DNA

virulent definition

the ability to cause disease or death

describe griffith’s bacterial experiment

he took two strains of the same bacteria type. one was virulent, was contained in a polysaccaride capsule, and looked smooth S , the other was not lethal, had no capsule, and looked rough R.

what were the results of griffith’s bacterial experiment

griffith killed some virulent S cells by boiling them then injected it into mice who survived - the carcasses of the cells do not cause death. a mixture of heat killed virulent S and nonvirulent R did kill the mice - the live R cells were transformed into live S cells by picking up some chemical component of the dead S cells.d

what are the three key properties of hereditary material

1. accurate replication of the genetic material at every cell division is cruical

2. Structural features of the genetic material must have information content

3. the structure of genetic material must be stable enough for an organism to rely on its encoded information but leaves some room for mutation as genetic material must be able to change on rare occasion.

what are the three components of DNA

1. phosphate

2. deoxyribose

3. four nitrogenous bases

what are the four nitrogenous bases of DNA

Adenine, Guanine, Cytosine, and Thymine

what is deoxyribose sugar

the sugar in DNA contains ribose sugars that are missing an oxygen atom

which of the nitrogenous bases of DNA are called purines

two of the nitrogenous bases, adenine and guanine have a double-ring structure characteristic of a class of chemicals called purines

which of the nitrogenous bases of DNA are called pyrimidines

two of the nitrogenous bases, cytosine and thymine have a single-ring structure characteristic of a class of chemicals called pyrimidines

what are deoxynucleotides

the chemical subunits of DNA

Chargaffs rules of base composition

1. the total amount of purine nucleotides always equals the total amount of pyrimidine nucleotides

2. the amount of A always equals the amount of T, same for G and C

3. A + T is not necessarily equal to G + C but it usually is the same in different tissues of the same organism

what does it mean for a genome to be AT-rich

it means that the genome has almost twice as much A +T than it does G + C

what does it mean for a genome to be GC- rich

it means that the genome has almost twice as much G + C than A + T

what does each base pair consists of

one purine base and one pyrimidine base

structure of DNA

DNA is a right-handed helix, twisting in a clockwise motion. the two strands are held together by hydrogen bonds between purine and pyrimidine bases of strand. outside the double helix is a sugar-phosphate backbone

what is the sugar phosphate backbone of DNA

the strand is formed by alternating phosphate and deoxyribose sugar units that are connected by phosphodiester linkages which will connect the 5- carbon atom of one deoxyribose to the 3- carbon atom of the adjacent deoxyribose

what direction are each sugar-phosphate backbone

they all have5- to 3- polarity

number of hydrogen bonds between C - G

three hydrogen bonds

number of hydrogen bonds between A - T

two hydrogen bonds

what could you predict by knowing the amount of hydrogen bonds between nitrogenous bases

that DNA containing many G-C base pairs would be more stable than DNA containing many A-T base pairs.

what part of DNA adds stability

Base pair stacking at the center of the double helix, which stabilizes the structure by excluding water molecules.

what are deep minor grooves

in DNA its occurs where the sugar-phosphate backbones are close together

what are shallow major grooves

in DNA it occurs where the sugar-phosphate backbones are far apart

why is the geometry of base pairs important

the geometry of base pairs creates shallow wide major grooves and narrow, deep minor grooves along the DNA helix, proteins that bind DNA interact specifically with either major or minor grooves

explain the semiconservative model for DNA replication

the double helix is unwound and each strand acts as a template to direct assembly of complementary bases. in semiconservative each of the new helices conserves one of the original strands (parent) and the other strand is new (daughter)

explain the conservative replication model

the parent DNA double helix is conserved, and a daughter double helix is produced consisting or two newly synthesized strands

explain the dispersive replication model

two new DNA double helices are produced, with each strand containing segments of both parental DNA and newly synthesized daughter DNA

what is a replisome

a large, multiprotein molecular machine that carries out DNA replication at the replication fork

how do the replisomes open the helix and prevent overwinding

the replisome contains proteins called helicases and topoisomerases respectively

what are helicases

enzymes that disrupt hydrogen bonds that hold the two strands of the double helix together

how do helicases work

helicase encircles single-stranded DNA at the replication fork where it uses energy from ATP hydrolysis to rapidly unzip the double helix ahead of DNA synthesis

how does unwound DNA stay that way

DNA stays unwound because of single-strand DNA-binding (SSB) which bind to the single-stranded DNA and prevent the duplex from re-forming

what does unwinding of DNA cause

unwinding of DNA causes extra twisting to occur ahead of repelication forks, and supercoils form to release the strain of the extra twisting

how does topoisomerases work

topoisomerases relax supercoiled DNA by breaking either a single DNA strand or both strands, which allows DNA to rotate into a relaxed molecule. They finish their job by religating the strands of the now relaxed DNA

what is the origin of replication called in E. coli

origin of chromosomal replication is oriC

what is oriC

it is the origin of replication for E. coli and it is 245 base pairs long and contains five copies of 9 -base pair sequences called DnaA and an adjacent DNA unwinding element that is AT-rich

what is the first step in replisome assembly

the binding of a protein called DnaA to the DnaA boxes, which helps other copies of DnaA bind at the origin in a process called oligomerization

what happens when DnaA is binding to the AT-rich region

this promotes unwinding to form a single-stranded DNA bubble. the A-T pairs are weaker and easier to separate

what happens when unwinding begins

with DnaA coating the origin, two DnaB helicases now bind and slide in a 5’ to 3’ direction to begin unzipping the helix at the replication forks

what purpose does DnaA have in DNA replication

DnaA is necessary for the assembly of the replisome. its job is to bring the replisome to the correct place in the circular chromosome of bacteria for the initiation of replication

what are the three functions of DNA polymerase 1

1) a polymerase activity that catalyzes DNA chain growth in the 5’ to 3’ direction

2)a 3’ to 5’ exonuclease activity that removes mismatched nucleotides

3) a 5’ to 3’ exonuclease activity that degrades single strands of DNA or RNA

what is exonuclease

an enzyme that removes nucleotides one at a time from the end of a DNA or RNA polynucleotide chain

what can and can’t DNA polymerases do

DNA polymerases can extend a chain but cannot start a chain. Synthesis must be initiated by a primer

what are primers synthesized by

primers are synthesized by a set of proteins called primosomes of which a central component is an RNA polymerase called primase

what does primase do

it copies the template DNA in the 5’ to 3’ direction, producing a short RNA of about 11 nucleotides.

what happens because DNA polymerases synthesize DNA only in the 5’ to 3’ direction

DNA replication is semidiscontinuous. only one of the two DNA template strands can serve as a temple for replication in the same direction as movement of each replication fork.

what direction does DNA pol 3 read the template strand

in the 3’ to 5’ direction

what direction does DNA pol 3 create new strands

5’ to 3’