Cell Membranes Dr. Nabil Khouri

Cell Cytoskeleton The “skeleton” on the cell Dynamic, elaborate series of rods running through the cytosol Consists of microtubules, microfilaments, and intermediate filaments

Cytoskeleton

Microfilaments Dynamic strands of the protein actin Attached to the cytoplasmic side of the plasma membrane Braces and strengthens the cell surface Attach to CAMs and function in endocytosis and exocytosis

Actin felaments Within the cell, actin filaments, also called microfilaments It is thin, flexible fibers approximately 7 nm in diameter and up to several micrometers in length Are organized into higher-order structures, forming bundles or three-dimensional networks with the properties of semisolid gels. Actin filaments are particularly abundant beneath the plasma membrane, where they form a network that provides mechanical support, determines cell shape, and allows movement of the cell surface

Intermediate Filaments Tough, insoluble protein fibers with high tensile strength Resist pulling forces on the cell and help form desmosomes

Dynamic, hollow tubes made of the spherical protein tubulin Determine the overall shape of the cell and distribution of organelles

Apical cell surface

Celia

Microvillus

Stereocilia Stereocilia are mechanosensing organelles of hair cells, which respond to fluid motion, or changes in fluid pressure in numerous types of animals for various functions, primarily hearing.

A cilium can be either of two types ‘“ Motile or Nonmotile. Motile cilia continuously move in one direction, which results in movement of cells, fluids, mucus, etc. Non-motile cilia, on the other hand, normally function as sensory organelles. Stereocilia are different from cilia, even though they have a similar name. In fact, they are more closely related to microvilli, and some may well consider stereocilia to be a variant of microvilli.

Basement membrane Basement membrane

Cell Division Essential for body growth and tissue repair Mitosis – nuclear division Cytokinesis – division of the cytoplasm

Cytokinesis Mitosis Prophase Metaphase Anaphase Telophase Cleavage furrow formed in late anaphase by contractile ring Cytoplasm is pinched into two parts after mitosis ends

Early and Late Prophase Asters are seen as chromatin condenses into chromosomes Nucleoli disappear Centriole pairs separate and the mitotic spindle is formed

Late Prophase

Metaphase Chromosomes cluster at the middle of the cell with their centromeres aligned at the exact center, or equator, of the cell This arrangement of chromosomes along a plane midway between the poles is called the metaphase plate

Metaphase

Anaphase Centromeres of the chromosomes split Motor proteins in kinetochores pull chromosomes toward poles

Anaphase

Telophase and Cytokinesis New sets of chromosomes extend into chromatin New nuclear membrane is formed from the rough ER Nucleoli reappear Generally cytokinesis completes cell division

Telophase and Cytokinesis