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16 Cards in this Set

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What is a gene?

units of heredity: They are passed from generation to generation and are carried onchromosomes. Each gene provides an organism with some type of function. they are segments of DNA within a chromosome that allow a particular polypeptide to be made. Anearlier version of this idea was the 'one gene – one enzyme' hypothesis advanced by Beadle and Tatum

What did beadle and Tatum work with? Why did they treat it with xrays? What were they looking for?

they worked with the bread mold Neurospora which can grow on a minimal medium w/ agar salts, glucose and biotin. X-rays cause damage to DNA, resulting in a loss of genetic information inrandom places throughout the genome. They then looked for mutants that were unable to grow onminimal media, but which could grow on a medium that was supplemented with all 20 essential aminoacids ('complete medium').

What did Beadke and Tatum find?

They found mutants that were unable to grow on MM, but were able to grow on MM + arginine. Hence,these mutants had a specific inability to make arginine: They could convert the precursors in MM to 19 ofthe 20 essential amino acids, just not arginine.

What did Beadle and Tatum conclude?

arginine is synthesized in a series ofdiscrete steps, and that each step iscatalyzed by an enzyme – the productof a gene. If minimal medium is supplementedwith a chemical that is after the blockin the pathway, then the Neurosporamutant will be able to grow, becauseit now has arginine (or can make it).

what is the central dogma??

DNA-RNA- protein

in what step is the message on an mRNA created? when is it converted into an amino acid sequence?

transcription. translation

What is the difference between prokaryotes and eukaryotes when it comes to transcription and translation?

Prokaryotes: s, transcription andtranslation are coupled – anmRNA that is not yet completelymade can begin to be translatedby ribosomes
Eukaryotes: mRNAs must be transported outof the nucleus to be translated. messengerRNAs often contain introns,which are removed. the 5' end is modifiedby covalent addition of a Cap (aguanine nucleotide), andaddition of multiple A bases(tens to hundreds) to the 3' endby another enzyme (PolyA polymerase). The modified ends function in nuclear export of the mRNA,protection of the ends of the molecule from enzymes, and in promoting translation.

Transcription occurs when..
and ends..

theenzyme RNA polymerase binds to the promoterregion, initiates transcription 5'-3
at the terminator

expressions of genes can be regulated by proteins called ...

transcription factors

What do transcription factors do?

bind to the promoter and either blocktranscription or cause it to increase

what does rna polymerase do?

initiate transcription byunwinding the DNA

Briefly summarize the three steps of transcription

initiation- incorporation ofnew NTPs will occur using the bottom strand as atemplate.
During elongation, synthesis occurs in the 5'-3'direction, similar to primase and DNA polymeraseduring DNA replication.

At termination, the RNA transcript is released, andRNA polymerase is no longer bound to the DNA

What are the 3 steps to priming an RNA. (Pre-RNA)

What is the genetic code?

its the triplet code by which three bases (a codon) specify a single amino acid. Three basestogether generate a total of 64 possible codons, whose corresponding acids are shown on a genetic codetable.

codons read..
what does a degenerate code mean?
what are the special codons?

a single amino acid can be specified by multiple codons
AUG= start
UAA UAg UGA = stop

How do you translate an mRNA

Within each messenger RNA (either a mature mRNA in eukaryotes, or theprimary transcript in prokaryotes) is an open reading frame – a coding region that begins with a start codon(AUG), proceeds three bases at a time to specify amino acids, and then ends with one of three stop codons(UAA, UAG or UGA). Stop codons are also called nonsense codons. Surrounding the coding region areportions of the mRNA that are not used for specifying the amino acid sequence, called untranslated regions(UTRs). There is usually a UTR at the 5' and 3' ends.