Ch. 10 and 12 (DNA Structure and Replication) Flashcards
describe the structure of DNA
Two COMPLEMENTARY and ANTIPARALLEL complementary nucleotide strands that form a double helix
what is the “central dogma”?
DNA –> RNA –> PROTEIN
DNA (transcription) –> RNA (translation) –> PROTEIN
- all information used to instruct the development of an organism is housed in the DNA
- theres way more info in DNA than we can ever use at any one time
what is the primary structure of DNA?
string of nucleotides joined together by phosphodiester linkages/bonds
(DNA is a “polymer”)
what is the secondary structure of DNA?
DNA’s stable 3 dimensional structure (watson and crick’s helical structure)
what is the tertiary structure of DNA?
complex packing of DNA into chromosomes
what makes up a nucleotide?
5 CARBON SUGAR
contains either ribose (RNA) or deoxyribose (DNA)
-both are pentose sugars, 5 carbons numbered 1’-5’
-ribose (has hydroxyl group on 2’ carbon - OH)
-deoxyribose (has H group on 2’ carbon)
NITROGENOUS BASE
purines and pyrimidines (attach to the 1’ carbon of the pentose sugar)
PHOSPHATE GROUP
(attach to 5’ carbon of pentose sugar)
-phosphates are negatively charged, accumulate negative charges on DNA molecules
what are purines?
- 2 ring structure
- Adenine + Guanine
“pure as gold”
what are pyrimidines?
- 1 ring structure
Cytosine + Thymine (dna) + Uracil (rna)
“Cut The Pyramid”
in which way does DNA grow?
always 5’ –> 3’
covalent bonds between 5’ phosphate of one nucleotide and 3’ carbon of next nucleotide
how many bonds to A-T nitrogenous base pairs have?
2 hydrogen bonds
how many bonds do G-C nitrogenous base pairs have?
3 hydrogen bonds
what do phosphodiester linkages do?
connects 5’ phosphate with 3’ OH (forms phosphodiester backbone)
what is the difference between hydrogen and covalent bonds?
covalent bonds (like gluing together) stronger, phosphodiester backbone
hydrogen bonds (like magnets) weaker, allow separation of DNA strands
how many amino acids are there to make up proteins?
20
what did Edwin Chargaff find?
the amounts of the four bases of DNA varied between species, but their ratios did not
“Chargaff’s rule”
- # G = # C
- # A = # T
what are dNTP’s?
“deoxyribonucleotide triphosphates”
- building blocks of DNA
- 3 phosphates (alpha, beta, and gamma)
- alpha binds, beta and gamma are lost
how are dNTP’S added to a growing strand of DNA?
they are added to the free 3’-OH by “DNA polymerases”
always 5’ –> 3’
NEVER ADD TO 5’
ALWAYS ADD TO 3’
what are some requirements of DNA replication?
- high fidelity (no errors)
- once and only once per cell cycle (avoid re-replication)
- complete (entire genome must be copied)
define “semiconservative” replication
- the way we replicate our DNA
- each strand serves as a template
- each of the original strands remain intact
- each DNA molecule is half (semi) conserved during replication
- each new strand is half original/half new
- replicates BIDIRECTIONALLY
define “origin of replication”
- different spots on chromosomes where you begin DNA synthesis
- origin of replication is recognized by the “origin recognition complex” (ORC)
how many origins of replication do bacteria have? eukaryotes?
eukaryotes - multiple origins of replication (need to replicate fast enough for large/complex organism)
bacteria - one origin of replication
what does DNA helicase do?
opens up the double helix of DNA, begins unwinding
what are single stranded binding proteins?
hold open the DNA and keep it form closing in on itself so replication can occur (naturally wants to close in on itself, doesn’t like to be single stranded)
what is a topoisomerase?
relaxes the torsion caused by unwinding of DNA
gyrase in bacteria
what is primase?
special kind of RNA polymerase used only in DNA replication
-synthesizes primers (small RNA’s, 10-12 nucleotides long)
what do primers do?
short stretches of RNA 10-12 nucleotides long
prime DNA stretches to allow for DNA syntheses
(make leading/lagging strands)
-gets a 3’ OH ready for DNA polymerase to add onto
what does DNA polymerase do?
- carries a 5’ –> 3’ exonuclease activity
- eats away RNA primers, replaces them with real DNA
what does DNA ligase do?
every time primer segment gets eaten away by DNA polymerase, fills in breaks in sugar backbone
-fills in “nicks”
what is significant about the helical structure of DNA?
forms major and minor grooves
-keeps DNA rungs with consistent widths
-(ex. checkpoints sense when there is a bulge, incorrect base pairing, imperfect helical shape)
DNA IS VERY STABLE
major groove usually houses more proteins because it is bigger
what did Griffith discover? how?
the principle of transformation
isolated 2 strains of strep and injected into mice
1. rough (type IIR) non virulent
2. smooth (type IIIS) virulent
injected heat killed IIIS into mice and the mice lived!
injected heat killed IIIS with IIR = mice died
dead IIIS regenerated itself when mixed with living IIR
what did Avery, McCloud, and McCarty discover?
they discovered that the “transforming principle” is DNA
-only DNA has the ability to transform
telomere shortening
usually associated with age
-telomeres shorten over time,may eat away important DNA as telomeres become shorter due to years and years of DNA replication
