mRNA
(messenger RNA) copies code from DNA in triplets (codons)
DNA starting codon
TAC
mRNA starting code
AUG
tRNA
(transfer DNA) anticodon at the other end from the amino acid
tRNA starting code
UAC
transcription
the process of making a mRNA molecule
Where does transcription take place?
the nucleus
What are the 3 steps in transcription, respectively?
initiation, elongation, termination
What is initiation in transcription?
When the RNA polymerase attaches to the promoter region of the coding strand of DNA
What is elongation in transcription?
RNA polymerase unwinds the coding strand of DNA and assembles a mRNA strand complimentary to the coding strand of DNA
What is termination in transcription?
RNA polymerase reaches the terminator region of the DNA. It is released along with the mRNA primary transcript.
introns
a segment of DNA that is transcribed intomessenger RNA; removed before mRNA leaves the nucleus.
exons
a segment of DNA that is transcribed into RNA and translated into protein, specifying the amino acid sequence of a polypeptide.
When does the splicing of introns and exons take place?
between transcription and translation
silent mutation
if a codon is mutated but the right amino acid is put in
down syndrome
having 3 #21 chromosomes
turners
having 1 X chromosome and no Y, only in females
klinefelters
having 2 X chromosomes and 1 Y, only in males
translation
assembly of proteins on ribosomes; mRNA directs the order of the amino acids
What are the steps in translation, respectively?
initiation, elongation, termination
What is initiation in translation?
the P site of the ribosome attaches to the start codon of mRNA
What is the elongation step of translation?
each tRNA attaches to the A site of the ribosome and then to the P site and continues this as the ribosome moves down the mRNA chain
What is the termination step in translation?
When the stop codon (UAG,UAA,UGA) reaches the A site. There is no anticodon, the tRNA drops off, they separate, and the polypeptide chain is released.
reading frame
a group of 3 bases in codons
virus
cannot reproduce by themselves (they need a host) and they have either RNA or DNA, not both
retroviruses
the message is coded in the RNA and so the DNA makes the copy by reverse transcription
nondisjunction
chromosomes that fail to separate in meiosis
monosomy
1 chromosome (ie=turners syndrome)
autosomes
any chromosome 1-22, any chromosome except the sex ones