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prokaryotes vs eukaryotes.docx

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Biology 1002B
Tom Haffie

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Prokaryotes Eukaryotes -can transcribe and translate a gene -transcribe and process mRNA in the nucleus simultaneously before exporting it to the cytoplasm for translation -promoter is immediately upstream of where -there are different polymerases for transcribing transcription begins and RNA polymerase binds for transcribing different genes (RNA polymerase and transcribes, the same RNA polymerase can II- protein coding genes, RNA polymerase I and III transcribe all the various types of genes are for non-protein coding RNAs), also the -terminators-signal the end of transcription promoters are also immediately pstream of the -act only after they have been transcription point and are more complex than transcribed after which they base prokaryotes pair w/themselves and form a hair- -have other sequences further upstream of the pin loop gene which regulate the rate of transcription -translation occurs throughout the cell -TATA box- key element of the promoter -translation initation does not use scanning, but - important in transcription inititation rather the rRNA ribosomal subunit finds the region - proteins called transcription factors of the start codon directly by base pairing w/ a bind to the TATA box and recruit specific RIBOSOME BINDING SITE on the mRNA polymerase, only once this binding which is UPSTREAM of the start codon occurs will the DNA unwind and -elongation stage of translation is faster in transcription begin prokaryotes than eukaryotes -produce pre-mRNA which is processed in the -are able to regulate the production of proteins nucleus to make translatable mRNA which then very quickly in response to changing leaves the nucleus environmental conditions since there is nuclear -5’cap- at the 5’ end of pre-mRNA envelope and so transcription and translation can -the initial attachment site for mRNAs to be coupled very closely ribosomes for translation -clipping sequence- there is no terminator sequence and so this clipping sequence at the 3’end signals for pre-mRNA to be cleaved at this point, and this signals the polymerase to stop transcription, proteins bind here and cleave it -3’ end remains and poly(A)tail is added which enables mRNA to be translated efficiently and be protected from RNA-digesting enzymes -introns are non-protein coding sequences which interrupt the protein-coding sequence -found in the transcription unit of a protein- coding gene/RNA-coding sequence -removed from pre-mRNA -don’t know much of their origin -exons- amino acid-coding sequences which are not removed and are still found in mRNA -mRNA splicing removes introns and joins exons together -translation mostly occurs in the cytoplasm (some in the mitochondria and chloroplast as well) -translation involves scanning until the start codon is reached -most proteins are in active when ribosomes release them and many proteins require chaperons to assist in their folding -other proteins can be activated by the removal of a covering segment of the amino acid chain and are subject to certain tgieers which remove a segment of the amino acids and covert, eg. enzymes into active forms mRNA splicing -occurs in the nucleus, removes introns, joins exons -occurs in a spliceosomea complex between pre-mRNA and snRNPs(snurps) (small ribonucleoprotein particles) -snRNAs base pair w/mRNA at junctions of intron and exons then snRNPs are recruited and loop out of the intron and bring the two exon ends closer together at this point the spliceosome cleaves the pre- mRNA at the junction btwn the 5’end of the intron and the adjacent exon and then the intron loops back to bond w/itself near it’s 3’end -the catalystic ability in splicing resides in the RNA component of the spliceosomes and not the proteins -some introns can even splice themselves -RNA molecule that is catalystic= a ribozyme Introns and Protein Variability -why have introns if we simply remove them? this seems wasteful -introns may provide a selective advantage to organisms by increasing the coding capacity of existing genes through a process called alternative splicing Alternative splicing -increases the number and variety of proteins encoded in the cell nucleus w/o increasing the size of the genome -different proteins can be made in different tissues from the same DNA gene Signal Peptides a.k.a tags -the first part of the polypeptide chain -signal pathway which sends proteins to the ER, other organelles -nuclear proteins also have tags which are never removed because these proteins need to reenter the nucleus each time the nuclear envelope is broken down and reformed during cell division cycle -this basic system of signals in eukaryotes also works in prokaryotes, only thing is that ER-directing signals direct the proteins to the plasma membrane as BACTERIA DON’T HAVE ER MEMBRANES Mutations -base-pair substitution mutations involve a change of one particular base to another in the genetic material -missense mutation- the wrong amino acid is placed in the peptide and the function of the polypeptide is slightly altered o -nonsense mutation- mutation changes a sense (amino acid-coding) coding to a nonsense (termina
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