Histones are proteins that form larger ball-like subunits called nucleosomes. Histones and nucleosomes
are used in condensing our DNA and serve as a scaffolding. Our DNA can be in 2 distinct states
eukromatin (uncondensed, low methylation, undergoing DNA transcription and translation, Eukromatin
is Used) or Heterochromatin (Tightly packed, highly methylated, and not being used in transcription or
translation)
DNA ---- RNA ---- Protein
In transcription there are 3 steps…
1. Initiation - An RNA polymerase binds to a promoter region, the DNA strand unwinds and the RNA pol
begins begins base pairing at the start point of the DNA template strand..
2. Elongation – The RNA pol moves doen the DNA and elongs the RNA strand it is making in the 5-3
direction… the DNA reforms its double helix as the RNA pol passes by…
REMEMBER we are only making one strand on RNA… RNA is single stranded…
3. Termination – eventually the RNA transcript is released and the polymerase detaches from the DNA..
A EUKARYOTIC promoter is sometimes called a TATA box… this box is about 25
nuclotides upstream from the transcription start point….. Transcription factors, which
are proteins, have to be recruited and must bind to the DNA before RNA polymerase 2
can do so…more factors are then recruited making the trasnscription initiation
complex…
The language of RNA is contained in 3 letter words called codons.
The first 2 letters are very important… however the 3rd nucleotide can wobble
There are also special codons called stop codons that tell the Ribosome that it is finished making a
protein these codons are UGA, UAA, UAG
AUG codes for methionine and is always the first amino acid we make
Pre messenger RNA contains Introns and Exons… RNA splicing is performed by SNRNPS… multiple
SNRNPS make up a Splicesosome which is used to recognize the ends of introns and snip them out..
Exons stay and exit the nucleus
Signal Peptides/SRP on a ribosome tell the ribosome to dock to ER and drop the proteins the make there
mRNA
5 Guanasine Cap – tells the ribosome where it is supposed to bind to start translation.
Poly-A Tail – Tells mRNA to leave the nucleus
Together they serve as protection and help it from not getting degraded
Translation page 337
Methionine comes in the P site first
EPA sites
Silent mutation- when the last letter of a codon is wrong.. remember the wobble
Frame shift- when there is addition or subtraction of a base pair…
Missense- Substitutions that change one amino acid to another one
Nonsense - Causes translation to quit prematurely, caused by changing an amino acid codon into a
stop codon.