Chapter 15 Flashcards
what is molecular biology
the study of heredity at the molecular level
- studies of bacteria and viruses
phages
viruses that infect bacterial cells
what were the phages labeled with in the Hershey Chase experiment
radioactive sulfur for proteins
radioactive phosphorus for DNA
nucleotides
building blocks for nucleic acids
what does the hydrogen bond hold together
complementary base pairs
phosphodiester bonds
hold DNA and RNA together linking sugar and phosphate groups
parental strand
serve as templates in the semi conservative model
how are the daughter strands made in each DNA synthesis model
semiconservative model= has one old and one new strand
conservative model= one daughter has both old strands & the other has both new strands
dispersive replication= each daughter has old and new DNA interspersed
semiconservative replication
parental strands separate & each is a template for new strand
- 2 DNA strands separate
- TRUE
conservative replication
parental molecule serves as template for entirely new molecule
dispersive replication
parent molecule cut into sections
antiparallel stands
5’ to 3’ polarities run in opposite directions
on which end are you always adding onto
3’ end
what is the origin of replication
replication bubble forms at specific sequence
replication bubble
forms when DNA is being synthesized
- grows in 2 directions
what direction does the replication bubble follow
follows direction replication fork moves
replication fork
region where DNA has been unwound and separated resulting in two branching prongs
DNA helicase
breaks hydrogen bonds between the 2 DNA strands to separate them
- unzips DNA strand
SSBPS
single strand DNA binding proteins
- holds strands apart
- prevent strands from closing
- come in and hold strands apart so it doesn’t close back in on itself
DNA polymerase
- works only in 5’ to 3’ direction on single strand template
- adds dNTPs to primer 3’ end
- synthesizes leading strand in 5’ to 3’ direction
what does DNA polymerase match
matches bases with high accuracy
- construction workers
- proofread: add nucleotide only if base pair is correct
RNA polymerase
builds RNA & makes primers
- provide framework that DNA can be built off of
DNA ligase
- joins Okazaki fragments
- attach fragments together
- links repaired strand to original undamaged DNA
primase
synthesizes RNA primer
- signals where DNA needs to be built
what build primers
enzyme primase
what does primase do on the lagging strand
adds an RNA primer close to end of chromosome
primer
act like flags to signal DNA polymerase where to build
- DNA polymerase builds from where primer is
topoisomerase
cuts and rejoins DNA to relieve then tension from the unwinding DNA helix
- “stress reliever”
- relives stress by cutting DNA in strategic points
how is the leading strand synthesized
5’ to 3’ direction
- toward the replication fork
how is the lagging strand synthesized
- away from replication fork
- short fragments called Okazaki fragments
which is faster; lagging or leading strand
leading strand
Okazaki fragments
- ## short, discontinues fragments that synthesize lagging strand
how is the okazaki fragments joined
DNA ligase
what is the replisome
- enzyme machine
- contains enzymes responsible for DNA synthesis around replication fork
telomeres
ends of linear chromosomes
- can be problematic
- may add to aging process
telomerase
- helps prevent or slow shortening process
- adding this to cells will cause more cell division
mismatch repair
occurs when mismatched bases are corrected after DNA synthesis is complete
what is the purpose of mismatch repair enzymes
- recognize mismatched pair
- remove section of new strand that has incorrect base
- fill in correct bases
nucleotide excision repair
recognizes types of damage
- removes damaged single stranded DNA
- uses intact strand as template for new DNA
what could happen at the end of replication that would be a problem
- single stranded DNA is left at end of lagging strand and is eventually degraded
- this would shorten the chromosome by 50-100 nucleotides each time replication occurs
- chromosomes would vanish
how can DNA be damaged
sunlight
x-rays
chemicals
DNA damage repair systems
come in, cut out damaged section, & put in a new copy
what did the Hershey-Chase experiment result in
only radioactive DNA was found inside the cells, therefore, genes must be composed of DNA
- DNA was inside E. Coli, but proteins were not
sulfur
proteins
phosphorus
DNA
