Cell Adhesion: L18

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Questions and Answers

What is the primary role of adherens junctions in multicellular structures?

Determining the shape of multicellular structures (correct)

Linking cells to extracellular matrix proteins

Providing electrical conductivity between cells

Ensuring nutrient transport between adjacent cells

Which type of proteins links the actin cytoskeletons at adherens junctions?

Cadherins (correct)

Integrins

Claudins

Selectins

Which statement correctly describes desmosomes?

They form regions that maintain mechanical strength and stability. (correct)

They are primarily found in invertebrate organisms.

They link to actin filaments for cell movement.

They provide electrical signals between cardiac muscle cells.

How do adherens junctions enable the reshaping of epithelial cells?

By utilizing myosin motor proteins for contractility Signup and view all the answers

In which type of junctions do intermediate filaments play a key role?

Desmosomes Signup and view all the answers

What is the primary role of cellulose in plant cell walls?

To form a rigid structure for strength Signup and view all the answers

Which of the following correctly describes hemicellulose?

It crosslinks cellulose microfibrils Signup and view all the answers

What is one of the components that can make up pectin in the primary cell wall?

Arabinogalactans Signup and view all the answers

What feature of the primary cell wall allows for cell expansion and remodeling?

Flexibility due to its multicomponent structure Signup and view all the answers

Xyloglucan is significant in the primary wall because it contributes to:

Crosslinking cellulose microfibrils Signup and view all the answers

Which of these polysaccharides can account for up to 20% of the primary wall dry weight?

Xyloglucan Signup and view all the answers

What structural feature is contributed by lignin in the secondary cell wall?

Strength and durability Signup and view all the answers

What distinguishes the primary cell wall from the secondary cell wall in plants?

The rigidity and strength Signup and view all the answers

What type of junction allows the movement and coordination of signals between cells in electrically excitable tissues?

Gap junctions Signup and view all the answers

Which protein structures constitute the channels in gap junctions?

Connexins and innexins Signup and view all the answers

What is a characteristic of tight junctions?

Block the passage of small molecules Signup and view all the answers

What autoimmune disease is associated with weakened cell adhesions due to antibodies against desmosomal cadherins?

Pemphigus Signup and view all the answers

In which type of junctions do adjacent cells express different connexin types?

Gap junctions Signup and view all the answers

Which organism uses innexins in their gap junctions instead of connexins?

Drosophila Signup and view all the answers

How are new connexons added to the gap junctions?

Via exocytosis Signup and view all the answers

What is the primary role of gap junctions in cardiac muscle cells?

Facilitate contraction synchronization Signup and view all the answers

What function do occluding junctions primarily serve in epithelial cells?

They create a selectively permeable barrier. Signup and view all the answers

Which of the following statements accurately describes anchoring junctions?

They attach cells to other cells and the extracellular matrix. Signup and view all the answers

What is a primary role of epithelial cells in vertebrates?

To enclose and partition the animal body. Signup and view all the answers

How do tight junctions contribute to glucose absorption in specialized epithelial cells?

They partition the transporters and prevent uncontrolled fluid flow. Signup and view all the answers

What characteristic is common among epithelial cells?

They are organized into sheets anchored to the basal lamina. Signup and view all the answers

What role do pectin methylesterases (PMEs) play in the modification of pectin?

They demethylate pectin, making it available for crosslinking. Signup and view all the answers

What components primarily make up the secondary cell wall in plants?

Cellulose, hemicellulose, and lignin. Signup and view all the answers

Which type of structure is primarily formed by the extracellular matrix (ECM) produced by bacteria?

Biofilm primarily made of polysaccharides, proteins, and nucleic acids. Signup and view all the answers

What is the primary function of tight connections between epithelial cells?

To prevent leakage between the cells. Signup and view all the answers

Which statement about cellulose microfibrils in secondary cell wall layers is true?

The orientation of cellulose microfibrils varies across S1, S2, and S3 layers. Signup and view all the answers

What are proteoglycans primarily composed of in animal tissue?

Proteins with covalently attached glycosaminoglycans (GAGs). Signup and view all the answers

What primary function does the biofilm produced by bacteria serve?

To provide mechanical stability and maintain cellular cohesion. Signup and view all the answers

What is the primary composition of the primary cell wall in plants?

Cellulose, hemicellulose, pectin, and small lipids. Signup and view all the answers

Study Notes

Lecture 18: From Cells to Tissues - Cell Adhesion & Communication

This lecture covers cell adhesion and communication, moving from cells to tissue formation.
Key learning outcomes include: a broad understanding of cell adhesion with other cells and the extracellular matrix (ECM), an understanding of different forms of adhesion junctions, and an understanding of the biological role of adhesion.
Cell adhesion facilitates tissue formation and function by linking cells to each other and to the ECM.

ECM of Plant Cells

Plant cell walls have a complex structure.
The primary cell wall is flexible, facilitating cell expansion and remodelling.
Polymers like cellulose, hemicelluloses, and pectins are important components.
Arabinogalactans and cell wall proteins also contribute.
The secondary cell wall is rigid and provides strength, mainly composed of cellulose, hemicellulose and lignin.

Plant Primary Cell Wall

Composed of cellulose microfibrils (1-4)-β-D-glucan).
Pectin (homogalacturonan, rhamnogalacturonan, arabinan, galactan).
Hemicelluloses (xyloglucan, xylan, glucomannan, arabinoxylan, callose (1-3) -β-D-glucan)).
Structural proteins.

Cellulose

Cellulose is a polymer of glucose.
Cellulose synthase rosettes are crucial for synthesis.
Fibrils and microfibrils are organized structures of cellulose.

Hemicellulose

Xyloglucans, xylans, galactoglucomannan, glucuronoxylan, arabinoxylan, mannan, glucomannan.
These contribute up to 20% of the primary wall dry weight.
Xyloglucan backbone is composed of 1,4-linked β-D-Glcp residues.
75% of these residues are substituted at 06 with mono-, di-, or triglycosyl side chains.

Pectin Polysaccharides

Rich in galacturonic acid.
Galacturonic acid (GalA) occurs in two domains.
Often linked covalently to form homogalacturonan (HG) and rhamnogalacturonan (RG).
Modifications/substitutions to HG and RG alter their properties and functions.

Pectin Crosslinks

Pectin methylesterases (PMEs) can demethylate pectin, making it available for crosslinking via Ca++ bridges.
Methylation prevents crosslinking.

Plant Secondary Cell Wall

Predominantly composed of cellulose, hemicellulose and lignin.
S1, S2 and S3 layers have different orientations of the cellulose microfibrils.
Leads to a rigid cellular structure.

Bacterial ECM

Capsule composed of high molecular weight polysaccharides.
Capsule or slime layer, providing an additional layer strongly or weakly adhered to the cell wall.

Some Bacteria Produce Biofilms

Extracellular polymeric substances (EPS) such as polysaccharides, proteins and nucleic aids form biofilm.
EPS provide mechanical stability, cohesion to surfaces, and form a network that immobilizes cells.
The biofilm functions as an external digestive system, keeping extracellular enzymes close to cells.

Summary

Overview of animal cell junctions: tight junctions, anchoring junctions, and communicating junctions described.
Different proteins and their functions in these junctions are highlighted.
Functions of junctions such as forming barriers and allowing communication are described.

Cell Junctions

Classification of junctions across plant and animal cell-to-cell interactions: tight, gap, and anchoring based on function.
Description of specific protein components and structural organization in different junction types.
Key functions of junctions such as sealing, support and communication are highlighted.

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Description

Test your knowledge on cell junctions and plant cell walls with this quiz. Explore the roles of adherens junctions, desmosomes, and various polysaccharides in maintaining cellular structure. Dive into the key components of primary and secondary cell walls in plants.