCULATION THROUGH THE HEART

The arterial blood that reaches systemic capillaries has a high PO2 and a low PCO2. The body cells and tissue fluid have a low PO2 and a high PCO2 because cells continuously use oxygen in cell respiration (energy production) and produce carbon dioxide in this process. Therefore, in internal respiration, oxygen diffuses from the blood to tissue fluid (cells), and carbon dioxide diffuses from tissue fluid to the blood. The blood that enters systemic veins to return to the heart now has a low PO2 and a high PCO2 and is pumped by the right ventricle to the lungs to participate in external respiration. Disorders of gas exchange often involve the lungs, that is, external respiration.

RELATED;

1.  PEUMONIA

2.  CONDITIONS AFFECTING THE RESPIRATORY SYSTEM

3.  ANATOMY AND PHYSIOLOGY

REFERENCES

ENTEROBACTERIACEAE

 

Introduction:  The family Enterobacteriaceae consists of a large number of closely related bacterial species that inhabit large intestine of man and animals, soil, water as well as decaying material.  These have also been referred to as enteric bacteria or coliform bacilli.  Some of the most important intestinal pathogens for humans are included in this family.  These include causative agents of typhoid fever (enteric fever), bacillary dysentery and enteritis.  Many members of this family do not cause any disease so long as they are confined to the gut but when their habitat is changed their pathogenicity is also manifested.

Characteristics of the family:  The members of family Enterobacteriaceae are gram negative bacilli that are either motile with peritrichous flagella or non-motile, grow both aerobically and anaerobically on simple laboratory media including MacConkey’s agar.  

These are oxidase negative, catalase positive and reduce nitrates to nitrites. They ferment glucose in peptone water with the production of either acid or acid and gas, and they breakdown glucose and other carbohydrates both fermentatively under anaerobic conditions and oxidatively under aerobic conditions.  

Inspite of an exhaustive definition, there are certain commonly occurring bacteria which may be confused with the family Enterobacteriaceae.  These include Acinetobacter, Pseudomonas, Vibrio, Aeromonas and Plesiomonas. However, there are certain important differences between all these.  Almost all the gram-negative bacilli which are of medical importance to human beings and which ferment lactose is included in this family in addition to many other genera which fail to ferment lactose.  

1.  NORMAL FLORA OF THE HUMAN BODY

2.  SALMONELLA

3.  PATHOGENICITY OF MICROORGANISMS

4.  PSEUDOMONAS AERUGINOSA

5.  BACTERIOLOGY 

6.  NORMAL FLORA OF THE HUMAN BODY 

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