Virus, bacteria, and eukaryotic cell(Fig. 18.1)

Viral structure (Fig. 18.2)

A simplified viral

reproductive cycle

(Fig. 18.3)

Lytic cycle of phage T4 (Fig. 18.4)

Life Cycles of Phage Lambda (Fig. 18.5)

Reproductive cycle of an

envelope virus (Fig. 18.6)

Classes of animal viruses

Class Diseases

double stranded (ds) DNA warts, smallpox

single stranded (ss) DNA roseola

double stranded (ds) RNA diarrhea

ss RNA (serves as mRNA) polio, common cold

ss RNA (template for mRNA) rabies, influenza

ss RNA (template for DNA synthesis)

AIDS

Transmission of plant viruses

• Horizontal transmission = infection of plant from external source of the virus. Damaged plants are more susceptible.

• Vertical transmission = inheriting viral infection from a parent during asexual or sexual reproduction. Virus particles spread throughout plant tissues by passing through plasmodesmata.

HIV, a retrovirus that causes

AIDS

Drug treatments for HIV infection

• Azidothymidine (AZT) interferes with DNA synthesis by reverse transcriptase curbing HIV reproduction.

• Protease inhibitors interfere with enzyme required for assembly of virus particles.

• Multidrug treatments (“cocktails”) including both types of drugs are most effective.

Hypothesis for prion propagation (Fig. 18.9)

Mutation in prokaryotes

• Spontaneous mutations in E. coli gene occur about 1 in every 107 cell divisions.

• About 1010 E. coli cell divisions occur in human gut every day.

• About 1000 mutant alleles for each gene each day in a single human individual.

• New mutations make a significant contribution to genetic diversity of bacteria.

Replication of the bacterial chomosome (Fig. 18.10)

Recombination in prokaryotes

• Genetic recombination = combining of DNA from two individuals into the genome of a single individual.

• Eukaryotes use sexual reproduction.• Prokaryotes use

– Transformation– Transduction– Conjugation

Detecting genetic recombination in bacteria (Fig. 18.11)

Transduction (Fig. 18.12)

Conjugation and

recombination in E. coli

(Fig. 18.14)

Insertion sequences, the simplest transposons (Fig. 18.15)

Insertion of a transposon

and creation of direct repeats

(Fig. 18.16)

Anatomy of a composite transposon (Fig. 18.17)

Regulation of a

metabolic pathway

(Fig. 18.18)

The trp repressible

operon (Fig. 18.19)

The lac inducible operon (Fig.

18.20)

Positive control: cAMP

receptor protein

(Fig. 18.21)