Biochemistry Lecture No.2: Proteins & Amino Acids
Thursday, September 7 , 2012
-Biochemistry is the study of life at the molecular level. It is a field of science closely linked to molecular
biology and focuses upon the four main molecules responsible for life: proteins, lipids, carbohydrates,
and nucleic acids.
The Central Biological Dogma:
-The central dogma in biology conveys the notion that all life forms store genetic information in the
form of DNA, which can be copied and transferred in the form of RNA through transcription. It is here
that this information is interpreted as codons for amino acids that give rise to proteins, the ultimate
expression of genes, by way of the process of translation.
-In summary, Francis Crick was of the opinion that all nucleic acids in an organism’s genome would
eventually become expressed in the form of proteins.
Exceptions To The Central Dogma:
-As credible as the central dogma appears, there are certain biological factors that actually violate this
reasoning. These include: epigenetic factors, micro RNA and post-translational modification.
-Epigenetic factors refers to environmental influences that attribute to disruptions in normal
transcription of DNA; a form of pre-transcriptional regulation. One such example of this is the
methylation of DNA which inhibits transcription and gives rise to gene silencing. Another example is the
acetylation of DNA by enzymes, which causes histones to loosen their association with DNA and make
the promoter more accessible for transcription.
-micro RNA (or miRNA) refers to the phenomenon in which newly discovered, small RNA molecules bind
other RNA molecules and render them incapable of being translated into proteins; a form of post-
-Let it also be noted that defects in DNA can lead to defects in proteins and that most diseases are the
result of defects in multiple genes.
Genotypes & Phenotypes:
-A genotype is the sum total of an organism’s inheritable potential; it describes their entire DNA
sequence. A phenotype is the sum of observable characteristics of an organism; physical appearance,
behaviour and biological performance are all associated with and organism’s phenotype.
-For example, in order for a human being to yield 4 pairs of abdominal muscles (usually 3), they must
have the genetic predisposition (or genotype) in order for the “8-pack” to be established as the person’s
phenotype. Personalized Medicine:
-Personalized Medicine is a recent medical model that presupposes the customization of health care to
each individual’s unique medical needs. Its decisions and practises are being tailored to the individual
patient (not the average human standard) by use of genetic or other personal information.
-It is an opposite approach to traditional clinical diagnosis and management, which focus upon the
patient’s phenotypic characteristics, and not exclusively on their genotype.