dna structure/replication Flashcards
what are the subunits of nucleic acids
nucleotides
what are the components of nucleotides
nitrogenous base
pentose sugar
phosphate group
nucleotides of DNA
purines (adenine and guanine)
pyrimidines (thymine and cytosine)
what are chargaffs rules
base composition of DNA varies in different species; bases present in particular ratios: A%=T%, G%=C%
human DNA: A=T=30.3%, G=C=19.9%
how did Franklin’s X-ray crystallography results contribute to the understanding
of the structure of DNA?
the image she captured was the first X-ray image of DNA and this image led to the discovery of DNA’s molecular structure by Watson and Crick; it revealed the helical shape of the DNA molecule
dna structure
-right-handed double helix
-two anti-parallel sugar-phosphate backbones
-nitrogenous bases paired in specific combos. in interior (A-T & C-W)
what do the subunits of dna look like
nucleotides consisting of a nitrogenous base, pentose sugar and phosphate group; purines and pyridimines
what bonds hold the subints of dna together
phosphodiester bonds
what is a phosphodiester bond
bond between hydroxyl (attached to the #3 carbon) of one nucleotide & phosphate (attached to the #5 carbon) of the next nucleotide
how do you distinguish the 5’ and 3’ ends of nucleic acids
dna is anti parallel so the 5’ end will have a free hydroxyl on the 5’ carbon while the 3’ end will has a free phosphate on the #3 carbon
what bonds hold together the two strands of DNA
hydrogen bonds (weak bond but multiple can make a stable bond)
what is the process of DNA replication
synthesis of DNA for growth, repair, and hereditary purposes
what is the central dogma of biology
theory stating that genetic information flows only in one direction from DNA –> RNA –> proteins, or RNA –>protein; nuceleotides are the language of DNA and RNA, while amino acids are the language of proteins
describe the chemical reaction of DNA replication
replication is semiconservative meaning that each strand in DNA double helix acts as a template for the synthesis of a new complementary strand; always one original strand
what is the origin of replication
sequence in a genome at which replication is initiated; eukaryotic chromosome may have hundreds or thousands of replication origins
what is the replication bubble
the structure formed by the seperation of two DNA strandsby the helicase enzyme
what is the replication fork
the point at which the two strands of DNA are seperated to allow replication of each strand; one replication bubble has two
helicase
unwinds double helix at replication forks; seperates into two strands
single stranded binding proteins
binds to and stabilizes single stranded DNA until it is used as a template; binds seperated strands and keep them single stranded
topoisomerase
relieves overwinding strain ahead of replication fork by breaking, swiveling, and rejoining DNA strands; relieves tension of over-twisted strands
primase
synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each okazaki fragment of the lagging strand; makes primer (short complementary strands of nucleotides) required to start DNA replication
DNA polymerase III
uses parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or pre-existing DNA strand; catalyzes formation of phosphodiester bonds between nucleotides; makes new dna 5’->3’; moves along template strand 3’->5’
DNA polymerase I
removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to the 3’ end of adjacent fragment; attaches, hydrolyses, primes, synthesizes DNA strand to full gap, falls off
DNA ligase
joins okazaki fragments of lagging strand; on leading strand join 3’ end of the DNA that replaces primer to rest of leading strand DNA; makes phophodiester bond between okazaki fragments
