TPR MCAT Biological Sciences: Molecular Biology
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Describe the 7 steps of replication in order
- 1. Helicase finds origin of replication, then separates, and unwind the strands.
- 2. Topoisomerases cut unwound DNA relieving tension
- 3. Single Strand Binding Proteins maintain separation and protect single strand DNA
- 4. Primase makes RNA primer
- 5. DNA-Polymerase elongates chain using primer adding ducleotides to 3' end of new chain
- 6. DNA ligase joins Okasaki fragments
- 7. Telomerase adds telomeres
fuction of DNA Polymerase
- Elongate chain adding nucleoties to 3' end only.
- Has exonuclease activity for proofreading/correcting errors in replication
function of primase?
- Primase is an RNA-polymerase enzyme
- It lays the RNA primer that DNA-pol uses to elongate new chain.
Function of Helicase
- Helicase is one of the most important enzymes because:
- It finds the origin of replication, then unwinds the ds-helix, and separates the strands
functon of topoisomerases
cut the DNA to relieve tension due to unwinding
function of single strand binding proteins
Maintain strand separation, and protec separated strands
function of DNA ligase
DNA ligase joins segments of DNA together, ither Okasaki fragments, or after reparation
function of nucleases
- enzymes that exise damaged or incorrect nucleotides for reparation.
- after nucleases exise bad nucleotides, DNA-pol must come in and fill the gap, and ligase then comes in and seals the job.
function of telomerases
enzymes that add the telomere ends to chromosomes
nucleotide sequences in DNA, that dont code for anything, and shorted during replication, allowing some play for thing to shorten without cutting coding DNA
What are Okasaki fragments?
- Fragments of new DNA, synthesized on lagging strand as replication fork opens.
- Later joined together by ligase
code for different aminoacid
little change in structure and function of product protein
is RNA single, or double stranded?
single stranded in ALL living forms, but ds in some known viruses
is RNA monocystronic or polycystronic`
- monocystronic in Eukariotes (1 gene = 1 protein)
- polycystronic in Proks
what's the promoter?
- sequence of codons that singnal the start of transcription
- includes TATA box, and Start Site
How does transcription initiation complex form?
- 1. Transcription factors bind to TATA box at promoter
- 2. RNA-pol II binds to transcription initiation factors and unwinds DNA
- This is forms transcription initiation complex
define each step in transcription
- 1. transcription initiation complex forms
- 2 RNA-pol II adds new nucleotides to 3' end of groing pre-mRNA chain
- 3. RNA polymerase transcibes a stop codon
- 4 Pre-mRNA gets modified
- 4.1 5' cap & poly(A) tail
- 4.2 splisosomes cut out introns and join exons
- 5 mRNA is exported to cytoplasm
3 phases of translation
- 1. initiation
- 2. elongation
- 3. termination
Energy expense of translation:
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