Converting the information encoded by a gene into its product starts with RNA synthesis, during which
enzymes use the gene's DNA sequence as a template to assemble a strand of RNA.
RNA usually occurs in a single-stranded form that is similar to a single strand of DNA
the fourth base in RNA is uracil (U), not thymine as it is in DNA
DNA's only role is to store genetic information
rRNA assembles amino acids into polypeptide chains
tRNA delivers amino acids to ribosomes
mRNA functions as the "messenger" between DNA and protiens
Transcription and translation are part of the process called gene expression
Transcription: DNA to RNA
The same base-pairing rules also govern RNA synthesis in transcription
DNA as a Template
DNA replication begins with one DNA double helix and ends with two DNA double helices
An RNA strand is structurally so similar to a DNA strand that the two can base-pair if their nucleotide
sequences are complementary (U pairs up with A)
A strand of DNA acts as a template upon which a strand of RNA is assembled from
Only part of one DNA strand (not the whole molecule) serves as the template
Produces a single strand of RNA, and DNA replication produces two DNA double helices
Process of Transcription
In eukaryotic cells, transcription occurs in the nucleus; in prokaryotes, it occurs in cytoplasm
The polymerase starts moving along the DNA, over the gene region
The polymerase unwinds and joins free RNA nucleotides in the order dictated by that DNA sequence
DNA and RNA are released. RNA polymerase follows base-pairing rules, so the new RNA strand is
complementary to the DNA strand from which it was transcribed
RNA Modification
Introns are removed in chunks from a newly transcribed RNA before it
leaves the nucleus
A tail of 50 to 300 adenines is added to the end of a new
mRNA (poly-A tail)
mRNA carries DNA's protein-building information which consist of codons
All codons make the genetic code
Each tRNA has an anticodon that can base-pair with a codon, and it binds to the amino acid specified by that
codon
Enzymatic rRNA and proteins make up the two subunits of ribosomes
RNA Players in Translation
In eukaryotic cells, RNA is transcribed in the nucleus
Finished RNA moves into the cytoplasm through nuclear pores
Ribosomal subunits and tRNA converge on an mRNA
A polypeptide chain forms as the ribosome moves
along the mRNA, linking amino acids together in the
order dictated by the mRNA codons
The ribosome then begins to assemble a polypeptide chain as it moves along the mRNA
The first tRNA is released and the ribosome moves to the next codon
The second tRNA is released and the ribosome moves to the next codon