GCD Chapter 12 Exam 2

Transcription

The act of making a copy of a DNA sequence into an RNA sequence. First step in gene expression

Transcriptional unit

Contains different base sequences that have different functions during transcription

Promoter sequence

Provides site where transcription starts and initiates it

Terminator

Signals the end of transcription

Promoter function

Directs exact location of start of transcription. Located upstream from start site.

Promoter elements in bacteria

-10 and -35 region are essential

RNA polymerase holoenzyme

Binds loosely to the DNA, moving along strands until the sigma factor recognizes -10 and -35

RNA polymerase holoenzyme function

Once bound to closed promoter complex, begins unwidning DNA at -10 due to fewer hydrogen bonds between A&T

Elongation stage

Makes RNA transcript

RNA polymerase

Moves along DNA, unwinding it. Binds nucleotides 5-3

Rho dependent termination (bacteria)

Terminates transcription. Rho protein has its binding site, then stem loop is formed in RNA transcript

Rho independent termination

RNA forms a uracil rich stem loop structure

Types of RNA polymerases in eukaryotic transcription

I, II, and III

RNA polymerase I

trascribes ribosomal (rRNA) genes

Ribosomes

Made of rRNA, build protiens by reading genetic material

RNA polymerase II

transcribes all structural genes (mRNA)

RNA polymerase III

trascribes tRNA and 5S RNA genes

tRNA

transfer RNA. reads codons on mRNA and is adapter between mRNA and amino acids during protein synthesis.

5S RNA

structural and funtional component of ribosomes

eukaryotic promoter contains

start site, TATA box, and regulatory elements

Core promoter

Short and consists of TATAAAA sequence called TATA box

TATA box

Found at -25 bp and determines start site for transcription

Basal transcription

core promoter can create low level of transcription on its own

Transcriptional termination of RNA polymerase II

occurs after 3 end is cleaved near polyA signal sequence

polyA tail

long chain of A nucleotides at 3 end of mRNA. Helps stability of mRNA and translation

polyA signal sequence

directs clevage of transcript and addition of polyA tail

Where do structural genes start in eukaryotes?

as long pre-mRNA

Spliceosome

splices pre-mRNA

Splicing

removes intron RNA and connects exon RNA

Introns and Exons

nucleotide sequences in eukaryotes. Introns are non coding, exons are coding

Alternative splicing

Allows different peptides to be made from the same gene

Peptide

short chain of amino acids act as cellular messengers

7-methylguanosine cap at 5 end

Found in mRNAs

Capping

allows exit of certain RNAs from nucleus, involved in early translation, helps efficancy of splicing introns near 5 end