Cell Theory History

Cell Theory Development

• All living things are composed of cells.
• Cells are the basic structural and functional units of life, exhibiting life's characteristics.
• Robert Hooke used a simple microscope to observe cork slices, noting compartments resembling cells.
• Anton van Leeuwenhoek improved the microscope, observing detailed sketches of pond water, blood, and other substances.
• He was the first to see individual cells and recognize them as living units, calling them animicules
• Mathias Jakob Schleiden concluded that all plants consist of cells in 1838.
• Theodor Schwann concluded that all animals consist of cells in 1839.
• Cells walls of plants were scientifically recognized to have lifeless contents, while inside the contents were labeled as "life".
• Protoplasm defines living materials.
• Better microscopes helped distinguish regions of protoplasm.
• The nucleus contains genetic information.
• Cytoplasm denotes the fluid portion of protoplasm surrounding the nucleus, containing organelles.

Cells and Organisms

• The cell is the smallest unit capable of performing life's activities.
• Prokaryotes and many eukaryotes exist as single cells.
• Plants and animals typically consist of millions of cells and described as multicellular organisms.
• Multi-cellular organisms undergo cellular modifications that cause them to do specialized functions.
• It is essential that cells should exchange materials and energy within the environment.

Basic Cell Types

• All cells share three traits outer membrane, cytoplasm, and genetic material.
• Eukaryotic cells contain their genetic material inside a nucleus.
• Prokaryotic cells contain their genetic material inside a nucleoid.
• Cells show variability in appearance, metabolism, structure, and biochemical traits.
• Eukaryotic cells make up plants, fungi, protozoa, animals, and algae.
• Prokaryotic cells that lack a nucleus are structurally simple and lack many organelles, making them up Bacteria and Archaea.

Cell Size

• Archaea and bacteria are smaller than eukaryotic cells.
• Prokaryotic cells range from 1 to 2 micrometers.
• Eukaryotic cells generally measure 10 to 100 times larger.
• Adequate material transfer through the membrane becomes difficult as cells enlarge, which limits cell size.
• As a cell's volume increases, it is the outer membranes surface area increases more quickly.
• A cell's metabolic needs increase alongside volume increase.
• Satisfaction declines due to surface area limitations
• Chicken egg yolks are single cells with an active part on a small surface area and are considered exceptions.

Cellular Membrane Structures

• Membranes consist of phospholipid and protein sheets.
• Fluid-mosaic model explains cellular membrane construction.
• It contains two layers of phospholipid molecules.
• Phospholipid molecules contain one water-soluble phosphate end (hydrophilic) and the one insoluble end has fatty acids (hydrophobic).
• Phospholipid molecules form a double-layered sheet in water.
• Hydrophilic parts of the molecules face away from it.
• The phospholipid bilayer refers to water-soluble portions who face each other.

Cellular Membrane Structure Details

• Two layers of phospholipids form an oily fluid where things can move laterally throughout the bilayer.
• It contains proteins and other molecules are embedded throughout the bilayer(mosaic).
• Some membrane proteins traverse the membrane.
• Others protrude from both surfaces
• Proteins transport, attach, and mark membrane bound lipids.
• Cholesterol stabilizes the membrane and provides a flexible structure in hydrophobic regions.
• Carbohydrates, located outside of cells, involve a binding reaction to regulate molecules.

Cell Organization

• Small organization in cells allows the cell to maintain appropriate internal conditions or homeostasis .
• Cells are typically selective barriers which allow contents to maintain an optimal environment for the contents inside the cell.
• This selectivity is seen in organelles with metabolic environments.
• DNA is concentrated in a small area.

Organelles Composed of Membranes

• Plasma Membrane
• Endoplasmic Reticulum
• Golgi Apparatus
• Lysosomes
• Peroxisomes
• Vacuoles and Vesicles
• Nuclear Membrane
• The Endomembrane System Interconversion of Membranes
• Energy Converters—Mitochondria and Chloroplasts

Plasma Membranes

• The outer limiting boundary of all cells that serves as a barrier for cell contents and external environment.
• composed of bilayers.
• It facilitates metabolic activities, movement of molecules, identification, attachment and transmission signals or signal transduction.

Plasma Membrane Specifics

• Reactions occur within the membrane on both sides.
• Cells gain nutrients, and excretes waste.
• Carbohydrates, proteins, and lipids serve a magnitude of functions.
• Surface proteins enable recognition.
• They attach to chemicals, bacteria and viruses.
• Signal transduction can be achieved by detecting it and transmitting it internally.
• Hormones help with this.

Endoplasmic Reticulum

• Tubes and folded membranes run throughout cell.
• It provides cells with surface area to perform various biochemical reactions.
• Rough ER has ribosomes for synthesis.
• Pancreas cells can synthesize large quantities of proteins because of extensive rough ER
• Extensive smooth ER allows for detoxification reactions.
• Liver cells are an example of this detoxification process.

Golgi Apparatus Details

• There are about 5 to 20 membranous sacs with several different functions.
• First: it modifies molecules shipped to it from elsewhere in the cell
• Second: manufactures some polysaccharides and lipids
• Third: packages molecules within sacs.
• Vesicles carry molecules across, and contain proteins.
• Then they bind with Golgi apparati which release contents into it for them to surface which helps produced the finished product.
• The apparatus also creates many vesicles.
• Some are transported within the cell and combine with the membrane; others migrate into the plasma where they create substances like cellular components of mucus, proteins, or mucus.

Lysosomes

• Contain enzymes that digest macromolecules. (proteins, lipids, nucleic acids)
• Golgi apparatus produces it.
• The acidic pH of approximately 5 allows them to only work in certain conditions.
• Cytoplasm at pH7 is used to keep them inactive and will do no damage when being moved.
• EX: Paramecium, where food vacuoles allow lysosomes to break down.

Lysosomes Detailed

• Lysosomes destroy disease causing micro-organisms that have been surrounded by membranes.
• White blood cells use it to engulf dangerous bacterias.
• It digests old organelles.

Peroxisomes

• ER membranes formulate peroxisomes instead of Golgi.
• It helps contain catalase enzymes that break apart peroxide and digests fatty substances.
• Finally, it helps synthesize lipids/steroids and nerve cell function by synthesizing lipids.
• Zellweger Syndrome is related to it.

Vacuoles and Vesicles

• Vacuoles and vesicles are membrane-enclosed stores for substance relocation storage.
• Vacuoles are large sacs.
• Protozoa, for example, uses its vacuoles to expel excess water from the cytoplasm.
• Vesicles are smaller sacs.

Nuclear Membranes

• Separates the genetic contents from the rest of the cell.
• There are cytoplasmic/nuclear differences, and contains of two bilayers.
• Contains nuclear pore complexes that move molecules like RNA into cytoplasm.

Endomembrane System and Interconversion

• Structures all membranes in cells contain made of phospholipid with associated proteins and other molecules.
• Membranous organelles change from one structural state to another through a constant swapping of pieces
• Plasma and the endoplasmic reticulum are always exchanging the membrane to grow as new walls, resulting in lager surfaces to become plasma membranes.

Energy Converting Organelles - Mitochondria

• They contain a small bag with a larger bag stuffed inside.
• The larger bag features folds called cristae.
• The cristae contain respiratory proteins which release ATP to oxygen through food.
• Unique enzymes are used though (mDNA).
• Energy needs drives mitochondria requirement.

Energy Converting Organelles - Chloroplast

• The organelle is sac-like and contains chlorophyll.
• The organelle uses photosynthesis to generate energy using sunlight (sugar).
• There are folded membranes called thylakoids located inside.
• Thylakoids collect together in grana piles surrounded by the stroma, which is the area with little chlorophyll.

Non-membranous Organelles

• Ribosomes
• Cytoskeleton
• Centrioles
• Cilia and flagella
• Inclusions

Ribosomes

• Ribonucleic acid and proteins combined.
• They are the site for protein production.
• They consist of two subunits
  • Large subunits
  • Small subunits
• Ribosomes are free floating within the cytoplasm for proteins and attached to the endoplasmic reticulum for synthesis.
• Active creation protein cells like the liver have ribosomes in heavy amounts.

Cytoskeleton

• It consists of three elongated linked proteins
• Microtubules, microfilaments, and intermediate filaments form cytoskeleton by connecting to the inside of the plasma membranes.
• The cytoskeleton is responsible for shaping, movement, and support in the cell.

Cytoskeleton Functions

• Microtubules and microfilaments move chromosomes during division.
• Also they can move organelles from place to place.
• Further, they can activate upon pressure by touch.

Centrioles

• Centrioles are composed of microtubule that are arranged at an angle.
• They consist of nine groups of microtubules cylinder short cylinder arrangements.
• Located in a region called centrosome within the nuclear membrane in several types of cells for organization of fibers from cell division.

Cilia and flagella

• These are projections similar to hairs which contains microtubule surrounded in place by pressure membranes.
• Nine microtubules center the arrangement.
• Flagella are longer, and few can undulate.
• Cilia are numerous, and can move back and forth.
• Paramecium exhibit coordinated cilia movement.
• Trachea also contains it, moving mucous.

Inclusions

• Are collections of components that do not posses specific structure.
• Are not necessary for cell life just for site of store.
• It might store certain granules, sulfur, or even oil droplets.

Nuclear Components

• Chromatin makes up of nuclear contents for the nuclear regions, that divides into chromosomes in the nucleus.
• Chromatin = DNA + proteins.
• The double layer protects and holds the contents through many pores that helps transport substances like RNA to the ribosomes for a nucleus in an area of ribosome synthesis.

Exchange Thru Membranes

• Materials enter and exit through the following six main methods:

1. Diffusion
2. Osmosis
3. Facilitated diffusion
4. Active transport
5. Endocytosis
6. Exocytosis

Diffusion

• Moving molecules across a concentration with high concentration to low.
• Movements equal in all directions create equilibrium.
• Diffusion is at a high rate when molecules are small and its faster when there is a larger concentration gradient.

Diffusion In Cells

• Diffusion plays an important role in all exchanged materials.
• Red blood cells have a lower concentration of oxygen, and is transported along the membrane to facilitate all oxygen flow and blood.

Diffusion in Cells Detailed

• Cell membranes have different degrees of permeability.
  • They only allow for molecules to pass through.
  • Size, chemical composition and solubility contribute. Diffusion is the process of side concentration. This process does not require an energy source and is passive.

Osmosis

• Water molecules are exchanged in selectively permeate membranes.
• Easily diffuses throughout cell
• This occurs when different water membrane differences occur to solute concentration, and that makes some become more osmotic.

Osmosis in Cells

• Balanced cells can stay balanced.
• To much balance can upset this if the environment is not managed correctly.

Osmosis Balanced - Detailed

• Having a cell at less water is hypertonic.
• Having more is hypotonic.
• Having equal is isotonic.

Transporting Molecules - Controlled Methods

• Cells can not depend on it always due to different sizes and concentration differences in cells.

Facilitated Diffusion Details

• Accomplished via either of the following : carrier proteins or ion channels.
• It follows a concentration with no energy required .
• Involves proteins
• Carrier.
• Ionic Channels.
• Attached carrier proteins, allow for molecules to move when it attaches and releases upon delivery back to state.
• Ionic channels contain controlled gates without being attached.

Active Transport

• The process that includes diffusion for molecules on membrane up their concentration gradient.
• This form needs external transport proteins with pumping characteristics, and require an energy input.
• EX: sodium

Endocytosis and Exocytosis

• Exocytosis transport material outside.
  • This happens when the plasma membrane joins the sacks and releases their contents (ex. mucus)
• Endocytosis transfer the content to the inside.
  • The cell is able to carry large molecules into the cytoplasm.

Endocytosis and Exocytosis Details

• Phagocytosis is engulfing large particles with food and materials inside a vacuole that white blood cells can digest.
• Pinocytosis is for cells that consume and drink liquids in a non selective manner.
• Lastly, there are cells from receptor-mediated endocytosis using them inside an external vacuole