Unit 2 Classification of Mircoorganisms

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which bacterial shape describes rod-shaped bacteria?

Bacilli (correct)

Cocci

Spirilli

Vibrio

What is one of the main functions of the bacterial cell membrane?

Synthesizes DNA

Stores nutrients

Carries out respiration (correct)

Provides communication with the environment

How do Gram-positive and Gram-negative bacteria differ primarily in terms of their cell walls?

Gram-positive bacteria have an outer membrane, while Gram-negative do not.

Gram-positive bacteria possess a thin layer of peptidoglycan.

Gram-negative bacteria have a thick peptidoglycan layer.

Gram-positive bacteria have a thick layer of peptidoglycan. (correct)

What type of ribosome is found in bacteria?

70s ribosomes Signup and view all the answers

What are plasmids primarily known for in bacterial cells?

Contain genes for antibiotic resistance Signup and view all the answers

Which of the following describes the composition of the bacterial cell wall?

Peptidoglycan consisting of NAG and NAM Signup and view all the answers

What is the purpose of endospores in bacteria?

Survival during unfavorable conditions Signup and view all the answers

Which of the following best describes the nucleoid in bacterial cells?

Contains circular DNA Signup and view all the answers

Which bacterial shape is characterized by rod-like structures?

Bacilli Signup and view all the answers

What is the primary function of a bacterial cell membrane?

Acting as a barrier for selective permeability Signup and view all the answers

How are Gram-negative bacteria characterized in terms of their cell wall structure?

Thin peptidoglycan layer surrounded by an outer membrane Signup and view all the answers

What is the function of ribosomes in bacteria?

Protein synthesis Signup and view all the answers

What role do plasmids play in bacterial genetics?

They facilitate genetic exchange and resistance traits Signup and view all the answers

Which type of bacteria is characterized by a rod-like shape?

Bacilli Signup and view all the answers

What is a primary function of the cell membrane in prokaryotic cells?

Regulating the passage of materials in and out of the cell Signup and view all the answers

How is a Gram-negative bacterium characterized in terms of its cell wall structure?

Thin peptidoglycan layer with an outer membrane Signup and view all the answers

What is the primary role of ribosomes in bacteria?

Protein synthesis Signup and view all the answers

What are plasmids and why are they significant in bacterial genetics?

Small circular DNA that can carry antibiotic resistance genes Signup and view all the answers

Which of the following statements is true regarding bacterial shapes?

Cocci can be found in chains or clusters. Signup and view all the answers

What is the significance of the lipid bilayer in the cell membrane of prokaryotic cells?

It provides a protective barrier and helps maintain homeostasis. Signup and view all the answers

Which process allows for genetic exchange between bacteria via plasmids?

Conjugation Signup and view all the answers

Study Notes

Bacterial Structure

The cell membrane in bacteria is responsible for a wide range of functions, including cell wall synthesis, DNA replication, protein secretion, respiration, energy capture, and cell transport.
The cell wall provides structural support, maintaining cell shape, and protecting it from osmotic pressure. It's composed of peptidoglycan, a unique polymer of NAG and NAM linked by peptide cross-links.
Bacteria are classified into Gram-positive and Gram-negative groups based on their cell wall structure:
- Gram-positive bacteria have a thick peptidoglycan layer.
- Gram-negative bacteria have a thin peptidoglycan layer and possess an outer membrane, leading to a more complex cell wall.
- Mycobacteria (Acid-fast bacteria) have minimal peptidoglycan but feature a thick lipid-rich wall.
The cytoplasm, the largest part of the bacterial interior, is primarily water-based and contains dissolved substances like enzymes, proteins, carbohydrates, lipids, and inorganic ions. Numerous metabolic reactions occur within the cytoplasm.
Ribosomes, non-membrane bound organelles, are responsible for protein synthesis. They are found throughout the cytoplasm of bacteria. Bacterial ribosomes are smaller than eukaryotic ribosomes but perform the same function. They are referred to as 70S ribosomes, based on their sedimentation rates (Svedberg units).
The nucleoid is a region within the cytoplasm where the bacterial DNA (mostly), along with some RNA and proteins, is located. It's not membrane-bound. Bacterial chromosomes are typically circular, with one being the norm, but exceptions exist.
Plasmids are small, extrachromosomal DNA molecules that carry genes which are not essential for survival but perform nonessential cellular functions. They can be exchanged between bacteria during conjugation, enabling genetic transfer.
Endospores are resting stages that allow bacteria to survive unfavorable conditions, including high temperatures, radiation, dehydration, and harsh chemicals. Their resilience makes them incredibly difficult to kill. They can remain viable for thousands of years.
The glycocalyx, a layer outside the cell wall, is mostly composed of polysaccharides. Its thickness can vary:
- A thin glycocalyx is referred to as slime.
- A thick glycocalyx is known as a capsule, which serves a protective function against desiccation and chemicals and aids in attachment.

Bacterial Movement

Flagella are long, thin helical appendages used for bacterial motility. About half of known bacteria exhibit movement.
Bacterial flagella differ structurally from eukaryotic flagella, being simpler in design.
The arrangement of flagella can be used to classify bacteria.
Pili are tiny, hollow projections that help bacteria adhere to surfaces. They are not involved in movement.
- Fimbriae are short attachment pili often linked to pathogenicity.
- Sex pili are long, modified pili used to transfer genes between cells during conjugation.
A biofilm is a layer of living cells that exist on a surface. These cells can adhere to either a surface or each other, often forming an extracellular matrix. Biofilms are living entities and can constitute a microbiome, comprising various species or a single species. A common example is dental plaque.

Prokaryotic vs. Eukaryotic Cells

Key differences between prokaryotic and eukaryotic cells:
- Nucleus: Absent in prokaryotes, present in eukaryotes.
- Membrane-bound organelles: Absent in prokaryotes, present in eukaryotes.
- Size: Prokaryotes are generally smaller (5-10 µm), while eukaryotes are larger (10-100s µm).
- Internal organization: Prokaryotes lack internal organization, while eukaryotes show division of labor.
- DNA/ Chromosomes: Prokaryotic DNA is circular, with plasmids present; no proteins for folding. Eukaryotic DNA is linear, with proteins involved in folding.
- Ribosomes: Prokaryotes possess 70S ribosomes, while eukaryotes have 80S ribosomes.
- Reproduction: Prokaryotes reproduce asexually through binary fission. Eukaryotes reproduce sexually or asexually.
- Cell membrane: Both have lipid bilayers, but prokaryotic membranes often display folding.
- Motility: Prokaryotic motility, if present, relies solely on flagella. Eukaryotes utilize flagella, cilia, or pseudopods.
- Capsule: Present in some prokaryotes, absent in eukaryotes.
- Pilus: Prokaryotes possess pili, while eukaryotes do not.

Microbiology Focus: Bacteria and Archaea

Prokaryotes: Feature the characteristics summarized in the table above.
Diverse metabolic pathways: Exhibit a remarkable array of metabolic pathways for obtaining carbon and energy from the environment.
Lack of membrane-bound organelles: This limitation necessitates small size and a single-celled structure.
Archaea:
- A group of prokaryotes with genetics and metabolic pathways more similar to eukaryotes.
- Often found in extreme environments, known as extremophiles, including methanogens, thermophiles, barophiles, and halophiles.
- They absorb nutrients from their environment.

Cellular Reproduction

Sexual Reproduction: An exchange of genetics, resulting in a genetically distinctive new organism compared to its parents.
Asexual Reproduction: Cellular reproduction where new cells are not derived from combined genetics. It involves a single organism reproducing, and the resulting new cells are clones of the parent cell.

Eukaryotic Cells

Include fungi, protists (including algae), and microscopic animals (or parts of their life cycles).
Protists:
- Eukaryotic cells.
- Mainly single-celled organisms.
- Acquire food through ingestion or photosynthesis.
- Can exhibit plant-like, animal-like, or fungi-like characteristics.

Algae:

A group of protists.
Microalgae (Phytoplankton): Form the foundation of most food webs in the oceans.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on bacterial structures, including cell membranes, cell walls, and classification of bacteria. This quiz covers essential topics such as Gram-positive and Gram-negative bacteria, as well as the functions of various cellular components.