BSCI Exam 4

Nucleotides

What DNA is made of (DNA is a polynucleotide)

Pyrimidines

type of base in DNA, one ring structure, C and T

Purines

type of base in DNA, two ring structure, A and G

Base Paring

A:T and C:G (Purine: Pyrimidine)

3’ end of DNA

OH

5’ end of DNA

PO4

Step 1 of DNA Replication

Unwind the Double Helix (helicase , breaking hydrogen bonds)

Step 2 of DNA Replication

Make new strands (DNA polymerase enzyme, makes phosphodiester bond)

Origin of Replication

Where replication starts, Eukaryotes - many origins, Prokaryotes - one origin

Helicase

Unwinds helix at the end of the replication forks

Single-strand binding protein

Binds to and stabilizes single-stranded DNA until used as template (lots of little proteins on the edge of the bubble)

Topoisomerase

Relieves over winding the strand, in front of the helicase

Primase

makes an RNA primer at 5’ end (for DNA replication)

DNA Polymerase 3

makes a new DNA strand by adding nucleotides to 3’ end of RNA primer

DNA Polymerase 1

replaces RNA primer from 5’ end to DNA

DNA Ligase

puts together DNA fragments by adding a phosphodiester bond

Leading strand

3’ end towards the fork

Lagging Strand

3’ end away from the fork, fragments

Transcription

the process of copying a segment of DNA into RNA

Initiation Site

+1, where transcription begins, the 5’ end of the RNA

Transcribed Region

Where the template dna provides info for rna downstream (+)

Promoter

Where the RNA polymerase binds to, upstream (-)

RNA polymerase

makes rna starting at +1, unwinds DNA and assembles RNA nucleotides

Terminator

Where the rna polymerase stops, 3’ end of rna

Basal transcription factors

bind to the promoter to recruit RNA polymerase, with their
presence or absence acting as an on/off switch for transcription. (Only in eukaryotes)

Enhancers

greatly increase transcription when bound
by transcriptional activators

Initiation

first phase of transcription - RNA polymerase interacts with the promoter at the TATA box to establish a
transcription complex. RNA polymerase can directly interact with the promoter in prokaryotes, but requires basal transcription factors in eukaryotes

Elongation

2nd phase of transcription - the RNA polymerase extends the new RNA by adding to the 3' end

Termination

the final phase of transcription where RNA polymerase detaches from the DNA, releasing the newly synthesized RNA molecule.

mRNA

has 5’ end cap (Gppp) and 3’ poly a tail

Splicing

removes introns and keep exons for coding in trasncription