+ B8.1 - Describe the structure of nucleotidesand 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
+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
+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
+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)
+Intermolecular forces
Hydrogen bonding occurs between the bases 3 bonds occur between guanine and cytosine 2 occur between adenine and thymine/uracil
+
Cytosine : Guanine bases
Molecules are polynucleotides
Sugar is linked to a phosphate and
nitrogenous base
Deoxyribose sugar (lacks oxygen atom on C2)
Adenine : Thymine bases
Double helix: two polynucleotide chains
held together by hydrogen bonds
Stable towards enzymes and chemicals
Millions of nucleotides per strand (long)
Ribose (pentose) sugar
Adenine : Uracil bases
Typically single-stranded (but can be
double in some cases)
Less stable towards enzymes or chemicals
100-1,000 nucleotides per strand (short)
+Nucleotide Bases
Purines are double-ringed structures Include adenine and
guaninePyrimidines are single-ringed Include cytosine,
thymine (in DNA), and uracil (in RNA)
Purines and pyrimidines bond with one another using hydrogen bonds.
+Phosphates
Link sugars together to create a strand backbone Phosphate heads have covalent phosphodiester bonds to
create a DNA or RNA strand
+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’
+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.
+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.
+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
+B.8.3 Explain the double helical structure of DNA.
Usefulness of the structure Hydrogen bonds strongest type of the
intermolecular forceStrong enough to maintain structure and
keep strands togetherWeak enough to separate easily
Replication can occur by breaking the hydrogen bonds
+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
+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
+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’
+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)
+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
+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
+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
+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
+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.
+The Steps of DNA Profiling
1. Samples of cells are obtained & DNA is extracted• 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
+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?
+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?
+sources
http://brakkeibchem1.wikispaces.com/file/view/TBD08+-+02.02.11+-+B8+Nucleic+Acids.pdf
http://www.usask.ca/education/coursework/mcvittiej/bio30unit1/overheads/1.23.htm
http://ookgm.meb.gov.tr/userfiles/file/programlar/ibo/chem_syllabusguideline(2009).pdf
http://www.microbiologyprocedure.com/genetics/chemical-nature-of-genetic-materials/molecular-structure-of-rna.htm