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BIO 211 Chapter 16, Section 1
Transcription and Translation: Transcription in Bacteria
29
Biology
Undergraduate 2
12/01/2010

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Term
RNA polymerase
Definition
synthesizes mRNA in 5' -> 3' direction b/c moves along DNA template in 3' -> 5' direction; unlike DNA polymerase, doesn't need primer to start transcription; only uses one of two DNA strands as template; large, globular and has several prominent channels running through interior (enzyme's active site, where phosphodiester bonds form, is located where several channels intersect)
Term
non-template strand also known as ____
Definition
coding strand b/c matches RNA (except U instead of T)
Term
sigma
Definition
detachable protein subunit; makes initial contact with DNA that starts transcription in bacteria (not RNA polymerase); regulatory in nature (tells RNA polymerase where and when to start synthesizing RNA); released once RNA synthesis is started; most bacteria have several types of this, each with distinctive structure and function (identity of sigma protein determines which types of genes will be transcribed)
Term
promoters
Definition
sections of DNA where transcription begins; binding sites between holoenzyme and DNA; located on non-template strand; 40-50 base pairs; have a particular section that looks similar, (-10 box, TATAAT) and another sequence centered about 35 bases upstream from +1 site (-35 box, TTGACA)
Term
-10 box
Definition
six-base pair sequence that is centered about 10 bases from point where RNA polymerase begins transcription
Term
+1 site
Definition
place where transcription begins
Term
downstream
Definition
DNA that is located in direction RNA polymerase moves during transcription
Term
upstream
Definition
DNA that is located in the opposite direction RNA polymerase moves during transcription
Term
ribonucleoside triphosphates (NTPs)
Definition
like dNTPs; enter a channel at the bottom of enzyme and diffuse to active site
Term
holoenzyme
Definition
consists of a core enzyme (RNA polymerase), which contains active site for catalysis, and other required proteins; made of RNA polymerase and sigma
Term
transcription begins when _____
Definition
sigma, as pat of the holoenzyme complex, binds to the -35 and -10 boxes (initiation phase)
Term
after sigma binds to a promoter, _____
Definition
DNA helix opens, template strand is threaded through a channel that leads to the active site inside RNA polymerase (initiation phase)
Term
RNA polymerization begins when _____
Definition
an incoming NTP pairs with a complementary base on template strand of DNA - catalzyed by RNA polymerase, exergonic, spontaneous b/c NTPs have so much energy from 3 phosphate groups (initiation phase)
Term
transcription occurs when ______
Definition
RNA polymerase matches base in NTP with complementary base in a gene, then RNA polymerase catalyzes formation of phosphodiester bond (initiation phase)
Term
enzyme's zipper
Definition
group of projecting amino acids that help open double helix at upstream end (elongation phase)
Term
rudder
Definition
nearby group of amino acids that help steer template and non-template strands through channels inside enzyme (elongation phase)
Term
enzyme's active site catalyzes addition of ______
Definition
nucleotides to 3' end of growing RNA molecule (elongation phase)
Term
during elongation, all prominent channels or grooves in enzyme are _______
Definition
filled
Term
double-stranded DNA goes into and out of one groove; NTPs enter another; growing RNA strand exits to the rear
Definition
elongation phase
Term
transcription stops when _____
Definition
RNA reaches a stretch of DNA sequences that functions as transcriptional terminal signal (termination phase)
Term
bases that make up transcription terminal signal have unusual property
Definition
as soon as it is synthesized, RNA sequence folds back on itself and forms a short double helix that is held together by complementary base pairing - secondary structure that results is hairpin - formation of hairpin disrupts interaction between RNA polymerase and RNA transcript, resulting in the physical separation of the enzyme and its product
Term
summary of transcription in bacteria
Definition
Transcription begins when sigma, as part of the holoenzyme complex, binds to the promoter at the start of a gene. Once binding occurs, RNA polymerase begins to synthesize mRNA by adding ribonucleotides that are complementary to the template strand in DNA. Transcription ends when a termination signal at the end of the gene leads to the formation of a hairpin in the mRNA, disrupting the transcription complex.
Term
nucleotides are added to the ____ end of RNA
Definition
3'
Term
function of -35 and -10 box in bacterial promoters
Definition
bind the sigma subunit that is associated with RNA polymerase
Term
transcription in order
Definition
(1) Sigma binds to RNA polymerase. (2) Sigma binds to the promoter region. (3) The double helix of DNA is unwound, breaking hydrogen bonds between complementary strands. (4) Transcription begins. (5) Sigma is released.
Term
[image]
Definition
Term
different eukaryotic RNA polymerases
Definition
[image]
Term
how transcription ends
Definition
[image]
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