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CH 16/17 (Inheritance (Protein's Role (types of DNA models…
CH 16/17
Inheritance
Protein's Role
are macromolecules with great heterogeneity
and carries functions essential for hereditary material
the basic principle
template strands comes from
hydrogen bonds being broken,
where the two chains unwind and separate
which goes on to find a companion chain
the two chains are complementary
and stores the information that is necessary to reconstruct with other chains
the reason why each strand is a template
is because
each strand orders nucleotides into a new, complementary strand
the nucleotides line up along the template strand
according to the base-pairing rules
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first there's one double-stranded DNA
and by the end of the process
there's two double-stranded DNA
both an exact replica of each other
types of DNA models
conservative
where the parent double-stranded DNA stays together throughout the whole process
semiconservative
two double-stranded DNA molecules
the parent double-stranded DNA switch strands with the new one
so that the daughter strand is paired with one parent strand
the parent strands come back together at the end
is the confirmed model
dipersive
when the parent double-stranded DNA first replicates
it's strand becomes mixed with new and old molecules
and keeps getting mixed with new molecules as it replicates
the process of DNA replication
chromosomal DNA replication begins at a particular site
which is the
origins of replication
that consist of short stretches of DNA that had specific sequence of nucleotides
then the proteins that initiated the replication
recognize the sequence and attach to the DNA
to separate the strands and open up the
replication "bubble"
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eukaryotic chromosomes
have hundreds or thousands replicative origins
multiple replication bubbles form and will later fuse,
which speed up the copying of long DNA molecules
in bacteria,
DNA replication proceeds in both directions in each origin
synthesis of a new DNA strand
begins with the initial nucleotide chain
that is produced during DNA synthesis
is missing RNA
and will be filled by an RNA chain called a
primer
which is then synthesized by
primase
it starts a complementary RNA chain with a single RNA nucleotide
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the new strand is catalyzed by
an enzyme called DNA polymerases
and adds nucleotides to the 3' end of the pre-existing chain
in E.coli, there's two ones who hold an important rule
DNA polymerases III
and DNA polymerases I
requires a primer and DNA template strand
Antiparallel Elongation
the two strands of DNA in a double helix are antiparallel
and are oriented in opposite directions to each other
so that the nitrogenous bases can fix together
and has to be anti-parallel to template strands
the antiparallel arrangement of double helix
with a property of DNA polymerases
has n important effect on how replication works
due to their structure,
DNA polymerases can add nucleotides only to
leading strand
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lagging strand
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bacterial DNA replication
proteins and their functions
helicase
unwinds parental double helix at replication fork
single-stranded binding protein
binds to and stabilizes
single-stranded DNA until it is used as a template
topoisomerase
relieves overwinding strain ahead
of replication fork by breaking
swiveling or rejoining DNA strands
primase
synthesize an RNA primer at 5' end of leading strand
and at the 5' end of each Okazaki fragment of lagging strand
DNA pol III
uses parental DNA as a template
to synthesize new DNA strand
by adding nucleotides to an RNA primer
or pre-existing DNA strand
DNA pol I
removes RNA nucleotides of primer from 5' end
and replaces it with DNA ones to 3' end of adjacent fragment
DNA ligase
joins Okazaki fragments of lagging strands
for leading strands,
joins 3' end of DNA that replaces primer
to the rest of the strand
replicating the ends of DNA molecules
telomeres
are the
special nucleotide sequences of eukaryotic chromosomal DNA molecules
consists of multiple repetitions of one short nucleotide sequence
has two protective functions
prevent staggering ends of daughter molecules
from activating the cell's systems
for monitoring DNA damage
a buffer zone
provides protection against gene's shortening
postpone the erosion of genes
Chromosomes
prokaryotic
has one-thousandth as much of DNA
DNA was longer than somatic cell
chromosomes are supercoiled
to fit inside the cell
eukaryotic
has linear DNA molecules associated with a large amount of protein
consists of 4.6 million nucleotide pairs
representing about 4.400 genes
the linear DNA molecule
is double helix
and averages 1.5 x 10^8 nucleotide pairs
combined with protein
called
chromatin
which fits in the nucleus
during interphase,
the centromeres and telomeres
are highly condensed
the irregular clumps are
heterochromatin
Genetic Material: DNA
DNA is the genetic material
Programming of Cells by Viral DNA
studies were conducted of viruses that infected bacteria
those viruses were
bacteriophages
(bacteria eaters)
or
phages
which were used as tools in molecular genetics
Alfred Hershey and Martha Chase
conducted an experiment that proved DNA provided the genetic material of the phage T2
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they had to discover what was the viral component
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an experiment was devised
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Erwin Chargaff
DNA is a polymer of nucleotides
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made DNA more credible for the genetic material
ratio of nucleotide bases
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Chargaff rules
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virus
a little more than DNA enclosed by a protective coat
which is often simply protein
need a host cell to reproduce
Transformation of Bacteria
in 1928, Frederick Griffith
attempted to develop a vaccine against pneumonia
which came about from studying Streptococcus pneumonia
he had two strands
one pathogenic (disease causing) and non-pathogenic (non-disease causing)
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a bacterium that causes pneumonia in mammals
Structure Model of DNA
by early 1950,
The arrangement of covalent bonds in a nucleic acid polymer was already established
so the focus was now on the 3D structure of DNA
Francis Crick
studied the protein structure with X-ray crystallography
and was visited by
James Watson
,
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along with Watson,
built models of the double helix
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contrasted with Franklin's sugar-phosphate backbone
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linus pauling
came up with a theory
that DNA came in three strands
and was proven wrong by
Rosalind Franklin's X-ray diffraction image
Gene Expression
is the process where DNA directs the synthesis of proteins
modification of RNA
RNA processing
is where both ends of the primary transcription is altered
the interior sections are cut out
and the remaining parts are spliced together
those modifications prepare mRNA for translation
split genes and RNA splicing
RNA splicing
is a stage in RNA processing in eukaryotic nucleus
where large portions of RNA molecules (introns) are removed
and the remaining portions (exons) are joined together
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introns
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Translation
Transfer RNA (tRNA)
consists of a single RNA strand
which is only about 80 nucleotides long
can fold back onto itself
and form a molecule with a 3D structure
anticodon
is a particular nucleotide triplet that base-pairs to a specific mRNA codon
helping the structure of a tRNA molecule fit its function
and are written as 3' to 5'
to align with
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transcription
RNA polymerases
is an enzyme that pries two strands of DNA apart
and joins together RNA nucleotides complementary to DNA template strand
thus, elongating the RNA polymerases
the stages of transcription
elongation
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termination
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initiation
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binding and initiation of transcription
the promoter has a transcription
start point
the nucleotide where RNA polymerase actually begins synthesis of the mRNA
and extends several dozen of nucleotide pairs upstream from the start point
the initiation of transcription at a eukaryotic promoter
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elongation of RNA strand
RNA polymerase moves along the DNA
untwisting the double helix
and exposes 10-20 DNA nucleotides
at the same time for the pairing with RNA nucleotides
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mutations
are responsible for the huge diversity of genes found among organism
point mutations
are changes in a single nucleotide pair of gene
types of small-scale mutations
substitutions
nucleotide-pair substitution
replacement of one nucleotide
and partners with other pairs of nucleotides
could transform one codon into another that is translated into same amino acid
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missense mutation
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nonsense mutation
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insertions and deletions
are additions or losses of nucleotide pairs in a gene
more damaging than substitution
as it alters the reading frame of the genetic message
frameshift mutation
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proteins for transcription and translation
basic principles
transcription
the synthesis of RNA using information in the DNA
the two nucleic acids are written in different forms of the same language
then the information is rewritten from DNA to RNA
the DNA serves as a template for assembling a complementary sequence of RNA nucleotide
the RNA molecule that's a transcript of the building instructions
called
messenger RNA (mRNA)
as it carries a genetic message from DNA
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translation
the synthesis of polypeptide using the information in the mRNA
the cells translate the nucleotide sequence of an mRNA molecule
into the amino acid sequence of a polypeptide
the site of translation are
ribosomes
where molecular complexes facilitate orderly linking of amino acids into polypeptide chains
occurs in both eukaryotic and bacteria
but different in the flow of genetic information
bacteria
does not have a nuclei
so membranes do not separate bacterial DNA and mRNA
from ribosomes
eurkayotic
nuclear envelope separates transcription
from translation of an mRNA in space and time
the transcription occurs in the nucleus
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