Download Untitled

1
Hershey and Chase’s experiment used different radioactive isotopes to label the DNA and
protein in T2.
Hershey and Chase’s first trial on figuring out which molecules were the genetic material
consisted of tagging the protein body of the phage, then they radioactively tagged the
phages DNA. They allowed the two batches of T2 to infect separate samples of
nonradioactive bacteria. Shortly after the onset of infection, they agitated the cultures in a
blender to shake loose any parts of the phages that remained outside the bacterial cells.
They then spun the mixtures in a centrifuge, the cells were deposited as a pellet at the
bottom of the centrifuge, but phages and parts of phages, being lighter, remained
suspended in the liquid. The researchers then measured the radioactive in the pellet and
the liquid. Hershey and Chase concluded by experiment that DNA is the genetic material.
2
DNA and RNA are nucleic acids consisting of long chains (polymers) of chemical units
(monomers) called NUCLEOTIDES.
DNA and RNA molecules have Sugar-phosphate backbones, which are a repeating pattern
of sugar-phosphate-sugar-phosphate.
Pyrimidines (Thymine (T) and Cytosine (C))
Purines ( Adenine (A) Guanine (G))
3
Watson and Crick solved the structure of the DNA double helix.
Rosalind Franklin contributed with an X-ray image looking down a double helix
3 hydrogen bonds when G-C
2 Hydrogen bonds when A-T
4
Semiconservative model- half of the parental molecule is maintained (conserved) in each
daughter molecule.
The parental molecule unwinds so that both parental strands serve as templates.
Molecules than have the opportunity needed to add the new base pairs to make a new
DNA molecule, with both having one new strand and an old strand that was used as a
template.
5
The DNA molecule being replicated can have many Origins of replication, which are the
starting points for replication, that create bubbles. These bubbles created have two
directions, which help give rise to the two daughter DNA molecules.
6
When replication begins a DNA polymerase molecule attaches itself at the 3’ end of the
parental strand and attaches nucleotides to the 5’ end. The DNA polymerase always goes in
the 3’ to 5’ direction. Notice how the bottom parental strand creates DNA fragments this
happens because as the parental molecule unwinds a new parental strand without base
pairs needs another DNA polymerase to bind at the new 3’ end. DNA ligase is responsible
for attaching the the DNA fragments.
7
8
Transcription, the transfer of genetic information from DNA into RNA molecule occurs
inside the cells nucleus.
9
Transcription, the transfer of genetic information from DNA into RNA molecule occurs
inside the cells nucleus. Once the mRNA is made and groomed it travels out into the
cytoplasm where translation occurs, which is the transfer of the information in the RNA
into a protein. The protein built is then used by the cell.
10
During DNA transcription in the nucleus DNA is used to make a strand of RNA. The RNA is
used for translation to make a polypeptide. The RNA is read as a series of three-base
words, called CODONS. Each codon codes for a specific amino acid.
11
12
RNA polymerase- the transcription enzyme that links the RNA nucleotides
Promoter- “the start transcribing” nucleotide sequence.
Terminator- sequence of bases in the DNA template that codes for stopping.
1. Initiation- The RNA polymerase binds to the promoter DNA sequence.
2. Elongation- The RNA polymerase unwindes and adds nucleotide sequences to a
daughter strand using the original DNA molecule as a template.
3. Termination The RNA polymerase reaches the terminator sequence and detaches the
completed RNA strand.
13
Introns- noncoding regions from the mRNA
Exons- coding regions- the parts that are expressed as amino acids.
RNA splicing- the process of cutting out the introns and gluing together the exons.
14
tRNA- converts the three-letter words (codons) of nucleic acids to the one-letter amino
acid words of protein.
Anticodons- a special triplet of bases that is complementary to specific amino acids.
15
16
1. Codon recognition- The anticodon of an incoming tRNA molecule, carrying its amino
acid, pairs with the mRNA codon in the A site of the ribosome.
2. Peptide bond formation- The polypeptide sperates from the tRNAfound in the P-site
and binds to the amino acid on the tRNA found in the A-site.
3. Translocation- The tRNA from the A-site moves into the P-site awaiting for the next
tRNA which brings the next amino acid.
17
Mutation- Any change in the nucleotide sequence of DNA.
Mutagen- a physical or chemical agent that promotes mutation.
Spontaneous mutations- Errors that occur during DNA replication or recombination
18
Lytic cycle- results in the lysis of the host cell and the release of the viruses that were
produced in within the cell as phages.
Lysogenic cycle- The DNA phage inserts into the bacterial chromosome by recombination,
while keeping the host cell alive.
19
Transformation- The uptake of foreign DNA from the surrounding environment.
20
Transduction- The transfer of bacterial genes by a phage.
21
Conjugation- A physical union of cells and the DNA transfer between them.
The donor cell have sex pili that bind and to the recipient cell that get pulled to form a
mating bridge.
22
F factor integration- The donor cell makes a copy of its chromosome and donates it through
conjugation to a recipient cell, followed by a recombination.
F factor as a plasmid- The donor cell will donate its plasmid to the recipient cell.
R plasmids provide cells with an advantage by being resistant to antibiotics. They carry
genes that make enzymes that destroy the antibiotics like penicillin and tetracycline.
23