- Human DNA and RNA.

Human DNA

All nucleic acids are polynucleotides. A nucleotide consists of three components:

1.     A nitrogenous base: (Adenosine and guanine which are based on purine rings, Thymine and cytosine which are based on pyrimidine rings).

2.     A pentose sugar (deoxyribose in DNA and Ribose in RNA) at 3′ end

3.     1-3 phosphate groups at 5′ end

 There are two kinds of nucleic acids:

o   Deoxyribonucleic acid (DNA)

o   Ribonucleic acid (RNA).

•Two polynucleotide chains are linear but antiparallel (i.e. one chain runs in a 5' to 3' direction; the other runs 3' to 5').

•   The sugar and phosphate groups form the linear backbone of the strands with the bases projecting inwards towards their partners held together by hydrogen bonds between the opposing bases:

ü  Adenine (A) pairs only with thymidine (T) (2 hydrogen bonds)

ü  Guanine (G) pairs only with cytosine (C) (3 hydrogen bonds).

· Multiple fragments that, together with a protein skeleton (chromatin), form chromosomes.

· Site: Nucleus and Mitochondria.

- Indications of genetic testing!

Medical applications (indications of genetic testing, karyotyping, chromosomal culture, analysis) :

1.     Multiple congenital anomalies:

Birth defects > one developmental regions of the body

A.    Confirmation of a clinical diagnosis

B.    Estimate recurrence risk of future sibling

2.     Dysmorphic features or well-defined syndrome e.g down syndrome

3.     Unexplained Mental retardation (chromosomal abnormalities are responsible for 1/3  50% of MR which is due to genetic factor)   

4.     Pubertal failure

5.     Ambiguous genitalia

Provide diagnosis e.g turner, klinfilter

If Normal karyotyping → other endocrinal disorders

6.     Infertility: at least 5% of infertile men are killfilter.

7.     Recurrent spontaneous Abortions and miscarriage:

High anion gap metabolic acidosis mnemonic.

High anion gap metabolic acidosis mnemonic.

(RUSH Kill ME)

Renal tubular acidosis (distal), Rhabdomyolysis (massive)

Uremia

Salicylate ingestion

Hypovolemia, Heart failure

 

Ketoacidosis (diabetic, starvation)

Inborn error of metabolism, Iron, Isoniazid ingestion

Lactic acidosis

Late metabolic acidosis of prematurity

 

Mitochondrial diseases, Methanol ingestion

Ethanol, Ethylene glycol ingestion

Modes of infectious disease transmission

 Modes of infectious disease transmission

An infectious agent may be transmitted from its natural reservoir to a susceptible host in different ways.

There are different classifications for modes of transmission. 

Here is one classification:

A.   General transmission

B.   Human-to-human transmission:

• Direct
  • Direct contact
  • Droplet spread
• Indirect
  • Airborne
  • Vehicleborne
  • Vectorborne (mechanical or biologic)

 more in this file