BSCI330: Central Dogma (pt. 1)

Steps of DNA to protein?

Transcribe (DNA to RNA) → Modify (only in eukaryotes) → EXPORT (nucleus to cytosol, only in eukaryotes) → Translate (RNA to proteins)

What transcribes DNA to RNA?

RNA polymerase!

What is mRNA?

messenger RNA, RNA after several processing steps

What happens to mRNA once it is exported from the nucleus to the cytosol?

It is translated into proteins by ribosomes

What is the flow of information called?

Central Dogma (DNA → RNA → protein)

What is the order of information content?

DNA → mRNA → protein

greatest to least

Does the Ceontral Dogma apply to all cases of biological information?

NO

There are well-known exceptions (DNA that uses RNA as a template to synthesize DNA)

ex. telomeres and retrotransposons (jumping genes)

What is RNA transcription?

Generates a single-stranded RNA molecule is complementary to the template DNA strand

What order is RNA synthesized in?

5’ to 3’

DNA is read 3’ to 5’ and we’re synthesizing something complementary to it!

What types of RNA polymerases do prokaryotes have?

3

Prokaryotes only have 1

Where does RNA transcription initiate?

It initiates at the promoters!

RNA polymerase starts at the promoters.

What does transcription require in eukaryotes?

General transcription factors!

Help position RNA polymerase and start the process!

How do eukaryotes and prokaryotes differ in the way they regulate the initiation of transcription?

Eukaryotes require extra things!

• general transcription factors

• modification of chromatin (chromatin remodeling complex and histone-modifying enzyme)

What does extension of RNA chain require?

Elongation factors (provide energy)!

They use ATP hydrolysis to help RNA polymerase move along chromatin.

When does RNA transcription stop in both PROKARYOTES and EUKARYOTES?

Prokaryotes - RNA polymerase encounters a terminator sequence

Eukaryotes - RNA polymerase reaches a polyadenylation signal which cleaves RNA and adds an additional signal

What does RNA in eukaryotes require?

Post-transcriptional processing!

What’s the first modification of RNA?

Addition of 7-methylguanosine “cap” to 5’ end of RNA

What’s the purpose of the 7-methylguanosine “cap”?

• Marks an mRNA to be

• Shows mRNA is intact at the 5’ end

• Serves as a binding site for ribosomes

What are introns and exons (MUST KNOW)?

Introns (must stay IN) are non-coding sequences and exons (EXpressed and EXit) are coding sequences are mRNA.

Brewer’s yeast doesn’t have introns!

What splices introns?

Introns are spliced by spliceosomes!

What are spliceosomes made up of?

Small nuclear ribonuceloproteins (snRNPs) + small nuclear RNAs (snRNAs) + multiple proteins

What is alternative splicing?

Precursor mRNA may form different mature mRNAs because different exons are kept.

What’s the third RNA modification?

RNA 3’ receives a poly-A-tail (a string of As not coded in DNA).

Must first cleave the 3’ end of original RNA.

Important for exportation out of the nucleus!

Where does RNA synthesis and proccessing occur?

In the nucleus!

How does mRNA exit to the cytosol?

It binds to a nuclear export receptor!

What are the other RNAs?

mRNA - 5%

rRNA - 80%

noncoding RNA - snRNAs, snoRNAs, tRNAs, siRNAs, miRNAs

What is mRNA?

messenger RNAs, code for proteins

What is rRNA?

ribosomal RNAs, form the basic structure of ribosome

What is tRNA?

transfer RNAs, central to protein synthesis

What is snRNA?

small nuclear RNAs, function in a variety of nuclear processes