Chapter 3 Part C

Chapter 3 – Part C

Cells: The Living Units

Part 2 – Cytoplasm

· All cellular material that is located between the plasma membrane and the nucleus

– Composed of:

· Cytosol: gel-like solution made up of water and soluble molecules such as proteins, salts, sugars, etc.

· Inclusions: insoluble molecules; vary with cell type (examples: glycogen granules, pigments, lipid droplets, vacuoles, crystals)

· Organelles: metabolic machinery structures of cell; each with specialized function

3.7 Cytoplasmic Organelles

· Membranous

– Mitochondria

– Endoplasmic reticulum

– Golgi apparatus

– Peroxisomes

– Lysosomes

· Nonmembranous

– Ribosomes

– Cytoskeleton

– Centrioles

Membranes allow compartmentalization, which is crucial to cell functioning

Mitochondria

· Called the “power plant” of cells because they produce most of cell’s energy molecules (ATP) via aerobic (oxygen-requiring) cellular respiration

· Enclosed by double membranes; inner membrane has many folds, called cristae

– Cristae are embedded with membrane proteins that play a role in cellular respiration

· Resemble bacteria; capable of same type of cell division bacteria use, called fission

Endoplasmic Reticulum (ER)

· Two varieties:

– Rough ER

– Smooth ER

Cytoskeleton

· Elaborate network of rods that run throughout cytosol

· Also act as cell’s “bones, ligaments, and muscle” by playing a role in movement of cell components

· Three types:

– Microfilaments

– Intermediate filaments

– Microtubules

· Microfilaments

– Thinnest of all cytoskeletal elements

– Semi-flexible strands of protein actin

– Some are involved in cell motility, changes in cell shape, or endocytosis and exocytosis

· Intermediate filaments

– Tough, insoluble, ropelike protein fibers

– Composed of tetramer (4) fibrils twisted together, resulting in one strong fiber

– Help cell resist pulling forces

Cytoskeleton (cont.)

· Microtubules

– Largest of cytoskeletal elements; consist of hollow tubes composed of protein subunits called tubulins

– Most radiate from centrosome area of cell

– Determine overall shape of cell and distribution of organelles

– Motor proteins: complexes that function in motility

· Can help in movement of organelles and other substances around cell

· Use microtubules as tracks to move their cargo on

3.8 Cellular Extensions

· Certain cells have structures extending from the cell surface:

– Cilia and flagella

– Microvilli are fingerlike projections that extend from the surface of the cell to increase surface area

o Cilia are whiplike, motile extensions on surfaces of certain cells (such as respiratory cells)

o Thousands of cilia work together in sweeping motion to move substances (example: mucus) across cell surfaces in one direction

· Flagella are longer extensions that propel the whole cell

o (example: tail of sperm; only human cell with flagella)

· Both structures are made up of microtubules

Microvilli

· Minute, fingerlike extensions of plasma membrane that project from surface of select cells (example: intestinal and kidney tubule cells)

· Used to increase surface area for absorption

Part 3 – Nucleus

· Largest organelle; contains the genetic library of blueprints for synthesis of nearly all cellular proteins

– Responds to signals that dictate the kinds and amounts of proteins that need to be synthesized

· Most cells are uninucleate (one nucleus), but skeletal muscle, certain bone cells, and some liver cells are multinucleate (many nuclei)

– Red blood cells are anucleate (no nucleus)

3.9 Structure of the Nucleus

· The nucleus has three main structures:

– Nuclear envelope

– Nucleoli

– Chromatin

The Nuclear Envelope

· Double-membrane barrier that encloses the jelly-like fluid, the nucleoplasm

o Nuclear pores allow substances to pass into and out of nucleus

Nucleoli

· Dark-staining spherical bodies within nucleus that are involved in ribosomal RNA (rRNA) synthesis and ribosome subunit assembly

Chromatin

· Consists of 30% threadlike strands of DNA, 60% histone proteins, and 10% RNA

· Chromosomes are condensed chromatin

– Condensed state helps protect fragile chromatin threads during cell division