Chapter 14 Flashcards
what sugar is in DNA and how many carbons is it?
deoxyribose, 5
what are the 4 nitrogenous bases?
adenine, guanine (purines) cytosine, thymine (pyrimidines)
where is the nitrogenous base attached in DNA?
to the 1’ carbon
where is the phosphate group attached in DNA?
5’ carbon
where is the free hydroxyl group attached in DNA?
to the 3’ carbon
how are monomers connected to eachother in DNA?
phosphodiester bonds
how are phosphodiester bonds formed?
between the phosphate group of one nucleotide and the 3’ OH- groups of the next nucleotide
what orientation do chains of nucleotides have?
5’ to 3’
what are Chargaff’s rules?
amount of adenine = amount of thymine
amount of guanine = amount of cytosine
who proposed the double helix structure?
watson and crick
what does the double helix consist of?
2 sugar-phosphate backbones with nitrogenous bases toward the interior of the molecule
what kind of bonds do the complimentary bases form and why is this important?
hydrogen bonds; weak and easy to break for replication and transcription
how do the 2 strands of DNA run?
antiparallel to each other
why do the 2 strands of DNA wrap around each other?
single ring pyrimidine vs double ring purine
when does DNA replication occur?
S phase
what are the 3 possible mechanisms of DNA replication?
- conservative model
- semiconservative model
- dispersive model
how does the conservative model work?
parent DNA is just photocopied
how does the semiconservative model work?
replicate parent DNA to get 1 original and 1 new strand, is the actual way it works, each strand of DNA acts as a template for the synthesis of a new strand, which is complementary to the old strand
how does the dispersive model work?
mix and match for two completely new strands
what 3 things does DNA replication require?
- something to copy (DNA)
- something to do the copying (enzymes and proteins)
- building blocks to make the copy (nucleotide bases)
where are the things required for replication located? give eukaryotes and prokaryotes
euk: nucleus
Pro: cytoplasm
what are the 5 steps of DNA replication? (USSST)
- unwind helix
- separate and stabilize the strands
- start the synthesis (initiation)
- synthesize new strands (elongation)
- terminate the process (termination)
what is needed when stabilizing the separated strands of DNA?
binding proteins bc DNA is like a spring and wants to stay coiled
list the 7 proteins involved in replication
- helicase
- DNA gyrase
- binding protein
- primase
- DNA polymerase III
- DNA polymerase I
- DNA ligase
what does helicase do?
unwinds helix (unzips ur genes)
what does DNA gyrase do?
keeps helix from rewinding (no gyration :()
what do binding proteins do?
stabilize templates
what does primase do?
synthesizes RNA primers
what does DNA polymerase III do?
DNA SYNTHESIS
what does DNA polymerase I do?
erases primers, fills gaps, fixes poly III’s mistakes like a tired older sibling
what does DNA ligase do?
joins DNA segments, repair
what is the 3 part process of DNA replication?
- initiation- replication begins at an origin of replication, requires a PRIMER
- elongation- new strands of DNA are synthesized by DNA POLYMERASE III, nucleotides are added
- termination- replication is terminated differently in prokaryotes and eukaryotes
how is DNA replication different in prokaryotes? (2)
- the DNA molecule is circular, so it’s easier
2. replication begins at one origin of replication and proceeds in both directions around the chromosome, so it’s faster
what end of DNA does DNA polymerase III add nucleotides to ?
3’ end
3 and 3
what is eukaryotic DNA replication and why?
semi-discontinuous bc the strands run antiparallel to each other, but pol III can only add nucleotides to the 3’ end of each strand, so each strand is put together differently
when the DNA strands zip apart in eukaryotes, what forms?
a replication fork with a leading and algging strand
which strand of the replication fork is synthesized continuously?
the leading strand, in the same direction as the fork
which strand of the replicaiton for is synthesized discontinuously, and what does it create?
the lagging strand, creating Okazaki fragments
what fixes the Okazaki fragments?
DNA ligase
where are the enzymes for eukaryotic DNA replication contained?
within the replisome
what 2 things does the replisome consist of?
- the primosome
2. 2 DNA polymerase III molecules
what does the primosome consist of?
primase and helicase
why must eukaryotic chromosomes be replicated from multiple points of replication?
their larger size and complex packaging
what does the removal of the last primer on the lagging strand of the linear eukaryotic DNA leave?
a gap that will shorten the chromosome each time its replicated
what is used to protect the ends of eukaryotic DNA?
telomeres
what are telomeres?
repeated DNA sequence on the ends of eukaryotic chromosomes to protect the ends, not made by the replication complex, but produced by telomerase
what are DNA damaging agents?
UV light
X rays
Chemicals
mutagens
what do specific DNA repair mechanisms do?
target a particular type of DNA damage
what do non-specific DNA repair mechanisms do, give an example
able to repair many different kinds of DNA damage
excision repair
what is excision repair?
to correct damaged or mismatched nitrogenous bases
