EXER 5: CENTRAL DOGMA

▪ Semiconservative

▪ Semidiscontinuous

▪ Synthesis is unidirectional/5’ to 3’ with respect to the daughter strand

▪ Progress is bidirectional with respect to the replication fork

Characteristics of DNA Replication (4)

Semiconservative

▪ Uses parent DNA strands as the template

Direction of Replication

▪ Synthesis is ALWAYS from 5’ to 3’ with respect to the growing/new strand

▪ New nucleotides are ALWAYS added at the 3’ OH end.

Replication Initiation

Starts at origin of replication (oriC)

Initiator proteins

__ partially open up the origin of replication.

Helicases

__ are loaded and unwind more DNA.

SSBPs, gyrase, primase

Other replication proteins bind to DNA

Helicase

The __ unwinds parent DNA to produce single-stranded DNA regions. It consumes ATP to unwind the parent DNA.

Single-strand DNA-binding proteins (SSBPs)

__ bind to ssDNA and prevent:

(1) reannealing

(2) the formation of internal pairings.

Topoisomerases or gyrases

__ relieve the strain produced by unwinding of the helicase. They break, swivel, and rejoin DNA to relieve the strain.

Primase

The __ makes RNA primers to help the DNA polymerase start synthesizing DNA.

DNA polymerases

__ cannot synthesize DNA de novo and require an existing 3’ OH.

Replication elongation

DNA synthesis is always in 5’ to 3’ direction with respect to the new strand

Leading strand

new strand that is synthesized continuously

Lagging strand

new strand that is synthesized discontinuously

DNA polymerase

The __ synthesizes the new DNA using the parent DNA strands as templates.

E. coli

__ has at least 3 DNA polymerases.

DNA Pol I

• Removal of primers and replacement with DNA

• Proofreading and repair

DNA Pol II

DNA repair

DNA Pol III

Main polymerase for DNA replication

Ligases

__ repair or seal the breaks produced during lagging strand synthesis

two identical daughter DNA.

DNA replication produces __

Transcription

synthesizes RNA using DNA as template.

Transcription

▪ uses 3’ to 5’ strand as the template strand (anticoding or antisense strand)

▪ synthesis is ALWAYS from 5’ to 3’ with respect to the RNA

RNA polymerase

___ synthesizes RNA in the 5’ to 3’ direction using the anticoding/antisense/template DNA strand.

Promoter

binding site of RNA polymerase

Coding region

region of a gene transcribed by the RNA polymerase

Terminator

signals the RNA polymerase to stop transcribing

1. Promoter

2. Coding region

3. Terminator

Gene structure (3)

sigma subunit

In E. coli, the __ guides the RNA polymerase to bind to the promoter region.

RNA polymerase

__ then unwinds the promoter by itself. It continues to synthesize RNA until it encounters a termination signal.

Rho-dependent termination

▪ Rho protein binds to and pulls the RNA during elongation.

▪ RNA polymerase pauses when it reaches the termination region.

▪ Pause time allows the rho protein to pull away the RNA and terminate transcription.

Translation

synthesizes polypeptides using mRNA as template.

Translation

occurs in a 5’ to 3’ direction with respect to the mRNA template

Ribosomes

are the sites for translation.

▪ have a large and a small subunit

▪ Prokaryotic ribosome (70S) = 50S subunit + 30S subunit

▪ Eukaryotic ribosome (80S) = 60S subunit + 40S subunit

codons

• mRNA is read in triplets of adjacent nucleotides called __

• One __ = one amino acid

• mRNA __ are read from 5’ to 3’ in a continuous but non-overlapping manner.

Genetic code

is almost universal, degenerate, contiguous, and unambiguous

Start codon

AUG

Stop codons

UAG, UAA, UGA

tRNAs

deliver the amino acids to ribosomes during translation.

▪ contain an anticodon which base pairs with codons in the mRNA