Archaea and Their Unique Features

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Questions and Answers

What type of linkages attach the branched chain hydrocarbons to glycerol in Archaeal cell membranes?

Amino linkages

Phospho linkages

Ester linkages

Ether linkages (correct)

Which unique feature distinguishes Archaea from both Bacteria and Eukarya?

Unique ribosomal RNA not found in Bacteria (correct)

Lack of peptidoglycan in cell walls

Genes for metabolism

Presence of membrane-bound organelles

What is a significant habitat where Archaea are commonly found?

Cold-blooded animal tissues

Deep ocean trenches

Anaerobic environments (correct)

Freshwater lakes

What is the typical size range for Archaeal rods?

1-2 x 1-5 μm Signup and view all the answers

Which of the following shapes is not found in Archaea?

Spirochetes Signup and view all the answers

What role does hemagglutinin play in viral infections?

It is involved in viral attachment to host cells. Signup and view all the answers

Which of the following is a unique behavioral characteristic of nonenveloped viruses?

They cause lysis of the host cell. Signup and view all the answers

What does the term 'septation' refer to in the bacterial cell cycle?

Separation of daughter cells. Signup and view all the answers

Which of the following statements is true about bacterial reproductive strategies?

Bacteria and Archaea reproduce only through asexual methods. Signup and view all the answers

Which process involves the assembly of a Z ring during bacterial cell division?

Cytokinesis. Signup and view all the answers

What is the function of neuraminidase in the influenza virus?

It has enzymatic activity that assists in the release of new virions. Signup and view all the answers

What is a directed feature of the bacterial cell cycle regarding DNA replication?

There is typically a single origin of replication. Signup and view all the answers

Which of the following methods do bacteria NOT use for reproduction?

Outcrossing with other bacterial species. Signup and view all the answers

Which type of media is designed to inhibit the growth of some microorganisms while allowing others to thrive?

Selective media Signup and view all the answers

What distinguishes differential media from selective media?

It differentiates microorganisms based on biological characteristics. Signup and view all the answers

Which technique is NOT used for isolating pure cultures?

Patch culture Signup and view all the answers

What does the presence of colony characteristics on agar surfaces indicate?

Differences in growth conditions affecting the microorganisms. Signup and view all the answers

Which method is commonly used to determine the turbidity for estimating the most probable number of viable microbes?

Counting chambers Signup and view all the answers

What is the primary structural difference between bacterial and archaeal ribosomes?

Archaeal ribosomes are more similar to eukaryotic ribosomes. Signup and view all the answers

Which of the following statements about eukaryotic microbes is correct?

Eukaryotic cells contain membrane-delimited nuclei. Signup and view all the answers

Which feature is common to both cilia and flagella?

Both contain microtubules in a 9+2 arrangement. Signup and view all the answers

Which statement about viral structure is accurate?

Viruses are unable to reproduce without a host. Signup and view all the answers

What characterizes an icosahedral virus?

It possesses 20 equilateral faces and 12 vertices. Signup and view all the answers

Which of the following describes capsids in viruses?

Capsids are composed of protein subunits known as protomers. Signup and view all the answers

What is a key feature of viral envelopes?

They originate from the host cell's membranes. Signup and view all the answers

What distinguishes the motility of cilia compared to flagella?

Cilia beat with two phases, while flagella move in an undulating fashion. Signup and view all the answers

What is the primary purpose of the lag phase in microbial growth?

Cells synthesize new components. Signup and view all the answers

What occurs during the stationary phase of bacterial growth?

Reproductive rate balances with death rate. Signup and view all the answers

Which statement accurately describes the exponential phase of microbial growth?

Rate of growth is constant and maximal. Signup and view all the answers

What environmental factor is crucial for microbial growth related to enzyme function?

Temperature Signup and view all the answers

What is a possible reason for the occurrence of the stationary phase?

Toxic waste accumulation Signup and view all the answers

Which of the following best describes the death phase in microbial growth?

A fraction of the population undergoes programmed cell death. Signup and view all the answers

Which factor is least likely to inhibit microbial growth?

Stable temperature environment Signup and view all the answers

What is the significance of generation (doubling) time in microbial population growth?

It indicates how quickly a population can double. Signup and view all the answers

In the context of microbial growth, what describes extremophiles?

Microorganisms that can grow under harsh conditions. Signup and view all the answers

What impact does high temperature have on microbial enzymes?

May inhibit enzyme function. Signup and view all the answers

Study Notes

Archaea

Share many features with Eukarya, specifically genes for replication, transcription and translation.
Share features with Bacteria specifically genes for metabolism.
Have unique rRNA not found in Bacteria.
Capable of methanogenesis.
Predominately known for growth in extreme environments such as anaerobic, hypersaline, high pH and high temperature habitats.
Also found in more temperate environments such as marine arctic and tropical waters.
Typically range in sizes of 1-2µm x 1-5 µm for rods and 1-5 µm in diameter for cocci.
The smallest observed archaea is 0.2 µm in diameter.
The largest observed archaea is a multicellular form that can reach a length of 30 mm.

Archaeal Lipids and Membranes

Unlike Bacteria and Eukaryotes, archaeal lipids have branched chain hydrocarbons that are connected to glycerol by ether linkages.
Some archaeal lipids have a monolayer structure instead of a bilayer structure.

Archaeal vs. Bacterial Cytoplasm

Both have a very similar cytoplasm, lacking membrane-enclosed organelles.
Both may contain inclusion bodies such as gas vesicles for controlling buoyancy.
Ribosomes are 70S in both archaea and bacteria, but the proteins in archaea are more similar to eukaryotes.
Nucleoid regions in archaea are single circular chromosomes, and some are complexed with histones.
Polyploidy is observed in some archaea.

Common Features of Eukaryotic Microbes

Have membrane-delimited nuclei.
Membrane-bound organelles that perform specific functions.
Intracytoplasmic membrane complex serves as a transport system.
Are structurally more complex and generally larger than bacterial or archaeal cells.

Cilia and Flagella for Motility

Flagella:
- About 100-200µm long
- Moves in an undulating fashion.
Cilia:
- 5-20µm long
- Beat with two phases, working like oars.
Both cilia and flagella contain a set of microtubules in a 9+2 arrangement.

Virus Structure and Life Cycles

Virion size ranges from 10-400 nm in diameter.
Most viruses must be viewed with an electron microscope.

General Properties of Viruses

All virions contain a nucleocapsid, which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid).
Viruses cannot reproduce independently and cannot carry out cell division.
Capsids are made up of protein subunits called protomers.
Capsids can be: helical, icosahedral, or complex.

Icosahedral or Complex Capsids

An icosahedron is a regular polyhedron with 20 equilateral faces and 12 vertices.
Some viruses have complex symmetry:
- Poxviruses are the largest animal viruses.
- Large bacteriophages have binal symmetry, the head resembles icosahedral, the tail is helical.

Viral Envelopes and Enzymes

Viral envelopes are usually derived from host cell plasma or nuclear membranes.
Envelope proteins are viral encoded and are involved in attaching to the host cell.
Envelope protein may have enzymatic or other activities, for example, neuraminidase of influenza virus.

Viral Life Cycles Have 5 Steps

Attachment (adsorption)
Penetration (entry)
Synthesis (replication and protein production)
Assembly (packaging)
Release
Nonenveloped viruses lyse the host cell to release progeny.
Enveloped viruses use budding to release progeny.

Bacterial Cell Cycle

Most bacterial chromosomes are circular.
Single origin of replication, site at which replication begins.
Terminus, site at which replication is terminated, located opposite of the origin.
Replisome, refers to a group of proteins needed for DNA synthesis.

Cytokinesis – Septation

Septation is the formation of a cross wall between dividing cells.
Occurs in several steps:
- Selection of the site of septum formation.
- Assembly of the Z-ring (composed of protein FtsZ).
- Assembly of the cell wall synthesizing machinery.
- Constriction of the cell and septum formation.

Microbial Population Growth

Generation/doubling time: time it takes for a population to double in size, this can vary depending on the species and environmental conditions.

Theoretical Estimation of Bacterial Growth

An example is given in the reading showing the theoretical biomass after 48 hours with a generation time of 20 minutes and a weight of 9.5 x 10^-13 g.

Bacterial Growth

Refers to population growth rather than the individual cells themselves.
Exponential growth is common but not always the case.

The Growth Curve

Shows the pattern of microbial growth in a batch culture.
Usually plotted as the logarithm of cell number versus time.
Contains five distinct phases:
- Lag Phase
- Exponential Phase
- Stationary Phase
- Death Phase
- Prolonged Decline in Growth

Lag Phase and Exponential Phase

Lag Phase:
- Cells synthesize new components; replenish spent materials.
- Adapt to new medium or conditions.
- Varies in length, can be short or even absent.
Exponential/Log Phase:
- Rate of growth and division is constant and maximal.
- Population is most uniform in terms of chemical and physical properties during this phase.

Stationary Phase

Total number of viable cells remains constant as active cells stop reproducing or the reproduction rate is balanced by the death rate.
Reasons for this phase include:
- Nutrient limitation
- Limited oxygen availability
- Toxic waste accumulation
- Critical population density reached

Death Phase and Prolonged Decline in Growth

Death Phase
- Programmed cell death, a fraction of the population may be programmed to die.
- The population continually evolves, successive waves of genetically distinct variants.
- Natural selection occurs.

Environmental Factors that Affect Microbial Growth

Most organisms grow in fairly moderate environmental conditions, but some are extremophiles.
Extremophiles can grow very well in harsh conditions that would kill most other organisms.
Organisms exhibit distinct cardinal growth temperatures:
- Minimal
- Maximal
- Optimal

Temperature Ranges for Microbial Growth

Psychrophiles: 0-20°C
Psychrotrophs: 0-35°C
Mesophiles: 20-45°C
Thermophiles: 45-80°C
Hyperthermophiles: 80-121°C

Growth Media

Culture media can be used to grow organisms. There are three types:
- Defined: Exact chemical composition is known.
- Complex: Composed of nutrients that are not chemically defined.
- Selective: Favor the growth of some microorganisms and inhibit growth of others.
- Differential: Distinguish between different groups of microorganisms based on their biological characteristics.

Selective Media

Favors the growth of some microorganisms and inhibits growth of others.
An example is MacConkey agar (bile salts and crystal violet) which selects for gram-negative bacteria.

Differential Media

Distinguish between different groups of microorganisms based on their biological characteristics.
Blood agar differentiates between hemolytic and nonhemolytic bacteria.
MacConkey agar (lactose and neutral red dye) differentiates between lactose fermenters and nonfermenters.

Isolation of Pure Cultures

Allows for the study of a single type of microorganism in a mixed culture.
Techniques include:
- Spread Plate
- Streak Plate
- Pour Plate

Microbial Growth on Solid Surfaces

Colony characteristics that develop when microorganisms are grown on an agar surface help with identification.
Differences in growth rate from center to edges are due to:
- Oxygen
- Nutrients
- Toxic products
- Cells may be dead in some areas

Measurement of Microbial Growth

Direct methods include:
- Counting chambers
- Flow cytometry
- Membrane filters
Indirect methods include:
- Turbidity
- Measures changes in the mass of the population
- Most probable number (MPN) of viable microbes.

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Description

Explore the fascinating world of Archaea in this quiz, focusing on their distinctive characteristics, growth environments, and lipid structures. Learn how they differ from both Bacteria and Eukarya in terms of genetics, metabolism, and cellular composition.