Cell Biology: Microfilaments and Cytoplasmic Streaming

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Questions and Answers

What is one of the main advantages of using CLSM in biological research?

Ability to produce 2D images only

High magnification up to 1,000,000x

Real time imaging of live cells (correct)

Requires thick specimens only

Which type of electron microscopy provides internal views of specimens?

Transmission Electron Microscopy (TEM) (correct)

Scanning Electron Microscopy (SEM)

Optical Electron Microscopy (OEM)

Reflective Electron Microscopy (REM)

What is the typical resolution capability of electron microscopy?

Up to 10 micrometers

About 100 nanometers

Down to about 1 nanometer (correct)

Approximately 1 millimeter

What imaging capability is NOT a feature of CLSM?

Surface scanning and 3D imaging Signup and view all the answers

In which fields is electron microscopy widely used?

Biological research and materials science Signup and view all the answers

What primary role do microfilaments serve within a cell?

Supporting the cell's shape and positioning organelles Signup and view all the answers

What protein interacts with actin in microfilaments to enable muscle contraction?

Myosin Signup and view all the answers

Which process is driven by the interaction of actin and myosin in plant cells?

Cytoplasmic streaming Signup and view all the answers

What is a key function of intermediate filaments?

Anchorage of the nucleus and organelles Signup and view all the answers

Which statement accurately describes prokaryotic cells?

They lack membrane-bound organelles. Signup and view all the answers

Which of the following is a characteristic of eukaryotic cells?

Membrane-bound organelles Signup and view all the answers

Which statement reflects a fundamental difference between prokaryotic and eukaryotic cells?

Eukaryotic cells undergo more complex cell division processes. Signup and view all the answers

Who is often recognized as the 'Father of Microbiology'?

Antonie van Leeuwenhoek Signup and view all the answers

What occurs during prophase of mitosis?

Chromosomes condense into visible structures Signup and view all the answers

Which statement accurately describes anaphase in mitosis?

Separase cleaves the cohesion that holds sister chromatids together Signup and view all the answers

What happens during the prometaphase stage of mitosis?

Nuclear envelope breaks down and spindle enters the nuclear area Signup and view all the answers

Which description best defines cytokinesis?

The division of the cytoplasm into two daughter cells Signup and view all the answers

Which of the following correctly defines bivalent and tetrad in meiosis?

Bivalent is one pair of homologous chromosomes in a tetrad Signup and view all the answers

What role does the enzyme desaturase play in membrane lipid composition?

It catalyzes the formation of double bonds in lipid tails. Signup and view all the answers

Which of the following describes the effect of cholesterol on membrane fluidity at cool temperatures?

Cholesterol prevents tight packing of phospholipids. Signup and view all the answers

What characteristic distinguishes integral proteins from peripheral proteins in the membrane?

Integral proteins span the hydrophobic core of the membrane. Signup and view all the answers

What major role do membrane proteins play in the cell membrane?

They determine most of the membrane's specific functions. Signup and view all the answers

Which statement regarding membrane fluidity and lipid composition is correct?

Membranes rich in unsaturated fatty acids are more fluid. Signup and view all the answers

What is the primary focus of passive transport across membranes?

It allows for diffusion of substances without energy investment. Signup and view all the answers

What is the significance of dynamic equilibrium in diffusion?

It shows that molecules move randomly while maintaining a balance. Signup and view all the answers

How do temperature fluctuations affect membrane composition?

They can adjust the fatty acid composition of the membrane. Signup and view all the answers

What occurs during Metaphase I of meiosis?

Bivalents separate, and sister chromatids remain attached. Signup and view all the answers

What is the outcome of Cytokinesis at the end of Meiosis I?

Two haploid cells are formed, each without homologous pairs. Signup and view all the answers

During which phase of meiosis do sister chromatids separate?

Anaphase II Signup and view all the answers

Which statement accurately describes the changes that occur during Prometaphase I?

Spindle apparatus is formed, and chromatids attach to microtubules. Signup and view all the answers

What distinguishes the sorting events of meiosis II from those of meiosis I?

There is no S phase between meiosis I and II. Signup and view all the answers

Study Notes

Microfilaments

Form 3D networks inside the plasma membrane to support cell shape and position organelles within the cells
Made of two intertwined strands of actin (G-actin monomer)
Appear as solid rods about 7nm in diameter, formed as a twisted double chain of actin subunits
Often contain the protein myosin in addition to actin when involved in cellular motility
In muscle cells, thousands of actin filaments are arranged parallel to each other, with thicker filaments composed of myosin interdigitating with the thinner actin fibers
Muscle contraction arises from the interaction between actin and myosin filaments, causing their movement relative to each other

Cytoplasmic Streaming

Refers to the circular flow of cytoplasm within cells, accelerating the distribution of materials within the cell
In plant cells, actin-myosin interactions and sol-gel transformations drive this process

Intermediate Filaments

Contribute to the maintenance of cell shape
Anchor the nucleus and certain other organelles
Form the nuclear lamina

Prokaryotic vs Eukaryotic Cells

Prokaryotic cells lack a true nucleus, with their DNA located in the nucleoid region.
Eukaryotic cells have a membrane-bound nucleus containing their DNA.
Prokaryotes lack membrane-bound organelles, while eukaryotes contain various organelles to compartmentalize functions.
Prokaryotes are generally smaller than eukaryotes.
Prokaryotes typically have a single circular chromosome, while eukaryotes have multiple linear chromosomes.
Prokaryotes divide through binary fission, while eukaryotes employ mitosis and meiosis (more complex processes).
Prokaryotes include bacteria and archaea, while eukaryotes include plants, animals, fungi, and protists.

Confocal Laser Scanning Microscopy (CLSM)

Enhanced resolution and depth penetration, ideal for studying intricate cellular arrangements
Used in fields like cell biology, neuroscience, and developmental biology for analyzing cellular processes and interactions within tissues
Offers live cell imaging, real-time imaging, multicolor imaging, high-resolution with minimal background noise in thick tissues, and 3-D imaging capabilities

Electron Microscopy

Uses beams of electrons instead of light for imaging, achieving extremely high magnifications and allowing visualization of cellular structures at the nanometer scale.
Offers 1,000,000x magnification, revealing details not visible with light microscopy.
Transmission Electron Microscopy (TEM) allows electrons to pass through thin specimens, providing detailed internal views.
Scanning Electron Microscopy (SEM) utilizes electrons to scan the surface of samples, generating 3D images with surface detail.
Provides a resolution of approximately 1 nanometer, suitable for studying the ultrastructure of cells, viruses, and materials.

Membrane Fluidity

Membranes transition from a fluid state to a solid state as temperatures cool.
The temperature at which a membrane solidifies depends on the types of lipids it contains.
The fatty acid composition of membranes can adjust to temperature fluctuations in the growth environment
Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
The enzyme desaturase facilitates the formation of double bonds within the tails of membrane phospholipids
Membranes typically have fluidity similar to salad oil, allowing them to function properly.
The steroid cholesterol plays a crucial role in maintaining structural integrity and regulating the fluidity of cell membranes.
At warm temperatures, cholesterol restricts the movement of phospholipids.
At cool temperatures, cholesterol helps maintain fluidity by preventing tight packing of the membrane.

Membrane Proteins

A membrane is composed of a mosaic of various proteins embedded within the fluid lipid bilayer matrix.
These proteins determine the majority of the membrane's specific roles.
Peripheral proteins are not embedded in the membrane, while integral proteins penetrate the hydrophobic core and often completely span the membrane.
Integral proteins spanning the membrane are called transmembrane proteins.
Six primary functions of membrane proteins include: transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix (ECM).

Membrane Transport

Passive transport refers to the diffusion of a substance across a membrane without any energy investment.
Diffusion is the tendency for molecules to spread out evenly within the available space.
Although each molecule moves randomly, the diffusion of a population of molecules can exhibit a net movement in a particular direction, eventually reaching a dynamic equilibrium.

Mitotic Cell Division

Prophase: Chromosomes condense into compact rodlike structures, becoming visible under a light microscope. Each chromosome is doubled due to replication. The centrosome divides into two parts, which separate and generate the spindle. The spindle starts forming in the cytoplasm.
Prometaphase: The nuclear envelope breaks down, the spindle enters the former nuclear region, and microtubules from opposite spindle poles attach to the two kinetochores of each chromosome.
Metaphase: The spindle is fully formed with chromosomes aligned at the spindle midpoint. Each sister chromatid pair is held in position by opposing forces: kinetochore microtubules pulling towards the poles and cohesins binding the sister chromatids together.
Anaphase: Separase cleaves the cohesin ring holding sister chromatids together, allowing the spindle to separate the sister chromatids and move them to opposite spindle poles. Chromosome segregation is then complete.
Telophase: Chromosomes decondense, returning to their extended interphase state. A new nuclear envelope forms around the chromosomes, and cytoplasmic division by furrowing begins.
Cytokinesis: The physical process of cell division that divides the parental cell's cytoplasm into two daughter cells.

Meiosis

Meiosis is the process used by sexually reproducing organisms to create gametes with half the required genetic material for zygotic formation.
A bivalent is a pair of chromosomes (homologous chromosomes) present in a tetrad.

Stage	Sister Chromatids	Bivalents
Attachment to Pole	A pair of sister chromatids is attached to just one pole.	A pair of sister chromatids is attached to both poles.
Alignment along the metaphase plate:	Sister chromatids align along the metaphase plate.	Bivalents align along the metaphase plate.
Type of separation at anaphase:	Sister chromatids separate.	Bivalents separate. A pair of sister chromatids moves to each pole.
Resulting Chromosomes after Anaphase:	A single chromatid, now called a chromosome, moves to each pole.	A pair of sister chromatids moves to each pole.

Meiosis I

Prophase I: Replicated chromosomes condense, bivalents form, and the nuclear membrane breaks down.
Prometaphase I: The spindle apparatus is complete, and chromatids are attached to kinetochore microtubules.
Metaphase I: Homologous chromosomes segregate. Connections between bivalents break, but the connections holding sister chromatids together remain intact. Each joined pair of chromatids migrates to one pole, and the homologous pair of chromatids moves to the opposite pole.
Telophase I: Sister chromatids reach their respective poles, decondense, and nuclear membranes reform.
Cytokinesis occurs.
The original diploid cell contained chromosomes in homologous pairs, while the two cells produced at the end of meiosis I are haploid, lacking pairs of homologous chromosomes.

Meiosis II

No S phase occurs between meiosis I and meiosis II.
The sorting events of meiosis II are similar to those of mitosis.
Sister chromatids are separated during anaphase II, unlike anaphase I.

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Description

Explore the fascinating roles of microfilaments in maintaining cell shape and facilitating muscle contraction through actin and myosin interactions. This quiz also covers cytoplasmic streaming, highlighting its importance in the distribution of materials within cells. Test your knowledge on these essential cellular components!