CH.15 - Eukaryotic & Archaeal Genome Replication and Expression

replisome

large protein complex that copies the DNA double helix to form two daughter chromosomes

eukaryotic chromosomes

linear therefore a mechanism for replication is needed

replicons

contains an origin of replication

origin of recognition complex (ORC)

a complex of 6 proteins that “marks” the start of replication in eukaryotic chromosomes

end-replication problem

results from the need to remove the Okazaki fragments at the 5’ end of eukaryotic chromosomes

Alpha-primase

carries out DNA and RNA synthesis in eukaryotes

DNA Polymerase Epsilon (Pol E)

catalyzes leading strand synthesis in eukaryotes

DNA Polymerase Delta (Pol D)

carries out lagging strand synthesis in eukaryotes

telomere

nucleotide sequence that repeats at the end of linear chromosomes

telomerase

enzyme in eukaryotes that replicates the ends of chromosomes

Telomeric DNA

contains tandem repeats of 6-8 bases

archaeal DNA replication

- circular chromosomes replicated by proteins similar to that of eukaryotes

- uses Pol B and Pol D

exon

eukaryotic genes that encode the polypeptide product

intron

eukaryotic genes that are excised from the transcript

pre-mRNA (primary RNA)

transcript of a gene that contains introns and exons that has yet to be processed

pre-mRNA modification

1. Addition of 5’ 7-methylguanosine cap

2. Addition of 3’ poly-A-tail

3. Excision of introns from transcript

RNA polymerase I

catalyzes rRNA synthesis in eukaryotes

RNA polymerase II

responsible for mRNA synthesis in eukaryotes

RNA polymerase III

synthesizes tRNA and 5S rRNA in eukaryotes

RNA polymerase

enzyme that catalyzes transcription in all organisms

spliceosome

complex of proteins and small RNAs that carries out RNA splicing in eukaryotes

alternative splicing

the use of different exons during RNA splicing to generate different polypeptides from the same gene

archaeal transcription

similar to that of eukaryotes

chaperones

proteins that assist in folding and stabilization of other proteins (i.e., DnaJ and DnaK in bacteria)

Sec system

system that transports a protein through or inserts it into a membrane

signal peptide

amino terminal sequence on a protein destined for transport through or into a membrane

N-formylmethionine

initiator tRNA for bacteria

Met-tRNA

initiator tRNA for archaea and eukaryotes

chromatin structure

- a major barrier to RNAPII in eukaryotes

- must be modified before gene can be expressed

enhancer

activator protein that is located far away from the gene they activate

silencers

repressor proteins that is able to regulate transcription even when far away from gene’s promoter sequence

insulators

proteins that prevent enhancers or silencers from affecting the transcription of the wrong gene

activation

the binding of initiation factors to the 5’ end of the mRNA and the binding of poly-A binding proteins to the 3’ end

eukaryotic DNA primer

initiates synthesis via a single stranded molecule w/ ribonucleotides and deoxyribonucleotides

Eukaryotic Replication Initiation

1. The ORC binds to the origin of replication

2. Two MCM helicases encircle both DNA strands

3. The CMG helicase complex forms

4. A protein factor ejects one strand from each helicase.

5. The helicases move in opposite directions to separate DNA strands.

G-tail

the guanosine-rich single stranded region at the very end of a linear chromosome

monocistronic

each gene has its own promoter and each transcript has only one gene (usually in eukaryotes)

Eukaryotic Translation Initiation

1. The initiator tRNA and 40S ribosomal subunit join to form the 43S complex.

2. The 43S complex binds the activated mRNA.

3. mRNA is scanned to identify the start codon

4. Initiation factors are released.

5. The 60S ribosomal subunit joins the assembling structure.

promoter

the binding site for the basal transcription factors

• contains core promoter and regulatory region

core promoter

minimal region needed for transcription

basal transcription factors

bind to core promoter and interact w/ transcription factors to attract RNAPII

Heat Shock Proteins (HSP)

protect cells from thermal damage due to dramatic increases in heat

• categorized by size