PHYSIOLOGY 1


THE GENETIC BASIS OF LIFE

NUCLEIC ACIDS

Nucleic acids are macromolecules that are polymers composed of nucleotides. A nucleotide is composed of three basic components: a Pentose Sugar [Ribose or Deoxyribose - specific for each nucleic acid) ; a Phosphate group ( PO4 3- ) and a Nitroge base: These can be one of:
Guanine, Adenine, Cytosine, Thymine or Uracil.

The backbone of the nucleotide is formed by the sugar and phosphate and the nitrogen bases juts into the centre.


S - N
nucleotide1.jpg
|
(P)


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A strand of nucleotide is formed by sugars binding to phosphates vertically, thus forming a S-P backbone of the strand, and the nitrogen bases, in the case of double stranded nucleic acids, will bond with one another in a very specific way: G - C And A - T

DNA


Double stranded helix
DNA_basic.jpgDNA_doubleHelix.jpg
Sugar = Deoxyribose + Phosphate group as backbone
Nitrogen bases : Guanine — Cytosine
Adenine — Thymine Bonds are weak hydrogen bonds
Nitrogen base triplet codes = unit of genetic information = gene
eg. GCA, TAC, CGA , CAT, ACG etc.
Theory: one gene, one amino acid ----.> protein synthesis

DNA is a self-replicating molecule. When the two strands separate from each other, each strand builds up a complement and thus 2 doubles strands are formed from the one strand. However, before the new DNA strand is formed, the DNA genetic code is copied by mRNA which vacates the spaces as soon and the message is copied and the nucleotides from the pool then build up the new DNA strand.

DNA_Repl_Process.jpgmRNAtranscription.jpgDNA_Replication1.jpg



RNA

Single stranded
Sugar = Ribose + Phosphate group as backbone
Nitrogen bases: Guanine, Cytosine, Adenine, Uracil
Based on DNA structure and formed during DNA replication.
mRNA copies information from DNA and acts as messenger to relay genetic info from nucleus to cytoplasm for formation of tRNA, which transfers the information to the ribosomes where it translates into rRNA which is responsible for protein synthesis.


VIRUSES

Viruses are macromolecules composed of a nucleic acid and protein coat. The nucleic acid is either DNA or RNA, never both in the same molecule. Viruses that contain RNA are referred to as retro-Viruses.
Since viruses are not living organisms, they depend on host cells to replicate. Once they have invaded a host cell, they make use of the host DNA material to multiply to the extent that the cells bursts and set the viruses free. The new viral colony can now invade other cells and repeat the process.
Because viruses are not living, antibiotics cannot be used to “kill” them or to stop their replication. There are ‘blockers’ to certain virus that can prevent them from attaching to and invading cells. A healthy cell has a membrane structured such that invasion by foreign bodies is extremely difficult... This is referred to as high resistance to some infectious diseases. For this reason in depth exploration of the structure of the cell membrane will be undertaken.

virusCell.jpgHIVstructure.jpg



BACTERIA
Bacteria are unicellular prokaryotic organisms. They have cellular structure and nuclear material, but the nuclear material lacks a nuclear membrane. Although it is embedded in the cell plasma, it is confined, i.e. not scattered everywhere. The cell membrane is surrounded by a special wall that can change with changing environmental conditions, thus they are able to withstand extreme and a variety of changes in their environment. The wall, in turn, is protected by a slimy capsule that shields it from direct contact with the environment and it can become hard and impenetrable during unfavourable conditions- forming what is known as a spore. It is thus very difficult to ‘kill them off’. Because bacteria are living, the do respond to antibiotic treatment. If antibiotics kill organisms, it poses a great danger to our living cells and it is vital that we supplement our intake of Vitamins such as A, C and E (particularly C) during treatment with antibiotics.
Bacteria are virtually heat resistant, drought resistant and flourish in wet conditions. They are, however, threatened by extremes in pH.
The general structure of a bacterium

bacterium.jpg

FUNGI

Fungi are multinucleate organisms. Some fungi are saprophytic and some are parasitic. Among the parasitic fungi there are ringworms, athletes foot, dandruff and thrush.
Of the saprophytic fungi are the breadmould, mushrooms, yeasts etc.

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Some parasitic fungi: causing athletes foot and other fungal infections that can be fatal

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