DNA Replication QUIZ Flashcards
What is the structure of DNA?
- 5 carbon sugar (deoxyribose)
- phosphate
- Nitrogenous base (Adenine + Guanine, Thymine + Cytosine)
What bonds hold the sugar-phosphate backbone together?
Covalent bonds/Phosphodiester bonds
How are the two chains in DNA oriented?
Oriented in opposite directions, ANTIPARALLEL
What type of bonds hold the chains together / What is they type of bond between bases?
Hydrogen Bonds
A-T –> 2 hydrogen bonds
C-G –> 3 hydrogen bonds
What did HAMMERLING do?
Discovered that instructions came from the nucleus
What did HERSHEY AND CHASE do?
Experiment - when phage takes over genetic machinery of bacterium, only genetic material (DNA) enters the cell
What did CHARGAFF do?
DNA of all members of any species have same ratio of A and T to G and C, differs from the ratio in other species
What did FRANKLIN do?
X-ray diffraction data provided information on spatial arrangements of atoms
What did WATSON AND CRICK do?
Physical model of DNA
What did MESELSON AND STAHL do?
Experiment:
- Grew bacteria (E. coli) in medium with heavy isotope of nitrogen (N15)
- Transferred bacteria to light isotope of nitrogen (N14)
- Density of nitrogen present in bacterial DNA after each generation reflects mode of DNA replication used by E. coli
- density gradient centrifugation to analyze density of DNA
- intermediate band never disappears
SEMICONSERVATIVE: Process of replication in which each DNA molecules is composed of one parent strand and one newly synthesized strand
What are the first 2 steps for SEPARATING DNA STRANDS?
- Proteins bind to replication origin
- prokaryotes = 1 site
- eukaryotes = multiple sites - DNA Helicase
- unwinds double helix
- breaks H bonds between bases
What are the last 2 parts in SEPARATING DNA STRANDS?
- Single Stranded Binding Proteins (SSBs)
- bind exposed DNA strands
- block H bonding
*complementary base pairs have tendency to recombine (anneal)
- DNA Gyrase
- relieves tension brought about by the unwinding of DNA strands during bacterial replication
- cuts both strands of DNA, so they can swivel around one another
- reseals cut strands
What is a REPLICATION FORK?
Junction where DNA strands are still joined
- prokaryotes = 1 fork
- eukaryotes = many forks
What is a REPLICATION BUBBLE?
Formed when 2 replication forks are near each other
- DNA replication proceeds toward the direction of replication fork on one strand, and away from fork on the other strand
What is RNA Primer?
- Sequence of 10-60 bases that anneals/pairs to the template strand for the purpose of initiating DNA replication
- primer synthesized by enzyme PRIMASE
What is DNA Polymerase III?
- Builds the complementary strand using the template as a guide
- DNA synthesized in 5’to 3’ direction
- Deoxyribonucleoside triphosphates –> from nucleoplasm are added to 3’ end of elongating strand
- energy released from breaking bond between first and second phosphate –> drives dehydration synthesis that adds complementary nucleotide to the elongating strand
- DNA polymerase only works in certain conditions
What are the different strands in DNA replication?
1) Leading strand
- 3’ to 5’ template strand as guide and builds the complementary strand
- CONTINUOUS
2) Lagging strand
- short fragments in opposite direction of replication fork
- DISCONTINUOUS
- Primers = continuously added as replication fork forms along the DNA parent strand
- DNA polymerase –> OKAZAKI FRAGMENTS
What is DNA Polymerase I?
- Removes RNA primers from leading strand and fragments of lagging strand
- replaces them with appropriate deoxyribonucleotides
What is DNA Ligase?
- Joins okazaki fragments into one strand by creating a PHOSPHODIESTER BOND
What happens as two strands of DNA are synthesized?
Two double stranded DNA molecules are produced that are automatically twisted into a helix.
What are other functions for DNA Polymerase I and III?
- Act as quality control checkers by proofreading newly synthesized strand
- Can function as EXONUCLEASE –> enzyme that cuts out nucleotides at end of a DNA strand
- Must work immediately to avoid mistake of being copied in subsequent replications
