Introduction to the Cell Part 2 Flashcards
Structure and function of the Plasma Membrane:
- lipid bilayer with embedded proteins
- interface between the cell and its environment
- functions as a permeability barrier.
Characteristics of plasma membrane lipids:
- amphipathic molecules:
- polar hydrophilic groups (exteriors)
- hydrophobic aliphatic side chains (interior)
The two classes of membrane proteins:
- Integral membrane proteins
- Peripheral membrane proteins
Integral Membrane Proteins:
- Proteins that traverse the entire width of the plasma membrane and have three domains:
- Cytoplasmic (hydrophilic)
- Membrane-spanning (hydrophobic)
- External (hydrophilic)
Peripheral membrane proteins:
- Proteins non-covalently attached to the cytoplasmic/extracellular regions of the plasma membrane.
Fluid structure is a characteristic of what part of the cell?
- Plasma membrane.
- many proteins and lipids can move laterally within the membrane.
When the plasma membrane is mechanically split, the internal (protoplasmic face) has more proteins associated with it. Why?
- Proteins associated with the P-face are stabilized by attachment to cytoskeleton of the cell.
How are transmembrane proteins stabilized?
- interaction with cytoskeletal proteins (actin, spectrin) that stabilize their position in the plasma membrane.
Hereditary spherocytosis:
- inherited disorder characterized by defects in RBC membranes.
- RBCs more spherical, less deformable, and more susceptible to destruction by phagocytic cells in the spleen.
- Mutations in spectrins are major cause.
What is the major cause of hereditary spherocytosis?
Mutations in spectrins.
Spectrins:
- cytoskeletal proteins that associate with several membrane proteins to stabilize the biconcave shape of normal erythrocytes (RBCs).
In the absence of spectrin, RBCs are more:
- more spherical (less biconcave)
- more sensitive to mild hypertonic solution
The 4 functions of membrane proteins:
LERT
-
linker/anchor molecules
- i.e. those that mediate interaction with intracellular cytoskeletal proteins (spectrin)
- enzyme function
- receptors that interact with signaling molecules
- transporter molecules governing the passage of substances into and out of the cell
Brush Border:
- a dense collection of microvilli protruding from the plasma membrane of some cells.
- e.g. small intestine - aids in nutrient absorption
Microvilli:
- extend as minute fingerlike projections from the top of the cells (apical surface)
- increase the absorptive surface
Junctional Complex:
- lateral borders of cells that allow cells to interact with one another.
- dark black line in-between cells in image.
Glycocalyx:
- consists of glycolipids, glycoproteins and proteoglycans.
- addition of the above occurs during biosynthesis in the RER.
- fuzzy coat is seen at the tips of the microvilli
- “Enteric Surface Coat” on slide
What is this an image of?
- cross section of individual microvilli
What supports the structure of individual microvilli?
- an internal cytoskeleton of actin filaments
Within the core of each microvillus are filamentous structures composed primarily of the structural protein:
- actin
- only seen via EM
Actin in microfilaments extends downward to terminate in a filamentous complex at the top of the cells called the:
- terminal web
- contains actin filaments as well as intermediate filaments, another cytoskeletal element.
What is the arrow pointing to?
- brush border formed by microvilli of intestinal cells
- LM
What are the arrows on the left side of the image pointing to?
- locations of the junctional complex
- i.e. TERMINAL BARS
- reddish dots at the tip of the arrowheads
Zonula occludens:
- tight or occluding junctions
Zonula adherens:
- intermediate junction, or “belt desmosome”
Macula adherens:
- arranged in circles in the lowermost position of junctional complexes
For most cells (except red blood cells), there are two major intracellular compartments.
What are they?
- nucleus
- cytoplasm
What is the top left arrow pointing to?
nuclear envelope
What is the arrow second from top pointing to?
nucleolus
What is the arrow third from the top pointing to?
euchromatin
What is the bottom arrow pointing to?
heterochromatin
The two components of the cytoplasm:
- cytosol
- organelles
Four components of the cytosol:
- cytoplasm outside the organelles
- free ribosomes/polysomes
- inclusions (lipids and glycogen)
- cytoskeleton (actin and tubulin)
Actin:
- an abundant cytoskeletal protein that contributes to microfilaments that are found throughout the cell:
- cytoskeleton (microfilaments)
- microvilli
- muscle cells (interact with myosin)
What is the bar structure and barrel structure in the image?
centrioles
Microtubules:
- component of the cytoskeleton
- small cylindrical structures widely distributed through the cell
- composed of the protein tubulin
Microtubules form the structural basis of:
- centrioles
- cilia
- mitotic spindles
Endoplasmic reticulum (ER):
- extensive cytoplasmic membrane system containing sites of protein and lipid synthesis and calcium storage.
- rough ER and smooth ER
Smooth ER:
- no ribosomes
- lipid and steroid biosynthesis
- detoxification of harmful substances
- metabolism of a variety of drugs
- site of storage for calcium
What kind of cell is this?
- cell that synthesizes steroid hormones
- abundance of smooth ER (SER), mitochondria (M) and lipid droplets
- relatively few rough ER
What is the arrow pointing to?
- ribosome of rough ER
The rough ER is continuous with:
the nuclear envelope
Rough ER:
- ribosome-studded membrane-bounded space
- surface ribosomes synthesize proteins that will be secreted
- lysosomal proteins and membrane proteins retained
Proteins synthesized on the rough ER are transported to the:
- golgi complex where they will be sorted to their ultimate destination
Golgi Complex:
- composed of flattened sacs of membrane.
- two networks:
- cis Golgi network
- trans Golgi network
- Secretory vesicles bud from the trans Golgi network.
____ are used to transport material between the Golgi cisternae.
vesicles
Cis Golgi:
- Forms the face directed toward the rough ER.
- Proteins enter the Golgi at the cis face.
Trans Golgi:
- Maturing face directed toward the secretory granules and the apical or peripheral cytoplasm.
- Proteins leave the Golgi at the trans face in the trans-Golgi network.
Constitutive Secretion:
- continual secretion of proteins.
- few, if any, secretory granules actually accumulate in the cell because of rapid release.
- e.g. plasma cells
Regulated Secretion:
- non-continuous secretion of proteins.
- large numbers of granules accumulate in cell.
- secretion initiated by an external stimulus.
Exocytosis:
- secretion of substance from a cell
Endocytosis:
- process of cells taking in a substance
- triggered by receptors in the cell membrane binding to signalling molecules or nutrients
- vesicle forms surrounded by coat proteins to form a coated pit and coated vesicle
Coated pit:
- pit that forms during endocytosis when a cell receptor binds to a molecule/nutrient that triggers endocytosis
Steps in endocytosis pathway:
- Signaling molecule/nutrient binds to receptors in the cell membrane.
- Receptor-ligand complexes enter cell via vesicle formation; stimulated by association of coat proteins with the cytoplasmic lipid layer.
- Ligand-receptor complexes and the coat proteins form a coated pit, which rapidly detaches from the surface to form a coated vesicle.
- Internalized vesicles fuse with early endosome.
Endosomes:
- organelles consisting of vesicles containing material that has entered the cell.
- In early endosomes, receptors and ligands are separated, and the receptors often recycle to the surface.
What is this an EM image of?
mitochondrion
note cristae
Mitchondria:
- flexible structures
- can change their shape and move throughout the cytoplasm with the aid of cytoskeletal proteins.
- surrounded by a double membrane
- Inner layer of the membrane is folded into a series of shelves or cristae.
What is this an image of?
- mitochondria in muscle cells
- note large number of cristae
- require a lot of energy
What are the circular images in this image?
- mitochondria in liver cells
- note low number of cristae
- don’t need much energy
What is the letter “G” referring to in this image?
glycogen granules/inclusions
Most mitochondrial proteins come from the:
- cytosol
- NOT from the rough ER and Golgi pathway.
What does the black arrow in this cell point to?
a lipid droplet (cell inclusion)
Lysosomes:
- enzymes active at acidic pH.
- sites of intracellular digestion.
- process molecules that enter the cell from the external environment
- degrade worn-out intracellular organelles as well as entire cells following phagocytosis
How is the acidic pH of lysosomes maintained?
- an ATP-driven proton pump in the lysosomal membrane
What structures are in this image?
lysosomes of eosinophil cells
What is this an image of?
peroxisomes
Peroxisomes:
- membrane bound organelles involved in hydrogen peroxide metabolism and multiple other important metabolic processes.
- Because of high enzyme concentrations, they usually have dense material in their matrix that forms a crystalline core.
Mitochondira Function:
- synthesize ATP via oxidative phosphorylation
- participate in apoptosis
