DNA Replication Flashcards
Allows genetic information to be inherited from a parent cell to daughter cells (by mitosis) and from generation to generation (starting with meiosis)
DNA replication
Where the replication of chromosomal DNA begins
Origins of Replication (ORI)
Unwinds and separates the parental DNA strands
Helicase
- Each nucleotide is bounded by a _________ which keeps the strands from re-healing (coming back together)
- Stabilizes the unwound parental strands
Single-stranded Binding Protein
An enzyme that helps relieve the strain of the double helix by breaking, swiveling, and rejoining DNA strands.
Topoisomerase
At each end of a replication bubble is a _______ ____, a Y-shaped region where the parental strands of DNA are being unwound.
Replication fork
Synthesizes RNA primers, using the parental DNA as template
Primase
An initial nucleotide chain that can be used as a pre-existing chain that is produced during DNA synthesis (short stretch of RNA)
Primer
New strand that DNA strands encode
“leading strand”
Lays the leading strand continuously and moves toward the helicase
DNA Polymerase III
other new strand that the other DNA strand which runs in the opposite direction encodes
“lagging strand”
formed when the DNA pol III adds DNA nucleotides to the primer
Okazaki fragment 1
forms a bond between the newest DNA and the DNA of fragment 1 (links the two Okazaki fragments together)
DNA ligase
replace the RNA primer (between the two Okazaki fragments) with DNA
DNA Polymerase I
using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
DNA polymerase III
other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors
mismatch repair
DNA-cutting enzyme
Nuclease
every double helix in the new generation of an organism consists of one complete “old” strand and one complete “new” strand wrapped around each other.
Semiconservative
Synthesis in __ to __ direction
5’ to 3’
a large protein complex that carries out DNA replication, starting at the replication origin.
replisome
Models of DNA Replication
- Conservative Model
- Semiconservative Model
- Dispersive Model
- Only transcribes rRNA genes
- Makes ribosomes
RNA polymerase 1
Transcribes genes into mRNA (messenger)
RNA polymerase 2
Only transcribes tRNA (transfer) genes
RNA polymerase 3
Building mRNA
- Initiation
- Elongation
- Termination
Assembly of initiation complex
Initiation
Adding N-bases bases
Elongation
two types of termination in building mRNA
- Rho-dependent
- Rho-independent
- Protein factor Rho
- Rho protein will go after the RNA polymerase and detach it from the template.
Rho-dependent
RNA polymerase encounters a GC sequence that has a triple bond
Rho-independent (GC-rich)
Eukaryotic mRNA need work after transcription
Primary transcript (pre-mRNA)
- mRNA splicing = edit out introns
- Protect mRNA from enzymes in cytoplasm
- Add 5’ cap
- Add polyA tail
mRNA processing (making mature mRNA)
non coding (inbetween) sequences
Introns
coding (expressed) sequences
Exons
- Proteins
- Fold the intron and cut them out of the mRNA
Small nuclear ribonucleoproteins
- Several snRNPS
- Recognize splice site sequence
- Cut and paste
Spliceosome
Prokaryote vs. Eukaryote genes
Prokaryote
- DNA in cytoplasm
- Circular chromosome
- Naked DNA
- No introns
Eukaryote
- DNA in nucleus
- Linear chromosomes
- DNA wound on histone proteins
- Introns vs. exons
- Triplet of bases
- Blocks of 3 nucleotides decoded into the sequence of amino acids
Codons
Translation in Prokaryotes
Bacterial chromosome > transcription > mature mRNA > translation > protein
Transcription and translation are simultaneous in bacteria
- DNA is in cytoplasm
- No mRNA editing
- Ribosomes read mRNA as it is being transcribed
Who determined the 3-letter (triplet) codon system
Crick
- Determined mRNA-amino acid match
- Added fabricated mRNA to test tube of ribosomes, tRNA and amino acids
- Created artificial UUUUU… mRNA
Nirenberg (1960) and Khorana (1968)
UUU coded for __
Phenylalanine
Strongest support for a common origin for all life
Code for ALL life
- Several codons for each amino acid
- 3rd base “wobble”
Code is redundant
Start codon
- AUG
- Methionine
Stop codons
- UGA
- UAA
- UAG
Why is wobble good?
Buffer for mutation
Transfer RNA structure
“Clover leaf” structure
- Enzyme which bonds amino acid to tRNA
- Bond requires energy
- ATP > AMP
- Energy stored in tRNA-amino acid bond
Aminoacyl tRNA synthetase
Facilitate coupling of tRNA anticodon to mRNA codon
Ribosomes
2 subunits ribosomal RNA
- Large
- Small
Holds tRNA carrying next amino acid to be added to chain
A site (aminoacyl-tRNA site)
Holds tRNA carrying growing polypeptide chain
P site (peptidyl-tRNA site)
Empty tRNA leaves ribosome from ___ ___
E site (exit site)
Brings together mRNA, ribosome subunits, initiator tRNA
Initiation
Adding amino acids based on codon sequence
Elongation
