Intro to DNA Flashcards
deoxyribonucleic acids (DNA)
stores genetic code
responsible for transmission of code from parent to daughter cells and generation to generation
ribonucleic acid (RNA)
intermediary between DNA and proteins
responsible for expressing the genetic code
DNA replication
transmission of genetic information to daughter cells
transcription
expression of genetic information contained in DNA through RNA
DNA repair
corrects damage resulting from replication errors or environmental insults
recombination
joins two parental DNA segments to form a hybrid molecule
central dogma
genomic DNA -> mRNA -> protein
nucleotides are made of
1) nitrogenous base (A, C, T, G, U)
2) 2’ deoxyribose sugar (DNA) or ribose sugar (RNA)
3) 5’ phosphate group
which nucleotides are purines
A and G (2 rings)
which nucleotides are pyrimidines
C, U, and T (1 ring)
what distinguishes T from U
THYmine has a meTHYl group
nucleoside
a nitrogenous base linked to a 5-carbon sugar via an N-glycosidic bond
-adenosine, guanosine, cytidine, uridine (RNA)
-deoxyadenosine, deoxyguanosine, deoxycytidine, deoxythymidine
nucleotide
a nucleoside with 1, 2, or 3 phosphate groups at the 5’ C position of the sugar
nucleic acid polymers
nucleotides are COVALENTLY bound together by 5’ to 3’ PHOSPHODIESTER BONDS, forming the DNA backbone
3’-azido-2’-deoxythymidine (AZT)
-a thymidine analog (3’ OH group replaced by the N3 azido group)
-used to treat HIV infection
-inhibits the reverse transcription of the HIV RNA to DNA; gets incorporated but cannot be extended so replication stops
acylovir (Zovirax)
-used to treat herpes simplex virus infections
-a guanosine analog
-incorporated into viral DNA chain, but cannot be extended
primary structure of DNA
polynucleotide chain, linked by phosphodiester bonds between nucleotides
*DIRECTIONAL: 5’ phosphate to 3’ OH group
endonucleases
enzymes that cleave INTERNAL phosphodiester bonds through hydrolysis
exonucleases
enzymes that cleave phosphodiester bonds from the ENDS of the DNA (specific for 5’ or 3’ end)
DNase treatment for cystic fibrosis
chops up the DNA that causes thick, sticky mucus buildup in the lungs
secondary structure of DNA
double helix (B-form most common); has major and minor grooves; formed by base pairing between 2 polynucleotide chains with complementary sequences that run ANTIPARALLEL
watson-crick base pairing
A and T - double hydrogen bond
C and G - triple hydrogen bond
promoter
site for transcription factors and RNA polymerase to bind and begin transcribing RNA (common elements are TATA and CAAT boxes)
enhancers/silencers
sequences that bind specific transcription factors that regulate transcriptional efficiency
exons
contain sequence that will eventually be translated into peptide; CODING sequences
introns
intervening sequences between exons; transcribed but removed during RNA processing
5’ UTR
5’ untranslated region; responsible for binding to ribosome for translation
3’ UTR
3’ untranslated region; contains poly-A binding sequence, which likely regulates mRNA stability
myotonic dystrophy
autosomal dominant disease caused by mutations in DMPK or CNBP; trinucleotide repeat expansion; s/s include myotonia (slowed relaxation of muscles), muscle pain, etc
trinucleotide repeat expansion diseases
-caused by unstable triplet repeat mutations
-number of repeats varies in everyone
-the repeat length correlates with the severity and/or age of onset of the disease
-demonstrate “genetic anticipation,” where earlier age of onset of more severe disease is observed in subsequent generations
tertiary structure of DNA
DNA can be relaxed (B-form double helix) or supercoiled (when the double helix coils upon itself)
DNA topoisomerases
relax supercoiling of DNA by introducing swivel points in the DNA helix; cause breaks and rejoin the strands without ATP
topoisomerase I
cuts a single strand of the double helix to remove supercoiling
topoisomerase II
cuts BOTH strands of DNA to remove supercoiling
quinolone drugs
target a bacteria-specific topoisomerase II [DNA gyrase]
-blocks gyrase, inhibiting bacterial DNA synthesis
*eukaryotes do not have gyrase, so we are unaffected
camptothecin (CPT)
-targets topo I and inhibits the reformation of the cleaved DNA
-leads to cell toxicity at DNA replication
*irinotecan/topotecan at derivates used as chemo
etoposide
binds to topo II and prevents re-ligation of the break, leading to double stranded breaks and cell death
nucleosome
contains ~146 bp of DNA and 2 copies of each of the core histones (H2A, H2B, H3, and H4)
-DNA is wrapped 1 3/4 turns around the outside of the histone octamer
chromatosome
2-turn particle with H1
(contrast to nucleosome, which is 1 3/4 turns)
histones
proteins with unusually high content of BASIC amino acids (Arg, Lys, and His), which are cationic and interact with the negatively charged DNA