Ch 2 Flashcards
What are cells?
the basic structural and functional unit of all multicellular organisms
what are the two major compartments of a cell
the cytoplasm and the nucleus
what does the cytoplasm contain?
- organelles - little organs
- cytoskeleton (microtubules, intermediate filaments, and actin filaments)
- inclusions
- cytoplasmic matrix - aqueous Gell with various solutes
cells of different types use similar mechanisms to perform basic functions like….
protein synthesis and energy transformation
what are specific functions identified with…
specific structural components and domains
what are membranous organelles?
membrane-limited compartments
what is the plasma membrane?
a lipid bilayer, 8-10 nm thick with two electron dense layers and an electron lucent intermediate layer q
what is the plasma membrane composed of
- phospholipids
- cholesterol
- integral membrane proteins
- peripheral membrane proteins
- lipid rafts
the plasma membrane participates in many___
physiological and biochemical activities
What is a lipid raft?
micro domains with high concentrations of cholesterol and glycosphingolipids
what are the various functions of membrane proteins?
- pumps
- channels
- receptors
- linkers
- enzymes
- structural proteins
what proteins are used to help the plasma membrane undergo remodeling to form vesicles?
- clathrin
- caveolins
- dynamin
What are signaling pathways initiated by?
the binding of primary messengers to receptors
What are the two types of vesicular transport?
- endocytosis
- exocytosis
what does endocytosis do?
bring molecules and other substances into the cell
what does exocytosis do?
where synthesized molecules and other substances leave the cell
what is endocytosis associated with?
the formation and budding of vesicles from the plasma membrane
- produces a coated vesicle (clathrin coat)
what is exocytosis associated with?
the fusion of vesicles originating from intracellular organelles with the plasma membrane
- primary secretary modality
what are pinocytosis and phagocytosis
What are two processes of phagocytosis
immune responce to a bacterium
non biological material
What are the steps in an immune response to a bacterium?
- The bacterium is surrounded by antibodies attached to the bacterial surface antigens.
- Fc receptors on the surface of the plasma membrane of phagocytic cells recognize the Fc portion of the antibodies.
- This interaction triggers rearrangement of the actin cytoskeleton.
- Depolymerizations and repolymerizations of actin filaments produce temporary projections of the plasma membrane called pseudopodia.
- They surround the phagocytosed particle, forming a phagosome.
- By targeted delivery of lysosomal enzymes, a phagosome matures into a lysosome that digests its phagocytosed contents.
What are the steps in phagocytosis of nonbiological materials?
- Nonbiologic materials such as inhaled carbon particles, inorganic dusts, and asbestos fibers, as well as cellular debris resulting from inflammation, are internalized without involvement of antibodies and Fc receptors.
- These particles are bound to multiple receptors on the plasma membrane.
the steps in the exocytosis pathway
- Newly synthesized proteins are made in the rough endoplasmic reticulum (rER).
- After initial post-translational modification, proteins are delivered in COP-II-coated vesicles to the Golgi apparatus.
- In the Golgi apparatus, proteins undergo further modification, sorting, and packaging.
- The final secretory product is transported to the plasma membrane in vesicles formed from the trans-Golgi network (TGN).
- Retrograde transport occurs between Golgi cisternae, mediated by COP-I-coated vesicles.
- two distinct pathways of exocytosis recognized
what are the two distinct pathways of exocytosis
Constitutive secratory pathway
- Proteins leave the cell immediately after synthesis.
-Few secretory vesicles accumulate in the cytoplasm.
Regulated Secretory pathway
- Protein secretion is regulated by hormonal or neural stimuli.
- Secretory proteins are concentrated and stored transiently in secretory vesicles within the cytoplasm.
- Upon appropriate stimulation, secretory vesicles fuse with the plasma membrane and release their contents.
What is Botulinum Toxin?
it is produced by the anaerobic bacterium Clostridium botulinum, and it blocks neuromuscular transmission
There are ____ distinct serotypes (____) of botulinum toxins, with each toxin ___________ at different sites.
This prevents the________ of the neurotransmitter __________ from the neuromuscular terminal and depolarization of muscle cell.
- seven
- (A to G)
- cleaving the SNARE proteins
- release
- acetylcholine
What is an endosome?
Tubulovesicular structures involved in endocytosis
where are endosomes located?
in the peripheral cytoplasm sort internalized proteins
how are early and late endoscopes formed?
- early endosomes are formed de novo from the invagination of the plasma membrane, forming vesicles containing cell surface proteins and soluble content from the extracellular space
- Late endosomes are near the Golgi and nucleus
what happens to early endosomes as they mature?
they become more acidic and sink into deeper regions of the cytoplasm to become late-sorting endosomes or late endosomes
how do early and late endosomes contrast each other?
they differ in;
1. cellular localization
2. morphology
3. state of acidification and function
what are early endosomes?
Initial sorting compartment for vesicles formed by endocytosis or pinocytosis.
what are late endosomes?
Intermediate compartment for further sorting and preparation for lysosomal degradation.
what can happen to endosomes
they may become lysosomes
what are exosomes?
Small, endosome-derived, membrane-bound vesicles released into extracellular space
what is the role of exoxomes?
they carry nucleic acids, proteins, lipids, and metabolites
they also act as mediators for cell communicaiton
where are there high concentrations of exosomes?
they are present in all body fluids, including blood, lymph, cerebrospinal fluid, vitreous body, interstitial fluids, saliva, breast milk, amniotic fluid, semen, and urine
what do exosomes released form cancer cells promote?
- neoplasia
- tumor growth
- metastasis formation
- resistance to therapy
how do cancer cells induce neoplastic transformation of other cells?
through the transfer of their miRNA cargo
what are exosomes important for?
vaccine development
- exosome-based mRNA vaccines that drive the expression of the immunogenic COVID-19 viral nucleocapsid and spike proteins have been tested
What are lysosomes?
Small organelles containing digestive enzymes break down macromolecules, particles, and organelles.
What type of enzymes are lysosomes rich in and give some examples?
hydrolytic enzymes such as proteases, nucleases, glycosidases, lipases, and phospholipases
How are lysosomes formed?
from late endosomes
What do lysosomes do?
Degrade macromolecules derived from endocytic pathways and the cell itself (autophagy)
what is special about the membrane of lysosomes?
resistant to hydrolysis
what else do lysosomes contain?
proton (H + ) pumps that transport H+ ions into the lysosomal lumen, maintaining a low pH (~4.7)
Where are lysosome membrane proteins synthesized?
in the rER and have a specific lysosomal targeting signal
how are some cells like osteoclasts (involved in bone resorption) and neutrophils (involved in acute inflammation) special?
they may release lysosomal enzymes directly into the extracellular space to digest components of the extracellular matrix
what are the four different types of cellular processes for internalizing and degrading substances?
- receptor-mediated endocytosis
- pinocytosis
- phagocytosis
- autophagy
- Receptor-Mediated Endocytosis (Red Pathway)
Purpose: Uptake of specific molecules (e.g., ligands) into the cell.
Steps:
1. Ligands bind to specific receptors on the cell surface.
2. The plasma membrane invaginates, forming a vesicle containing the receptor-ligand complex.
3. Vesicles are delivered to early endosomes for sorting.
4. Contents may be sent to late endosomes and eventually degraded in lysosomes.
- Pinocytosis (Red Pathway)
Purpose: “Cell drinking” – the uptake of extracellular fluid and small dissolved solutes into the cell.
Steps:
1. The plasma membrane invaginates non-specifically to form vesicles containing extracellular fluid.
2. Vesicles fuse with early endosomes, where contents are sorted and transported.
- Phagocytosis (Blue Pathway)
Purpose: “Cell eating” – engulfment of large particles (e.g., bacteria or cellular debris).
Steps:
1. The plasma membrane surrounds the particle, forming a phagosome.
2. The phagosome fuses with lysosomes to form a phagolysosome.
3. The contents are degraded by lysosomal enzymes.
- Autophagy (Green Pathway)
Purpose: Degradation of damaged organelles or cytoplasmic components.
Steps:
1. A damaged organelle (e.g., mitochondrion) is enclosed by a double membrane, forming an autophagosome.
2. The autophagosome fuses with a lysosome, forming an autolysosome.
3. The contents are degraded by lysosomal enzymes, recycling cellular components.
what are proteasomes?
- Non-lysosome protein degradation
- proteins tagged with ubiquitin
what is the rough endoplasmic reticulum (rER)?
-Interconnected, membrane-limited, flattened sacs (cisternae) with ribosomes.
- Involved in protein synthesis.
- Site of post-translational modifications and protein folding.
how is rER stained?
with the basic dye is called ergastoplasm
where is the rER most highly developed?
in secretory cells
what do free ribosomes do?
synthesize proteins that will remain in the cell as cytoplasmic structural or functional elements
what are nissl bodies?
The large basophilic bodies of nerve cells
what do nissl bodies consist of?
both rER and large numbers of free ribosomes
what is the smooth endoplasmic reticulum (sER)
Short, anastomosing tubules without ribosomes.
what is the sER involved in?
- lipid metabolism and synthesis
- steroid synthesis
- calcium sequestration.
- biogenesis of peroxisomes.
- detoxification of the xenobiotics
what do cells with large amounts of smooth endoplasmic reticulum may exhibit?
distinct cytoplasmic eosinophilia (acidophilia) – making it pink when stained
what does sER tend to be like?
tubular rather than sheet-like
what is sER also called in skeletal and cardiac muscle?
sarcoplasmic reticulum
where is lots of sER found
in the liver
- uses Cytochrome P450
what is the Golgi apparatus?
Series of stacked, flattened cisternae and tubular extensions.
what does the Golgi do?
- post-translational modification
- sorting
- packaging of proteins.
what networks does the Golgi apparatus contain?
cis-Golgi network (CGN) and a trans-Golgi network (TGN).
the Golgi can be ________ form the rER
close or away
what is unique about the Golgi apparatus regarding staining?
it is well developed in secretory cells and does not stain with hematoxylin or eosin
what travels through the Golgi stacks an undergoes a series of post translational modifications?
proteins and lipids
what is posttranslational modifications?
involve remodeling of N-linked oligosaccharides previously added in the rER
what does mitochondria look like?
Two membranes, inner and outer, that delineate distinct compartments.
- Inner membrane forms cristae.
what does mitochondria do?
- Generate ATP via the citric acid cycle and oxidative phosphorylation.
- Regulate apoptosis.
what has Video microscopy confirmed about mitochondria?
it can change location and shape
what is the endosymbiosis theory?
Mitochondria evolved from aerobic bacteria that were engulfed by eukaryotic cells
mitochondrial DNA is ______ in nature and is inherited exclusively from the ______
- haploid
- mother
Mitochondria possess a complete system for _______, including the synthesis of their own
- protein synthesis
- ribosomes
Mitochondria are present in all cells except _______ cells and _________
- red blood
- terminal keratinocytes
what are peroxisomes?
Single-membrane-bound organelles with oxidative enzymes
what are peroxisomes involved in?
- lipid metabolism
- fatty acid breakdown
- detoxification
how can peroxisomes be formed?
de novo (sER) or from preexisting peroxisomes (division)
where are peroxisomes most abundant?
in liver and kidney cells,
although peroxisomes are found in almost all cells in the body
what does the catalase in peroxisomes carefully regulate?
the removal of ROIs, thus protecting the cell
what are the types of nonmembranous organelles?
- microtubules
- actin filaments
- intermediate filaments
- centrioles and microtubule-organizing centers (MTOC)
- basal bodies
what are microtubules?
Elongated polymeric structures composed of α-tubulin and β-tubulin.
where do microtubules grow from?
γ-tubulin rings within the microtubule organizing center (MTOC).
what are microtubules involved in and what do they do?
intracellular transport and cell structure
-Serve as guides for motor proteins.
microtubules are dynamic structures that undergo ___________
polymerization and depolymerization.
what are the functions of microtubules?
- Intracellular vesicular transport (i.e., movement of secretory vesicles, endosomes, and lysosomes). Microtubules create a system of connections within the cell, frequently compared with railroad tracks originating from a central station, along which vesicular movement occurs.
- Movement of cilia and flagella
- Attachment of chromosomes to the mitotic spindle and their movement during mitosis and meiosis
- Maintenance of cell shape, particularly its asymmetry
- Regulatory effect on cell elongation and movement (migration)
what else are microtubules associated with?
motor proteins
what are the two types of motor proteins?
- Dyneins - move towards plus end - away from MTOC
- Kinesins - towards minus end - toward MTOC
what do actin filaments look like?
Thinner, shorter, and more flexible than microtubules.
what are actin filaments composed of?
polymerized G-actin molecules that form F-actin.
what are actin filament involved in?
cell-to-extracellular matrix attachment and cell movement.
where are actin filaments seen?
muscle cells
what are actin filaments regulated by?
actin-binding proteins (ABPs).
what are intermediate filaments?
Heterogeneous group of cytoskeletal elements.
how many classes are there of intermediate filaments?
Six major classes based on gene structure, protein composition, and cellular distribution.
what do intermediate filaments do?
Provide mechanical strength and support to cells.
Intermediate filaments also do not typically _______________ in the continuous manner characteristic of most microtubules and actin filaments.
disappear and re-form
what are the first to classes of intermediate filaments?
classes 1&2 keratins
what are centrioles?
paired, short, rod-like cylinders that form the focal point of the MTOC.
what is Microtubule-Organizing Centers (MTOC)
the region where most microtubules are formed.
Centrioles provide ________ for cilia and flagella and align the __________ during cell division.
- basal bodies
- mitotic spindle
what does the MTOC contain?
centrioles and pericentriolar material, including γ-tubulin.
Centrioles and Microtubule-Organizing Centers (MTOC):
Duplication is synchronized with cell cycle events.
- duplicated during S phase
what are basal bodies?
Structures derived from centrioles necessary for the assembly of cilia and flagella.
- “Each cilium requires a basal body.”
what are inclusions
Non-living components of the cytoplasm.
what are examples of inclusions?
glycogen and lipid droplets.
what does glycogen appear as with some stains?
a “purple haze”
what do lipid droplets appear as in some sections?
empty holes
what is the cytoplasmic matrix (cytosol)?
Aqueous gel containing solutes.
what does the cytosol include?
inorganic ions and organic molecules.
The cell controls the concentration of _______ within the matrix, which influences ____________.
- solutes
- metabolic activity
