SELU BIO Unit 15

Central Dogma of Biology

DNA → RNA → Protein(s)

Transcription

mRNA is synthesized from DNA template

Initiation (transc)

RNA polymerase binds to the promoter(allows RNA polymerase to separate strands); transcription factors help RNA polymerase bind to the promoter

The promoter(TATA BOX)

region that signals the start of transcription and allows RNA polymerase to separate the two strands of DNA

Elongation (transc)

RNA polymerase moves along the DNA strand and adds complementary RNA nucleotides(a, u, c, or g) to form the mRNA strand

RNA is synthesized(and DNA is replicated)…

5’ to 3’

DNA is read…

3’ to 5’

Termination(Transc)

transcription ends; when RNA polymerase reaches a certain sequence in the DNA (called the terminator); RNA polymerase detaches from the DNA and the newly synthesized pre-mRNA is released

5’ capping

Only in Eukaryotes; a protective cap is added to the 5’ end of the mRNA

Poly-A

Only in Eukaryotes; a poly-a tail is added to the 3’ end of the mRNA to stabilize it & aid in its transport from the nucleus

Splicing

Only in eukaryotes; introns are removed from the pre-mRNA and exons are joined together to form mature mRNA

intron

non-coding region

exons

coding regions

Translation

process in which mRNA is used to synthesize a protein.

Location of translation

in the cytoplasm @ the ribosome

Initiation (transl)

small ribosomal subunit binds to the large ribosomal subunit; the small ribosomal unit binds to the mRNA @ the 5’ cap and moves along the mRNA until it finds the start codon. The initiator tRNA binds to the start codon (AUG; methionine)

tRNA function

carries anticodon/ adds amino acids to the growing polypeptide chain in the process of translation

Elongation(transl)

the ribosome reads the mRNA codons and tRNA brings the corresponding amino acids. Each tRNA has an anticodon that pairs w/ the mRNA (ensures correct amino acid is added)

Three Sites

A,P,E

A site

holds the tRNA carrying the AMINO ACID

P site

holds the tRNA carrying the growing POLYPEPTIDE CHAIN

E site

Releases the EMPTY tRNA after it adds it’s amino acid to the polypeptide chain

Termination(transl)

stops when the ribosome encounters a stop codon (UAA, UAG, UGA); Release factor binds to the stop codon and polypeptide chain is released from the ribosome; ribosome disassembles

Stop codons

UAA, UAG, UGA

RNA Polymerase (II if eukaryote)

catalyzes transcription; and sm more

mRNA

carries genetic info from DNA/ nucleus to the cytoplasm/ ribosome

tRNA

brings amino acids to the ribosome during translation

rRNA

site of protein synthesis

ribosome

facilitates translation of mRNA into a polypeptide chain

codon

a three-nucleotide sequence in mRNA that codes for a specific amino acid

Amount of codons

64

Amount of amino acids

20

Difference of prokaryotes

• Transcription and translation are coupled (translation starts while mRNA is still processing)

• Only a single RNA polymerase

Difference in eukaryotes

• transcription occurs in the nucleus

• translation occurs in the cytoplasm

• Three different types of DNA polymerase