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molecular biology

DNA is the molecular basis of heredity, exploring the structure of DNA and how it replicates

bacteriophages (phages)

bacterial viruses, structure consists of of DNA and protein, DNA containing head, tail and tail fibers that attach to surfaces susceptible to bacteria.

Hershey and Chase experiment

knew that phages held genetic information, made only of only proteins (20 different monomers) and DNA (4 monomers) one goes into the host cell, 1. they mixed radioactively labelled phages with bacteria, the phages infect bacteria, they wanted to track where the DNA went and where the Protein goes. Put it in centrifuge and tested for radioactivity. the protein caused radioactivity outside the cell, DNA radioactivity was found inside the pellet. discovered DNA was the genetic info of phages.

nucleic acids

DNA and RNA are _______ ____


chemical units of of polymers (long chains)


polymer built of nucleic acids, example is the structure of DNA with the arrangement of the nucleotides A, T, C, and G

sugar-phosphate backbone

the nucleotides are joined to one another by covalent bonds between the sugar of one nucleotide and the phosphate of the next, ________________ a repeating pattern of sugar-phosphate, nitrogenous bases are arranged along this backbone

chemical structure of a single nucleotide

Phosphate Group, Sugar, and Nitrogenous base

four nucleotides found in DNA

Thymine (T), Cytosine (C), Adenine (A), guanine (G),
T and C are single ringed structures, A and G are double ring structures

uracil (U)

RNA has a nitrogenous base of this instead of thymine.

Watson and Crick experiment

used copy of Photo 51, and knowledge to gather that 1. DNA is a double helix, 2. helix diameter is uniform, 3. Phosphate on outside of helix is negatively charged.

double helix

two strands of DNA held together by hydrogen bonds


inside the cell

Chargaffs rule

A=T, C=G relative proportions of basis of DNA in every species, later changed to Base pair rule

Rosalind Franklin

X ray crystalography, found structure of a model of DNA, photo 51, didn't share it.

Photo 51

Found by Franklin, Wilkins stole Photo 51, copied it on newspaper with W and C, returned photo and Franklin never knew, shows X which means double helix, horizontal line through X (at the angel it is rotated) tells how tight the helix is.


Polymerase Chain Reaction, the process of copying DNA, DNA replication

anti parallel

the orietnation of DNA strands, running in opposite directions, copmliment, 3 prime to 5 prime then opposite would run 5 prime to 3 prime

number of carbons

______________ __ ________ only go from 5 prime to 3 prime and 3 prime to 5 prime, one direction

The three theories of DNA replication

1. conservative model: whole DNA molecule would be consumed 1rst gen: 1 exact parent replication and 1 new, 2nd gen: 1 original 3 new
2. semiconservative: produces DNA molecules 1 strand old and 1 strand new.
3. Disperative model: each strand of both daughter molecules contain a mixture of old and newly synthesized parts

Meselon- Stahl

density experiment to find the way DNA replicates, Nitrogen 15( number of neutrons, does not change property of atom, all DNA made of nitrogen, then bacteria grows and divides)they tracked old heavy DNA, with new lighter DNA, used a centrifuge and gel electrophysis to separate molecules on size- grows and divide in 20 minutes, just once, centrifuged it then found medium Density DNA so no to the conservative method, found that DNA replicates semi-conservatively.

replication fork

split the two strands of DNA, 2 strands separate and separate the two nucleotide strips that are complementary to each other (a and T, c and G)


the enzyme that unzips the double helix and holds them apart


single strand binding protein, bind to DNA strands and holds them apart

DNA polymerase

reads the genetic code of A's, T's, C's, and G's, can only build 5 to 3

DNA polymerase on leading strand

travels down reading each of the sequences on the parental strips and putting the complementary nucleotide on the leading strand, DNA polymerase build 5 to 3, leading strands run in opposite direction 3 to 5 so it works

DNA polymerase on lagging strand

cannot build because both are going from 5 to 3 so needs to build in fragments, builds away from the replication fork, goes in opposite direction.

Okazaki fragments

fragments that are built on the lagging strand


enzyme that can start from scratch to build DNA primer, which allows DNA polymerase to add nucleotides

RNA primer

built by primase then DNA polymerase can add more nucleotides to them

DNA ligase

forms a covalent bond from one fragment to the next

replication bubble

where the DNA strands split apart- splits in more than one place

radioactive probe

short radioactive DNA piece, once separated and treat gel, have specific code

restriction enzymes

enzyme that cuts DNA at a specific sequence of nucleotides

Parental DNA

strand of DNA before it splits

Leading strand

built continously, DNA polymerase

lagging strand

built in pieces, RNA clamp attaches to DNA polymerase, joined together removes RNA replaces DNA

RNA segments

built by primase, then DNA polymerase can add more nucleotides to them

DNA polymerase

builds new strand by adding new nucleotides

DNA ligase

joins pieces together

heating and cooling

______________ DNA breaks the bonds like helicase and __________ puts DNA back together like DNA ligase

lytic cycle

a cycle that leads to the lysis (breaking open) of the host cell

lysogenic cyle

viral DNA replication occurs without phage production or death of the host cell


the phage of DNA once inserted into the bacterial chromosome

DNA microarrays

makes it easy to determine exactly what genes are active in particular cells at particular times

gel electrophoresis

a method for physically sorting macromolecules proteins or nucleic acids- primarily on the basis of their electrical charge and size

genetic marker

a chromosomal landmark whose inheritance can be studied

restriction fragments

extract DNA from some of cells and treat it with a restriction enzyme, mixture of DNA pieces, the number of these and their sizes reflect the specific sequence of nucleotides in your DNA

repetitive DNA

nucleotide sequences present between genes, in many copies of the genome


type of repetitive DNA at each end of a eukaryotic chromosome


"jumping genes", a segment of DNA that can move from one site to another within a cell and serve as an agent of genetic change


HUman Genome Project, map the entire human genome, determining the complete nucleotide sequence of human DNA

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