Biology Chapter: Cell Types and Research Models

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Questions and Answers

What type of organism is Paramecium classified as?

Multicellular organism

Ciliated protozoa (correct)

Bacterial cell

Green algae

Which feature is unique to Chlamydomonas compared to Paramecium?

Presence of cilia

Large size

High gene count

Capability of photosynthesis (correct)

What led to the diversity and complexity of cell types in modern plants and animals?

The evolution of single-celled organisms

The presence of chloroplasts

Cell division alone

Increased specialization and division of labor (correct)

Which of the following is NOT a type of tissue in animal cells?

Photosynthetic tissue Signup and view all the answers

How many types of cells are present in Volvox algae?

Two types of cells Signup and view all the answers

What is the primary function of epithelial tissue?

Covering surfaces and protecting internal organs Signup and view all the answers

Which cell types are involved in connective tissue?

Osteoblasts, chondrocytes, and adipocytes Signup and view all the answers

How do animal cells differ from plant cells?

Animal cells are more diverse in types of tissues Signup and view all the answers

What significant advancement in transgenic research occurred in the 1980s?

Development of the first knock-out mice Signup and view all the answers

How many base pairs are there in the published mouse genome?

2.6 billion Signup and view all the answers

What percentage of mouse genes have a human counterpart?

99% Signup and view all the answers

Why are male mice predominantly used in research?

To avoid interference from sex hormones Signup and view all the answers

What is a major reason for including both sexes in research studies?

To ensure that findings are universally applicable Signup and view all the answers

Which model organism is primarily used for studying basic molecular processes?

Escherichia coli Signup and view all the answers

What role does Arabidopsis thaliana serve in agricultural studies?

Improvement of plant species and pest resistance Signup and view all the answers

Which model organism is associated with developmental genetics and nervous system research?

Caenorhabditis elegans Signup and view all the answers

What is the significance of Morgan's fly room created at Columbia University?

It established fruit flies as a model organism for genetic experimentation. Signup and view all the answers

Which genetic phenomenon did Morgan discover that involves the exchange of chromosome parts?

Crossover Signup and view all the answers

What is a notable feature of the fruit fly's life cycle that makes it ideal for genetic studies?

Short life cycle of 10 to 15 days. Signup and view all the answers

What was revealed by the complete sequencing of the fruit fly genome in March 2000?

It is composed of approximately 180 million base pairs. Signup and view all the answers

What type of organism is Arabidopsis thaliana and what is its primary study focus?

Plant, focusing on molecular biology. Signup and view all the answers

What type of responses does research on Arabidopsis thaliana cover?

A range of processes including flowering and stress response. Signup and view all the answers

What conclusion did Morgan's research establish regarding genes?

Genes located closely on chromosomes are likely to be related to each other. Signup and view all the answers

Which of the following statements about Drosophila’s contribution to genetics is correct?

Drosophila has uncovered many genes controlling animal development. Signup and view all the answers

What kind of areas are seen as dark in electron microscopy due to high electron affinity structures?

Electrodense areas Signup and view all the answers

Which step of histological processing is primarily aimed at stopping degradation of cells after death?

Fixation Signup and view all the answers

What is the purpose of using cryoprotective substances during cryofixation?

To prevent ice crystal formation Signup and view all the answers

Which microscopy technique is specifically used to obtain 3D images at high magnification?

Scanning electron microscopy Signup and view all the answers

In tissue embedding, what is the main objective of replacing water within tissues?

To provide hardness for cutting Signup and view all the answers

What happens to tissues during physical cryofixation?

They are frozen below -70ºC. Signup and view all the answers

What role do electrons play in the formation of the final image in scanning electron microscopy?

They reflect off heavy metal ions to form dark areas. Signup and view all the answers

Which method in histological processing is reversible, unlike chemical fixation?

Cryofixation Signup and view all the answers

What is the main purpose of immunohistochemical techniques?

To identify specific proteins in tissue sections Signup and view all the answers

Which of the following is a characteristic of indirect immunohistochemical techniques?

A secondary antibody, which is conjugated, amplifies the signal Signup and view all the answers

Which substances are commonly used in electron microscopy to enhance sample contrast?

Uranium acetate and lead citrate Signup and view all the answers

What is the primary function of flow cytometry?

To quantitate cell populations and analyze their properties Signup and view all the answers

Why are indirect immunohistochemical methods the most widely used?

They allow the same secondary antibody to be used for multiple primary antibodies Signup and view all the answers

Which component of a flow cytometer is responsible for converting light into a digital signal?

Electronic detector Signup and view all the answers

Which of the following describes a direct immunohistochemical technique?

Employs a primary antibody conjugated to a detectable substance Signup and view all the answers

What is one key use of hematoxylin and eosin in microscopy?

To distinguish between basic and acidic structures in cells Signup and view all the answers

What does forward scatter (FSC) primarily indicate about a cell?

Relative size Signup and view all the answers

Which method is commonly NOT used for breaking down cells?

Photolysis Signup and view all the answers

What type of centrifugation produces forces around 500,000 times greater than gravity?

Differential centrifugation Signup and view all the answers

What happens to cellular components during density gradient centrifugation?

They are separated by the gradient of a dense substance Signup and view all the answers

Which statement about subcellular separation is true?

Cells must first have their plasma membrane broken Signup and view all the answers

Which cellular component is likely to settle the fastest during centrifugation?

Nucleus Signup and view all the answers

What does side scatter (SSC) indicate about a cell?

Granularity or internal complexity Signup and view all the answers

What is a primary use of the ultracentrifuge?

To separate cellular components based on size and density Signup and view all the answers

Study Notes

Unit 1: Overview of the Cell and Cell Research

Biology is the study of the composition, development, functioning, links, and distribution of living things.
A cell is the fundamental unit of living beings, capable of independent reproduction.
Cell biology is a discipline focused on analyzing cell structure, function, components, interactions, and properties.
Cell biology draws on knowledge from genetics, biochemistry, immunology, and other areas.
Molecular biology studies life processes from a molecular perspective, focusing on macromolecules like nucleic acids and proteins.
The difference between cell and molecular biology is their focus. Cell biology focuses on the overall functioning of cellular systems, while molecular biology focuses on the roles of individual molecules within a cell.

1.1 Origin and Evolution of Cells

The cell is the fundamental unit of all living organisms.
Different cell types exist, and multicellular organisms evolved from them.
Robert Hooke (1635-1703) made early observations of cells in cork.
Antoni van Leeuwenhoek (1632-1723) observed protozoa, bacteria, and other cells using microscopes.
Cell theory, formulated in 1839, states that all organisms are made of cells, cells are the basic unit of structure and organization, and cells come from pre-existing cells.

1.2 Cells as Experimental Models

Different types of cells, including unicellular and multicellular organisms, are used as experimental models for various studies.
Unicellular models include Escherichia coli and Yeast.
Multicellular models include Arabidopsis thaliana, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, and Mus musculus.
All cells have a common ancestor with conserved fundamental properties.
Studying one type of organism reveals insights applicable to others.

1.3 Cell Biology Instruments (a)

Optical microscopy:
- Magnification: a factor by which an image appears to be enlarged. The Light microscope can magnify images only up to approximately 1000 times.
- Resolution: minimum distance between two points visible as separate points. Resolution of a light microscope is about 0.2 μm.
Electron microscopy:
- Much higher magnification and resolution
- It uses beams of electrons instead of light.
- Resolution of electron microscopes can be 1-2 nm.
Super-Resolution Microscopy: An advanced light microscopy technique with improved resolution beyond the diffraction limit of optical microscopes.

1.3 Cell Biology Instruments (b)

Specimen preparation
Flow cytometry
Subcellular separation
Growth of animal cells in culture
Viruses

Specimen Preparation

Histological processing involves fixation, tissue embedding, sectioning, and staining.
Fixation: Stops cell degradation processes by preserving protein integrity.
Tissue embedding: Replacing water with a solid medium (like paraffin) for support during cutting.
Sectioning: Cutting thin tissue slices with a microtome.
Staining: Enhancing contrast with dyes or stains for easier visualization.

Fixation

Physical: Cryofixation (-70°C), for quick freezing and avoiding ice crystal damage.
Chemical: Using chemicals that interact with tissue molecules and stabilize them.

Tissue Embedding

Paraffin: Primarily for light microscopy, a wax used to embed samples and support delicate cutting.
Resins: More rigid material suitable for electron microscopy (EM) providing better structural support in sample preparation.

Sectioning

Microtome: used for paraffin-embedded thin slicing (3-5 μm).
Cryostat: for frozen samples, producing thicker slices (6-8 µm or more), allowing viewing of intact subcellular structures.

Other Sample Preparation Methods

Some samples, like blood smears, are prepared directly without fixation or sectioning.

Staining

Dyes are used in microscopy to enhance contrast among structures.
Histological Staining: -Basic dyes (hematoxylin): bind to acidic structures (e.g., DNA). -Acidic dyes (eosin): bind to basic structures (e.g., proteins)
Electron Microscopy: -Heavy metals (lead citrate, osmium tetroxide, uranium acetate): increase contrast by interacting with cellular materials.

Immunohistochemical Techniques

Purpose: Identifying specific proteins in tissue sections using specific antibodies
Direct technique: Primary antibody is directly labeled.
Indirect technique: A secondary antibody recognizes the primary.
These techniques are crucial in diagnostics (e.g. viral proteins, oncogene overexpression).

Flow Cytometry

Analyze cells in a suspension.
It quantifies cells, differentiates cell types, and measures cellular complexity
Instruments include fluidic sample transport system, optical laser illumination, and electronic detectors.

Subcellular Separation

Isolating specific organelles and other subcellular particles.
Physical Methods: Osmotic shock, ultrasound, mechanical grinding
Enzymatic Methods: Lysozyme to degrade the cell wall.

Differential Centrifugation

Separating cellular components by varying speeds and forces exerted on the sample using centrifugation. This separates components based on their differential densities and sizes.

Density Gradient Centrifugation

A technique involving applying a dense gradient in a centrifuge tube in order to separate biological components based on their density.

Cell Cultures

In vitro cell growth and maintenance.
Primary cultures: derived directly from tissue samples.
Secondary cultures: derived from primary cultures allow more convenient study by controlling the culture conditions.
Immortalized cells: derived from tumors, that continue to proliferate indefinitely within a cell culture.

HeLa cells

Example of an immortalized cell line widely used in research.
Derived from a cervical tumor patient in 1951
Enables investigating various cellular processes, including development of polio vaccine.

Cell Culture Media

A crucial component for successful cell culture.
Composed of salts, glucose, amino acids, vitamins, and growth factors.
Required for cell survival, growth, and division in a laboratory environment.

Viruses

Viruses are obligate intracellular parasites needing a host for their lifecycle.
Laboratory research relies on virus cultured in suitable host cell lines for studying viral functions, molecular mechanisms, genetic potential, and oncogenes.

Other Model Organisms:

A. thaliana (Plant): plant biology, agricultural applications, stress response, etc.
C. elegans (Nematode): animal development, aging, cell death, genetics, nervous system.
D. melanogaster (Fruit fly): animal development, genetics (especially for gene function).
D. rerio* (Zebrafish): Vertebrate development, regeneration of tissues, genetics of human diseases, etc.
M. musculus (Mouse): Neuroscience, pharmacology, physiology, transgenic research, and genetic studies in mammals.

The Choice of Model Organisms

Choosing appropriate organisms for research depends on the research question.
Specific characteristics, such as ease of culture, size, and genetic accessibility, of different species allow scientists to understand a wider array of biological phenomena.

Trends in Cell Biology

New model organisms are being discovered, including cnidarians.

Human Organoids

Sophisticated model systems created using human cells to study diseases and cellular mechanisms in a three-dimensional, more realistic structure.

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Description

Test your knowledge on the classification of organisms, the unique features of various algae, and the complexities of plant and animal cells. This quiz also delves into important model organisms used in scientific research and advancements in genetic studies. See how well you understand the diverse world of cellular biology and its applications.