Cell Division and Cytoplasm Composition

Cell Structure

• Condensed and highly coiled chromatins (chromosomes) appear during cell division.

Cytoplasm

• Cellular material between the plasma membrane and the nucleus.
• Site for cellular metabolic activities.
• Consists of cytosol, organelles, and inclusions.

Cytosol

• Viscous, semitransparent fluid in which other cytoplasmic contents are suspended.
• Contains dissolved substances such as water, proteins, salts, sugars, and other solutes.

Inclusions

• Chemical substances that may or may not be present – glycogen, lipid and pigment granules, water vacuoles, etc.

Organelles

• Membranous organelles: mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and golgi apparatus.
• Non-membranous organelles: cytoskeleton, centrioles, and ribosomes.

Endoplasmic Reticulum (ER)

• Connected to nuclear envelope.
• Highway of the cell.
• Rough ER: studded with ribosomes; synthesizes proteins.
• Smooth ER: no ribosomes; synthesizes lipids.

Ribosomes

• Site of protein synthesis.
• Found attached to rough ER or floating free in cytoplasm.
• Produced in nucleolus (in nucleus).

Golgi Apparatus

• Stores, modifies, and packages proteins.
• Transport vesicles from ER fuse to the ‘cis face’ of the Golgi apparatus.
• Proteins then pass through the Golgi apparatus to the ‘trans face’.
• Vesicles leave the ‘trans face’ of the Golgi stack and move to designated parts of the cell.

Lysosomes

• Garbage disposal of the cell.
• Contain digestive enzymes that break down wastes.
• Break down ingested bacteria, viruses, and toxins.
• Degrade non-functional organelles.
• Break down glycogen and release thyroid hormone.
• Break down non-useful tissue.
• Break down bone to release Ca²⁺.

Mitochondria

• “Powerhouse of the cell”.
• Cellular respiration occurs here to release energy for the cell to use.
• Controls level of water and other materials in cell.
• Recycles and decomposes proteins, fats, and carbohydrates.
• Bound by a double membrane.
• Has its own strand of DNA.

Peroxisomes

• Membranous sacs containing oxidases and catalases.
• Detoxify harmful or toxic substances.
• Neutralize dangerous free radicals.

Cytoskeleton

• Acts as skeleton and muscle.
• Provides shape and support.
• Helps move organelles around the cell.
• Made of three types of filaments.

Centrioles

• Aids in cell division.
• Usually found only in animal cells.
• Pinwheel array of nine triplets of microtubules.
• Form the bases of cilia and flagella.

Cilia and Flagella

• Whiplike, motile cellular extensions on the exposed surface of certain cells.
• Ciliary action moves substances in one direction across the cell surface.
• Flagella are longer and less in number than cilia, but serve much the same purpose.

Plasma Membrane

• Has two distinct membrane proteins: integral and peripheral proteins.
• Integral proteins are inserted into the lipid bilayer.
• Peripheral proteins are not embedded in the lipid bilayer; they attach loosely to the integral proteins.
• Glycoproteins are proteins attached with carbohydrates.

Nucleus

• Consists of nuclear envelope (membrane) with pores, nucleoli, and chromatin (or chromosomes).
• Contains genes (genetic materials), which control synthesis of cellular structure and most cellular activities.

Nuclear Envelope

• Selectively permeable double membrane barrier containing pores.
• Encloses jellylike nucleoplasm, which contains essential solutes.
• Outer membrane is continuous with the rough endoplasmic reticulum (rough ER) and is studded with ribosomes.
• Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus.
• Pore complex regulates transport of large molecules into and out of the nucleus.

Nucleolus

• Dark-stained spherical bodies found within the nucleus.
• Not membrane-bounded.
• Site of ribosome production.

Chromatin

• Fine, unevenly stained network composed of deoxyribonucleic acid (DNA) chain, histone proteins, and ribonucleic acid (RNA) chain.