Download Nucleic Acids

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B.8 Nucleic Acids
+ B8.1 - Describe the structure of nucleotides
and their condensation polymers
(nucleic acids or polynucleotides).

Nucleic Acid – class of biopolymer, carries genetic
information, also known as polynucleotides

Nucleotide – monomers of nucleic acids, combine to form
polynucleotides
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Composition of a nucleotide

Phosphate group

Pentose sugar

Organic nitrogenous base
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Nucleotide Composition (con’t)

Phosphate – allows more nucleotides to be added to the
chain, forming long strands; ionized, partially responsible for
solubility of nucleic acids in water

Pentose Sugar – deoxyribose in DNA, ribose in RNA

Base – Continually synthesized within the cell
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Bonding within nucleotides

Phosphate group is bonded covalently with the 5’ carbon
of the pentose sugar

Nitrogenous base is bonded covalently with the 1’ carbon
of the pentose sugar
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Full nucleotide
H atom
H atom
+ Formation of polynucleotides
 Condensation
reaction occurs between the
hydroxyl group on the 3’ carbon of one sugar and
the phosphate group on the 5’ carbon of the other
sugar

releases water and forms a covalent bond (known as
phosphodiester bond)
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Intermolecular forces

Hydrogen bonding occurs between the bases

3 bonds occur between guanine and cytosine

2 occur between adenine and thymine/uracil
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B.8.2 Distinguish
between the
structures of DNA
and RNA.
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Deoxyribose sugar (lacks
oxygen atom on C2)
Adenine : Thymine bases
Ribose (pentose)
sugar
Cytosine : Guanine
bases
Double helix: two
polynucleotide chains
held together by
hydrogen bonds
Molecules are
polynucleotides
Stable towards enzymes
and chemicals
Sugar is linked to a
phosphate and
nitrogenous base
Millions of nucleotides
per strand (long)
Adenine : Uracil bases
Typically singlestranded (but can be
double in some cases)
Less stable towards
enzymes or chemicals
100-1,000 nucleotides
per strand (short)
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DNA and RNA* nucleotide structure
*RNA has ribose sugar rather
than deoxyribose
+ Nucleotide Bases
 Purines
are doubleringed structures
 Include
adenine and
guanine
 Pyrimidines
ringed
are single-
 Include
cytosine, thymine
(in DNA), and uracil (in
RNA)
Purines and pyrimidines
bond with one another
using hydrogen bonds.
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Phosphates

Link sugars together to create a strand backbone

Phosphate heads have covalent phosphodiester bonds to create a
DNA or RNA strand
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DNA is double-stranded
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RNA forms

Messenger mRNA

Transfer tRNA

Ribosomal rRNA

Only RNA that can contain thymine
tRNA and rRNA can be either single or double stranded. However,
double-stranded RNA does not form a helix like DNA.
+ B.8.3 Explain the double helical
structure of DNA.
 DNA
consists of two linear
polynucleotide strands which are
wound together in the form of a
double helix
 Both
chains coil around the same axis
 Bases
are on the inside of the helix
 Sugar-phosphate
backbone on the
outside
 Strands


are anti-parallel
run in opposite directions
3’  5” and 5’  3’
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B.8.3 Explain the double helical
structure of DNA.

Two chains held to together by hydrogen bonds between
the bases

Double helical structure is largely due to hydrogen
bonding between base pairs.

Four bases
 Each have an exposed hydrogen, nitrogen, or oxygen
 These can bond to other exposed hydrogen, nitrogen, or
oxygen

Hydrogen bond
 Special type of dipole-dipole interaction involving an
attraction between an H atom bonded to an O, N, or F and
an O, N, or F atom in another molecule.
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Guanine
Adenine
Cytosine
Thymine
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B.8.3 Explain the double helical
structure of DNA.
 Hydrogen
bonds are weak attractions
between a hydrogen atom on one side and an
oxygen or nitrogen atom on the other.
 Hydrogen
atoms of bases serve as the
hydrogen bond donors
 The
carbonyl oxygens and ring nitrogens
serve as hydrogen bond acceptors
 The
specific location of hydrogen bond donor
and acceptor groups gives the bases their
specificity for hydrogen bonding in unique
pairs.
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B.8.3 Explain the double helical
structure of DNA.
 Complementary
base pairing
 Adenine to Thymine
 Cytosine to Guanine
 A to T  2 hydrogen bonds
 C to G  3 hydrogen bonds
 One
purine is paired with one
pyrimidine
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B.8.3 Explain the double helical
structure of DNA.
 Usefulness
of the structure
 Hydrogen bonds strongest type of the
intermolecular force
 Strong enough to maintain structure and keep
strands together
 Weak enough to separate easily
 Replication can occur by breaking the
hydrogen bonds
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B.8.3 Explain the double helical
structure of DNA.
 Base
stacking
 Rigid bases stack on top of
one another (much like
stacking coins)
 Purine and pyrimidines
have the same width
 Hydrophobic interactions
and van der Waal’s forces
hold the bases together
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B.8.3 Explain the double helical
structure of DNA.

Van der Waal’s forces draw the bases
closer to each other and the DNA twists
to accommodate their positions

The middle of the molecule where the
bases are is hydrophobic and the polar
groups are in the sugar-phosphate
backbone which interacts with the
aqueous solution.
 The hydrophobic interactions
between the bases helps to stabilize
the DNA molecule.
+ 8.4 - Describe the role of DNA as the repository of
genetic information, and explain its role in protein
synthesis.

DNA consists of genetic information inherited from both
parents

DNA is transcribed into mRNA during transcription

mRNA is processed before leaving the nucleus

mRNA is used as a template for protein synthesis during
translation
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Transcription
 DNA
is transcribed into messenger RNA
(mRNA)
 RNA

polymerase binds to the promoter
Unwinds the dsDNA to form an open promoter complex and
initiate a transcription bubble
 RNA
polymerase adds nucleoside
triphosphates from a 3’ to 5’ direction on
the DNA (antisense) template strand


5’ end of RNA comes out first
Nucleoside Triphosphates are being added 5’ to 3’
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Transcription (con’t)

The transcription bubble moves from the DNA promoter
region towards the terminator

The terminator is a sequence of nucleotides that, when
transcribed, causes the RNA polymerase to detach from the
DNA

The transcript carries the code of the DNA and is referred to
as messenger RNA (mRNA)
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Translation

Basic Information
 mRNA is read in triplets by the tRNA
 Triplets of mRNA are called codons
 tRNA molecules have 3 bases which make anticodons
 Respond to a specific amino acid that they carry
 The complimentary tRNA link with mRNA and the amino
acids start to line up in the right order and form peptide
bonds to make a polypeptide strand
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Translation

The genetic code

A triplet code

Same in all organisms - universal

Sequence of bases in DNA dictates the sequence of amino acids
in all proteins via RNA

This area of biology is called the central dogma
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8.5 DNA Profiling

Outline the steps involved in DNA profiling and state its use

Aim 8: include forensic and paternity tests

DNA profiling uses the techniques of genetic engineering to
identify a person from a sample of their DNA


Blood, tissue, urine, bodily fluids
Used for criminal cases and paternity tests
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DNA

DNA contains coding and non coding DNA

There are large portions of DNA that are identical in everyone. But
some fragments of our DNA are unique to each individual

They are called the non-coding regions or “satellite DNA”

Do not code for anything and are highly repetitive in sequence (5-300
bases long)

Creates the dense and less dense regions of a DNA fingerprint used
to differentiate between individuals
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STRs

Thenon-coding regions that repeat are called short-tandem
repeats (STRs).

Theseare looked form in multiple locations of the genome to
make the tests (DNA profiling tests) more discriminating.
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The Steps of DNA Profiling
Samples of cells are obtained & DNA is extracted
1.
•
The sample is usually taken from blood or urine
2.
Using restriction enzymes, the DNA is cut into small, double stranded
fragments
3.
PCR (polymerase chain reaction)is used to copy and amplify the DNA
sample to produce a sufficient amount of DNA to analyze
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The Steps of DNA Profiling (cont’d)
4. The fragments of DNA are then separated by gel
electrophoresis into bands of different lengths
•
Remember: DNA fragments are negatively charged due to the
phosphate groups
•
Place DNA in the negative side because the molecules will be
attracted to the positive terminal
•
Shorter fragments will move further through the gel.
5. The bands are then analyzed and compared for results

The bands need to be visualized by
fluorescent staining and using UV light or
by using a radioactive 32P-labelledDNA
probe which is exposed using X-ray film
+ DNA Profiling – Paternity Tests

The chromosomes of the mother
and father are cut with the same
restriction enzymes

A band present in the child must
come from either the mother of the
father

Who is the child’s father?
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DNA Profiling – Paternity Tests

Example 2 : Who is Eileen’s father?
+ DNA Profiling – Forensic Investigations

A sample of DNA is taken from the
victim or from the crime scene

DNA samples are then taken from 3
suspects

The bands of the suspects are
compared to the sample at the crime
scene

The victim’s DNA is also eliminated from
the sample at the crime scene

Which suspect committed the crime?
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sources
 http://brakkeibchem1.wikispaces.com/file/vie
w/TBD08+-+02.02.11++B8+Nucleic+Acids.pdf
 http://www.usask.ca/education/coursework/m
cvittiej/bio30unit1/overheads/1.23.htm
 http://ookgm.meb.gov.tr/userfiles/file/progra
mlar/ibo/chem_syllabusguideline(2009).pdf
 http://www.microbiologyprocedure.com/gene
tics/chemical-nature-of-geneticmaterials/molecular-structure-of-rna.htm