Cell Structure and Function

• Chapter focuses on the general features applicable to all cells.
• Cell structures and functions, the cytosol, endomembrane system, semiautonomous organelles as well as the extracellular matrix and plant cell walls are covered.

Cell Theory

• All organisms consist of one or more cells.
• All come from pre-existing cells by cell division.

Cells: The Simplest Units of Life

• A cell constitutes the smallest unit exhibiting the characteristics of life.

Cell History

• Robert Hooke coined the term "cell".
• Anton van Leeuwenhoek discovered what he termed "animalcules".

Microscopy

• Allows for the visualization of individual cells and their components.

Cell Size

• Limited by the ratio of surface area to volume.

Cell Types

• Two primary cell types exist: prokaryotes and eukaryotes
• Prokaryotes include Domains Bacteria and Archaea.
• Eukaryotes comprise Domain Eukarya, which includes plants, animals, protists, and fungi.

Cell Characteristics

• All cells have features in common:
• Plasma (cell) membrane
• Cytoplasm
• Nucleic acids - DNA and RNA
• Ribosomes
• Cells represent variations on a common pattern.

Cell Type Comparisons

• Includes archaea, bacteria and eucaryotes
• Cell wall: archaea is usually present; bacteria is usually present, and eukaryotes are uauslly present and made of cellulose and chitin
• Cell number: archaea and bacteria are unicellular; eukaryotes are either uni- or multi-cellular
• Plasma membrane: all three contain plasma membranes
• Membrane-bound organelles: no in archaea and bacteria, yes with multiple types in eukaryotes
• Ribsomes: yes in archaea and bacteria, but larger in eucharyotes
• Chromosome: archaea and bacteria have single circular, but eucharyotes have multiple linear
• DNA Location: nucleoid in archaea and bacteria and nuceleus in eukaryotes
• Cilia: none in archaea and bacteria, rare in eukaryotes
• Flagella: yes in all three, but more complex in eukaryotes
• Cell division: Asexual in archaea and bacteria, both asexual and sexual in eukaryotes

Prokaryotic Cells: Bacteria

• Usually small, between 1µm and 10µm in diameter.
• Very abundant in the environment.
• Some are pathogens that cause disease.

Prokaryotic Cells: Archaea

• Usually small cells, range in size from 1µm to 10µm in diameter.
• Less common than bacteria.
• Extreme environments are common habitats.

Typical Bacterial Cell

• Ribosomes synthesize polypeptides.
• The cytoplasm is the site of metabolism.
• Pili enable bacteria to attach to surfaces and each other.
• Flagella aids in movement.
• The nucleoid contains the DNA.
• A plasma membrane encloses the cytoplasm.
• A cell wall provides support and protection.

Eukaryotic Cells

• Larger and more complex than prokaryotic cells
• Display more variety among organisms.
• Contain membrane-bound compartments: organelles

Animal and Plant Cell Organelles

• Centrosome: where microtubules grow and centrioles exist
• Nuclear pore: passageway for molecules in/out of the nucleus.
• Nucleus: genetic material organized and expressed.
• Nuclear Envelope: encloses the nucleus.
• Nucleous: ribosomes assemble
• Rough ER: where porting sorting and secretion happens
• Smooth ER: detoxification and lipid synthesis
• Mitochondrion: ATP Synthesis.
• Cytoskeleton: protein filaments provide shape and aid in movement.
• Peroxisome: hydrogen peroxide broken down to safe molecules
• Golgi apparatus: where molecules get modified, sorted and secreted
• Cytosol: where many pathways of molecules are made
• Lysosome: where macromolecules are degraded
• Ribosome: where polypetides are synthesized
• Plasma membrane: membrane controls moves in and out
• Additional plant cell specific organelles:
• Central vacuole: storage and water regulation.
• Chloroplast: converts light to energy
• Cell Wall: provides cell structure

Factors Determining Cell Characteristics

• Multicellular organisms produce different cells.
• Although the DNA (genome) in different cells is identical, they have different proteomes.
• Proteomes vary in different ways:
• Differing proteins are expressed
• Level of expression varies
• Proteins have differing modifications

Cytoplasm

• Contains everything inside the plasma membrane:
• Cytosol
• Cytoskeleton
• Endomembrane system
• Semiautonomous organelles

Cytoskeleton

• Provides the cell with shape, internal organization, and movement.
• Microtubules:
  • Long, hallow cylindrical structures.
  • Demonstrate dynamic instability.
• Intermediate filaments:
  • Mid-sized.
  • Twisted, rope-like structures.
• Actin Filaments:
  • Also known as microfilaments.
  • Long, thin fibers

Cytoskeletal Filaments in Eukaryotic Cells

• Microtubules: Hollow tubule of tubulin proteins, helps w/ shape, organizes organelles, sorting, and movement. 25 nm diameter.
• Intermediate filaments: Twisted filament of proteins, provides strength and anchors the cell. 10 nm diameter.
• Actin filaments: spiral made with actin protein, helps with strength, muscle contradiction, and movement. 7nm diameter.

Flagella and Cilia

• Flagella: 9 + 2 microtubule array and are longer than cilia, they appear individually or in pairs.
• Cilia: 9 + 2 microtubule array and are shorter than flagella, often cover the cell surface.

Nucleus

• Nuclear envelope:
  • Pores guarded by proteins.
• Nucleolus:
  • Site of synthesis of rRNA and ribosomal sub units.
• DNA Protein complex form:
  • Tread-like chromatin associated with histone proteins.
  • Condenses to form linear chromosomes.

Ribosomes

• Non-membranous organelles.
• Composed of large and small subunits.
  • Subunits are composed of proteins and ribosomal RNA.
• Site of protein synthesis

Endomembrane System

• Directly connected or pass materials using vesicles.
• Involved in production, storage or distribution of lipids and proteins.
• Contains : Nuclear envelope, lysosomes, peroxisomes, vacuoles, ER, Golgi, and the plasma members

Rough Endoplasmic Reticulum (RER)

• Covered with ribosomes (for protein synthesis).

Smooth Endoplasmic Reticulum (SER)

• Lacks ribosomes.
• Responsible for lipid and carbohydrate synthesis.

Golgi Apparatus

• Chemically alters, sorts, and packages molecules from the endoplasmic reticulum (ER).
• Functions include: renewing and modifying the plasma membrane, organizing cell wall components, producing membranous storage organelles, and releasing secretory products.

Lysosomes

• Powerful enzyme-containing vesicles.
• Hydrolyze molecules taken in by endocytosis.
• Recycle damaged organelles.
• Implement apoptosis.

Peroxisomes

• Enzyme-containing vesicles.
• Catalyze multiple chemical reactions.
• Often involved in detoxification.
  • Neutralize hydrogen peroxide.

Vacuoles

• Functions vary between cell types and environmental conditions.

Semiautonomous Organelles

• Include both mitochondria and chloroplasts.
• Contain own DNA and ribosomes.
• Capable of growth and division to reproduce themselves.
• They neither function completely independently nor are part of the endomembrane system.

Mitochondria

• Site of cellular respiration.
• Converts energy from food into ATP.

Chloroplasts

• Site of photosynthesis.
• Transforms solar energy into organic compounds (sugars).
• Originated from symbiotic ancestral purple cells.

###Cell Components General Functions

• Each components performs a specialized function:
  • Nucleus: holds genetic information
  • Endomembrane system: modifies protein & lipid
  • Cytosol: metabolism coordination
  • Semiautonomous Organelles: energy synthesis

Evolution of Mitochondria and Chloroplasts

• Developed through ancient symbiotic relationships.
• Endosymbiosis refers to the dynamic where a smaller species lives internally within a larger species.
• Endosymbiosis theory suggests mitochondria and chloroplasts originated from bacteria entering and living inside primordial eukaryotic cells.

Extracellular Matrix and Cell Walls

• Cells secrete materials to form protective structures outside the membrane.
• An extracellular matrix exists in animals.
• A cell wall exists in plants, fungi, and algae.

Plant Cell Walls

• Provide strength, rigidity, and support.
• Primary cell wall is made first.
  • Flexible, enabling cell growth.
  • Composed of various polysaccharides.
• Secondary cell wall is made second, between the call membrane and the primary wall.
  • Made in layers primarily of cellulose.

Animal Cells

• Lack cell walls but secrete a protective mixture of sugars and proteins forming the extracellular matrix.
• Functions: provide strength and structural support, organization and in cell signaling.

An overview of cell structures, functions, and cell theory. Includes cell history, microscopy, cell size limitations, and the two primary cell types: prokaryotes and eukaryotes. Covers cell characteristics applicable to all cells.