dna: the genetic material molecular genetics section 1 griffith performed the first major...
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DNA: The Genetic Material
Molecular GeneticsSection 1
Griffith Performed the first major experiment that led to
the discovery of DNA as the genetic material
Molecular Genetics
Avery
Identified the molecule that transformed the R strain of bacteria into the S strain
Concluded that when the S cells were killed, DNA was released
R bacteria incorporated this DNA into their cells and changed into S cells.
DNA: The Genetic Material
Section 1
Molecular Genetics
Hershey and Chase
Used radioactive labeling to trace the DNA and protein
Concluded that the viral DNA was injected into the cell and provided the genetic information needed to produce new viruses
DNA: The Genetic Material
Section 1
Molecular Genetics
DNA Structure Nucleotides
Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base
DNA: The Genetic Material
Section 1
Molecular Genetics
Chargaff rule: for every adenine there is a thymine. For every guanine there is a cytosine,
Chargaff’s rule: C = G and T = A
DNA: The Genetic Material
Section 1
One team
Molecular Genetics
X-ray Diffraction
X-ray diffraction data helped solve the structure of DNA
Indicated that DNA was a double helix
DNA: The Genetic Material
Section 1
James Watson (Left) and Francis Crick (right)
Molecular Genetics
Watson and Crick
Built a model of the double helix that conformed to the others’ research
1. two outside strands consist of alternating deoxyribose and phosphate 2. cytosine and guanine bases pair to each other by three hydrogen bonds 3. thymine and adenine bases pair to each other by two hydrogen bonds
DNA: The Genetic Material
Section 1
Molecular Genetics
DNA Structure
DNA often is compared to a twisted ladder.
Rails of the ladder are represented by the alternating deoxyribose and phosphate.
The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.
DNA: The Genetic Material
Section 1
Molecular Genetics
Orientation
On the top rail, the strand is said to be oriented 5′ to 3′.
The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.
DNA: The Genetic Material
Section 1
DNA: The Genetic Material
Molecular Genetics
Chromosome Structure DNA coils around histones to form nucleosomes,
which coil to form chromatin fibers. The chromatin fibers supercoil to form chromosomes
that are visible in the metaphase stage of mitosis.
Section 1
Replication of DNA
Molecular Genetics
Semiconservative Replication
Parental strands of DNA separate. They serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA.
Let’s draw
Section 2
Molecular Genetics
Steps. Of DNA Replication
1. DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix.
2. DNA polymerase, another enzyme, adds appropriate nucleotides using the original DNA as a templete.
3. The leading strand is build continuously, the lagging strand is build discontinuously in Okazaki fragments.
4. DNA ligase, another enzyme, closes up any gaps in the new DNA strand.
Replication of DNA
Section 2
Replication of DNA
Molecular Genetics
Comparing DNA Replication in Eukaryotes and Prokaryotes
Eukaryotic DNA unwinds in multiple areas as DNA is replicated.
In prokaryotes, the circular DNA strand is opened at one origin of replication.
Section 2
DNA, RNA, and Protein
Molecular Genetics
RNA
Contains the sugar ribose and the base uracil instead of thymine
A-U G-C
Usually is single stranded
Section 3
Molecular Genetics
Messenger RNA (mRNA) Long strands of RNA nucleotides that are
formed complementary to one strand of DNA
Ribosomal RNA (rRNA) Associates with proteins to form ribosomes
in the cytoplasm
Transfer RNA (tRNA) Smaller segments of RNA nucleotides that
transport amino acids to the ribosome
DNA, RNA, and Protein
Section 3
DNA is unzipped in the nucleus and RNA polymerase binds to a specific section where an mRNA will be synthesized.
Molecular Genetics
Transcription
Through transcription, the DNA code is transferred to mRNA in the nucleus.
DNA, RNA, and Protein
Section 3
Molecular Genetics
RNA Processing
The code on the DNA is interrupted periodically by sequences that are not in the final mRNA.
Intervening sequences are called introns.
Remaining pieces of DNA that serve as the coding sequences are called exons.
DNA, RNA, and Protein
Section 3
DNA and Genes
Molecular Genetics
The Code
Experiments during the 1960s demonstrated that the DNA code was a three-base code.
The three-base code in DNA or mRNA is called a codon.
DNA, RNA, and Protein
Section 3
Molecular Genetics
Translation In translation, tRNA
molecules act as the interpreters of the mRNA codon sequence.
At the middle of the folded strand, there is a three-base coding sequence called the anticodon.
Each anticodon is complementary to a codon on the mRNA.
DNA, RNA, and Protein
Section 3
Molecular Genetics
DNA, RNA, and Protein
Section 3
Molecular Genetics
Mutations
A permanent change that occurs in a cell’s DNA is called a mutation.
Types of mutations
Point mutation Insertion Deletion
Gene Regulation and Mutation
Section 4
Molecular Genetics
Gene Regulation and Mutation
Section 4
Molecular Genetics
Protein Folding and Stability
Substitutions also can lead to genetic disorders.
Can change both the folding and stability of the protein
Gene Regulation and Mutation
Section 4
Molecular Genetics
Causes of Mutation
Can occur spontaneously
Chemicals and radiation also can damage DNA.
High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic.
Gene Regulation and Mutation
Section 4
Molecular Genetics
Body-cell v. Sex-cell Mutation
Somatic cell mutations are not passed on to the next generation.
Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.
Gene Regulation and Mutation
Section 4