Chapter 17 Flashcards
gene expression
the process by which DNA directs the synthesis of proteins (or in some cases, just RNA)
one gene-one enzyme hypothesis
says that a gene dictates which specific enzyme is produced
transcription
o Synthesis of RNA using info from DNA
o DNA–>RNA
o Information is simply ‘re-written’ from DNA to RNA
o DNA can serve as complementary sequence to producing RNA
o Synthesis of any kind of RNA from a DNA template
ribosomes
sites for translation
• Facilitate the linking of amino acids into polypeptide chains
primary transcript
o The initial RNA transcript from any gene that is not translated into protein
o Initial RNA transcript–> pre-mRNA –> mRNA
o Includes the genes specifying RNA
o
Triplet code
the genetic instructions for a polypeptide
o triplet code–> mRNA–> amino acids
o Is then transcribed into 3-nucleotide (non overlapping) words in mRNA
o Responsible for the flow of info from gene –> protein
template strand
the strand being transcribed
o provides the template for the sequence of nucleotides in an RNA transcript
codon
mRNA nucleotide triplets
o There are 64
o Written in 5’→3’ direction
o This term is also used for DNA nucleotide triplets along the nontemplate strand
o Each codon specifies which amino acid will be placed in certain position along a polypeptide
o There are 3x the amount amino acids as there is protein product
Initiation (Transcription)
After RNA polymerase binds to promoter, DNA strands unwind and polymerase initiates RNA synthesis at starting point
Elongation (Transcription)
The polymerase moves downstream, unwinding DNA and elongating RNA 5’-→3’. Then, DNA strands reform a double helix
• Nucleotides are added to the 3’ end of growing RNA molecule
• Occurs at 40 nucleotides/sec.
• **A single gene can be transcribed by several molecules of RNA polymerase
Termination (Transcription)
RNA transcript is released and polymerase detaches from DNA
RNA polymerase
separates the 2 strands of DNA and joins RNA nucleotides complementary to DNA template strand
• Essentially elongates RNA polynucleotide
• Works only 5’→3’
• Doesn’t require a primer
promoter
area where RNA polymerase attaches and begins transcription
terminator
the sequence that signals the end of transcription
RNA polymerase II
used for pre-mRNA synthesis
transcription unit
stretch of DNA ‘downstream’ from the promoter (direction of transcription) that is transcribed into RNA molecule
start point
nucleotide where synthesis begins
transcription factors
collection of proteins in eukaryotes that mediate the binding of RNA polymerase and the initiation of transcription
transcription initiation complex
the complex of transcription factors and RNA polymerase II bound to the promoter
• 1) Eukaryotic promoter contains the TATA box. A nucleotide sequence containing ‘TATA’
• 2) Several transcription factors (including one recognizing the TATA box) must bind to the DNA before the RNA polymerase II can bind in correct location and orientation.
• 3) DNA, RNA, polymerase II, and other transcription factors bind to form the transcription initiation complex.
RNA polymerase II then unwinds DNA double helix, and RNA synthesis begins at start point on template strand.
TATA box
crucial promoter DNA sequence
• Found in eukaryotic promoter
• Nucleotide sequence containing ‘TATA’
upstream/downstream
upstream-5’ end
downstream-3’ end
RNA processing
enzymes in the nucleus modify pre-mRNA in ways that the message is sent to the cytoplasm
• This produces mRNA ready for translation!
• When mRNA reaches the cytoplasm and attaches to it with its modified ends, ribosome attachment is facilitated!
• Remember, 5’-cap and poly-A tail are not translated into protein
5’ cap
A modified form of guanine nucleotide added onto 5’ end of an pre-RNA molecule after transcription of first 20-40 nucleotides
• Part of the pre-mRNA molecule which is synthesized first
o Then the 3’ end of pre-mRNA is modified before mRNA exits nucleus
poly-A tail
when an enzyme adds 50-250 adenine nucleotides to the 3’ end of an pre-RNA molecule
