Viruses and Prokaryotes. Chapter 21 Part 1

Transcription

1 Viruses and Prokaryotes Chapter 21 Part 1

2 Impacts, Issues The Effects of AIDS Some viruses and bacteria help us; others, such as the HIV virus that causes AIDS, can kill

3 21.1 Viral Characteristics and Diversity A virus consists of nucleic acid and protein A virus is smaller than any cell and has no metabolic machinery of its own

4 Viruses Viruses Noncellular infectious particles that multiply only inside living cells Consist of genetic material and a protein coat; some also have a lipid envelope Some viruses cause disease (pathogens); others control disease-causing organisms

5 Characteristics of a Virus

6 Examples of Viruses Viruses that infect plants (tobacco mosaic virus) Viruses that infect bacteria or archaeans (bacteriophages) Naked viruses (adenoviruses) Enveloped viruses (herpesviruses)

7 Examples of Viruses

8 RNA protein subunits of coat Fig. 21-2a, p. 334

9 DNA inside protein coat sheath tail fiber Fig. 21-2b, p. 334

10 Fig. 21-2c, p. 334

11 Fig. 21-2d, p. 334

12 viral DNA and enzymes lipid envelope with protein components protein coat inside envelope Fig. 21-2e (1), p. 334

13 lipid envelope with protein components protein coat inside envelope Fig. 21-2e (2), p. 334

14 Effects of Plant Viruses

15 Viral Origins and Evolution Viruses may have descended from cells that were parasites of other cells Viruses may be genetic elements that escaped from cells Viruses may represent a separate evolutionary branch

16 21.2 Viral Replication All viruses replicate only inside host cells, but the details of the process vary among viral groups

17 Steps in Viral Replication

18 Stepped Art Table 21-2, p. 336

19 Bacteriophage Replication Lytic pathway Under direction of viral genes, the host makes an enzyme that lyses and kills the cell Lysogenic pathway Virus enters a latent state Host replicates viral genes and passes them on to descendents before entering lytic pathway

20 Bacteriophage Replication

21 A Virus particle binds, injects genetic material. E Lysis of host cell lets new virus particles escape. Lytic Pathway A1 Viral DNA is inserted into host chromosome by viral enzyme action. Lysogenic Pathway A2 Chromosome and integrated viral DNA are replicated. D Accessory parts are attached to viral coat. C Viral proteins selfassemble into a coat around viral DNA. B Host replicates viral genetic material, builds viral proteins. A4 Viral enzyme excises viral DNA from chromosome. A3 Cell divides; recombinant DNA in each daughter cell. Fig. 21-4, p. 337

22 A Virus particle binds, injects genetic material. E Lysis of host cell lets new virus particles escape. Lytic Pathway A1 Viral DNA is inserted into host chromosome by viral enzyme action. Lysogenic Pathway A2 Chromosome and integrated viral DNA are replicated. D Accessory parts are attached to viral coat. C Viral proteins selfassemble into a coat around viral DNA. B Host replicates viral genetic material, builds viral proteins. A4 Viral enzyme excises viral DNA from chromosome. A3 Cell divides; recombinant DNA in each daughter cell. Stepped Art Fig. 21-4, p. 337

23 Animation: Bacteriophage multiplication cycles

24 Animation: Lytic pathway

25 Animation: Lysogenic pathway

26 Replication of an Enveloped DNA Virus Example: Herpes Viral envelope fuses with host membrane; viral DNA enters host cytoplasm Viral DNA enters nucleus, directs synthesis of new viral DNA and proteins New viral particles are assembled and enveloped in host nuclear membrane New viral particles exit cell by exocytosis

27 Replication of a Retrovirus Example: HIV Virus binds to receptors on certain white blood cells; viral envelope fuses with host membrane; viral RNA enters host cytoplasm Enzyme (reverse transcriptase) converts viral RNA to DNA, which integrates with host DNA Host cell produces viral RNA and proteins which assemble into new viral particles New viruses are enveloped in host plasma membrane and exit by exocytosis

28 HIV Replication

29 viral coat proteins one of two strands of viral RNA viral enzyme (reverse transcriptase) lipid envelope with proteins A Viral RNA and protein enter the host cell. B Viral reverse transcriptase uses viral RNA to make doublestranded viral DNA. C Viral DNA gets integrated into the host s chromosome. nucleus viral DNA D Viral DNA gets transcribed along with the host s genes. viral proteins viral RNA E Some RNA transcripts are new viral RNA. Others are translated into viral proteins. RNA and proteins assemble as new virus particles. F Viral particles bud from the infected cell. Fig. 21-5, p. 337

30 Animation: HIV replication cycle

31 21.3 Viroids and Prions Viroids and prions are infectious particles that are even simpler than viruses Viroid Infectious RNA, not surrounded by a protective protein coat Prion Proteins in the nervous system that can misfold, and cause other prions to misfold

32 Viroid Disease in Plants

33 Prion Diseases Scrapie: A prion disease that affects sheep Bovine spongiform encephalopathy (BSE or mad cow disease): Affects cattle that have eaten feed made with infected sheep Variant Creutzfeldt-Jacob disease (vcjd): Affects humans who have eaten infected beef

34 Prion Diseases

35 Key Concepts: Viruses and Other Noncellular Infectious Particles Viruses are noncellular particles made of protein and nucleic acid; they replicate by taking over the metabolic machinery of a host cell Viroids are short sequences of infectious RNA Prions are infectious misfolded versions of normal proteins

36 21.4 Prokaryotes Enduring, Abundant, and Diverse Prokaryotes Structurally simple cells that lack a nucleus Evolved before eukaryotes Prokaryotes still persist in enormous numbers and show great metabolic diversity

37 Evolutionary History and Classification Automated gene sequencing and comparative biochemistry helps classify species and subgroups (strains) of prokaryotes

38 to ancestors of eukaryotic cells DOMAIN BACTERIA DOMAIN ARCHAEA biochemical and molecular origin of life p. 339

39 Abundance and Metabolic Diversity Prokaryotes are Earth s most abundant organisms Metabolic diversity contributes to their success Example: Saprobes that break down wastes or remains are important decomposers All four forms of nutrition are used by prokaryotes

40 Prokaryotic Nutritional Modes

41 21.5 Prokaryotic Structure and Function Prokaryotic cells have many structural features that adapt them to their environment The typical prokaryote is a walled cell with ribosomes but no nucleus

42 Prokaryotic Cell Characteristics Prokaryotic structure Nucleoid region contains a single, circular chromosome Cell wall surrounds the plasma membrane, with a slime layer (capsule) outside the cell wall Flagella rotate like propellers Pili extend from the cell surface for adhesion or motion

43 Prokaryotic Cell Characteristics

44 Prokaryotic Body Plan

45 Prokaryotic Cell Size and Shape Prokaryotic cells are much smaller than eukaryotic cells (about the size of mitochondria) Prokaryotes have three typical shapes:

46 coccus bacillus spirillum Fig. 21-8a, p. 340

47 cytoplasm, with ribosomes DNA, in nucleoid region pilus bacterial flagellum outer capsule cell wall plasma membrane Fig. 21-8b, p. 340

48 Prokaryotic Reproduction Prokaryotic chromosome A circular, double-stranded DNA molecule Prokaryotic fission DNA replicates; parent cell divides in two

49 Prokaryotic Fission

50 A The bacterial chromosome is attached to the plasma membrane prior to DNA replication. C The DNA copy becomes attached at a membrane site near the attachment site of the parent DNA molecule. E Lipids, proteins, and carbohydrates are built for new membrane and new wall material. Both get inserted across the cell s midsection. B Replication starts and proceeds in two directions from a certain site in the bacterial chromosome. D Then the two DNA molecules are moved apart by membrane growth between the two attachment sites. F The ongoing, orderly deposition of membrane and wall material at the midsection cuts the cell in two. Fig , p. 341

51 A The bacterial chromosome is attached to the plasma membrane prior to DNA replication. C The DNA copy becomes attached at a membrane site near the attachment site of the parent DNA molecule. E Lipids, proteins, and carbohydrates are built for new membrane and new wall material. Both get inserted across the cell s midsection. B Replication starts and proceeds in two directions from a certain site in the bacterial chromosome. D Then the two DNA molecules are moved apart by membrane growth between the two attachment sites. F The ongoing, orderly deposition of membrane and wall material at the midsection cuts the cell in two. Stepped Art Fig , p. 341

52 Animation: Prokaryotic fission

53 Horizontal Gene Transfers Conjugation Transfer of a plasmid (non-chromosomal DNA) between prokaryotic cells via a sex pilus Transduction Transfer of prokaryotic genes via bacteriophages Transformation Prokaryotic genes acquired from the environment

54 Conjugation

55 sex pilus A Conjugation in E. coli begins when a cell with a specific type of plasmid extends a sex pilus to another E. coli cell that lacks this plasmid. The pilus attaches the cells to one another. When it shortens, the cells are drawn together. Fig a, p. 341

56 nicked plasmid conjugation tube B A conjugation tube forms, connecting the cytoplasm of the cells. An enzyme nicks the plasmid in the donor cell. C As a single strand of plasmid DNA moves into the recipient, each cell makes a complimentary DNA strand. D The cells separate and the plasmid resumes its circular shape. Fig (b-d), p. 341

57 sex pilus A Conjugation in E. coli begins when a cell with a specific type of plasmid extends a sex pilus to another E. coli cell that lacks this plasmid. The pilus attaches the cells to one another. When it shortens, the cells are drawn together. nicked plasmid conjugation tube B A conjugation tube forms, connecting the cytoplasm of the cells. An enzyme nicks the plasmid in the donor cell. C As a single strand of plasmid DNA moves into the recipient, each cell makes a complimentary DNA strand. D The cells separate and the plasmid resumes its circular shape. Stepped Art Fig , p. 341

58 Animation: Prokaryotic conjugation

59 Key Concepts Features of Prokaryotic Cells Prokaryotes are single-celled organisms that do not have a nucleus or the diverse cytoplasmic organelles found in most eukaryotic cells Collectively, prokaryotes show great metabolic diversity; they divide rapidly and exchange DNA by a variety of mechanisms