Cell Organelles: Structure and Function Study Guide

Cell Organelles: Structure and Function

I. Introduction to Cells

Cells are the fundamental units of life, forming the basis of all living organisms. Understanding their structure and function is essential in Anatomy & Physiology.

• Basic Unit of Life: The cell is the smallest unit capable of performing all life processes.

• Cell Theory: The cell theory outlines the foundational properties of cells. The six basic properties are:

  1. All living things are composed of one or more cells.

  2. The cell is the basic unit of structure and organization in organisms.

  3. All cells arise from pre-existing cells.

  4. Cells contain hereditary information (DNA) passed from cell to cell during division.

  5. All cells are basically the same in chemical composition.

  6. All energy flow (metabolism and biochemistry) of life occurs within cells.

• Cytology: The study of cells is called cytology.

II. Cell Structure

Cells are surrounded by a membrane and contain various structures that perform specific functions necessary for life.

• Plasma Membrane: The structure that encloses a cell is called the plasma membrane (or cell membrane).

• Cytoplasm: The material inside the cell, excluding the nucleus, is called the cytoplasm. It consists of the cytosol (fluid) and small structures called organelles.

• Plasma Membrane and Fluid Compartments: The plasma membrane separates two regions filled with fluid:

  • Intracellular Fluid (ICF): Fluid inside the cell.

  • Extracellular Fluid (ECF): Fluid outside the cell.

• ECF Subdivisions: The ECF consists of two main compartments:

  • Interstitial Fluid: Fluid between cells (outside blood vessels).

  • Plasma: Fluid component of blood, found within blood vessels.

• Other Terms: Another name for intracellular fluid is cytoplasm or cytosol (context-dependent).

• Major Constituents of Cytosol: Water, proteins, carbohydrates, lipids, and ions.

III. Cell Organelles

Organelles are specialized structures within cells, often surrounded by membranes, that perform distinct functions. They are categorized based on the presence or absence of a surrounding membrane.

• Membranous Organelles: Surrounded by a lipid bilayer (e.g., nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes).

• Non-membranous Organelles: Not surrounded by a membrane (e.g., ribosomes, cytoskeleton, centrioles).

Examples of Organelles and Their Functions

Organelle	Structure	Function
Ribosomes	Small, non-membranous granules	Protein synthesis
Smooth Endoplasmic Reticulum (SER)	Network of membranous tubules	Lipid and carbohydrate synthesis, detoxification
Rough Endoplasmic Reticulum (RER)	Membranous network with ribosomes attached	Protein synthesis and modification
Golgi Apparatus	Stack of flattened membranous sacs	Modification, packaging, and transport of proteins
Lysosomes	Membrane-bound vesicles	Digestion of cellular waste and foreign material
Mitochondria	Double-membraned organelle	ATP production (cellular respiration)
Cytoskeleton	Network of protein filaments	Cell shape, support, and movement
Cilia	Short, hair-like projections	Movement of substances across cell surface
Flagella	Long, whip-like projection	Cell movement (e.g., sperm cell)
Microvilli	Microscopic membrane extensions	Increase surface area for absorption

IV. The Nucleus

The nucleus is the control center of the cell, containing genetic material and directing cellular activities.

• Nuclear Envelope: Double membrane that surrounds the nucleus, separating it from the cytoplasm.

• Nuclear Pores: Openings in the nuclear envelope that allow exchange of materials between nucleus and cytoplasm.

• Nucleoplasm: The semi-fluid substance inside the nucleus.

• Nucleolus: Dense region within the nucleus responsible for ribosome synthesis.

• Function of Nucleolus: Synthesizes ribosomal RNA (rRNA) and assembles ribosome subunits.

• Chromatin: DNA and associated proteins in a loose, thread-like form.

• Chromosomes: Condensed, tightly coiled DNA-protein structures visible during cell division.

DNA Organization

• When DNA is tightly coiled around proteins, it forms chromosomes.

• When DNA and proteins are loosely coiled, it is called chromatin.

Labeling Nuclear Structures

• Key structures to identify in a nucleus diagram: chromatin, nuclear envelope, nucleolus, nuclear pore.

V. Organelle Functions and Interactions

Organelles work together to maintain cellular function. For example, the nucleus, rough endoplasmic reticulum (RER), Golgi apparatus, and vesicles coordinate protein synthesis and transport.

• Protein Synthesis Pathway:

  1. The nucleus contains DNA, which is transcribed into mRNA.

  2. mRNA exits the nucleus and is translated by ribosomes on the RER.

  3. Proteins synthesized in the RER are packaged into vesicles and sent to the Golgi apparatus.

  4. The Golgi modifies, sorts, and packages proteins for delivery inside or outside the cell.

Organelle Identification by Function

• Responsible for protein synthesis: Ribosomes, RER

• Synthesis and breakdown of lipids and carbohydrates: Smooth ER

• "Post office" of the cell: Golgi apparatus

• Helps digest ingested food: Lysosomes

• Sites of ATP production: Mitochondria

• Increases surface area of plasma membrane: Microvilli

Additional info: The study guide includes diagrams for labeling and short-answer questions to reinforce understanding of cell structure and function. For exam preparation, focus on the definitions, functions, and interactions of each organelle, as well as the organization of cellular compartments.