CELL STRUCTURES Sources Campbell N 1993 Biology Third

CELL STRUCTURES Sources: Campbell, N. 1993 Biology Third Edition. Benjamin Cummings Publishing. United States. Wallace, S. 1993 Biology

The Cytoskeleton § The cytoskeleton (high voltage transmission electron microscope) l Microfilaments (very fine; 6 nm in diameter). mostly made up of protein actin. Have a variety of roles depending on the type of proteins they are associated with: • one is to provide support to the plasma membrane • form supportive network of microvilli (intestinal wall) • also involved in the pinching of the cell membrane during cell division

l l Intermediate filaments (diameter 7 nm): Role is poorly understood. • Found in epithelial cells, nerve cells, muscle cell fibers and blood cells. • Made up of the protein keratin. Microtubules (diameter 22 nm): • Formed from the globular protein tubulin • form cilia, flagella, centrioles, basal bodies • Important in cell division where they take a spindle form.

The Endoplasmic Reticulum (ER) Endoplasmic = inside the cytoplasm; Reticulum = network § Function l Plays a role in the cell’s synthetic ability: newly synthesized proteins, lipids and carbohydrates are transported within the endoplasmic reticulum’s lumen.

The ER. . . § Structure: l The ER consists of membranous tubules and sacs called cisternae. Membranes separate the cytosol from the internal compartment of the lumen l Have the same phospholipid bilayer seen in the plasma membrane l The ER membrane is continuous with the outer of the two membranes of the nuclear envelope

§ The Rough Endoplasmic reticulum (RER) l Occurs in cells that manufacture proteins for secretion outside of the cell (i. e digestive enzymes and hormones) § The Smooth Endoplasmic reticulum (SER) l l Abounds in cells that synthesize secrete, and store carbohydrates, steroids, lipids and other non-protein products. Found in testis cells; oil glands; some hormone producing gland cells; intestinal cells, where they collect products of lipid digestion; in liver cells the SER is associated with glycogen, the animal storage carbohydrate (starch).

Ribosomes § Structure: Large molecular structures consisting of ribosomal r. RNA sub-units and proteins. l l l Consists of 2 sub-units (large and small) which join together to form a functional ribosome only when they attach to m. RNA Ribosomes are constructed in the nucleolus from RNA Are too large to be considered molecules. The ribsomal sub-units in prokaryotes are smaller and differ chemically.

Ribosomes. . . § Function: Where the cell assembles proteins following genetic (DNA) instructions. Ribosomes translate message from m. RNA § There are two forms: l l Polyribosomes or polysomes: Free Bound ribosomes: Attached to the ER

The Golgi Apparatus Sometimes called Dyctiosomes in plant cells § Structure (see diagram) l l Component of the endomembrane system Made up of flattened bag-like sacs called cisternae. Found near the nucleus. (cis phase = forming face; trans face = maturing phase) § Function l Manufacturing, warehousing, sorting, and shipping center of materials in the cell

Mitochondria § Structure (see diagram) l l Have double membranes Have their own circular DNA and ribosomes (make their own proteins) Smaller than chloroplasts develop from pre-existing mitochondria

Mitochondria. . . § Function l ATP (adenosine tri-phosphate) generating molecules

Peroxisomes (Microbodies) § Structure: l Sacs bound by a single membrane § Function: (see transparency) l l organelles found in nearly all eukaryotic cells that contain specialized enzymes for specific metabolic activities All contain peroxide-producing oxidases (enzymes) that transfer H from various substrates to O producing H 2 O 2