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What is Cell Theory
- 1. All organisms are composed of cells.
- 2. Cells are the smallest living things.
- 3. Cells arise only from pre-existing cells.
- 4. All cells today represent a continuous line of descent from the first living cells.
Surface area-to-volume ratio
- as a cell increases in size, the
- volume increases 10x faster than the surface area as a result there is far less
- surface available to service each unit of volume.
can resolve structures that are 200nm apart.
can resolve structures that are 0.2nm apart.
lack a membrane-bound nucleus.
genetic material is present in the nucleoid (not Nucleus)
Two types of prokaryotes
Prokaryotic cells possess
- *genetic material (DNA) in the
- *plasma membrane
- *cell wall
- *flagellum(long threadlike structure) to move
- *Pili (used for exchange of genetic information between cells.)
- *no membrane-bound organelles
Are more complex that prokaryotic cells. They compartmentalize many cellular functions within organelles and the endomembrane system. They posses a membrane-bound nucleus and a cytoskeleton.
- * A delicate sheet of molecules encasing all living cells.
- *All plasma membranes have the same basic structure of proteins embedded in a sheet of lipids, called Fluid Mosaic Model.
- * It is also a selective barrier that allows passage of oxygen, nutrients and waste
- *Composed of a phospholipid bilayer
*stores the genetic material of the cell in the form of multiple, linear chromosomes
surrounded by a nuclearenvelopecomposed of 2 phospholipid bilayers
DNA is wound tightly around proteins to form compact units chromatin
a special structure for proteinsynthesis. There are different forms of ribosomes. There is a special form called ribosomal RNA, rRNA found in the region within thenucleus called Nucleolus.
- *a series of membranes throughout the cytoplasm
- *divides cell into compartments where different cellular functions occur
- 1. endoplasmic reticulum
- 2. Golgi apparatus
- 3. lysosomes
is an extensive system of internal membrane. The term Endoplasmic means within the cell and Reticulum means little net, hence the name.
Rough endoplasmic reticulum (RER)
- • membranes that create a network of
- channels throughout the cytoplasm
• attachment of ribosomes to the membrane gives it a rough appearance
• synthesis of proteinsto be secreted, sent to lysosomes or plasma membrane
Smooth endoplasmic reticulum (SER)
-relatively few ribosomes attached
-synthesis of membrane lipids
-detoxification of foreign substances
-flattened stacks of interconnected membranes- looks like pancakes stacked one on top of the other.
- -functions in the collection, packaging, and distribution of molecules manufactured in the
- -The rough ER, smooth ER and Golgi work together as an endomembrane transport
- system in the cell
- -Organelles that arise from Golgi
-Membrane bound vesicles containing digestive enzymes to break down macromolecules
-Destroy cells or foreign matter that the cell has engulfed by phagocytosis
-Are the recycling centers of the cells
- structures with various functions depending on the cell type
- are different types of vacuoles:
- -central vacuole in plant cells functions as a
- storage center for large amounts of water, and other materials such as sugars,
- ions, and pigments.
-contractile vacuole of some protists
-vacuoles are basically for storage
Mitochondria: Powerhouses of the Cell
- -organelles present in all types of
- eukaryotic cells
- -contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP
- -found in all types of eukaryotic cells- surrounded by 2 membranes
- -smooth outer membrane
- -folded inner membrane with layers called cristae (singular Crista)
- -matrix is within the inner membrane
- - intermembrane space is located between the two membranes
- - contain their own DNA
- -organelles present in cells of plants and some other eukaryotes but not found in animal or fungal cell
- -contain chlorophyll for photosynthesis
- -surrounded by 2 membranes
- -thylakoids are membranous sacs within the
- inner membrane
- -grana are stacks of thylakoids
- -proposes that eukaryotic organelles evolved through a symbiotic relationship
- -one cell engulfed a second cell and a symbiotic relationship developed
- -mitochondria and chloroplasts are thought to have evolved this way
Much evidence supports that Mitochondria and chloroplasts evolved through endosymbiosis such as
- -have 2 membranes
- -possess DNA and ribosomes
- -are about the size of a prokaryotic cell
- -divide by a process similar to bacteria
Cytoskeleton: Interior Framework of the Cell
- -network of protein fibers found in all eukaryotic cells
- -supports the shape of the cell
- -keeps organelles in fixed locations
- -helps move materials within the cell
Cytoskeleton fibers include
- -Actin filaments(microfilaments) –
- are long, thin fibers that occur in bundles or mesh-like networks. Consists of
- two chains of globular actin monomers twisted to form a helix. Found throughout
- the cell but are highly concentrated inside the plasma membrane. Responsible
- for cellular contractions, crawling, “pinching” during cellular division, and
- formation of cellular extensions
-Microtubules – are hollow tubes. Composed of a globular protein tubulin that occurs as α tubulin and β tubulin. Assembly brings these two together as dimers and the dimers arrange themselves in rows. Regulation of microtubule assembly is under control of a microtubule organizing center (MTOC): the main MTOC is called a centrosome. Provide organization to the cell and move materials within the cell
-Intermediate Filaments- are between actin filaments and microtubules in size. Are rope‑like assemblies of fibrous polypeptide. Some support the nuclear envelope; others support plasma membrane and form cell‑to‑cell junctions
- •Centrioles are short cylinders with a ring
- pattern of microtubule triplets.
- •In animal cells and most protists, centrosome contains two centrioles lying at right angles to each other.
- •Plant and fungal cells have the
- equivalent of a centrosome, but they do not contain centrioles.
- •Centrioles serve as basal bodies for cilia and flagella.
- Cell movement takes different forms.
- -Crawling is accomplished via actin filaments and the protein myosin. White blood cells exhibit this ability.
- -Swimming with Flagella & Cilia
- -Cilia can be arranged in rows on the surface of a eukaryotic cell to propel a cell forward.
This is a mixing process in which molecules move from higher concentration to lower concentration i.e. down the concentration gradient e.g. Drop a red dye in a jar of water, the dye will move about randomly from the region where the dye is abundant to a region where it is scarce. Eventually, the dye will achieve a state of equilibrium, when the jar is completely red. This simply means there no net movement of the molecules toward a particular direction but individual molecules are still in motion and there is no net change in direction.
Osmosis is the process by which water moves across a cell membrane down its concentration gradient.
- Remember water is polar.
- Ions and Polar molecules cannot cross the very nonpolar environment found in the lipid core of the membrane phospholipid bilayer.
Interestingly, water is able to freely cross the plasma due to specialized water channels called aquaporins that span across the membrane.
•are the molecules dissolved in a solution e.g. sugar
•is a liquid or gas that dissolves a solid, liquid, or gaseous solute, resulting in a solution. The most common solvent in everyday life is water.
•is a mixture of molecules dissolved in water. The concentration of all molecules dissolved in a solution (the solutes) is called osmotic concentration of the solution.
is a description of the relative solute concentration in a solution as compared to another solution. Also the ability of a solution to cause osmosis across a cell membrane.
•a solution of the same concentration of solutes as the cell. A solution surrounding a cell that contains a lower concentration of solutes than the does the cell.
- •A solution surrounding a cell that
- contains a lower concentration of solutes than the does the cell.
•solution surrounding a cell that contains a higher concentration of solutes than does the cell.
•the process of engulfing materials by folding the plasma membrane around it, forming a vesicle. When the material is an organism e.g. a bacterium or some other fragments of organic matter, the process is called Phagocytosis (cell eating) But when the material is a liquid, it is called Pinocytosis (cell drinking)
•is the process of discharging materials from vesicles at the cell surface. Proteins and many other molecules are secreted from the cells in small pockets called secretory vesicles whose membranes fuse with the plasmamembrane thereby releasing their contents to the cell surface.
•is the ability of the cell to control what enters and leaves the cell through the plasma membrane. The plasma membrane has proteins that act as transporters or channels for certain molecules (e.g. ions).
is the mechanism of transport by which molecules move freely through channels in order to equalize the concentration of such molecules on both sides of the membrane. Selective transport of materials across the membrane is achieved by facilitated diffusion and active transport.
•is the transport of molecules across the plasma membrane from high concentration to low concentration with the help of carriers. Since the substances move along the direction of their concentration gradients, energy is not required.
For example, polar molecules and charged ions dissolved in water can not diffuse freely across cell membrane due to its hydrophobic lipids.
A kind of transport wherein ions or molecules move against a concentration gradient, which means movement in the direction opposite that of diffusion – or – movement from an area of lower concentration to an area of higher concentration. Hence, this process will require expenditure of energy, and the assistance of a type of protein called a carrier protein.