Eukaryotic cell structures

Eukaryotic Cell Structures

• Eukaryotic cells contain organelles enclosed by membranes
• Understanding the structures and functions of these organelles is crucial to understanding cellular processes

Learning Outcomes

• Students need to understand the structures of eukaryotic organelles
• Explaining the structure, role, and function of the nucleus is essential
• Understanding ribosomes, their roles, and functions is crucial
• The endomembrane system is crucial to explaining how mitochondria and chloroplasts generate energy for the cell
• The cytoskeleton network, its composition, and its function in cellular activities is key

Modern Cell Theory

• All living things are comprised of cells
• Cells can have specialized functions within different organisms
• The cell is the smallest living unit within all organisms
• DNA and RNA are the hereditary information
• Cells manufacture new molecules
• Cells use organic molecules as energy sources for cellular metabolism
• All cells originate from pre-existing cells

Eukaryotic and Prokaryotic Cell Similarities

• Both have DNA
• Both contain ribosomes
• Both have cytoplasm
• Both have cell membranes

Eukaryotic and Prokaryotic Cell Differences

• Prokaryotic cells lack a nucleus
• Prokaryotic cells lack membrane-bound organelles (like mitochondria or chloroplasts)
• Eukaryotic cells have a nucleus
• Eukaryotic cells have membrane-bound organelles
• Prokaryotic cells are generally smaller
• Prokaryotic cells have circular DNA without a nucleus (nucleoid)

Compartmentalisation of Activities

• Organelles compartmentalize tasks within the cell
• This concentrates enzymes and necessary compounds allowing for more efficient processes
• This system allows for specialization in specialized eukaryotic cells
• This is crucial in multicellular organisms

Membrane-bound Organelles

• Membrane-bound organelles in eukaryotes help compartmentalize and organize functions
• Organelles include: nucleus, ribosomes, and the endomembrane system

Nucleus

• The nucleus is surrounded by the nuclear envelope
• The nuclear envelope is a double membrane
• The nuclear matrix maintains the shape of the nucleus
• Nuclear pores are channels that allow regulated movement of biomolecules into and out of the nucleus

Endomembrane System

• The endomembrane system consists of inter-related membrane sacs
• This system is responsible for protein synthesis, modification, and transport
• Structures of the endomembrane system include: the nuclear envelope, rough ER, smooth ER, Golgi, and lysosomes

Ribosomes

• Ribosomes are responsible for protein synthesis.
• Ribosomes consist of two subunits: small (40S) and large (60S)
• Ribosomes are crucial to the process of translation
• Ribosomes contain three binding sites for tRNA (P, A, and E sites)

Endoplasmic Reticulum - Rough ER

• The rough ER is studded with ribosomes
• Rough ER is responsible for the formation of new peptides
• Rough ER increases surface area
• Rough ER is a network of interconnected membranous channels
• These channels are called cisternae, which are the spaces surrounding the rough endoplasmic reticulum

Endoplasmic Reticulum - Smooth ER

• Purpose of smooth ER—production and metabolism of fats and steroid hormones
• Calcium storage
• Detoxification of drugs and toxins
• Smooth and rough ER can be connected to function in a continuous network.

Golgi Complex

• The Golgi complex is responsible for protein sorting and modification
• Proteins are received from the endoplasmic reticulum
• Proteins are modified (removing or adding amino acid chains)
• Proteins are then transported to other parts of the cell.
• Proteins can potentially be secreted.

Secretory Vesicles

• Vesicles contain specialized membrane signals to prepare for fusion with the cellular membrane
• Fusion of membranes occurs to release secreted vesicles' contents out of the cell
• Membranes integrate with the cellular membrane during secretion

Lysosomes and Peroxisomes

• Lysosomes contain hydrolytic enzymes for breaking down cellular wastes or invading substances
• Peroxisomes metabolize nitrogen compounds and also break down lipids

Energy and Eukaryotes

• Eukaryotic cellular function is greatly dependent on mitochondria (organelles)
• Mitochondria involve the fundamental process to generate energy.

ATP (Adenosine Triphosphate)

• Energy in cells is primarily in the form of ATP molecules
• ATP is an energy-rich molecule with high phosphoryl transfer potential (energy transfer)
• ATP-ADP cycle is crucial for transferring energy needed for cellular processes
• ATP functions are fundamental in biological systems
• ATP is the immediate energy source, not a long-term storage molecule

Mitochondria

• Mitochondria are involved in cellular respiration.
• Consist of outer and inner membranes (Cristae)
• The matrix is found inside the inner membrane
• Contains a small circular mitochondrial DNA

Chloroplasts

• Chloroplasts are the energy-producing organelles in plant cells
• Similar structure to mitochondria with inner and outer membranes.
• The stroma contains thylakoids
• The thylakoids are stacked to form grana
• Photosynthesis in plants takes place in chloroplasts

Cytoskeletal Network

• The cytoskeleton is made up of microtubules, microfilaments, and intermediate filaments.
• The cytoskeleton helps with maintenance of cell shape and internal transport of molecules

Cytoskeletal Architecture

• The cytoskeleton is made up of small subunits that polymerize (combine structures into one large structure)
• This process makes it possible for the cell to create and disassemble structures easily and quickly.
• Addition of subunits adds a polarity to the cytoskeletal structures

Microtubules

• Microtubules are made of alpha and beta tubulin.
• They have polarity with plus and minus ends.
• Microtubules have a diameter of 25nm
• Microtubules are used in cell organization, intracellular transport, and chromosome movement.

Centrosome

• Microtubules are nucleated in the cytoskeleton by the centrosome
• Centrosome contains barrel-shaped centrioles.

Role of Micro tubules

• Microtubules help with cell shape, polarity, intracellular transport of vesicles and organelles, and chromosomal movement.

Role of Microfilaments

• Microfilaments help with cell shape and polarity
• They also help with cell locomotion, cytokinesis, muscle contraction, and intracellular transport.

Actin Protrusions

• Actin protrusions form structures called lamellipodia and filopodia used for cellular movement and adhesion.

Role of microfilaments 2)

• Role of microfilaments in cell locomotion
• The proteins in the cytoskeleton enable the motion.

Intermediate Filaments

• A cytoskeletal composed of multiple proteins
• Intermediate filaments have a diameter between 8 to 12nm
• They maintain the structure and shape of cells
• Nuclear lamina is a type of intermediate filament

Four Classes of Intermediate Filaments

• Keratins are in epithelial cells
• Vimentin and related proteins are in connective tissue
• Desmin is in muscle tissue
• Neurofilaments are in nerve tissue
• Nuclear lamins are in all animal cells

Disorders of Intermediate Filaments - Keratin Filaments

• Genetic disorders involving mutations in proteins that create keratin filaments
• These result in defects and easy blistering in the skin.

Disorders of the Nuclear Lamina Progeria

• Rare genetic disorder that causes premature aging
• Mutated progerin is improperly formed and unable to maintain the nuclear lamina
• It limits the cells ability to divide

Summary

• Eukaryotic cells have a cytoskeletal structure of filaments to maintain shape.