dna the molecule of life. what is dna? deoxyribonucleic acid chargaff’s law a=t, g=c r. franklin...
TRANSCRIPT
DNA
The Molecule of Life
What is DNA?
DeoxyriboNucleic Acid Chargaff’s Law
A=T, G=C R. Franklin and M. Wilkins
Crystal X-ray J Watson and F Crick
Model of DNA Double stranded structure Bases inside
What is DNA Made of?
Deoxyribose sugar Phosphate Base
Purine A, G
Pyrimidine T, C
What are the Structures of the Bases?
Purines Adenine
Guanine
What are the structures of the bases?
Pyrimidines Thymine
Cytosine
Assembly of the parts
Purines and pyrimidines form chemical bonds with deoxy-ribose (5-carbon) sugar. The carbon atoms on the sugar are designated 1', 2', 3', 4' and 5'.
It is the 1' carbon of the sugar that becomes bonded to the nitrogen atom at position N1 of a pyrimidine or N9 of a purine. RNA contains ribose.
The resulting molecules are called nucleosides and can serve as elementary precursors for DNA (and RNA synthesis)
Nucleosides (examples)
Nucleosides become Nucleotides
Nucleosides form bonds with phosphate groups.
Phosphate groups bind to the 5’ C of the deoxyribose sugar.
Nucleosides + phosphate group = NUCLEOTIDE
A Nucleotide
A, G, C or T
What makes DNA Different from RNA?
Forms sugar Phosphate Backbone
A Single Strand of Nucleotides
The nucleotides connect by a series of 5' to 3' phosphate-deoxyribose bonds.
Note the sequence of the bases in the next diagram.
Polynucleotide sequences are referenced in the 5' to 3' direction
Polynucleotide
Polynucleotide pairs are Complementary:
One strand of DNA is arranged 5’ to 3’The partner strand is arranged exactly 3’
to 5’.Chargaff’s law states A = T and C=GThe strands are held together by H-
bonds between the bases
Base pairing: how it works
Hydrogen Bonding between bases:A-T Bonding
2 hydrogen bondsG-C Bonding
3 hydrogen bonds
H-Bond Orientation
H-bonds between O```H and N```H
Orientation in space
PAIRING of A with T,
PAIRING of G with C
Double Stranded DNA: Complementary strands (cont.)
The bases pair COMPLEMENTARY to one another.
Use
This complementarity allows for DNA replication and transcription
DNA:
Two complementary strands of polynucleotides
Like a zipper but held together by H-bonds (which really are not bonds, but forces)
DNA: The Double Helix
Like a ladder twisted about its axis
Each cell in our body contains 2 m worth of DNA.
The CODE
The specific base pairing and the sequence of the bases are significant.
We call the specific arrangement of bases the CODE The sequences of code form the GENE for a
specific trait. Genes are special sequences of hundreds to thousands of nucleotide base pairs that form templates for protein making
It codes for specific RNA bases for the making of specific proteins for the trait.
GENE
Exon: regions that form the code for the trait
Intron: regions that are part of the gene but are excised
Genes
Total number of genes is unknown, it estimated to be 30 000 to 120 000
Genes comprise only 3% of the chromosome—the rest is called junk DNA—its code is meaningless “junk”
What is important about base pairs?
Can predict sequence of one strand based on the sequence of the other because it is complementary
Replication and Transcription: a single strand of DNA acts as a TEMPLATE for a new strand, or for making RNA.
Repair of damaged DNA—the template DNA allows for repairs.
DNA: From Chromatin to Chromosome
DNA supercoils around tiny proteins called HISTONES.
The resulting strand with histones supercoils on itself.
Size
CHROMOSOMES
The supercoiled DNA further coils until it further supercoils as chromatin.
This is how 2 m of DNA can be packed into the nucleus of a single body cell.
At interphase of MITOSIS or MEIOSIS I, the DNA replicates itself. The chromatin become visible as double stranded DNA (DNA that has replicated).
Chromosomal Wrapping
Replication:
Why? When cells replicate, each new cell needs it’s own copy of
DNA. Where?
Nucleus in Eukaryotes. Cytosol in Prokaryotes
When? S phase of cell cycle
What? Many proteins: major is DNA Polymerase
How?
Replication
How?5’3’ directionalityStarts with RNA primerLeading StrandLagging Strand
Okasaki FragmentsSequence determined by basepairing
Nova-Cracking the Code of LifeThe Structure of DNA
Transcription
DNA RNA What is the difference between DNA and
RNA? Ribose Sugar Uracil not thymine
Transcription
Where? Nucleus in Eukaryotes Cytosol in Prokaryotes
What? RNA Polymerase plus some minor proteins
When? When RNA is needed
Why? RNA’s serve many important functions in cells
How?
Transcription
How?5’3’ directionalityUsually only one strandUses Base-pairingSame idea as with DNA replication
RNA Synthesis Animation
Translation
What? RNA Protein
Where? Cytosol
When? When proteins are need, after RNA is made
Why? Proteins are vital for cells
How?
Translation
How?Ribosomal Subunits
Small subunitLarge subunit
CodonTriplet code used
tRNA, rRNA, mRNATranslation Animation
The Genetic Code
Why is this important?
Genetic EngineeringGene Splicing
MutationsCloning
In Summary
1. A nucleotide is made of three parts: a) A phosphate group
b) A five carbon sugar (deoxyribose)
c) And a nitrogen containing