Eukaryotic Cells Overview

Learning Outcomes

• Students should be able to distinguish prokaryotic and eukaryotic cell features.
• Students should be able to discuss cytoplasm and organelles.
• Students should be able to describe cell surface specializations and their role in cell survival.
• Students should be able to explain the two basic cell types (body cells and sex cells).

Eukaryotic Cells

• Eukaryotic cells have a nucleus and other organelles.
• They are generally more complex than prokaryotic cells.
• Eukaryotic organisms include plants, animals, protists, and fungi.

Features of Eukaryotic Cells

• Eukaryotic cells contain internal membrane-bound structures.
• DNA is contained within the nucleus, forming multiple chromosomes.
• Chromosomes are complexed with proteins.
• The nucleus is enclosed by a nuclear envelope.
• Eukaryotic cells have 80S ribosomes composed of 40S and 60S subunits.

Prokaryotic vs Eukaryotic

• Eukaryotic cells have a complex internal structure.
• Prokaryotic cells have a simple internal structure.

Animal Cell Features

• Animal cells include a nucleus, ribosomes, rough ER, smooth ER, Golgi body, lysosomes, plasma membrane, cytoskeleton, mitochondria, and centrioles.

The Cytoplasm

• Cytoplasm is a viscous fluid containing all cell organelles except the nucleus.
• Major components include cytosol, organelles, and inclusions.
• Cytoplasm is mainly water (75%) and proteins (25%).
• Non-protein molecules like ions and ATP are also present.
• Proteins (enzymes and structural) make the cytoplasm viscous.

Four Divisions of Eukaryotic Cells

• The nucleus and ribosomes
• Organelles of the endomembrane system
• The energy-related organelles
• The cytoskeleton

The Nucleus

• The nucleus is the control center of the cell.
• It encloses chromosomes and nucleoli.
• It is a spherical structure enclosed by a double membrane.
• The nucleus is a crucial organelle, serving as the information processing and administrative center of the cell.

Functions of Nucleus

• Keeps DNA separate from the cytoplasm's metabolic machinery.
• Stores the cell's hereditary material (DNA).
• Organizes DNA for copying prior to cell division.
• Coordinates the cell's activities.

Components of Nucleus

• Nuclear envelope
• Nuclear pores
• Nucleolus
• Chromatin

Nuclear Envelope

• Two lipid bilayers form the nuclear envelope.
• The innermost surface of the nuclear envelope has DNA attachment sites.
• Pores span the bilayer, allowing for the passage of ribosomal subunits, mRNA, and proteins.

Nucleolus

• A dense mass of materials located in the nucleus, visible when the cell is not dividing.
• Involved in ribosome synthesis and assembly.
• Contains RNA for protein manufacture.

Chromatin

• A collection of DNA and associated proteins within the nucleus.
• During cell division, chromatin condenses to form chromosomes.
• Chromosomes are shortened and thickened structures composed of DNA associated with proteins.
• Chromatin is also where hereditary information resides.

The Endomembrane System

• A group of related organelles where lipids and polypeptide chains are assembled and modified.
• Products are sorted and delivered to various destinations.

Components of Endomembrane System

• Endoplasmic reticulum (ER)
• Golgi bodies (apparatus)
• Vesicles

Endoplasmic Reticulum

• A continuous network of membranes within animal cells connected with the nuclear membrane.
• Extends throughout the cytoplasm.
• Two regions: Rough ER and Smooth ER.

Rough ER

• Arranged in flattened sacs.
• Ribosomes on the surface give it a rough appearance.
• Modifies polypeptide chains entering the rough ER.
• Involved in protein secretion.

Smooth ER

• No ribosomes on its surface; a series of tubules.
• Important in lipid assembly.
• Involved in waste and drug detoxification.

Golgi Apparatus

• Stack of flattened saccules (cisternae).
• Receives vesicles from the ER.
• Modifies molecules received from the ER.
• Sorts and packages molecules for transport to other destinations.
• Produces some lysosomes.

Lysosomes

• Vesicles with digestive enzymes.
• Digest molecules or portions of the cell.

Vesicles

• Membranous sacs that move through the cytoplasm.

Energy-Related Organelles

• Mitochondria
• Chloroplasts

Mitochondria

• ATP-producing powerhouses.
• Have a double membrane system.
• Conduct energy-releasing reactions requiring oxygen.
• Site of most efficient energy-releasing reactions.

Mitochondrial Structure

• Outer membrane facing the cytoplasm.
• Inner membrane folds back on itself, forming compartments for ATP-making machinery.

Chloroplasts

• Convert sunlight energy to ATP through photosynthesis.
• Found in plant cells, have a double membrane system with thylakoid compartments.

Cytoskeleton

• Present in all eukaryotic cells.
• Basis for cell shape and internal organization.
• Allows organelle movement and, in some cases, cell motility (flagella, cilia).

Cytoskeletal Elements

• Microtubules
• Microfilaments
• Intermediate filaments

Accessory Proteins

• Involved in functions like attaching to microtubules and actin, motor functions, and crosslinking.

Microfilaments

• Small, hollow cylinders.
• Assembly controlled by centrosomes.
• Help maintain cell shape and function as pathways for other molecules.

Microtubules

• Intermediate in size.
• Ropelike assemblies.
• Stretch from the nucleus to the cell membrane.

Centrioles

• Made of 9 sets of microtubule triplets.
• Two centrioles are at right angles to each other.
• Important in animal cells, not present in plant cells.

Cilia and Flagella

• Important in cell movement or fluid movement past the cells.
• Similar construction in both eukaryotes.
• Cilia are shorter and more numerous than flagella.

False Feet (Pseudopods)

• Temporary, irregular cellular projections.
• Used for locomotion in amoebas and other cells to capture prey.
• Use microfilament contractions to move.

Other Eukaryotic Organelles

• Centrioles: cylindrical microtubule structures playing a role in cell division.

Cell Surface Specializations

• Eukaryotic cell walls
• Matrixes between animal cells
• Cell junctions

Cell Walls

• Structural components surrounding the plasma membrane.
• Found in plants, some fungi, and some protists.

Matrixes Between Animal Cells

• Animal cells lack cell walls.
• Surrounded by a matrix of cell secretions and other materials maintaining cell structure and function.

Extracellular Fluid (ECF)

• Two major compartments: Interstitial fluid (ISF) and blood plasma.
• Interstitial fluid surrounds cells, while plasma is the extracellular component of blood.
• Other minor compartments: transcellular fluid (e.g., digestive juices) and lymph.

Cell Junctions

• Structures connecting cells in tissues.
• Types in animals include tight junctions, adhering junctions, and gap junctions.

Cell Junctions - Tight

• Plasma membranes closely join together.

Cell Junctions - Adhering

• Internal cytoplasmic plaques joined by intercellular filaments.

Cell Junctions - Gap

• Allow passage of small molecules/ions between cells.

Two Basic Cell Types

• Body cells (somatic cells) are differentiated into cells with specialized functions. Through mitosis, they replicate.
• Sex cells (gametes) participate in reproduction. Through meiosis, their genetic material is combined.