week 5: The Cytoskeleton and Cell Study

These flashcards cover key concepts related to the cytoskeleton, cell structure, and microscopy techniques as discussed in the lecture.

Cytoskeleton

The internal skeleton of the cell providing strength, controlling cell shape, and facilitating transport and movement.

Actin Filaments

Thin filaments 5-9 nm in diameter that can bundle together to provide structural support and strength to the cell.

Microtubules

Hollow cylinders larger than actin filaments, with a diameter of 25 nm, involved in cell shape, division, and transport.

Intermediate Filaments

Diverse filaments providing mechanical strength and connecting cells in tissues, forming structures such as the nuclear lamina. 8-12 micro metres

Plasma Membrane

A thin, fluid lipid bilayer surrounding the cell that holds cellular contents and maintains shape under pressure.

Actin Polymerization

The process by which actin filaments grow and shrink, allowing cells to respond to environmental changes and movement.

Microtubule Organizing Centre (MTOC) (typically called a centresome)

A structure where microtubules organize, with their minus ends localizing, typically near the nucleus.

Chemotaxis

The movement of cells in response to chemical signals, facilitated by the dynamic nature of the cytoskeleton.

Flagella

Long, whip-like structures covered in microtubules that enable cell movement in fluid.

Fluorescence Microscopy

A microscopy technique that uses fluorescent substances to visualize structures within cells.

How do actin filaments provide mechanical strength to cells?

They reinforce the plasma membrane against internal pressure that would otherwise cause cell rupture.

From which ends do actin filaments grow and shrink?

Grow at the plus (+) end and shrink at the minus (–) end.

What are microtubules and their diameter?

Hollow, rigid cylinders made of tubulin with a diameter of ~25 nm.

How are microtubules oriented in the cell?

The Minus ends at the MTOC(microtubule organising centre)-sometimes called a centrosome which is located near the nucleus

The plus ends extend toward the plasma membrane.

How do microtubules grow and shrink?

Tubulin is added to the plus end; capping stabilises them, and cap removal allows shrinkage.

What are intermediate filaments and their size?

Rope-like fibres, 8–12 nm in diameter, composed of diverse proteins.( More than actin and microtubles)

What is the nuclear lamina?

A network of intermediate filaments beneath the nuclear membrane that anchors chromosomes and nuclear pores.

What is the main function of intermediate filaments?

Provide tensile mechanical strength and connect cells within tissues.

How do actin filaments contribute to cell migration?

Actin polymerisation pushes the plasma membrane forward during movement (e.g. chemotaxis).

how are microtublues key for movement of cells

microtubles(mt) are arranged down the length of the flagells or cilia as doublets.

Along the mt doublets there are motor proteins called dynein

the doublets can then be crosslinked with a protein called nexin

What is the resolution limit of standard light microscopy?

~200 nm.

modern microsope

built-in light source that is focused using a collector lens
onto a mirror.

The mirror bounces the light
through a condenser lens which focuses it
on the specimen, located on the microscope
stage.

The light from the specimen is magnified by the objective and projection
lenses until it arrives at the detector.

What does Hematoxylin & Eosin stain?

Hematoxylin stains acidic structures such as the nuclei (purple);

Eosin stains basic structures cytoplasm (pink)

What is fluorescence microscopy?

A light microscopy technique using fluorophores that emit light when excited. only letting blue light (450 to 490nm)

What is a fluorophore?

A molecule that absorbs light and emits it at a longer wavelength.

What is GFP (green fluorescent protein) and where does it come from?

A fluorescent protein originally isolated from the jellyfish Aequorea victoria.

Why were GFP mutants developed?

to improve folding, stability, brightness, and function at 37 °C.

How does GFP fluorescence arise?

From the tripeptide Ser65-Tyr66-Gly67.

Why is the C-terminus usually tagged with GFP?

To maximise correct folding and function of the fusion protein.

5 Limitations of using fluorescent proteins

Photobleaching: destruction of the fluorescent protein by high intensity laser
light.
• Phototoxicity: Toxicity caused by high-intensity laser light (mainly due to free
radical formation).
• Overexpression: Tagged genes are often expressed at very high levels in order
to produce a good signal. Excess protein may be handled by the cell differently
to normal levels of protein.
• Protein folding: Fluorescent proteins may affect the folding of the fusion
protein and therefore affect its function.
• Cellular distribution: The large fluorescent proteins may alter the cellular
distribution of the tagged proteins. This is especially important for membrane
proteins