Cell Biology: Theory and Microscopy

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Questions and Answers

What is the primary role of the plasma membrane in a prokaryotic cell?

Storing genetic information

Regulating the entrance and exit of substances (correct)

Providing structural support to the cell

Facilitating photosynthesis

Which of the following correctly describes the bacteria Mycoplasma?

Lacks a cell wall and therefore has no definite shape (correct)

Is primarily found in aquatic environments

Contains only a single plasmid

Has a well-defined cell wall and shape

What is the composition of the cell wall in typical bacteria?

Cellulose

Peptidoglycan (correct)

Lipid bilayer

Chitin

What differentiates a capsule from a slime layer in glycocalyx?

Capsules are well-organized and firmly attached Signup and view all the answers

What is the primary function of glycocalyx in bacteria?

Protecting against desiccation and immune responses Signup and view all the answers

What is a characteristic of prokaryotic DNA?

It is circular and termed naked DNA Signup and view all the answers

Which statement correctly describes plasmids in prokaryotic cells?

Plasmids replicate independently of chromosomal DNA Signup and view all the answers

In prokaryotic cells, what is the function of the cell wall?

To maintain the shape of the cell Signup and view all the answers

Which statement best describes cell theory?

All living things are composed of one or more cells. Signup and view all the answers

What is the primary function of a light microscope?

To magnify objects using light for visualization. Signup and view all the answers

Which of the following parameters does NOT apply to microscopy?

Refractive index Signup and view all the answers

Which of the following cell types does NOT possess a membrane-enclosed nucleus?

Prokaryotic cells Signup and view all the answers

What structure is common to all prokaryotic cells?

Cell membrane Signup and view all the answers

Which category of prokaryotic cells is specifically known for thriving in extreme environments?

Archaea Signup and view all the answers

Which structure is involved in increasing the genetic diversity of prokaryotic cells?

Pili Signup and view all the answers

What is the resolution capability of an electron microscope?

2 nm Signup and view all the answers

What is the primary role of the cytosol in a eukaryotic cell?

Central coordinating region for metabolic activities Signup and view all the answers

Which of the following statements best describes catabolism?

Breakdown of a molecule into smaller components Signup and view all the answers

What distinguishes microtubules from intermediate filaments?

Microtubules participate in intracellular transport Signup and view all the answers

How do actin filaments contribute to cellular movement?

By bearing tension for maintenance of cell shape Signup and view all the answers

Which function is specifically associated with intermediate filaments?

Bear tension to maintain cell shape and rigidity Signup and view all the answers

What is the dynamic instability characteristic of microtubules?

They oscillate between phases of growth and shortening Signup and view all the answers

In which cellular processes do microtubules play critical roles?

Separation of chromosomes during cell division Signup and view all the answers

Which of the following statements accurately describes the cytoskeleton's function?

It provides a framework that helps with tissue formation Signup and view all the answers

What occurs when a peptide sequence contains a stretch of 20 hydrophobic amino acids?

An additional transmembrane segment is synthesized. Signup and view all the answers

What is the main role of glycosylation in proteins?

To assist in protein folding and protection. Signup and view all the answers

What distinguishes N-linked glycosylation from O-linked glycosylation?

N-linked glycosylation attaches carbohydrates to asparagine while O-linked attaches carbohydrates to serine or threonine. Signup and view all the answers

How do essential molecules like glucose enter a cell through the plasma membrane?

Via active transport mechanisms. Signup and view all the answers

Which of the following substances would most likely have difficulty crossing the plasma membrane?

Ions and hydrophilic molecules. Signup and view all the answers

Where does N-linked glycosylation primarily begin?

In the endoplasmic reticulum. Signup and view all the answers

What is the structure associated with the oligosaccharide chain in N-linked glycosylation?

Dolichol phosphate. Signup and view all the answers

What type of carbohydrate chain is typically found in O-linked glycosylation?

Short chain of 1-4 sugar residues. Signup and view all the answers

What structure forms the basic framework of biological membranes?

Phospholipid bilayer Signup and view all the answers

What characteristic allows phospholipids to arrange themselves in a bilayer formation?

Amphipathic nature Signup and view all the answers

What describes the fluid-mosaic model of membranes?

Membranes are a mosaic of lipid, protein, and carbohydrate molecules that exhibit fluid properties. Signup and view all the answers

Which type of membrane protein is known for being embedded within the hydrophobic region of the phospholipid bilayer?

Transmembrane proteins Signup and view all the answers

What is true about the movement of proteins in the membrane?

Some proteins are attached to other structures and cannot move. Signup and view all the answers

Which region of a phospholipid molecule is hydrophilic?

Phosphate group Signup and view all the answers

What type of diffusion is described when phospholipids move from one leaflet of the membrane to another?

Transverse diffusion Signup and view all the answers

What role do membrane carbohydrates primarily serve?

Cell recognition and signaling Signup and view all the answers

Study Notes

Cell Theory

All living organisms are composed of one or more cells
Cells are the smallest units of living organisms
New cells come only from pre-existing cells by cell division

Microscopy

Microscopic tools are used to understand the structure and function of cells
Magnification, resolution, and contrast are important parameters in microscopy
Magnification: Ratio of the size of an image produced by a microscope and its actual size
Resolution: Ability to observe two adjacent objects as distinct from one another
Contrast: The ability to visualize a particular cell structure may depend on how different it looks from an adjacent structure. Contrast can be enhanced using dyes.
Two types of microscopes based on illumination:
- Light Microscopes: Use light for illumination. They have a resolution of 0.2 µm.
- Electron Microscopes: Use an electron beam for illumination. They have a much better resolution of 2 nm.

Cell Types

Based on cell structure, there are two types of cells:
- Prokaryotic: Simple cell structures lacking a membrane-enclosed nucleus. These cells are much smaller than eukaryotic cells and are present in great numbers in the air, water, soil and even in the human body. There are two categories of prokaryotes: bacteria and archaea.
- Eukaryotic:

Prokaryotic Cells

Prokaryotic cells contain:
- Cell wall
- Cell membrane
- Cytoplasm
- DNA
- Ribosomes
Additional structures found in some prokaryotic cells:
- Capsule
- Plasmids
- Flagella
- Pili
- Membrane infolding

Prokaryotic Cell Structure: The Cell Envelope

The cell envelope includes the plasma membrane, cell wall, and glycocalyx (a layer of polysaccharides outside the cell wall).
- Plasma membrane: A phospholipid bilayer similar to the plasma membrane of eukaryotic cells. It plays an important role in regulating the entrance and exit of substances into the cytoplasm.
- Cell wall: Composed of peptidoglycan (amino disaccharides and peptide fragments). The cell wall maintains the overall shape of a bacterial cell (coccus, bacillus, and spiral). Mycoplasma are bacteria that lack a cell wall and have no definite shape.
- Glycocalyx: A layer of polysaccharide lying outside the cell wall. Glycocalyx helps against drying out by trapping water and assists bacteria in resisting a host’s immune system. It allows the bacterium to attach itself to inert surfaces (like teeth or rocks), eukaryotes (e.g., streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony).

Prokaryotic Cell Structure: Glycocalyx or Capsule

When glycocalyx is firmly attached, it is called a capsule, otherwise it is a slime layer.
It is a well-organized layer of polysaccharide.
It protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells.
It is made from starch or glycolipid.
It helps to protect bacteria from drying out (desiccation).
It helps to stop detection from the immune system.
It also protects against viruses.
It has adhesion properties.

Prokaryotic Cell Structure: Inside the Cell

No nucleus: The nucleoid floats in the cytoplasm.
One chromosome: The chromosome is circular.
No histone proteins: DNA is called naked DNA because there are no histone proteins associated with it.

Prokaryotic Plasmid

Smaller circular DNA
Contains resistance genes, which can be transferred to other organisms.
Non-essential genes
Replication is independent of chromosomal DNA.

Cytosol

The region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane.
Cytoplasm includes everything inside the plasma membrane: the cytosol, the endomembrane system and the semiautonomous organelles.
Cytosol is the central coordinating region for many metabolic activities of eukaryotic cells.
- Catabolism: Breakdown of a molecule into smaller components.
- Anabolism: Synthesis of cellular molecules and macromolecules.

Cytoskeleton

Serves as an internal skeleton that maintains cell shape (construction and organization) and assists in the movement of its parts. It strengthens the cell and holds organelles in place. There are three types:
- Microtubules: Long cylindrical structures composed of polymers of alpha and beta tubulin.
  - Alpha and beta subunits form a dimer, which pairs with each other to form a sheet-like structure, which is further folded into a cylinder-shaped structure.
  - They have a polar structure, with a plus end and a minus end.
  - A single microtubule can oscillate between growing and shortening phases: dynamic instability.
  - They play key roles in:
    - Intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles).
    - The axoneme of cilia and flagella.
    - The mitotic spindle.
    - Synthesis of the cell wall in plants.
- Intermediate filaments: Tend to be more stable than microtubules and actin filaments, which readily polymerize and depolymerize.
  - They function in the maintenance of cell shape and rigidity by bearing tension.
  - They are found in the cytoplasm, in the nucleus, and also outside of the cell, binding cells together.
  - Composed of keratin family proteins.
- Actin filaments: Composed of two intertwined actin chains (also known as microfilaments).
  - Actin filaments support the plasma membrane and provide strength and shape to the cell.
  - Participate in some cell-to-cell or cell-to-matrix junctions.
  - Involved in phagocytosis.
  - Provide tensile strength.

Cytoskeleton Function

Maintaining cell shape
- Microfilament: Cytoplasmic streaming. Circulating cytosol so that all organelles receive cytoplasm. Cytokinesis of animal cells. Helps in cell division.
- Microtubule: Segregation of chromosomes during cell division (anaphase). Interacts with centromere for separating sister chromatids. Helps in motility. Are part of flagella, cilia.
- Intermediate filament: Helps in forming stable tissues.

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Description

Test your knowledge on the fundamentals of cell theory, including the composition and division of cells. Explore the principles of microscopy, including magnification, resolution, and contrast, to understand how cells are observed. This quiz also covers the different types of microscopes used in biological studies.