Regents Biology Ch Viruses Overview: A Borrowed Life  Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli  Viruses lead “a kind of borrowed life” between life-forms and chemicals  The origins of molecular biology lie in early studies of viruses that infect bacteria © 2011 Pearson Education, Inc.

Regents Biology Figure mm

Regents Biology Concept 19.1: A virus consists of a nucleic acid surrounded by a protein coat Structure of Viruses  Viruses are not cells  A virus is a very small infectious particle consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope © 2011 Pearson Education, Inc.

Regents Biology Viral Genomes  Viral genomes may consist of either  Double- or single-stranded DNA, or  Double- or single-stranded RNA  Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus © 2011 Pearson Education, Inc.

Regents Biology Capsids and Envelopes  A capsid is the protein shell that encloses the viral genome  Capsids are built from protein subunits called capsomeres  A capsid can have various structures © 2011 Pearson Education, Inc.

Regents Biology Figure 19.3 Capsomere of capsid RNA Capsomere DNA Glycoprotein Glycoproteins Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber 18  250 nm 80  225 nm 70–90 nm (diameter) 80–200 nm (diameter) 20 nm 50 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses(d) Bacteriophage T4

Regents Biology  Some viruses have membranous envelopes that help them infect hosts  Viral envelopes surround the capsids of influenza viruses and many other viruses found in animals  Derived from the host cell’s membrane  Contain a combination of viral and host cell molecules © 2011 Pearson Education, Inc.

Regents Biology  Bacteriophages, also called phages, are viruses that infect bacteria  Have the most complex capsids found among viruses  Have an elongated capsid head that encloses their DNA  A protein tail piece attaches the phage to the host and injects the phage DNA inside  how-a-flu-virus-works/ how-a-flu-virus-works/ © 2011 Pearson Education, Inc.

Regents Biology Overview: Masters of Adaptation  Utah’s Great Salt Lake can reach a salt concentration of 32%  Its pink color comes from living prokaryotes Ch Prokaryotes © 2011 Pearson Education, Inc.

Regents Biology  Thrive almost everywhere, including places that are too:  Acidic  Salty  Cold/Hot  Most are microscopic, but what they lack in size they make up for in #s  There are more in a handful of fertile soil than the number of people who have ever lived  Prokaryotes are divided into two domains:  Bacteria  Archaea © 2011 Pearson Education, Inc. Prokaryotes

Regents Biology Concept 27.1: Structural and functional adaptations contribute to prokaryotic success  Most likely 1 st organisms on Earth  Most are unicellular, although some species form colonies  Sizes are usually 0.5–5 µm  Eykaryotic cells are usually 10–100 µm  Come in a variety of shapes, the 3 most common shapes are:  spheres (cocci)  rods (bacilli)  spirals © 2011 Pearson Education, Inc.

Regents Biology Cell-Surface Structures  Cell wall:  Maintains cell shape  Protects the cell  Prevents cell from bursting in a hypotonic environment  A eukaryotic cell wall is made of cellulose or chitin  Bacterial cell walls contain peptidoglycan  A network of sugar polymers cross-linked by polypeptides © 2011 Pearson Education, Inc.

Regents Biology  Archaea contain polysaccharides and proteins but lack peptidoglycan  Scientists use the Gram stain to classify bacteria by cell wall composition  Gram-positive bacteria have simpler walls with a large amount of peptidoglycan  Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic © 2011 Pearson Education, Inc.

Regents Biology Figure 27.3 (a) Gram-positive bacteria: peptidoglycan traps crystal violet. Gram-positive bacteria Peptido- glycan layer Cell wall Plasma membrane 10  m Gram-negative bacteria Outer membrane Peptido- glycan layer Plasma membrane Cell wall Carbohydrate portion of lipopolysaccharide (b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye.

Regents Biology  Many antibiotics target peptidoglycan and damage bacterial cell walls  Gram-negative bacteria are more likely to be antibiotic resistant  A polysaccharide or protein layer called a capsule covers many prokaryotes © 2011 Pearson Education, Inc.

Regents Biology Figure 27.4 Bacterial cell wall Bacterial capsule Tonsil cell 200 nm

Regents Biology  Some prokaryotes have fimbriae, which allow them to stick to their substrate or other individuals in a colony  Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA © 2011 Pearson Education, Inc.

Regents Biology Figure 27.5 Fimbriae 1  m

Regents Biology Motility  In a heterogeneous environment, many bacteria exhibit taxis:  the ability to move toward or away from a stimulus  Chemotaxis is the movement toward or away from a chemical stimulus  Towards nutrients  Away from toxins © 2011 Pearson Education, Inc.

Regents Biology  Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends  Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently © 2011 Pearson Education, Inc.

Regents Biology Figure 27.6 Flagellum Hook Motor Filament Rod Peptidoglycan layer Plasma membrane Cell wall 20 nm

Regents Biology Evolutionary Origins of Bacterial Flagella  Bacterial flagella are composed of a motor, hook, and filament  Many of the flagella’s proteins are modified versions of proteins that perform other tasks in bacteria  Flagella likely evolved as existing proteins were added to an ancestral secretory system  This is an example of exaptation, where existing structures take on new functions through descent with modification © 2011 Pearson Education, Inc.

Regents Biology Internal Organization and DNA  Prokaryotic cells usually lack complex compartmentalization  Some prokaryotes do have specialized membranes that perform metabolic functions  These are usually infoldings of the plasma membrane © 2011 Pearson Education, Inc.

Regents Biology  The prokaryotic genome has less DNA than the eukaryotic genome  Most of the genome consists of a circular chromosome  The chromosome is not surrounded by a membrane; it is located in the nucleoid region  Some species of bacteria also have smaller rings of DNA called plasmids © 2011 Pearson Education, Inc.

Regents Biology Figure 27.8 Chromosome Plasmids 1  m

Regents Biology  There are some differences between prokaryotes and eukaryotes in DNA replication, transcription, and translation  These allow people to use some antibiotics to inhibit bacterial growth without harming themselves © 2011 Pearson Education, Inc.

Regents Biology Reproduction and Adaptation  Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours  Key features of prokaryotic reproduction:  They are small  They reproduce by binary fission  They have short generation times © 2011 Pearson Education, Inc.

Regents Biology  Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries © 2011 Pearson Education, Inc.

Regents Biology Figure 27.9 Coat Endospore 0.3  m

Regents Biology  Their short generation time allows prokaryotes to evolve quickly  For example, adaptive evolution in a bacterial colony was documented in a lab over 8 years  Prokaryotes are not “primitive” but are highly evolved © 2011 Pearson Education, Inc.