this very large molecule called deoxyribonucleic acid contains information. dna information codes...
TRANSCRIPT
DNAInstructions for life
What does DNA do? This very large molecule
called Deoxyribonucleic acid contains information.
DNA information codes for proteins that make up muscle, enzymes, & the structures of organisms.
A gene is a section of DNA coding for a protein.
Four Key Features
DNA has a uniform diameter (Franklin) DNA is a double helix (Watson and
Crick) Adenine pairs with Thymine & Guanine pairs with Cytosine (Chargaff) The two strands are built in opposite
directions.
The parts—backbone
Backbone or rails of the ladder: alternating deoxyribose and phosphate.
Deoxyribose: a sugar Phosphate: a negative
ion containing phosphorus
Alternating pattern
The rungs of the ladder
Nitrogenous bases contain nitrogen Pairs:
› A-T› G-C
Pyrimidines: 1 ring› Thymine› Cytosine
Purines: 2 rings› Adenine› Guanine
Join 2 strands
Hydrogen bonds connect A-T or G-C pairs.
H bonds are weak forces between partial positive and negative charges on atoms—works like magnets.
History of DNA’s Discovery
Patterns of Inheritance--1857 Gregor Mendel studied peas the and
passage of traits from one generation to another.› What could carry the information from one
individual to another?
Frederick Griffith--1928
Experiment: mice and 2 types of pneumonia (virulent and non-virulent).
Proved chemical transfer of information.
Erwin Chargaff—1950’s Chargaff studied the DNA of different species from
different kingdoms and different phyla. The amount of Adenine was close to equal to the
amount of Thymine. The amount of Guanine was close to the amount of
Cytosine. Chargaff’s Rule http://www.dnalc.org/resources/3d/21-chargaff-ratios.html
Rosalind Franklin—1950’s
Studied the structure of DNA using a technique called X-ray diffraction.
The repeating ‘x’ patterns imply a twisting coiled shape: helix.
The molecule has uniform diameter and uniform repeat to the twist.
Francis Crick and James Watson—1952
They worked to develop three dimensional model of DNA that would explain properties of the molecule.
Franklin’s work gave them a vital clue.
The molecule was a double helix with the bases making the rungs of a ladder.
One page paper was published April 1953
DNA Replication
To pass information to another organism, the data which is stored in the DNA must be copied.
Process is called DNA Replication A replica is an exact copy How does DNA replicate? How does its structure work to make
copies?
Replication Both strands carry the
same information. 1) Unwind the helix. 2) Unzip the strands
to make two templates to use in making copies.
3) Build a complementary strand one nucleotide at a time for two identical molecules.
Replication Fork
Build a complementary strand
Follow Chargaff’s Rule: A=T and G=C Find the bases that complement this
strand:A T T T GCG TAACCGA TAAA CGCAT T GGCT
Does the new DNA have any of the original molecule in it?
Which model would work?
Helicase
Enzyme that unwinds the double helix.
Name comes from the helix shape of DNA that the enzyme straightens out.
Helicase
DNA Polymerase This protein enzyme that connects the
nucleotides together to make the polymer.
It proofreads the sequences. Most accurate enzyme
Polymerase
DNA Polymerase
DNA Packaging
DNA is an enormously long molecule. How do you pack and move DNA?
http://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html
CoilingSupercoiling
Wind DNA around histone core like a spool of thread.
Nucleosome Wind coiled DNA
into second supercoil.
Condensed chromosome
DNATranscription
DNA—source of information The human genome contains about 3.2
billion base pairs. The information is grouped into genes
—estimated total for the number of human genes range from 30,000 to 65,000.
Most genes code for proteins
RNA
DNA is used to make a complementary strand of messenger RNA.
RNA is RiboNucleic Acid. RNA has 3 differences from DNA:
› Uracil substitutes for Thymine› Ribose replaces deoxyribose› Single strand instead of the double
strand
Uracil
Uracil is a pyrimidine. Uracil forms two hydrogen bonds with
Adenine.
Uracil bonding with Adenine
Similar geometry to Thymine. Same pattern of hydrogen bonds.
Ribose
This monosaccharide is very similar to deoxyribose.
Ribose has one more oxygen.
mRNA—single strand
mRNA is the template to construct a protein and needs one strand.
DNA—getting from data to structure
DNA is an information structure To make something the data needs to be
transcribed to a working template. Transcription is the process of copying
DNA to a messenger RNA(mRNA).› In the nucleus
Translation is the process of converting the data sequence in mRNA into amino acids linked together to make a protein.› Out in the cell