Chapter 7: From DNA to Protein, How Cells read the Genome Flashcards
What does DNA sequence make a portion of in transcription
RNA, about 5% of sequence RNA
Transcription produces RNA that…
is complimentary to one strand of DNA
What do signals in DNA tell RNA polymerase to do?
Where to start and stop transcription
What does EUkaryotic RNA polymerase require?
general transcription factors
WHere are mRNAS processed in eukaryotes?
in the nucleus
Transcription
flow of genetic information from DNA to RNA
DNA is transcribed into RNA by the enzyme RNA polymerase
Genes
segments of DNA that are transcribed into RNA
template strand
used to guide the synthesis of the RNA molecule
coding strand
nontemplate strand of the gene (here, shown at the top) is sometimes called the coding strand because its sequence is equivalent to the RNA product
Describe the process of DNA being transcribed into RNA by RNA polymerase
RNA polymerase moves stepwise along the DNA, unwinding the DNA helix in front of it. As it progresses, the polymerase adds ribonucleotides one-by-one to the RNA chain, using an exposed DNA strand as a template.
The resulting RNA transcript is thus single-stranded and complementary to the template strand
As the polymerase moves along the DNA template, it displaces the newly formed RNA, allowing the two strands of DNA behind the polymerase to rewind. A short region of hybrid DNA/RNA helix (approximately nine nucleotides in length) therefore forms only transiently, causing a “window” of DNA/RNA helix to move along the DNA with the polymerase.
Function of mRNAs
-messenger proteins
- code for proteins
Function of rRNAs
-ribosomal RNAs
- form the core of the ribosome’s structure and catalyze protein synthesis
Function of miRNAs
-microRNAs
- regulate gene expression
Function of tRNAs
-transfer RNAs
- serve as adaptors between mRNA and amino acids during protein synthesis
Function of other noncoding RNAs
- used in RNA splicing, gene regulation, telomere maintenance, and many other processes
What is the role of TFIIH in transcription?
- general transcription factor
- unwinds DNA
- phosphorylates RNA polymerase so that capping, splicing, and polyadenylation enzymes can bind and put on 5’ cap, splic out introns, and put on the poly A tail in the nucleus
eukaryotic mRNA
has a cap at the 5ʹ end and a poly-A tail at the 3ʹ end. In addition to the nucleotide sequences that code for protein, most mRNAs also contain extra, noncoding sequences
The noncoding portion at the 5ʹ end is called the 5ʹ untranslated region, or 5ʹ UTR, and that at the 3ʹ end is called the 3ʹ UTR
Introns
noncoding sequences
Removed from Pre-mRNAs by RNA Splicing (intervening sequences, removed in nucleus by splicesome)E
Exons
gets translated to protein
protein coding sequences of most eukaryotic genes (exons) are interuppted by noncoding sequences(introns)
What happens to mature eukayrotic mRNAs?
exported from nucleus
mRNAs are eventually degraded into the cytosol
What structure carries out splicing of introns?
snRNPs
sense splice junctions; senses RNA portion of snRNP base pairs with sequences that signal splicing
proteins help form a loop to aid process
successful splices marked by exon junctions
Specialized RNA-binding proteins
signals compelted mRNA is ready for export to the cytosol
mRNA ready for export?
the 5’ cap and poly-A tail of a mature mRNA molecule are “marked” by proteins that recognize the modifications.
Once an mRNA is deemed “export ready,” a nuclear transport receptor (discussed in Chapter 15) associates with the mRNA and guides it through the nuclear pore. In the cytosol, the mRNA can shed some of these proteins and bind new ones,
If a cell has a mutation that carries into low levels of transcription of mRNA from mutated transcription factor TFIIH, what would be the fate of the mRNA syntehsized?
would stay in nucleus
