Bacteria and Viruses

Soja AP - biology

2007-2008

Domain BacteriaDomain Archaebacteria

DomainBacteria

DomainArchaea

DomainEukarya

Common ancestor

Bacteria live EVERYWHERE!Bacteria live in all ecosystems

on plants & animalsin plants & animalsin the soilin depths of the oceansin extreme coldin extreme hotin extreme salton the livingon the dead

Microbes alwaysfind a way tomake a living!

Bacterial diversityrods and spheres and spirals… Oh My!

Prokaryote StructureUnicellular

bacilli, cocci, spirilliSize

1/10 size of eukaryote cell 1 micron (1um)

Internal structure_________________________________

_____________________________ _____________________________

_________________________________ not wrapped around proteins

prokaryotecell

eukaryote cell

Prokaryote Cell Wall Structurepeptide side

chains

cell wallpeptidoglycan

plasma membrane

protein

Gram-positive bacteria

Gram-negative bacteria

peptidoglycan

plasmamembrane

outermembrane

outer membrane of lipopolysaccharides

cell wall

peptidoglycan = polysaccharides + amino acid chainslipopolysaccharides = lipids + polysaccharides

That’simportant foryour doctorto know!

Genetic variation in bacteriaMutations

bacteria can reproduce every 20 minutes ______________________

error rate in copying DNA 1 in every 200 bacteria has a mutation you have billions of E. coli in your gut!

lots of mutation potential!

Genetic recombinationbacteria swap genes

____________________ small supplemental

circles of DNA

____________________ direct transfer of DNA

conjugation

Bacteria as beneficial (& necessary)Life on Earth is dependent on bacteria

___________________________ recycling of nutrients from dead to living

___________________________ only organisms that can fix N from atmosphere

needed for synthesis of proteins & nucleic acids plant root nodules

___________________________ digest cellulose for herbivores

cellulase enzyme produce vitamins K & B12 for humans

_________________________ from yogurt to insulin

Structure of VirusesViruses

Are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope

Not Considered to be living organisms

Viral GenomesViral genomes may consist of

Double- or single-stranded DNADouble- or single-stranded RNA

Figure 18.4a, b

18 250 mm 70–90 nm (diameter)

20 nm 50 nm(a) Tobacco mosaic virus(b) Adenoviruses

RNADNACapsomere

Glycoprotein

Capsomereof capsid

Capsids and EnvelopesA capsid

Is the protein shell that encloses the viral genome

Can have various structures

Viral EnvelopesSome viruses have envelopes

Which are membranous coverings derived from the membrane of the host cell

Figure 18.4c

80–200 nm (diameter)

50 nm(c) Influenza viruses

RNA

Glycoprotein

Membranousenvelope

Capsid

BacteriophagesBacteriophages, also called phages

Have the most complex capsids found among viruses

Figure 18.4d

80 225 nm

50 nm(d) Bacteriophage T4

DNA

Head

Tail fiber

Tail sheath

General Features of Viral Reproductive CyclesViruses are obligate intracellular parasites

They can reproduce only within a host cellEach virus has a host range

A limited number of host cells that it can infect

Viral ReproductionViruses use enzymes, ribosomes, and small

molecules of host cellsTo synthesize progeny viruses

VIRUS

Capsid proteins

mRNA

Viral DNA

HOST CELL

Viral DNA

DNACapsid

Figure 18.5

Entry into cell anduncoating of DNA

ReplicationTranscription

Self-assembly of new virus particles and their exit from cell

The Lytic CycleThe lytic cycle

Is a phage reproductive cycle that culminates in the death of the host

Produces new phages and digests the host’s cell wall, releasing the progeny viruses

The Lysogenic CycleThe lysogenic cycle

Replicates the phage genome without destroying the host

Temperate phagesAre capable of using both the lytic and lysogenic

cycles of reproduction

RetrovirusesRetroviruses, such as HIV, use the enzyme

reverse transcriptase To copy their RNA genome into DNA, which can

then be integrated into the host genome as a provirus

Figure 18.9

Reversetranscriptase

Viral envelope

Capsid

Glycoprotein

RNA(two identicalstrands)

The reproductive cycle of HIV, a retrovirus

Figure 18.10

mRNA

RNA genomefor the nextviral generation

Viral RNA

RNA-DNAhybrid

DNA

ChromosomalDNA

NUCLEUSProvirus

HOST CELL

Reverse transcriptase

New HIV leaving a cell

HIV entering a cell

0.25 µm

HIV Membrane of white blood cell

The virus fuses with thecell’s plasma membrane.The capsid proteins areremoved, releasing the viral proteins and RNA.

1

Reverse transcriptasecatalyzes the synthesis of aDNA strand complementaryto the viral RNA.

2

Reverse transcriptasecatalyzes the synthesis ofa second DNA strandcomplementary to the first.

3

The double-stranded DNA is incorporatedas a provirus into the cell’s DNA.

4

Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins.

5

The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER).

6

Vesicles transport theglycoproteins from the ER tothe cell’s plasma membrane.

7 Capsids areassembled aroundviral genomes and reverse transcriptase molecules.

8

New viruses budoff from the host cell.

9

Vaccines

VaccinesAre harmless derivatives of pathogenic microbes that

stimulate the immune system to mount defenses against the actual pathogen

Can prevent certain viral illnesses

Viral Diseases in PlantsMore than 2,000 types of viral diseases of

plants are knownCommon symptoms of viral infection include

Spots on leaves and fruits, stunted growth, and damaged flowers or roots

Figure 18.12