Please enable JavaScript.
Coggle requires JavaScript to display documents.
A tour of the cell/membrane structure & function (Cell Fractionation,…
A tour of the cell/membrane structure & function
Cell Fractionation
Definition: The process used to separate cellular components while preserving individual functions of each component.
Steps:
The resulting mixture (homogenate) is centrifuged
The liquid above the pellet is poured into another tube and centrifuged at a higher speed for a longer period
homogenize cells in a blender to break them up
This process is repeated several times
. This “differential centrifugation” results in a series of pellets, each containing different cell components
Importance: If a biology student is trying to identify and study different components of the cell, Cell Fractionation could be useful
Surface Area vs. volume ratio
Being multicellular is better than just being a bigger cell, because as a cell increases in size, its volume grows proportionately more than its surface area
The need for a surface area large enough to accommodate the volume helps explain the microscopic size of cells
Larger organisms do not have larger cells than smaller organisms; instead, they just have more.
Types of microscopes & their different functions
Light Microscope (in a light microscope visible light is passed through a specimen and then through glass lenses)
Bright field (stained):
Staining with various dyes enhances contrast. Most staining procedures require that cells be fixed (preserved), thereby killing them
Phase contrast
Variations In density within the specimen are amplified to enhance contrast in unstained cells; this is especially useful for examining living, unpigmented cells
Bright field (unstained):
Light passes directly through the specimen. Unless the cell is naturally pigmented or artificially stained, the image has little contrast
Fluorescence:
Using a laser, this “optical sectioning” technique eliminates out-of-focus light from a thick sample, creating a single plane of fluorescence in the image. By capturing sharp images at many different planes, a 3-D reconstruction can be created.
Electron microscope: a microscope that uses a beam of accelerated electrons as a source of illumination
Scanning Electron Microscope (3D)
A microscope that uses an electron beam to scan the surface of a sample, coated with metal atoms, to study details on its topography
Transmission Electron Microscope (2D)
A microscope that passes an electron beam through very thin sections stained with metal atoms and is primarily used to study the internal structure of cells
Dissecting microscope (2D)
All organelles detailed structure and functions
plant cell (plasmodesmata)
Nucleus
Nucleolus
-Chromatin
Nuclear envelope
Golgi apparatus
Mitochondrion
Peroxisome
Plasma membrane
Cell Wall:
outer layer that maintains cell’s shape and protects cell from mechanical damage; made of cellulose, other polysaccharides and proteins
Wall of adjacent cell
Plasmodesmata
cytoplasmic channels through cell walls that connect the cytoplasms of adjacent cells
Chloroplast:
photosynthetic organelle
Cytoskeleton (microfilaments & microtubules)
Central vacuole
prominent organelle in older plant cells; functions include storage, breakdown of waste products, and hydrolysis of macromolecules; enlargement of the vacuole is a major mechanism of plant growth
Ribosomes
Rough & smooth endoplasmic reticulum
animal cell (tight junctions, desmosomes, and gap junctions)
Flagellum
motility structure present in some animal cells, composed of a cluster of microtubules within an extension of the plasma membrane
Centrosome:
region where the cell’s microtubules are initiated; contains a pair of centrioles
Cytoskeleton:
reinforces cell shapes; functions in cell movement; components are made of proteins
Microfilaments
Intermediate filaments
Microtubules
Microvilli:
: projections that increase the cell’s surface area
Peroxisome
organelle with various specialized metabolic functions; produces hydrogen peroxide as a by-product and then converts it into water
Mitochondrion:
organelle where cellular respiration occurs and most ATP is generated
Lysosome:
digestive organelle where macromolecules are hydrolyzed
Golgi apparatus:
: organelle active in synthesis, modification, sorting, and secretion of cell
Ribosomes
: complexes that make proteins; free in cytosol or bound to rough ER or nuclear envelope
Plasma membrane
membrane enclosing the cell
Nucleus:
Nucleolus:
non membranous structure involved in production of ribosomes, a nucleus has one or more nucleoli
Chromatin
material consisting of DNA and proteins
Nuclear envelope
: double membrane enclosing the nucleus, perforated by pores, continuous with ER
Endoplasmic reticulum:
network of membranous sacs and tubes; active in membrane synthesis (has a rough and smooth ER)
cellular membranes are fluid mosaics of lipids & proteins
in the fluid mosaic model, amphipathic proteins are embedded in the phospholipid bilayer
phospholipids move sideways within the membrane
The unsaturated hydrocarbon tails of some phospholipids keep membranes fluid at lower temperatures, while cholesterol helps membranes resist changes in fluidity
membrane proteins and lipids are synthesized in the endoplasmic reticulum and modified in the ER and Golgi apparatus
Active transport (uses energy)
electrochemical gradient drives ions across a membrane as they can have chemical gradient & an electrical gradient
cotransport (when a membrane protein enables the downhill diffusion of one solute to drive the uphill transport of the other
Na/K pump
Bulk Transport
exocytosis
transport vesicles migrate to the membrane (brings things out)
endocytosis
the cell takes in macromolecules by forming vesicles
Phagocytosis (cell eating)
Pinocytosis (cell drinking)
Receptor-mediated endocytosis
Passive Transport (no energy)
diffusion: the spontaneous movement of a substance down its concentration gradient from High to low
facilitated diffusion
a transport protein speeds the movement of water or a solute across a membrane down its concentration gradient. Ion channels facilitate the diffusion of ions across a membrane. Carrier proteins can undergo changes in shape that translocate bound solutes across a membrane
osmosis
a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one
simple diffusion
crosses through or between phospholipids
dialysis
Prokaryotes vs. Eukaryotes
Prokaryotes
Plasma membrane : membrane enclosing the cytoplasm
Cell wall: rigid structure outside the plasma membrane
Ribosomes: complexes that synthesize proteins
Glycocalyx: outer coating of many prokaryotes, consisting of a capsule or a slime layer
Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane)
Flagella: locomotion organelles of some prokaryotes
Fimbriae: attachment structures on the surface of some prokaryotes
Eukaryotes
DNA in a nucleus that is bounded by a double membrane
Membrane-bound organelles
Cytoplasm in the region between the plasma membrane and nucleus
membrane function/structure
membrane proteins:
Signal Transduction:
relay chemical messages as the signaling molecule may cause the protein to change shape allowing it to relay the message to the inside of the cell, usually by binding a cytoplasmic protein
Intercellular Joining:
membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junction or tight junctions.
Enzymatic Activity:
Several enzymes in a membrane are organized as a team that carry out Sequential steps in metabolic pathway
Cell-cell Recognition:
glycoprotein identification tags that are specifically recognized by membrane proteins of other cells
Transport
Provides a Hydrophilic channel across the membrane. Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane
Attachment to the cytoskeleton and extracellular matrix (ECM):
Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins.
structure:
The plasma membrane allows passage of enough oxygen, nutrients, and wastes to service the entire cell
The plasma membrane consists of a double layer (bilayer) of phospholipids with various proteins attached to or embedded in it
The hydrophobic parts of phospholipids and membrane proteins are found in the interior of the membrane, while the hydrophilic parts are in contact with aqueous solutions on either side.
Carbohydrate side chains may be attached to proteins or lipids on the outer surface of the plasma membrane.