Cell Anatomy and Division: Study Notes for Anatomy & Physiology

Cell Anatomy and Division

Learning Outcomes

Upon completion of this topic, students should be able to:

• Identify cell organelles on models and other laboratory material.

• State a function of each organelle.

• Identify the nucleus and plasma membrane of cells under a microscope.

• Identify the parts of a cell's life cycle, including the stages of interphase and mitosis.

• Identify phases of mitosis in live cells.

• Simulate mitosis in a model.

Introduction to Cell Anatomy

Overview of Cells

Cells are the basic structural and functional units of all living organisms. The study of cells began in 1665 when Robert Hooke observed small compartments in cork, which he called "cells." Modern cell theory states that all animals and plants are composed of cells, and all cells come from preexisting cells. Cells perform physiological functions, and homeostasis at the cellular level is essential for the coordinated activity of all cells in an organism.

Cell Structure and Organelles

Generalized Cell Structure

Most cells are composed of three main parts:

• Plasma Membrane: The outer boundary that regulates the movement of substances in and out of the cell.

• Nucleus: The control center containing genetic material (DNA).

• Cytoplasm: The region between the plasma membrane and nucleus, containing organelles and cytosol.

Key organelles and their functions:

• Nucleolus: Site of ribosome synthesis within the nucleus.

• Mitochondrion: Produces ATP through cellular respiration; known as the "powerhouse" of the cell.

• Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

• Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis. Rough ER has ribosomes and synthesizes proteins; Smooth ER synthesizes lipids and detoxifies chemicals.

• Ribosome: Site of protein synthesis; can be free in cytoplasm or attached to rough ER.

• Golgi Complex: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosome: Contains digestive enzymes to break down waste materials and cellular debris.

• Centriole: Involved in organizing microtubules during cell division.

• Secretory Vesicle: Transports substances out of the cell via exocytosis.

Definitions of Key Terms

• Plasma Membrane: A selectively permeable barrier that surrounds the cell.

• Cytoplasm: The fluid and organelles between the plasma membrane and nucleus.

• Nucleus: Contains the cell's genetic material and controls cellular activities.

• Nucleolus: Dense region within the nucleus where ribosomal RNA is produced.

• Mitochondrion: Organelle responsible for energy production.

• Rough Endoplasmic Reticulum: ER with ribosomes; synthesizes proteins.

• Lysosome: Organelle containing enzymes for intracellular digestion.

• Ribosome: Structure that assembles amino acids into proteins.

• Golgi Complex: Organelle that processes and packages proteins and lipids.

• Centriole: Organelle that helps organize cell division.

Microscopic Observation of Cells

Cell Types and Their Structures

Cells vary in size, shape, and organelle composition depending on their function. Common cell types observed under the microscope include:

• Blood Cells: Specialized for transport of oxygen (red blood cells) and immune response (white blood cells).

• Muscle Cells: Elongated cells containing contractile proteins for movement.

• Neurons: Nerve cells with long extensions for transmitting electrical signals.

When observing cells, label the nucleus, plasma membrane, cytoplasm, and any visible organelles.

Cell Division

Overview of Mitosis

Cell division is essential for growth, repair, and maintenance of tissues. Most cells spend the majority of their life cycle in interphase, where they grow and perform normal functions. When new cells are needed, a cell enters mitosis, the process of dividing its nucleus and cytoplasm to produce two identical daughter cells.

Definition of Mitosis

• Mitosis: The process by which a cell divides its nucleus and contents to produce two genetically identical daughter cells.

Phases of Mitosis

Mitosis consists of four main phases:

1. Prophase: Chromatin condenses into visible chromosomes; the nuclear envelope dissolves; the mitotic spindle forms.

2. Metaphase: Chromosomes align at the cell's equatorial plane (metaphase plate).

3. Anaphase: Sister chromatids are pulled apart toward opposite poles of the cell.

4. Telophase: Chromatids reach the poles; nuclear envelopes reform; chromosomes decondense.

Cytokinesis

• Cytokinesis: The physical separation of the cytoplasm, resulting in two distinct daughter cells.

Summary Table: Phases of Mitosis

Phase	Main Events
Prophase	Chromatin condenses, nuclear envelope dissolves, spindle forms
Metaphase	Chromosomes align at the metaphase plate
Anaphase	Sister chromatids separate and move to opposite poles
Telophase	Nuclear envelopes reform, chromosomes decondense
Cytokinesis	Cytoplasm divides, forming two daughter cells

Formula: Chromosome Number in Mitosis

After mitosis, each daughter cell has the same number of chromosomes as the original cell:

$\text{Number of chromosomes in daughter cell} = \text{Number of chromosomes in parent cell}$

Applications and Examples

• Example: Skin cells divide by mitosis to replace cells lost due to injury.

• Application: Understanding mitosis is essential for studying cancer, where cell division becomes uncontrolled.

Additional Info

• Cells also undergo meiosis for sexual reproduction, which differs from mitosis by producing genetically unique cells.

• Cell organelles work together to maintain homeostasis and support cell function.