Eukaryotic cell

Eukaryotic Cell: An Overview

Lesson Developer: Manju A. LalCollege/Department: Kirori Mal College, University of DelhiInstitute of Lifelong Learning, University of Delhi

Table of Contents

  • Introduction

  • Cell Wall

  • Plasma Membrane

  • Cytoplasm

  • Nucleus

  • Organelles involved in various metabolic reactions

    • Mitochondria

    • Chloroplasts

    • Peroxisomes

    • Endomembrane system

      • Endoplasmic Reticulum

      • Golgi Apparatus

      • Lysosomes

      • Vacuoles

  • Ribosomes

  • Cytoskeleton

  • Origin and Evolution of Eukaryotic Cell

    • Origin of Cell

    • Origin of Biomolecules

    • The First Cell

    • Evolution of Eukaryotic Cells

  • Summary

  • Exercise/Practice

  • Glossary

  • References/Bibliography/Further Reading

Eukaryotic Cell Overview

  • Eukaryotes have a well-defined nucleus, unlike prokaryotes.

  • Eukaryotic cells are complex, compartmentalized into membrane-bound organelles:

    • Plasma Membrane: Surrounds the cell, maintains a selective permeability.

    • Nucleus: Contains genetic material and regulates cellular functions.

    • Organelles: Execute metabolic functions, classified into three types:

      • Double membrane-bound (e.g., nucleus, chloroplasts, mitochondria)

      • Single membrane-bound (e.g., ER, Golgi apparatus, lysosomes)

      • Non-membrane bound (e.g., ribosomes, cytoskeleton)

  • Key differences between plant and animal cells:

    • Plant cells possess a cell wall, large vacuoles, and plastids.

    • Centrioles are present in animal cells but absent in plant cells.

Cell Wall

  • Plant cells are unique due to their cell wall providing rigidity and skeletal support.

  • Composed of cellulose microfibrils, hemicellulose, and pectic substances.

  • Primary Wall: Elastic and present in young cells.

  • Secondary Wall: Formed with additional cellulose and lignin, providing rigidity.

  • Plasmodesmata: Cytoplasmic channels allowing communication between adjacent cells.

Plasma Membrane

  • Composed of lipids (phospholipids) and proteins, exhibiting selective permeability.

  • Integral and peripheral proteins fulfill various roles (transport, signaling).

  • Glycoproteins and glycolipids present, serving as receptors and structural components.

Cytoplasm

  • Area between plasma membrane and nucleus, containing organelles and cytosol.

  • Cytosol carries out critical metabolic reactions (e.g., protein synthesis, glycolysis).

  • Cytoskeleton: Composed of microtubules, microfilaments, intermediate filaments that maintain cell shape and assist with movement.

Nucleus

  • Double membranous organelle; houses DNA complexed with histones (chromatin).

  • Contains nucleoli for ribosome synthesis.

  • Nuclear pores regulate traffic between nucleus and cytoplasm.

Organelles for Metabolism

Mitochondria

  • Function as the powerhouse of the cell, involved in aerobic respiration.

  • Double membrane structure: outer (permeable) and inner (folded into cristae).

  • ATP is synthesized via oxidative phosphorylation in the matrix by the electron transport chain.

  • Mitochondria have their own circular DNA and ribosomes, making them semi-autonomous.

Chloroplasts

  • Present only in plant cells; site of photosynthesis.

  • Contains thylakoids where light reactions occur and stroma where Calvin cycle happens.

  • Also possess circular DNA and 70 S ribosomes.

Peroxisomes

  • Contain enzymes for oxidative reactions, producing and degrading hydrogen peroxide.

  • Associated with lipid metabolism and detoxification processes, especially in liver and kidney cells.

Endomembrane System

  • Composed of ER, Golgi apparatus, and lysosomes, involved in protein synthesis and transport.

Endoplasmic Reticulum

  • Network of membranes; Rough ER for protein synthesis; Smooth ER for lipid synthesis.

Golgi Apparatus

  • Modifies, sorts, and packages proteins for secretion or delivery to lysosomes.

Lysosomes

  • Membranous vesicles containing hydrolytic enzymes, involved in digestion.

Vacuoles

  • Storage vesicles; provide structure and support in plant cells.

Ribosomes

  • Non-membrane organelles synthesizing proteins, differing in size between prokaryotic and eukaryotic.

Cytoskeleton

  • Internal framework providing shape and aiding in motility and transport within cells.

  • Comprised of:

    • Microtubules: Thick, hollow structures involved in cell division.

    • Microfilaments: Thin strands aiding in movement and supporting cell shape.

    • Intermediate filaments: Provide structural support and stability.

Origin and Evolution of Eukaryotic Cells

  • Life likely originated from simple biomolecules leading to the first cells.

  • Endosymbiotic theory suggests mitochondria and chloroplasts originated from engulfed prokaryotes.

  • Autogenous origin may explain the formation of organelles through infolding of plasma membranes.

  • Molecular evolution studies reveal relationships among life forms through genetic material comparisons.

Summary

  • Eukaryotic cells have a complex structure, characterized by a nucleus and various organelles.

  • Distinct organelles execute functions such as energy production (mitochondria, chloroplasts) and digestion (lysosomes).

  • Genetic and biochemical similarities support evolutionary relationships among organisms.