Lecture 5 Cell Structure and Function Part 2

Mitochondria and Chloroplasts

• Mitochondria are the sites of cellular respiration, generating ATP through oxygen-based metabolic processes.
• Chloroplasts, found in plants and algae, are responsible for photosynthesis.
• Peroxisomes are oxidative organelles, but their relationship to other organelles is unknown.

Mitochondria Structure and Function

• Mitochondria have a smooth outer membrane and an inner membrane folded into cristae, creating two compartments: intermembrane space and mitochondrial matrix.
• Cristae provide a large surface area for enzymes that synthesize ATP.
• Mitochondrial matrix is where some metabolic steps of cellular respiration occur.

Chloroplasts Structure and Function

• Chloroplasts contain the green pigment chlorophyll and enzymes involved in photosynthesis.
• Chloroplasts are found in leaves and other green organs of plants and in algae.
• Chloroplast structure includes thylakoids, membranous sacs stacked to form a granum, and stroma, the internal fluid.

Peroxisomes

• Peroxisomes are specialized metabolic compartments with a single membrane, containing enzymes that remove hydrogen atoms from substances and transfer them to oxygen, forming hydrogen peroxide.
• Functions of peroxisomes include breaking fatty acids into smaller molecules for fuel, detoxifying alcohol and other harmful compounds in the liver, and converting fatty acids to sugar in plant seeds.

Cytoskeleton

• The cytoskeleton provides support and maintains cell shape, interacts with motor proteins to produce cell motility.
• Vesicles and other organelles can use motor protein "feet" to travel along tracks provided by the cytoskeleton.

Components of the Cytoskeleton

• Three main types of fibers make up the cytoskeleton: microtubules, microfilaments, and intermediate filaments.
• Microtubules are the thickest, microfilaments are the thinnest, and intermediate filaments have diameters in a middle range.

Microtubules

• Microtubules are hollow rods, 25 nm in diameter, and 200 nm to 25 microns long.
• They are constructed of dimers of tubulin and have functions such as shaping the cell, guiding movement of organelles, and separating chromosomes during cell division.

Centrosomes and Centrioles

• In animal cells, microtubules grow out from a centrosome near the nucleus.
• Centrosomes have a pair of centrioles, each with nine triplets of microtubules arranged in a ring.

Cilia and Flagella

• Microtubules control the beating of flagella and cilia, microtubule-containing extensions that project from some cells.
• Cilia and flagella have a common structure, including a group of microtubules, a basal body, and a motor protein called dynein.

Microfilaments (Actin Filaments)

• Microfilaments are solid rods, 7 nm in diameter, built as a twisted double chain of actin subunits.
• They help support the cell's shape, forming a cortex just inside the plasma membrane.

Cell Walls of Plants

• The cell wall is an extracellular structure that distinguishes plant cells from animal cells.
• Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein.
• Plant cell walls may have multiple layers, including primary cell wall, middle lamella, and secondary cell wall.

Extracellular Matrix (ECM) of Animal Cells

• Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM).
• The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin.
• Fibronectin and other ECM proteins bind to receptor proteins in the plasma membrane called integrins.