Lecture 2 - Exam 2 Flashcards
Clamps remain associated with DNA polymerase allowing uninterrupted synthesis of many thousands of DNA nucleotides. But, how does DNA unwind in front of the polymerase?
Helicases.
What do helicases do?
Helicases unwind (in counterclockwise rotation) the two strands of parental DNA ahead of the replication fork.
After helicase unwinds the two strands of parental DNA ahead of the replication fork, what happens?
The unwound DNA strands are then stabilized by single-stranded DNA-binding proteins so that they can serve as templates for new DNA synthesis.
As the two strands of template DNA unwind, the DNA ahead of the replication fork is forced to…?
Rotate in the opposite direction, causing circular molecules to become twisted around themselves.
As the two strands of template DNA unwind, the DNA ahead of the replication fork is forced to rotate in the opposite direction, causing circular molecules to become twisted around themselves. How did cells evolve to handle this?
Topoisomerases.
What do topoisomerases do?
Topoisomerases catalyze the reversible breakage and rejoining of DNA strands.
The transient breaks introduced by topoisomerases serve as…?
Swivels that allow the two strands of DNA to rotate freely around each other.
We should have 1/100 errors in base pair matching but we only have __________. Why?
1/1,000,000,000
This number is so small because DNA polymerase helps select the correct base for insertion into the new DNA molecule. Binding of dNTPs actually causes conformational change in the polymerase that is necessary for incorporation .
___ out of ____ eukaryotic DNA polymerases (epsilon and zeta) have ____’ to _____’ __________ activity.
2 out of 3 ;
3’ to 5’ ;
exonuclease
Replication origins in eukaryotic chromosomes: Replication initiates at …?
Replication initiates at multiple origins (ori), each of which produces two replication forks.
Origins (ori) are typically ____ rich and serve as…?
A/T rich.
Serve as binding sites for proteins that start replication.
An S. cerevisiae ______ element in the DNA contains an ____________ and three additional elements that contribute to origin function:
ARS ;
11-base-pair ARS consensus sequences (ACS) ;
B1, B2, and B3
What binds to the ACS and B1?
The origin recognition complex (ORC) binds to the ACS and B1.
What additional proteins does ORC recruit to the origin, after it binds to he ACS and B1?
MCM DNA helicase.
DNA polymerase extends only in the 5’ to 3’ direction, so it can’t copy…?
The extreme ends with an overhanging 3’ end.
What is telomeric DNA?
A simple repeat sequence with an overhanging 3’ end.
Describe telomerase.
Telomerase carries its own RNA molecule (it’s a reverse transcriptase) which is complementary to telomeric DNA, as part of the enzyme complex.
The overhanging end of telomeric DNA binds to the …? Which then serves as…?
The overhanging end of telomeric DNA binds to the telomerase RNA, which then serves as a template for extension of the template strand by one repeat unit.
After the overhanging end of telomeric DNA binds to the telomerase RNA, which then serves as a template for extension of the template strand by one repeat unit, then what happens?
The lagging strand of the telomeric DNA can then be elongated by conventional RNA priming and DNA polymerase activity. Of course, then the RNA primer is removed and then telomeric DNA is extended by one unit repeat.
What prevents RNA nucleotides (NTPs) from becoming incorporated into a growing DNA strand?
DNA polymerase discriminates against nucleotides containing the ribose sugar.
What is the central dogma of molecular biology?
An explanation of the flow of genetic information within a biological system.
It deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid.
What are the 6 steps in the central dogma of biology?
- Transcription
- Processing
- Transport out of nucleus
- Translation
- Protein folding and modification
- Carry out function
What is transcriptional control and what is its major role?
Regulation of gene expression in response to:
- Environmental changes
- Intracellular signals
- Cell-to-cell interactions within the organism
Basically, what makes us, us. It is about what genes are turned on and off in cells.
The human genome encodes approx. ________ genes, about the same number as that for _____ and nearly twice as many as that for the common ______.
25,000 ;
Corn ;
Fruit fly
