Molecular Biology-DNA Structure Flashcards
purines
G, A: double rings
pyrimidines
C, T, U: single rings
nucleoside
ribose or deoxyribose with a purine or pyrimidine linked to the 1’ carbon
nucleotides=nucleoside triphosphates
phosphate esters of nucleosides, with 1-3 phosphate groups joined to the ribose ring of the 5’ hydroxy group
what is the backbone of DNA?
the sugar/phosphate portion, this is the portion of DNA that is invariant
how are nucleotides in the DNA chain?
by covalent phosphodiester bonds between the 3’ hydroxy group of one deoxyribose and the 5’ phosphate group of the next deoxyribose
oligonucleotide
a polymer of several nucleotides linked together
polynucleotide
a polymer of many nucleotides
what’s the convention of writing nucleotide sequence?
5’ to 3’
Watson-Crick model
cellular DNA is a right-handed double helix held together by hydrogen bonds between bases
A bonds to:
T with two hydrogen bonds
G bonds to:
C with three hydrogen bonds
two chains of DNA are complementary if:
each strand can hydrogen bond when the strands are oriented in an antiparallel fashion
annealing/hybridization
the binding of two complementary strands of DNA into a double-stranded structure
melting/denaturation
the separation of DNA strands
right-handed double helix
corkscrews in a clockwise motion
what stabilizes the double helix?
van der Waals interactions between the bases stacked upon each other
genome
the sum total of an organism’s genetic information
chromosome
each piece of ds-DNA
what composes prokaryotic (bacterial) genomes?
a single circular chromosome
is there a correlation between genome size and evolutionary sophistication?
no
DNA gyrase
an enzyme in prokaryotes that uses ATP energy to twist the gigantic circular molecule to make it more compact and sturdy; breaks the DNA and twists the two sides of the circle around each circle to result in a twisted circle composed of ds-DNA to create supercoils
supercoil
coils of a structure that is already coiled
how is eukaryotic DNA packaged?
wrapped around globular proteins (histones) and further compacted/condensed
nucleosome
“beads” of DNA wrapped around an octamer of histomes
chromatin
fully packed DNA, composed of closely stacked nucleosomes
heterochromatin
darker and denser regions of chromosomes; rich in repeats
euchromatin
less dense region of chromosomes
density of DNA indicates:
extent of coiling or compactness, patterns are constant and heritable
lighter/less dense regions have:
higher transcription rates and higher gene activity because loose packing=DNA more accessible to enzymes and proteins
centromere
the region of the chromosome to which spindle fibres attach during cell division
kinetochores
multiprotein complexes that act as anchor attachment sites for spindle fibers
what are centromeres made of?
heterochromatin and repetitive DNA sequences
centromere position defines the ratio between:
the p and q arm
p arm
short
q arm
long
what are the four centromere positions?
metacentric, submetacentric, acrocentric, telocentric
telomeres
the ends of linear chromosomes, distinct nucleotide sequences repeated 50-hundreds of times
what is the typical telomere sequence in vertebrates?
5’-TTAGGG-3’ (guanine rich)
specialized telomere caps
distinguish telomeres from double-stranded breaks (because telomeres can be single or double-stranded) and prevents activation of repair pathways
what is the function of telomeres?
to prevent chromosome deterioration and also prevent fusion with neighbouring chromosomes
how come prokaryotes do not have telomeres?
because circular DNA has no “end”
