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THE CENTRAL DOGMA AND THE MOLECULAR UNITY OF LIFE (bypassing of regular…
THE CENTRAL DOGMA AND THE MOLECULAR UNITY OF LIFE
the central dogma
dogma: a principle or set of principles laid down by an authority as incontrovertibly true
flow of biological information in a cell is unidirectional
nucleotide sequence in DNA molecule - transcription - rRNA/mRNA/tRNA - ribosome - translation - amino acid sequence in polypeptide chain in protein
DNA codes for RNA, and RNA codes for protein.
transcription: the process by which DNA is copied (transcribed) to mRNA, which carries the information needed for protein synthesis
translation: mRNA formed in transcription is transported out of the nucleus, into the cytoplasm, to the ribosome (the cell's protein synthesis factory). Here, it directs protein synthesis
proteins are then responsible for traits and phenotypes
eg α and β thalassemia is caused by mutations in the α or β globin genes
thalassemia is an inerited blood disorder in which the body makes an abnormal form of haemoglobin resulting in large numbers of red blood cells being destroyed, which leads to anemia
eg. mono-amine-oxidase A polymorphisms (different forms) are linked with aggressive behaviour
catabolises amine neurotransmitters (Serotonin, melatonin, noradrenaline, adrenaline, dopamine...)
some genetic polymorphisms such as Trychohyalin SNP rs11803731, EDAR SNP rs3827760 and FGFR2 SNP rs4752566 influence hair thickness and curliness
rouge proteins can convert normal proteins to their own image
bypassing of regular unidirectional flow of information
eg. retroviruses
single-stranded RNA virus with a DNA intermediate which targets a host cell
once inside the host cell cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome (the reverse of the usual pattern) (RNA → DNA)
the new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus
thehost cell then treats the viral DNA as part of its own genome, translating and transcribing the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the viru
prions
prion: an infectious agent composed entirely of protein material, called PrP (short for prion protein), that can fold in multiple, structurally distinct ways, at least one of which is transmissible to other prion proteins, leading to disease that is similar to viral infection.
prion replication: lack nucleic acid so cannot reproduce, but they replicate by stimulating normal cellular prion protein to refold into a form called PrP scrapie (PrPSc)
prion work: over time, work on prions has suggested that the "infectious agent" is actually a misfolded protein -- which causes a normal cellular protein to change its shape to the misfolded form
DNA and protein are colinear
the positions of mutations in the gene are in the same linear order as amino acid replacements in the mutant proteins
DNA sequence determines amino acid sequence in a point-to-point manner
the genetic code
there are 4³ = 64 different codon combinations possible with a triplet codon of three nucleotides
in reality, all 64 codons of the standard genetic code are assigned for either amino acids or stop signals during translation
features of the genetic code
non-overlapping
only one DNA strand is transcribed for any one gene and they don't overlap
but viral genes can overlap
nearly universal
contains no punctuation marks
mRNA is translated codon by codon by tRNA moleciles which then carry the amino acid tro be added to the polypeptide chain
unambiguous
each codon specifies a particular amino acid and only that amino
degenerate/redundant
some amino acids can be specified by more than one codon
features of the genetic code
amino acids that share synthetic pathways tend to have the same first base in their codons
there is a link between the middle base and the hydrophobic - hydrophilic spectrum
amino acids with similar physical properties tend to have similar codons.
if the first two bases are fixed, varying the third base often codes for the same amino acid
coding in eukaryotic mRNAs is discontinuous