LESSON 2 - CELL THEORY

WHAT IS THE CELL THEORY?

• All organisms are composed of one or more cells

• The cell is the basic structural and functional unit of all living organisms

• Cell arise only from the division of preexisting cells

WHAT ARE UNICELLULAR ORGANISMS?

Carry out all activities necessary for life

WHAT ARE MULTICELLULAR ORGANISMS?

The activities of life are divided among numerous types of specialized cells

WHAT ARE THE SIZES OF CELLS?

• Most are too small to be seen by the naked eye

• ranging from about 0.5 μm (bacteria) to a few hundred micrometers (plant cells)

• We must use microscopes to see them

WHAT ARE THE 2 TYPES OF MICROSCOPES?

• Light Microscopes: Use light to illuminate the specimen

• Electron Microscopes: Use electrons to illuminate the specimen

WHAT IS DISPROVING SPONTANEOUS GENERATION?

Proves that living things do not come from non-living things on their own

WHAT IS MAGNIFICATION?

The ratio of the object as viewed to its real size

WHAT IS RESOLUTION?

The minimum distance that two points in the specimen can be separated and still be seen as two points (depends on wavelength of light or elctrons used to illuminate the specimen)

WHY ARE CELLS SO SMALL?

• Limited by surface area-to-volume ratio

• Volume determines the amount of chemical activity that can take place within the cell

• Surface area determines the amount of substances that can be exchanged between a cell and the outside environment

WHAT IS SURFACE AREA-TO-VOLUME RATIO?

Is the amount of a cell’s surface area compared to its volume

WHAT IS THE PLASMA MEMBRANE?

A bilayer made of lipids with embedded protein molecules that all cells are surrounded by

WHAT IS A LIPID BILAYER?

A hydrophobic barrier to water-soluble substances

• Selected water-soluble substances can penetrate cell membranes through transport protein channels

• Selective transport of ions and water-soluble molecules maintain the specialized internal environments required for cellular life

WHAT IS DNA?

Is concentrated in a central area of the cell and stores hereditary information (genes)

WHAT ARE GENES?

Are segments of DNA that code for individual proteins

WHAT IS CYTOPLASM?

• Located between the plasma membrane and the central region

• Corresponds to the cytosol and cytoskeleton

WHAT IS CYTOSOL?

An aqueous solution containing ions, various organic molecules, and organelles

WHAT IS CYTOSKELETON?

• Is an interconnected system of protein fibres and tubes that extend throughout the cytoplasm

• Maintains cell shape

• Plays key roles in cell division, chromosome segregation, and transportation within the cell

• In animal cells, it is compromised of microtubles, intermediate filaments, and microfilaments

WHAT DOES A PROKARYOTIC CELL HAVE IN IT?

• Domains of bacteria and archaea

• Nucleiod region has no boundary membrane

• Many bacteria and archaea species contain few of any internal membranes

WHAT DOES A EUKARYOTIC CELL HAVE IN IT?

• Domain of eukarya

• Has a nucleus

• Has cytoplasm containing extensive membrane systems that form organelles

WHAT ARE THE 3 COMMON SHAPES OF PROKARYOTIC CELLS?

1. Spherical

2. Rodlike

3. Spiral

WHAT IS PROTEIN PRODUCTION?

Information from DNA is copied into messenger RNA (mRNA)

• mRNA carries the info to ribosomes in the cytoplasm

• Ribosomes assemble amino acids into proteins

WHAT IS A FLAGELLA?

• Used for many bacteria and archaeans to move

• The bacterial flagellum rotates in a socket and pushes the cell through a liquid medium

WHAT IS PILI?

• Hairlike structures that attach the cell to surfaces or other cells

• A special sex pilus joins bacteria during mating

WHAT IS THE CELL WALL AND GLYCOCALYX?

• The plasma membrane is surrounded by a rigid external cell wall coated with polysaccharides called the glycocalyx

• Slime layer: Glycocalyx loosely associates with the cell

• Capsule: Glycocalyx firmly attaches to the cell

ANIMAL CELL

PLANT CELL

WHAT IS THE ENDOMEMBRANE SYSTEM?

A series of interconnected organelles that communicate with one another

• Divides the eukaryotic cell into functional and structural compartments

• Connected directly (physically) or indirectly by vesicles (small membrane-bound sacs that transfer substances between parts of the system)

• Components

  • ER

  • Nuclear envelope

  • Golgi apparatus

  • Lysosomes

  • Vacuoles

  • Plasma membrane

WHAT IS THE ENDOPLASMIC RETICULUM (ER)?

• Extensive interconnected network (reticulum) of membranous channels and cisternae

• Each cisternae is formed by a single membrane that surrounds an enclosed space (ER lumen)

WHAT ARE THE 2 FORMS THAT ER OCCURS IN?

• Rough

• Smooth

WHAT IS ROUGH ER?

• Has many ribsomes attached to its outer surface

• Proteins that are made on ribosomes attach to the ER, enter the ER lumen, or become integrated into the ER membrane

• Chemical modifications occur in the ER lumen like the addition of carbohydrate groups to produce glycoproteins

• Proteins are delivered to other regions of the cells using small vesicles that form the ER

WHAT IS SMOOTH ER?

• Membranes have no ribosomes attached to their surfaces

• Converts drugs, poisons, and toxic by-products into substances that can be tolerated or more easily and removed from the body

WHAT IS THE GOLGI COMPLEX?

• Sorts proteins to ensure they are delivered to their final destination

• Consists of a stack flattened, membranous sacs (cisternae)

• Proteins from the ER enter the golgi on the cis face of the complex, delivered by transport vesicles that fuse with the membrane

• Proteins are chemically modified by removing segments, adding functional groups, lipids, or carbohydrate units

• Modified proteins exit from the trans face of the golgi in vesicles that bud off the membrane

• Proteins to be secreted from the cell are transported to the plasma membrane in secretory vesicles, which release their contents to the exterior by exocytosis

WHAT IS EXOCYTOSIS?

• Brings material OUT of the cell

• Proteins to be secreted from the cell are transported to the plasma membrane is secretory vesicles

• The vesicles release their contents to the exterior exocytosis

• The vesicle membrane fuses with their plasma membrane and becomes part of it

WHAT IS ENDOCYTOSIS?

• Brings material INTO the cell

• Brings molecules into the cell from the exterior

• The plasma membrane forms a pocket that bulges inward and pinches off into the cytoplasm as an endocytic vesicle

• Endocytic vesicles carry material to the golgi complex, lysosomes, or other destinations

WHAT ARE LYSOSOMES?

• Are small, membrane-bound compartments containing hydrolytic enzymes that digest complex molecules that cells recycles

• Are found in animals and plants

• Are formed by budding from the golgi complex by their hydrolytic enzymes are synthesized in the rough ER

• Are acidic (pH = 5), which is lower than cytosol (pH = 7.2)

• Lysosomal enzymes digest food molecules, worn out organelles (autophagy), and materials engulfed by phagocytes (cells of the immune system)

• In lysosomal storage diseases, one of the hydrolytic enzymes normally found in the lysosome is absent

WHAT IS THE MITOCONDRIA?

• Membrane-bound organelles where cellular respiration occurs’Cellular respiration breaks down energy-rich food molecules into water and carbon dioxide, converting energy into ATP

• Require oxygen to keep the process going

• In animals, breathing provides the oxygen needed for cellular respiration

• Has two membranes surrounding the inner soluble compartment called the mitochondrial matrix

WHAT ARE THE 2 MEMBRANES OF THE MITOCOHNDRIAL MATRIX ?

• Outer Membrane: Covers the organelle

• Inner Membrane: Expanded by folds called cristae

WHERE DOES ATP-GENERATING REACTIONS OCCUR IN?

• Cristae

• Matrix

WHAT IS THE ENDOSYMBIOSIS THEORY?

Explains that mitochondria and chloroplasts are thought to have developed from free-living prokaryotic cells

• Mitochondria: Developed from ingested prokaryotes capable of using oxygen for aerobic respiration

• Chloroplasts: Developed from ingested photosynthetic prokaryotes

• Symbiotic relationship: The prokaryotic ancestors of modern mitochondria and chloroplasts were engulfed by larger prokaryotic cells and lived together in a symbiotic relationship

WHAT ARE THE EVIDENCE SUPPORTING PROKARYOTIC ORIGIN OF MITOCHONDRIA AND CHLOROPLASTS?

• Morphology: Size and shape are similar to that of prokaryotic cells

• Reproduction: Divide by binary fission in the same way as prokaryotic cells

• Genetic Information: Contain their own DNA with genes essential for organelle function

•  Transcription & Translation: Contain separate set of transcription and translational machinery

• Electron Transport: Like prokaryotic cells, mitochondria and chloroplasts have electron transport chains

• DNA Sequence Analysis: Has shown that these organelles belong on the bacterial branch of the tree of life

WHAT IS THE NUCLEAR ENVELOPE AND ER FORMATION?

The nuclear envelope is a double membrane that surrounds the nucleus and is connected to the endoplasmic reticulum (ER), which forms a network of membranes throughout the cell

WHAT IS VERTICAL GENE TRANSFER?

Genetic inheritance from one generation to the next within a species

WHAT IS HORIZONTAL GENE TRANSFER?

Genetic inheritance between unrelated species and has shaped evolution of eukaryotic cells

WHAT ARE MICROTUBULES?

• Outer diameter of 25 nm

• Assembled from dimers of α- and β-tubulin proteins.

  Dimers are organized head-to-tail, giving microtubules polarity (+ and − ends)

  Dynamic structures that change length by adding or removing tubulin dimers

• Provides tracks for vesicles to move between the cell interior and plasma membrane

• Separate and move chromosomes during cell division (mitosis)

• Help move some eukaryotic cells

WHAT IS THE CENTROSOME (CELL CENTRE)

• Serves as the MTOC (microtubule-organizing centre) in many animal cells

• Organizes microtubule arrays involved in mitosis and holding organelles in position

• Made up of two short, barrel-shaped structures called centrioles, which are formed from microtubules

WHAT ARE MOTOR PROTEINS?

• Eukaryotic cell movements are generated by motor proteins that push or pull against:

  • Microtubules: dyneins and kinesins

  • Microfilaments: myosins

• One end of a motor protein is attached to a cell structure, such as a vesicle

• The other end has reactive groups that “walk” along a microtubule or microfilament, using ATP for energy

HOW DOES A KINESIN MOLECULE “WALKS”?

WHAT ARE INTERMEDIATE FILAMENTS?

• Are intermediate in size between microtubules and microfilaments (8-12 nm)

• Assembled from a large and varied group of intermediate filament proteins

• Intermediate filaments occur singly, in parallel bundles, and in interlinked networks

• Provides structural support in many cells and tissues and are tissue-specific in their protein composition

WHAT ARE MICROFILAMENTS?

• Are thin (5-7 nm diameter) protein fibres assembled from actin subunits

• Has polarity (+ and – ends). 

• Has many structural and locomotor functions:

  • Components of contractile elements in muscle fibres

  • Involved in cytoplasmic streaming, which transports nutrients, proteins, and organelles in animal and plant cells, and is responsible for amoeboid movement

  • Divide the cytoplasm when animal cells divide

WHAT ARE FLAGELLA AND CILIA?

• Are elongated, motile structures that extend from the cell surface

• Cilia are shorter than flagella and occur in greater numbers

• Movements of a flagellum propel a cell through a watery medium, and cilia move fluids over the cell's surface

WHAT IS EUKARYOTIC FLAGELLUM?

WHAT ARE FLAGELLAR AND CILIARY BEATING PATTERNS?

WHAT ARE THE SPECIALIZED STRUCTURES OF PLANT CELLS?

• Structures found in plants cells but not in animal cells:

  • Chloroplasts

  • A large central vacuole

  • Plant cells

• Chloroplasts also occurs in algal protists and cell walls in algal and fungi

WHAT ARE PLASTIDS?

• Chloroplasts are yellow-green plastids; the sites of photosynthesis in plant cells

• Other plastids are colorless and store starch (or other molecules), while others are brightly colored with pigments such as carotenoids or lycopene

• All plastids contain DNA genomes and molecular machinery for gene expression and the synthesis of proteins on ribosomes

• Some of the proteins within plastids are encoded by their genomes; but most are encoded by nuclear genes and are imported into organelles from the cytosol

WHAT ARE CHLOROPLASTS?

• Are surrounded by an outer membrane and an inner membrane which completely enclose an interior aqueous/soluble compartment, the stroma

• Within the stroma is a third membrane system consisting of flattened, closed sacs (thylakoids)

• In higher plants, thylakoids are stacked, forming grana

• Thylakoid membranes enclose a soluble compartment called thylakoid lumen

• Thylakoid membranes contain chlorophyll, a green pigment that absorbs light energy that is ultimately converted into chemical energy in photosynthesis

WHAT ARE CENTRAL VACUOLES?

• Are large vesicles that perform specialized functions unique to plants

• In a mature plant cell, 90% or more of the cell volume may be occupied by one or more large central vacuoles

• The membrane that surrounds the central vacuole, the tonoplast, contains transport proteins that move substances into and out of the central vacuole

WHAT ARE THE FUNCTIONS OF CENTRAL VACUOLES?

• Supports cell structure

• Store salts, organic acids, sugars, storage proteins, pigments, and, in some cells, waste products

• Pigments concentrated in the vacuoles produce colors of many flowers and fruits (Ex. Red-blue anthocyanin pigments)

• Contain enzymes that break down biological molecules

• Contains molecules that provide chemical defends against pathogenic organisms

WHAT ARE THE FUNCTIONS OF CELL WALLS?

• Support individual cells

• Protect cells against invading bacteria and fungi

WHAT DO CELL WALLS PRIMARILY CONSIST OF?

Cellulose

• Long polymers of glucose; the most abundant macromolecule of Earth

• Aggregate into bundles called microfibrils

• Embedded in a network of other polysaccharides

WHAT IS THE WALLS OF ADJACENT CELLS HELD TOGETHER BY A LAYER OF POLYSACCHARIDES (PECTIN) CALLED?

The Middle Lamella

WHAT ARE THE PRIMARY AND SECONDARY CELL WALLS THAT ARE PERFORATED BY CALLED?

Plasmodesmata

• Plasma membrane-lined channels that connect the cytosol of adjacent cells

• Allows ions and small molecules to move directly from one cell to another through the cytosol

WHAT ARE THE 3 SPECIALIZED STRUCTURE THAT ORGANIZES LEVELS OF ANIMAL CELLS?

• Individual cell adhesion molecules: Bind cells together

• Cell junctions: Seal the spaces between cells and provide direct communication between cells

• Extracellular matrix (ECM): Supports and protects cells and provides mechanical linkages between tissues

WHAT ARE CELL ADHESION MOLECULES?

• Are glycoproteins in the plasma membrane that bind to specific molecules on other cells

• Organize animal cells into tissues and organs

• Cancer cells often lose these adhesions, allowing them to break loose and migrate to new locations

• Cell junctions reinforce cell adhesions and provide avenues of communication

WHAT ARE ANCHORING JUNCTIONS?

• Form bottom like spots or belts that run entirely around cells, “welding” adjacent cells together

• Are most common in tissues that are subject to stretching, shear, or other mechanical forces

WHAT ARE DEMOSOMES?

Are anchoring junctions with intermediate filaments that anchor the junction in underlying cytoplasm

WHAT ARE ADHERENS JUNCTIONS?

Are anchoring junctions with microfilaments as anchoring cytoskeleton component

WHAT ARE TIGHT JUNCTIONS?

Are regions of tight connections between membranes of adjacent cells

• Seal spaces between cells in cell layer that cover internal organs, outer surface of the body, or layers that line internal cavities and ducts

• Is formed by direct fusion of proteins on the outer surfaces of plasma membranes of adjacent cells

WHAT ARE GAP JUNCTIONS?

Are open direct channels that allow ions and small molecules to pass directly from one cell to another

• Hollow protein cylinders embedded in plasma membranes of adjacent cells connect the cytoplasm of one cell with the cytoplasm of the next

• Communicate between cells within a tissue, such as heart muscle tissue