CH 12: Wave 6

Transcription

first step in gene expression, means the act or process of making a copy, and is DNA —> RNA; and structure of DNA is not altered as a result of this process.

Structural genes/protein encoding genes

transcription produces mRNA (messenger RNA), mRNA determines amino acid sequence of polypeptide in translation, and the functional proteins determines the organism’s traits.

central dogma of genetics

path from gene to trait.

DNA: general random info

the sequence of this defines beginning and end of a gene and regulates the level of RNA synthesis. Proteins must recognize and act on DNA for transcription to occur.

DNA: Regulatory sequences

site for binding of regulatory proteins; role of regulatory proteins is to influence the rate of transcription and can be found in variety of locations. upstream of the promoter and binds proteins that influence transcription.

DNA: Promoter

Site of RNA polymerase binding; signals/promotes the beginning of transcription and resides upstream of the gene. ORIENTATION DEPENDENT (put in backwards or downstream and the gene won’t work). At location where there is major groove. The sequence here is NOT included in the RNA.

DNA: Terminator

Signals the end of transcription. downstream

mRNA: Ribosome Binding Site (RBS)

site for ribosome binding. translation begins near this site in mRNA. In eukaryotes, ribosome scans mRNA for start codon.

nontemplate strand

= coding strand = sense strand

template strand

= noncoding strand = antisense strand

how many codons are there?

64

anatomy of an RNA

RNA polymerase in bacteria

enzyme involved in transcribing. doesn't need primer. binds to promoter and allows transcription to take place. has 6 subunits (its a complex): 2 alpha subunits, one beta, beta prime, omega, and sigma factor. these 6 make the holoenzyme.

sigma factor

“eyes” for the enzyme to find the promoter. helps RNA polymerase to find the promoter and search for the major groove. Has special secondary protein structural element called helix turn helix. Helix turn helix helps get/penetrate into the major groove

transcription factor

protein complex to influence transcription—can recognize promoter and regulatory sequences to control transcription.

mRNA: Start codon

specifies first amino acid in polypeptide sequence. codes for methionine in eukaryotes and formylmethionine in bacteria. formyl group is attached to the nitrogen and looks like OCHN—-. Immune system in eukaryotes like us search for formulated methionine to detect bacterial proteins. RBS and codons direct translation.

codons

3 nucleotide sequence in mRNA that specify certain amino acids.

stop codon:

specifies end of polypeptide synthesis

amino acid math

each coding region of mRNA has roughly 1200 nucleotides, so 1200 nucleotides(1codon/3nuc.)(1 aa/1 codon)(110 g/mol / 1aa) =

Transcription 3 stages

Initiation, elongation, termination. these are dynamic. and involve protein DNA interactions.

Transcription beginning requires?

requires to melt DNA. RNA polymerase melts DNA s it slides down, does not melt whole gene open at once because that requires too much energy.

open complex

little area/bubble where RNA polymerase is transcribing. and is melting.