Microbiology (Ch.5): Eukaryotic Cell Structure

Identify the 3 filaments that make up the cytoskeleton of eukaryotic cells and describe their functions

1) Microfilaments 2) Intermediate filaments 3) Microtubules

Microfilaments

1) Microfilaments: They play a major role in cell motion and changes in cell shape. (Composed of actin may be scattered throughout the matrix or organized into networks and parallel arrays.)

Intermediate filaments

2) Intermediate filaments are particularly prominent in nuclear lamina. (Along with microfilaments and microtubules, are major components of the cytoskeleton)

Microtubules

3) Microtubules help maintain cell shape, are involved (with microfilaments) in cellular movement, participate in intracellular transport of substances, and participate in organelle movements; they also form the mitotic spindle during cell division and are present in cilia and flagella

Typical Eukaryotic Cell

A. Eukaryotic cells have membrane encased nuclei B. In addition to the nucleus, eukaryotic cells have membrane-bound organelles that perform specific functions within the cell; this allows simultaneous independent control of cellular processes C. Eukaryotic cells also contain a large intracytoplasmic membrane complex, which provides a large surface area allowing greater respiratory and photosynthetic activity; this complex of membranes also serves as a transport system to move materials to different cell locations

Eukaryotic Cell Envelopes

A. Eukaryotic membranes are phospholipid bilayers with sphingolipids and sterols, but the lipids in the outer layer have been shown to differ from those in the inner layer B. Certain microdomains in the membranes differ in lipid and protein content to suit specific functions C. The cell wall composition in eukaryotic microbes varies and can include the polymers cellulose, glucan, or chitin, while others have a rigid silica shell

Draw a Chloroplast and identify its component parts

Chloroplasts are the site of photosynthesis in protists and higher plants Chloroplasts are surrounded by two membranes; the inner membrane encloses a fluid matrix called the stroma; within the stroma is a system of flattened membrane sacs called thylakoids which often form stacks known as grana a. The formation of carbohydrates from carbon dioxide and water (dark reactions) occurs in the stroma b. The trapping of light energy to generate ATP, NADPH, and oxygen (light reaction) occurs in the thylakoid membranes of the grana

Describe the structure of Chromosomes

Chromatin is the dense fibrous material seen within the nucleoplasm of the nucleus; the nucleoplasm is the DNA-containing part of the nucleus; when the cell is dividing, chromatin condenses into visible chromosomes

Describe the structure of eukaryotic flagella and cilia

Cilia and flagella are structurally similar; both are membrane-bound cylinders composed of microtubules, in a 9+2 arrangement, embedded in a matrix; basal bodies have a 9+0 microtubule pattern

Differentiate the 2 types of endoplasmic reticulum in terms of structure and fuction

Complex interconnected array of internal membranous tubes and sacs that may have ribosomes attached (rough endoplasmic reticulum; RER) or may be devoid of ribosomes (smooth endoplasmic reticulum; SER) RER: In cells synthesizing a great deal of protein for purposes such as secretion, a large part of the ER is studded on its outer surface with ribosomes. SER: Other cells, such as those producing large quantities of lipids, have ER that lacks ribosomes.

Phagocytosis

Endocytosis of large particles by engulfing them into a phagocytic vacuole (phagosome)

Pinocytosis

Endocytosis of small amounts of liquid with its solute molecules; There are three types of pinocytosis: fluid-phase endocytosis; receptor-mediated endocytosis using clathrin-coated pits and vesicles; and a type of endocytosis that forms special vesicles (caveolae), whose contents are not degraded

Compare and contrast eukaryotic, bacterial, archaeal cells

Eucaryotic cells have a membrane-enclosed nucleus. Procaryotic cells lack a true, membrane-delimited nucleus. Bacteria and Archaea are procaryotes; all other organisms—fungi, protists, plants, and animals—are eucaryotic. The presence of the eucaryotic nucleus is the most obvious difference between these two cell types. Procaryotes are simpler functionally in several ways.

Describe the structure of Eukaryotic Ribosomes

Eukaryotic ribosomes are responsible for synthesis of cellular proteins; they can either be attached to the ER (rough ER) or are free in the cytoplasm a) ER-associated ribosomes synthesize integral membrane proteins or proteins that are secreted out of the cell b) Free ribosomes synthesize nonsecretory, nonmembrane proteins

List the types of motility observed in eukaryotic microbes

Flagellar and Cilliary movement

Draw a mitochondrion and identify its components

Mitochondria have an outer membrane and an inner membrane enclosing a fluid matrix a. The inner and outer membranes have different lipids and enzymes b. The enzymes of the tricarboxylic acid cycle and the beta-oxidation pathway for fatty acid degradation are located within the matrix c. Electron transport and oxidative phosphorylation occur only in the inner mitochondrial membrane

Compare and contrast mitochondria and hydrogenosomes in terms of their structure and the chemical processes they carry out

a) Mitochondria are the site of the energy-conserving tricarboxylic acid cycle and the generation of ATP by electron transport and oxidative phosphorylation Mitochondria use their own DNA and their own ribosomes to synthesize some of their proteins; mitochondrial DNA and mitochondrial ribosomes are similar to bacterial DNA and ribosomes in terms of size and structure; mitochondria reproduce by binary fission b) Hydrogenosomes are small organelles in some anaerobic protists that conserve energy by fermentation and generate hydrogen; composed of a double membrane they share some features with mitochondria

Describe the structure of the Nucleus

The nucleus is bound by a double-membrane (two lipid bilayers) nuclear envelope structure which is penetrated by nuclear pores; the nuclear pores allow materials to be transported into or out of the nucleus

Outline the pathway of molecules through the secretory pathway, noting the structures involved and their role in the process

Proteins destined for the cell membrane, lysosomes, or secretion are recognized by amino acid targeting sequences and are transported in vesicles that bud off the ER and join the cis face of the Golgi apparatus; the proteins are modified and transported in vesicles that bud off of the trans face of the Golgi apparatus Transport vesicles move the material to the cell membrane or lysosome; secretory vesicles hold their contents until signaled to release them through fusion with the plasma membrane Proteasomes are a nonlysosomal protein degradation system found in eukaryotic cells that degrades proteins marked with ubiquitin (RER -> (Cis - Arrival) Golgi Apparatus (Trans - Departure) -> Transport Vesicles -> Cell membrane (Lysosome) -> Secretory Vesicles )

Cytoplasm of Eukaryotes (Functions)

The cytoplasmic matrix provides the complex structured environment required for many cellular activities. Several physical changes seen in cells—viscosity changes, cytoplasmic streaming, and others— are also due to the cytoplasmic matrix.

Cytoskeleton

The cytoskeleton is a vast network of interconnected filaments and tubules important for motion and act as a scaffold for maintaining cell organization.

Describe the structure of the Nucleolus

The nucleolus is a very noticeable structure within the nucleus; it is involved in the synthesis of rRNA and the production of ribosomes

List the endocytic pathways observed in mammalian cells, noting the structures involved and their role in the process, and noting those pathways that have been observed in eukaryotic microbes

a. Phagocytosis b. Pinocytosis Most endosomes fuse with early lysosomes (newly formed lysosomes) to form late lysosomes; late lysosomes are important to cell functioning a. Some function as food vacuoles, digesting and releasing nutrients into the cytoplasm b. Some function to destroy invading bacteria c. Autophagosomes fuse lysosomes to selectively digest portions of the cell's own cytoplasm as part of the normal turnover of cellular components (macrophagy) 3. Undigested materials accumulate in lysosomes called residual bodies