The Structural Organization of Human Cells (Cytoplasm and Organelles)

Cytoplasm

Includes all materials between plasma membrane and nucleus. (Cytosol, Inclusions, Organelles)

Cytosol

A viscous fluid containing water and many dissolved substances such as: ions, nutrients, proteins, carbohydrates, lipids, other small molecules

Inclusions

Some cells store this in their cytosol

Inclusions are chemicals such as

Pigments (ex: melanin in skin cells) Nutrient stores (ex: glycogen in muscle cells) protein (ex: dissolve proteins)

Organelles

Structures in cells that perform specific functions (The type and number of organelles reflect the cell’s function)

Membrane-bound organelles

Contents are separate from cytosol. Endoplasmic reticulum, golgi apparatus, lysosomes, peroxisomes, mitochondria

Non membrane bound organelles

Contents are in direct contact with cytosol. Ribosomes, cytoskeleton, centrosomes, centrioles, cilia, flagella, microvilli

Endoplasmic Reticulum

Network of intracellular membrane-bound tunnels. Smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER)

Cisternae

Inclosed spaces are called

Smooth ER (SER)

Smooth due to lack of ribosomes. Continuous with rough ER

Functions of Smooth ER

Synthesis, transport, and storage of lipids including steroid hormones, metabolism of carbohydrates, detoxification of drugs, alcohol, and poisons

Rough ER (RER)

Rough due to attachment of ribosomes. RER receives newly synthesized proteins form ribosomes

Functions of Rough ER

Modifies the proteins and package them into transport vesicles. Proteins will be secreted inserted into plasma membrane or included in a lysosome

Golgi Apparatus

Receive material from ER for modification, sorting, and packaging. (Not producing anything just sending it off)

Lysosomes

Job is to break down or cut down. Vesicles generated by golgi apparatus. Contain enzymes used to digest and remove waste products and damaged organelles within the cell. When a cell is dying it releases lysosomal enzymes that digest the cell

Peroxisomes

Sacs formed by pinching off from RER. Smaller than lysosomes. Detoxify harmful molecules in a cell. Abundant in liver cells

Mitochondria

Organelles with double membranes (Cristae). Produce ATP, cells that require more energy (ex: muscle cells) have more of this

Ribosomes

Responsible for protein synthesis, free ribosomes float in cytosol, fixed ribosomes are attached to RER

Cytoskeleton

Proteins organized in the cytosol as solid filaments or hollow tubes.

Three cytoskelet components

Microfilament, intermediate filaments, microtubules

Centrosome

Non membranous, spherical structure adjacent to nucleus. Contains pair of centrioles at right angles to each other

Centriole

Attached to chromosomes during cell division causing chromosomal migration

Cilia and Flagella

Projections from cell containing cytoplasm and microtubules capable of movement

Cilia

On exposed surfaces of certain cells, move objects across their surface (ex: cells of respiratory passage use cilia to move mucus

Flagella

Longer than cilia, usually singular whiplike tails (ex: sperm)

Microvilli

Tiny projections from plasma membrane increase the surface area for membrane transport (ex: small intestine - increase absorption of nutrients)