Molecular Biology

nucleic acids

found in the nucleus
possws many acidic phosphate groups

nucleotide components

• sugar

• aromatic nitrogenous base

• 1-3 phosphate groups

purines

A and G

pyrimadines

C T U

nucleoside

doesn’t have phosphate groups and consists of a sugar and a nitrogenous base

nucloeside triphosphates (NTP/dNTP)

3 phosphates

backbone of DNA

sugar + phosphates

DNA bonds

• phosphodiester

• between 3’ hydroxy and 5’ phosphate

• ALWAYS WRITTEN 5’ TO 3’

how does DNA exist in the nucleus?

double strande, antiparallel, hydrogen bonds between bases (AT, CG), right handed double helix (stabalized by van der waals)

binding/seperation of dna strands

annealing, hybridization/melting, denaturation

when will DNA be bonded more tightly?

when DNA contains more purines than pyrimadines (think of the hydrogen bonds)

genome

sum of organism’s total genetic information

chromosome

piece of ds-DNA

how many chromosomes do humans have?

46; 23 from each parent

bacterial chromosomes

1 circular chromosome

viral chromosomes

linear or circular, DNA or RNA

size difference in higher eukaryotic genomes

repetitive DNA that has no known function

what do prokaryotes use for making their chromosome compact?

enzyme called DNA gyrase uses energy of ATP to twist the molecule
functions by breaking DNA ans twsiting two sides of circle around eachother

twists created by DNA gyrase

supercoils; they are coils of a structure that is already coiled

eukaryotic DNA packaging

wrapped around globular proteins called histones

what are nucleosomes?

structure that appears after being wrapped around histones but before being completely packed away
appears like beads on a string
composed of DNA wrapped around an octomer of histones

what is chromatin

“fully packed“ DNA, composed of closely stacked nucleosomes

heterochromatin

darker and denser regions seen when DNA is stained
rich in repeats

euchromatin

lighter and less dense regions of DNA seen when stained

why is euchromatin more likey to be heritable

less compact, more accessible to enzymes and proteins

centromere

region of chromosome where spindle fibers attach during cell divison

made up od heterochromatin and repetitive DNA

kinetochores

how spindle fibers attach

multiprotein complexes that act as anchor attatchment sites for spindle fibers

chromosome legs

p (short) and q (long) determined by centromere position

telomeres

ends of linear chromosomes

distinguished by repetitice DNA sequences (guanine rich)

composed of both single + double stranded DNA

protect chromosomes

prevent them from binding with other chromosomes

why is single stranded DNA found at the very end of a chromosome (telomere)

300 base pairs help form a knot, held together by telomere associated proteins

do prokaryotes have telomeres

no, their DNA is circular