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Chapter 9 and some of 8DNA and the Molecular Structure
of Chromosomes
Chapter Outline
Functions of the Genetic MaterialProof That Genetic Information Is
Stored in DNAThe Structures of DNA and RNAChromosome Structure in Prokaryotes
and Viruses
Functions of the Genetic Material
The genetic material must replicate, control the growth
and development of the organism, and allow the
organism to adapt to changes in the environment.
Functions of the Genetic Material
Genotypic Function: ReplicationPhenotypic Function: Gene ExpressionEvolutionary: Allows for Mutation
Chromosomes
Genes are located on chromosomes.Chromosomes contain proteins and
nucleic acids.The nucleic acids are deoxyribonucleic
acid (DNA) and ribonucleic acid (RNA).
Proof that Genetic Information is Stored in DNA
In most organisms, the genetic information is encoded in DNA. In some viruses, RNA Is the genetic
material. Viroids are infectious naked RNA molecules, and prions are
infectious, heritable proteins (not TRUE).
DNA Mediates Transformation
Convert IIR to IIIS By DNA?
Avery MacLeod and McCarty Experiment Circa 1943
The Genetic Material of Bacteriophage T2 is DNA
The Genetic Material of Tobacco Mosaic Virus is RNA
Viroids and Prions
Viroids are infectious, naked RNA molecules.
Prions are heritable (What do they mean here?), infectious proteins that do not contain nucleic acids.
Key Points
The genetic information of most living organisms is stored in deoxyribonucleic acid (DNA).
In some viruses, the genetic information is present in ribonucleic acid (RNA).
Viroids and prions are infectious naked molecules of RNA and protein, respectively.
The Structures ofDNA and RNA
DNA is usually double-stranded, with adenine paired with thymine
and guanine paired with
cytosine. RNA is usually single-
stranded and contains uracil in
place of thymine.
WhenDo weFind RNAMixed with The DNA?
nucleoside = sugar +base
nucleotide = sugar + base + phosphate
Ribonucleotide Reductase
Pyrimidines have the longer name and smaller basePurines have the shorter name and bigger base
Structure of aPolynucleotide
Chain
Why do weAlways talk aboutDNA going in the 5’ to 3’ direction?
Deoxyribonucleotides
What is dideoxyadenosine triphosphate (ddATP)?Why are dideoxynucleotides useful in Mol.Bio.?
One of Chargaff’s Rules
X-ray Diffraction Pattern of DNA
The Double Helix
? ?
? ?
I hate when DNA is not depicted properly!
DNA Structure
Complementary Base Pairs (A with T, G with C
Antiparallel StrandsRight-handed double helix (B-DNA)(No obvious reason to me why Right-
handed is better than left-handed)
A-DNA, B-DNA and Z-DNA
The Z-DNA helix is left-handed and has a structure that repeats every 2 base pairs. The major and minor grooves, unlike A- and B-DNA, show little difference in width
A-DNA, B-DNA and Z-DNA
Supercoiling(higher order structure)
What circular DNA exists in humans?
Key Points
DNA usually exists as a double helix, with the two strands held together by hydrogen bonds between the complementary base pairs: adenine paired with thymine and guanine paired with cytosine.
The complementarity of the two strands of a double helix makes DNA uniquely suited to store and transmit genetic information.
Key Points
The two strands of a DNA double helix have opposite chemical polarity.
RNA usually exists as a single-stranded HELIX containing uracil instead of thymine.
Why Does RNA form a helical structure?
STACKING OF BASES
The DNA of Prokaryotes and Viruses
Prokaryotes are monoploid.Most viruses and prokaryotes have a
single set of genes stored in a single chromosome, which contains a single molecule of nucleic acid.
The E. coli Chromosome
Key Points
The DNA molecules in prokaryotic and viral chromosomes are organized into negatively supercoiled domains.
Bacterial chromosomes contain circular molecules of DNA segregated into about 50 domains.
The Genetics of Bacteria
Bacteria contain genes that mutate to produce altered phenotypes.
Gene transfer in bacteria is unidirectional—from donor cells to
recipient cells.
Bacteria
One main chromosome with a few thousand genes.
Variable number of plasmids and episomes.
Asexual reproduction by simple fission.
Recombination in Bacteria
Does this recombination process interferewith DNA cloning experiments?
Key Points Bacteria usually contain one main chromosome.
Wild-type bacteria are prototrophs; they can synthesize everything they need to grow and reproduce given an energy source and some inorganic molecules.
Auxotrophic mutant bacteria require additional metabolites for growth.
Key Points
Gene transfer in bacteria is unidirectional; genes from a donor cell are transferred to a recipient cell, with no transfer from recipient to donor.
Mechanisms of Genetic Exchange in Bacteria
Bacteria exchange genetic material through three different
parasexual processes.
Transformation inBacillus subtilis (NOT TRUE
for E.Coli)
Streptococcus pneumoniae Phenotypes
Transformation-Griffith’s Expt1928