Human Anatomy - Cells

Microfilaments

- 7 nanometers (nm) in diameter - Composed of actin proteins intertwined in helical strands - Maintain and change cell shape - Participate in muscle contraction and cell division

Intermediate Filaments

- 8−12 nm in diameter - Protein composition varies - Provide structural support

Endoplasmic Reticulum (ER)

- A network of intracellular membrane-bound tunnels - Two types of ER: 1. Smooth endoplasmic reticulum (SER) 2. Rough endoplasmic reticulum (RER)

Plasma Membrane

- Also called the cell membrane - An extremely thin outer border on cell - Serves as a selective barrier that regulates the passage of gases, nutrients, and wastes between the internal and external environments of the cell

Ribosomes

- Comprised of a large and small subunit - Responsible for protein synthesis 1. Free ribosomes float unattached within the cytosol 2. Fixed ribosomes are attached to the outer surface of rough ER

Nucleus

- Control center for cellular activity - Composed of three major components: 1. Nuclear envelope 2. Nucleoli 3. DNA, chromatin, and chromosomes

Nucleoli

- Dark-staining bodies within the nucleus - Composed of RNA, enzymes, and various proteins - Responsible for making the components of the small and large units of the ribosome

Nuclear Envelope

- Double membrane structure - Controls entry and exit of molecules from nucleus and cytoplasm - Outer membrane is continuous with endoplasmic reticulum - Nuclear pores are selectively permeable channels that allow specific molecules in and out of the nucleus

Integral Proteins

- Embedded in phospholipid bilayer - Span the entire thickness of the membrane - Exposed to the outside and inside of the cell - Also termed transmembrane proteins - Can have carbohydrates (sugars) attached to outer surface: *glycoproteins* - Have many varied functions

Mitochondria

- Function to produce a high energy containing molecule called ATP on the cristae - Cells that require more energy have more mitochondria than cells requiring less energy

Microtubules

- Hollow tubes 25 nm in diameter - Composed of tubulin protein - Radiate from centrosome - Many functions, including: 1. Fix organelles in place 2. Maintain cell shape and rigidity 3. Direct movement of organelles in the cell 4. Allow cell motility (in cilia and flagella) 5. Move chromosomes during cell division

2 types of proteins found within cell membranes:

- Integral - Peripheral

Organelles

- Means "little organs" - Many types; each perform different function: --- A division of labor --- The type and number of organelles within a cell is a reflection of the cell's function

Peripheral Proteins

- Not embedded in the lipid bilayer - Loosely attached to the external or internal surface of the plasma membrane - Have many varied functions *Example: Enzymes

3 types of lipids found within cell membranes:

- Phospholipids - Cholesterol - Glycolipids

Cytoskeleton

- Proteins organized in the cytosol as solid filaments or hollow tubes - Three cytoskeletal components: 1. Microfilaments 2. Intermediate filaments 3. Microtubules

Membrane Proteins

- Responsible for most of the membrane functions (*Proteins: complex molecules made of amino acids chains)

DNA, Chromatin, and Chromosomes

- The nucleus houses deoxyribonucleic acid (DNA), a complex molecule containing genetic material --- When the cell is not dividing, nuclear DNA is unwound into fine filaments called chromatin --- During cell division chromatin coils tightly to form chromosomes

Microvilli

- Thin, microscopic projections extending from the plasma membrane - Extensions of cell not capable of motion - Increase the surface area for membrane transport *Example: On surface of cells of the small intestine; increase absorption of nutrients

Protein-Specific Functions of the Plasma (Cell) Membrane

- Transport - Anchorage for the cytoskeleton - Enzyme (catalytic) activity - Cell-cell recognition

Peroxisomes

- Vesicles formed by pinching off from the rough ER; smaller than lysosomes - Use O2 and the enzyme catalase to detoxify harmful molecules taken into the cell

Lysosomes

- Vesicles generated by the 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 (autolysis)

Rough ER

- Walls appear rough due to attachment of ribosomes on outside of the RER membrane --- Ribosomes synthesize proteins The RER functions to synthesize, transport, or store proteins for: 1. Secretion by the cell 2. Incorporation into the plasma membrane 3. Creation of lysosomes

Smooth ER

- Walls have a smooth appearance - Continuous with rough ER Functions include: 1. Synthesis, transport, and storage of lipids including steroid hormones 2. Detoxification of drugs, alcohol, and poisons

Organelles can be classified in two types:

1. Membrane-bound 2. Non-membrane-bound

Most human cells have three basic parts

1. Plasma membrane - Selective outer barrier 2. Cytoplasm - Cellular contents; cytosol, and organelles 3. Nucleus - Control center

Protein Flow through the Golgi Apparatus

1. Proteins synthesized in RER get packaged into transport vesicles. 2. Transport vesicles pinch off from RER and fuse with the receiving cis-face of the Golgi apparatus. 3. The proteins move between and are modified in the cisternae of the Golgi apparatus. 4. Modified proteins are packaged in secretory vesicles. 5. Secretory vesicles either participate in exocytosis or become lysosomes in the cell.

Cytosol

A viscous, syruplike fluid containing many different dissolved substances, such as: - Ions - Nutrients - Proteins - Carbohydrates - Lipids - Other small molecules

Cytoplasm

All materials between plasma membrane and nucleus: - Cytosol - Organelles

Cellular Functions

Covering Lining Storage Movement Connection Defense Communication Reproduction

Membrane-Bound Organelles:

Examples: - Endoplasmic reticulum - Golgi apparatus - Lysosomes - Peroxisomes - Mitochondria

Golgi Apparatus

Function to receive proteins and lipids from the RER for modification, sorting, and packaging

Cilia

Grouped on cells that move objects across their surface *Example: Cells of the respiratory tree and oviduct

Flagella

Longer than cilia, and usually singular; used to propel a cell *Example: Sperm

Cytology

the study of cells