Cytoskeleton and Cell Wall

Cytoskeleton

• A network of fibers that helps support the cell and maintain its shape
• Provides anchorage for organelles
• Interacts with motor proteins to produce motility
• Made up of three main fiber types: Microtubules, Microfilaments (Actin filaments), and Intermediate filaments

Microtubules

• The thickest component of the cytoskeleton
• Hollow rods made from globular protein dimers called tubulin
• Help shape and support the cell
• Help in organelle movement
• Divide chromosomes during cell division
• Control the beating of cilia and flagella

Microfilaments (Actin Filaments)

• The thinnest component of the cytoskeleton
• Thin solid rods made from molecules of globular actin subunits
• Bear tension and resist pulling forces in a cell
• Reinforce cell shape and hold organelles in place

Cell Wall

• Extracellular structure that distinguishes between plant and animal cells
• Made up of cellulose microfibers embedded in polysaccharides and other proteins

Cell Wall Functions

• Protects the plant cell
• Maintains cell shape
• Prevents excess water uptake

Plasma Membrane

• The essential boundary separating the living cell from its external environment
• Selective permeability allows some substances to cross the membrane more easily than others
• Controls the exchange of materials

Phospholipids

• Most abundant lipids in membranes
• Found in the cytosol (free ribosomes), on the outside of the Endoplasmic Reticulum (bounded ribosomes), and on the outside of the Nuclear Envelope (bounded ribosomes)

Endomembrane System

• A group of organelles that work together to modify, package, and transport proteins and lipids
• Components include the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane

Endoplasmic Reticulum

• A network of membranous sacs and tubules that extends throughout the cytoplasm
• Two types: Smooth ER and Rough ER

Smooth ER

• Tube-like and lacks ribosomes
• Synthesizes lipids
• Metabolizes carbohydrates
• Detoxifies poisons and drugs
• Stores calcium ions

Rough ER

• Surface is studded with ribosomes
• Has bounded ribosomes that secrete glycoproteins (proteins bound with carbohydrates)
• Produces transport vesicles
• The membrane factory for the cell

Golgi Apparatus

• Modifies the products of the ER
• Makes certain macromolecules
• Sorts and packages materials into transport vesicles

Lysosomes

• Membranous sacs with hydrolytic enzymes used for the digestion of molecules
• Lysosomal enzymes work best in the acidic environment of lysosomes
• Some sacs engulf others by phagocytosis, making a food vacuole
• Recycle cells by digesting dead organelles in a process called autophagy

Vacuoles

• Large vesicles derived from the Golgi apparatus and ER
• The inner solution is not like cytosol
• Function in storage and can help maintain turgor pressure in plant cells

Prokaryotic Cells

• Bacteria and Archaea
• Smaller than eukaryotic cells (1-5 micrometers)
• Lack a nucleus and membrane-bounded organelles
• DNA is unbound in the nucleoid

Eukaryotic Cells

• Protists, Fungi, Animal, and Plant cells
• Larger than prokaryotic cells (10-100 micrometers)
• Have a nucleus that contains most of the cell's DNA
• Have membrane-bounded organelles

Common Features of Prokaryotic and Eukaryotic Cells

• Plasma membrane
• Semifluid cytosol
• Chromosomes
• Ribosomes

Nucleus

• The membrane-bound organelle that contains the cell's hereditary information
• In eukaryotic cells, the nucleus contains most of the DNA; ribosomes use the information from DNA to make proteins.

Nucleus Structure

• Nuclear envelope: encloses the nucleus and separates it from the cytoplasm; consists of a phospholipid bilayer
• Nuclear membrane: double membrane; each layer consists of a phospholipid bilayer, which maintains the shape of the nucleus
• Nuclear pores: regulate entry and exit of molecules
• Nuclear lamina: protein filaments that maintain the shape of the nucleus
• Nucleolus: located within the nucleus; the main site for ribosomal RNA synthesis
• DNA is organized into discrete units called chromosomes; each chromosome is one long strand of DNA
• When DNA and proteins are bound, they form chromatin

Ribosomes

• Complexes of ribosomal RNA and proteins
• Carry out protein synthesis in the cytoplasm (free ribosomes) or on the endoplasmic reticulum and nuclear envelope (bound ribosomes)

This quiz covers the key components and functions of the cytoskeleton, including microtubules and microfilaments, as well as the structure of the cell wall. Understand how these components support cell shape, motility, and distinguish plant cells from animal cells. Test your knowledge on the essential roles they play in cellular function.