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