Hereditary information flows from DNA to RNA to protein.
Replication is the copying of DNA to make more DNA.
Transcription, the first step in gene expression,
is the copying of information from DNA to RNA.
"Central dogma":
Hereditary information flows from DNA to RNA to protein.
- Copying DNA to make more DNA is called replication.
- Copying DNA to make RNA is called transcription.
- Translation uses messenger RNA (mRNA) to control
the synthesis of a protein sequence.
- DNA, mRNA, and protein sequences are all colinear—
they have corresponding codons or amino acids in the same linear order.
Replication:
- Two DNA strands unravel
a bit to make a Y-shaped replication fork.
- Each strand helps synthesize a matching strand, so each new
DNA molecule is half newly synthesized and half conserved
(semiconservative replication).
- Nucleotide triphosphates (ATP = Adenosine TriPhosphate, TTP, GTP, CTP)
use some of their stored energy to add a new nucleotide:
- ATP can only add A opposite T
- TTP can only add T opposite A
- GTP can only add G opposite C
- CTP can only add C opposite G
Transcription is the copying of a DNA strand to make RNA (usually
messenger RNA), which can only occur if the DNA unravels to expose the
active strand.
- After transcription, excision removes some intervening
sequences (introns) that will not be translated into protein,
leaving a shorter sequence called an exon.
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