BIOL 112 - LECTURE 9: Cells 2; Mitochondria, Chloroplasts, Cytoskeleton & Cell Adhesion

What are mitochondria and chloroplasts?

Mitochondria are the powerhouses of cells, producing ATP. Chloroplasts convert light energy into chemical energy during photosynthesis. Both are endosymbiotic organelles with double membranes.

What is the evidence that mitochondria and chloroplasts are descendants of bacteria?

They have their own circular DNA, ribosomes similar to bacterial ones, and a unique system for protein and lipid import, supporting their origin from an ancient bacterial endosymbiosis.

What occurs in the matrix of mitochondria and the stroma of chloroplasts?

In mitochondria, the citric acid cycle occurs in the matrix. In chloroplasts, carbon fixation occurs in the stroma, yielding sugars, amino acids, and fatty acids.

What is the structure of mitochondria's inner membrane?

The inner membrane has invaginations called cristae, which increase the surface area for embedding respiratory enzymes that produce ATP.

How do mitochondria and chloroplasts produce energy?

Mitochondria produce ATP via cellular respiration, while chloroplasts convert light energy into chemical energy through photosynthesis.

What is the role of the cytoskeleton?

The cytoskeleton provides structural support for the cell, facilitates movement, and is involved in processes like cell division, intracellular transport, and shape changes.

What are actin filaments and their function?

Actin filaments are thin filaments that are involved in cell shape, movement, muscle contraction, cytokinesis, and cytoplasmic streaming. They are polar and polymerize/depolymerize dynamically.

How do actin filaments and myosin work together in muscle contraction?

Myosin II forms complexes with actin filaments, walking toward the plus end of actin, causing contraction when bound to antiparallel actin filaments.

What are microtubules (MTs) and their function?

Microtubules are cylindrical structures made of tubulin dimers, involved in intracellular transport, organelle movement, and chromosome separation during cell division.

What are motor proteins associated with microtubules?

The motor proteins kinesin and dynein move along microtubules in opposite directions, crucial for intracellular transport and chromosome movement.

How do cilia and flagella move?

Cilia and flagella bend due to the action of dynein motors sliding microtubule doublets past each other, with elastic proteins linking the doublets.

What are intermediate filaments and their role?

Intermediate filaments are structural elements that provide mechanical strength to cells, such as keratin in skin cells and lamins in the nucleus.

What is the extracellular matrix (ECM)?

The ECM provides structural support and stability to cells, consisting of proteins like collagen and elastin, and plays a role in cell adhesion.

What is integrin and how does it function in cell adhesion?

Integrin is a transmembrane protein that binds to the ECM and connects to the actin cytoskeleton via adaptor proteins, facilitating cell-matrix adhesion.

What are focal adhesions?

Focal adhesions are sites where integrins bind cells to the ECM, connecting the cell's cytoskeleton to the extracellular environment.

How did cell adhesion evolve?

Cell adhesion evolved from cell recognition processes, particularly phagocytosis, which was the earliest form of obtaining nutrients.

What is an epithelium?

An epithelium is a sheet of tightly connected cells with distinct apical (facing the outside) and basolateral (facing the interior) sides.

What is the function of tight junctions?

Tight junctions seal cells together, preventing the passage of larger molecules between them, and maintain compartmentalization within tissues, like in the intestinal epithelium.

What are gap junctions and their role?

Gap junctions are channels that connect adjacent cells, allowing small molecules like calcium ions to pass freely, essential for coordinated cellular activities like heart muscle contraction.

How are membrane proteins sorted and directed to specific destinations?

Membrane proteins are sorted by tags on their amino acid sequences, which direct them to specific vesicles. Vesicles transport the proteins to their target membrane, like the apical or basolateral sides in epithelial cells.