transcription and RNA processing

central dogma of modern biology

DNA (transcription) RNA (translation) protein

what is a gene

made up of DNA and encodes an RNA and/or a protein

1. prokaryotes

multiple genes are organized in units called operon

2. prokaryotes

multiple proteins are coded in a single mRNA: polycistronic mRNA

eukaryotes

single gene encodes a single protein: monocistronic mRNA

initiation of transcription

sigma subunit of prokaryotic RNA polymerase recognizes consensus sequences found in the promoter region upstream of the transcription start site. the sigma subunit dissociates from the polymerase after transcription has been initiated

cis-acting elements

DNA regulatory sequences

1. cis-acting element types

promoter

2. cis-acting element types

enhancer

3. cis-acting element types

suppressor

4. cis-acting element types

TATA box

trans-acting or transcription factors

proteins that bind to regulatory DNA sequences

1. trans-acting or transcription factor types

sigma factor

2. trans-acting or transcription factor types

TATA box binding proteins

3. trans-acting or transcription factor types

activators

4. trans-acting or transcription factor types

repressors

template strand

3' to 5' strand of the DNA double helix is the template to make RNA from 5' to 3'

RNA polymerase I

rRNA

RNA polymerase II

mRNA

RNA polymerase III

tRNA and one type of rRNA

elongation of transcription

RNA polymerase tracks along the DNA template, then synthesizes mRNA in the 5' to 3' direction, and unwinds and rewinds the DNA as it is read

is elongation endergonic or exergonic

exergonic

termination of transcription

liberates (sets free) the mRNA strand

termination in prokaryotes: Rho-independent

controlled by sequences in the DNA strand

termination in prokaryotes: Rho-dependent

controlled by the Rho protein

termination in eukaryotes

transcription factors and poly adenylation signal sequence are involved in termination

1. RNA processing

GTP is added to the 5' end as g-caps

2. RNA processing

poly A tail is added to the 3' end of mRNA for protection from degradation

3. RNA processing

introns (intervening regions) are removed

4. RNA processing

Exons (expressed regions) are connected

prokaryotes: transcription

occurs in cytoplasm

prokaryotes: nature of mRNA

polycistronic mRNA (many proteins from one mRNA)

prokaryotes: RNA processing

introns are absent and no RNA processing

prokaryotes: translation

occurs simultaneously in cytoplasm

eukaryotes: transcription

occurs in nucleus

eukaryotes: nature of mRNA

monocistronic mRNA (one protein from one mRNA)

eukaryotes: RNA processing

occurs in nucleus to add g-caps and poly A tail, removes introns, and joins exons

eukaryotes: translation

occurs separately in the cytoplasm

What is the relationship between DNA, genes, and chromosomes?

A chromosome can contain hundreds of genes, which are composed of DNA.

what is part of RNA processing in eukaryotes

addition of GTP at the 5' end of RNA, addition of several adenines at the 3' end of RNA, removal of introns, joining of exons

What are the unique aspects of gene expression of prokaryotes compared to eukaryotes?

transcription and translation occurs at the same time, prokaryotic genes don't have introns that code for any information

What are the main benefits of adding G-cap and poly A tail?

stabilizes mRNA and protects it from degradation by RNase while it is transported from nucleus to cytoplasm