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Late 1800s, scientist thought that chromosomes played a role in heredity
and heredity material was chemical in nature
Chromosomes contained both protein and nucleic acid, so both were viable
contenders;
till 1940’s, protein were favored because it had so much variety and also it
had so many functions
Hershey and Chase wanted to make sure; in 1950’s, viruses were seen as
infectious particles that changes cells into virus factories; non genetic part of
the virus remains outside of the cell
The cell burst and releases new viruses out to environment; virsues are
usually specific to certain cell types
The scientists used the T2 Bacteriophage because it was simple in structure
--------DNA has phosphorus but not sulphur
Proteins have sulphur but not phosphorous
Hershey and Chase made viruses which were radioactive with either sulphur
or phosphorus
Then, they infected the bacteria
Since the DNA is actually genetic material, the bacteria became radioactive
with phosphorus, but the protein radioactivity in the other culture had no
effect on the bacteria there
...
4 nm apart
There was a repeating structure with a gap of 0
...
Bacterial DNA difference is that eukaryotic DNA is
associated with proteins called histone
Prokaryotes/bacteria usually don’t have DNA associated with anything like
histones; thus, it is called “naked”
Histones are used to package DNA into structures called nucleosomes,
which is made up of eight histone proteins at the core with DNA coiled
around proteins
The octamer (eight protein structure in the middle) is made of two copies
of four different types of histones
“linker DNA” is a short section of DNA that connects nucleosome to
nucleosome; and the H1 histone binds DNA to the core particle
Histones in DNA contributes to supercoiling; it allows for a great length of
DNA to be packed into smaller space within nucleus

The nucleosome is an adaptation that facilitates the packing of large
genomes in eukaryotes; the H1 histone binds in such a way to make
30nm fiber which allows further packing
DNA replication is continuous on the leading strand and
discontinuous on the lagging strand
On the leading strand synthesis occurs as the fork opens; on the other
one it is replicated in fragments moving away from the fork; new
fragments are created on the lagging strand as the fork exposes more of
the template strand, these fragments are called okazaki strands
DNA replication is carried out by complex system of enzymes
Helicase unwinds the DNA at replication fork and the enzyme
topoisomerase released the strain that develops ahead of the helicase;
singe stranded binding proteins keep the strands apart long enough to
allow the strand to be copied
RNA primer is required for starting replication; which is used only once on
leading strand but several times on the lagging strand
DNA primase creates all the RNA primers
DNA polymerase is responsible for covalently linking the
deoxyribonucleotide monophosphate to the 3’ end of the growing strand;
diff
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kinds of DNA polymerases each with different

functions like proof reading, polymerization and removal of RNA primers
when no longer needed
DNA ligase connects gaps between fragments
DNA polymerase can only add nucleotides to the 3’ end of a
primer
In DNA molecules, DNA replication starts at sites called origins of
replication; in eukaryotes there are many while prokaryotes only have
one
Replication occurs in both directions away from the origin; shows up as
replication bubble in electron micrographs
The phosphate attaches on the 5th carbon on ribose and the second
phosphate attached on the 3rd carbon; thus replication occurs in the 5’ to
3’ direction
Some regions of DNA don’t code for proteins but have other
functions
The cell operates according to a genetic code; DNA is used as a guide for
polypeptide production using the genetic code
Only some DNA makes code for polypeptide production; these are called
coding sequences
There are many non coding sequences in genomes with other jobs such
as those to guide the production of tRNA and rRNA, also gene expression
such as enhancers and silences
Must of eukaryotic genome is non coding
Within the genome, repetitive sequences can be common; there are 2
types
 Moderately repetitive
 Highly repetitive (satellite DNA)

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Together they make up between 5 and 60% of the genome;
60% applies to humans

One area they occur in are the ends of eukaryotic chromosomes called
telomeres, which has a protective function
In interphase, enzymes that replicated NDA annot continue it all the way
to the end of the choromsome
If cells replicated without telomeres, they would lose genes at the end of
the chromosomes; repetitive sequences found in telomeres are used as
sacrifice material

The Function of the Promoter

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A variable number tandem (VNTR) is a short nucleotide sequence that
shows variations between individuals in terms of number of times
sequence is repeated
Each variety can be inherited as an allele; the VNTR allele combinations in
individuals is the bases behind DNA profiling in genealogical investiagions
Locus is the location of a heritable element on the chromosome
Paternal lineage is deduced by analyzing short tandem repeats from the Y
chromosome
Maternal lineage is determined through mitochondrial DNA variations in
single nucleotides at specific locations called hypervariable regions

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Determination of the sequence of bases in a genome is carried out using
fluorescence
Many copies of the unknown DNA that is to be sequenced are put in test
tubles with all the materials include such as the deoxyribonuclelotides and
enzymes for replication
Also small quantities of dideoxyribonucelotides are put with different
fluorescent markers
The dideoxyribonucelotides will be put into some of the new DNA, when
they are copied they will stop replication at the point they were added
The fragments are separated by length using electrophoresis and the
sequences of bases can be analysed by comparing color of fluorescence
with length of the fragment
Promoter is an example of non-coding DNA with a function

Only some DNA sequences make polypeptides (coding); others are non
coding and they have function such as producing tRNA and mRNA
Some other ones play a role in gene expression regulation (enhancers
and silencers)
Promoter is a sequence that is located near a gene; it’s the binding site of
RNA polymerase, the enzyme that catalyses the formation of covalent
bonds between nucleotides during RNA synthesis
The promoter isn’t transcribed but it plays a role in transcription

Proteins and Gene Expression

6/11/2016 7:51:00 PM

Gene expression is regulated by proteins that bind to specific base
sequences in DNA
Some proteins are expressed in an unregulated manner (essential to
survival) and other need to be produced at certain times, or must be
regulated
Gene expression in prokaryotes occurs due to variation in environmental
factors
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EG: in E

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