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Questions and Answers
What is the role of COP II in cellular transport?
What is the role of COP II in cellular transport?
How does the Smooth Endoplasmic Reticulum differ from the Rough Endoplasmic Reticulum?
How does the Smooth Endoplasmic Reticulum differ from the Rough Endoplasmic Reticulum?
Which of the following statements is true about retrograde transport?
Which of the following statements is true about retrograde transport?
What occurs to cargo when it reaches its target during transport?
What occurs to cargo when it reaches its target during transport?
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Where do free ribosomes primarily reside and what do they produce?
Where do free ribosomes primarily reside and what do they produce?
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What specific modifications occur within the GER cisterna?
What specific modifications occur within the GER cisterna?
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How do coatomers function in the cellular transport process?
How do coatomers function in the cellular transport process?
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Which of the following is NOT true regarding the functions of COP I?
Which of the following is NOT true regarding the functions of COP I?
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What structures are involved in the formation of cilia?
What structures are involved in the formation of cilia?
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What is the composition of the axoneme in cilia?
What is the composition of the axoneme in cilia?
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What is the function of the perinuclear cisternal space?
What is the function of the perinuclear cisternal space?
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Which process is referred to as ciliogenesis?
Which process is referred to as ciliogenesis?
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What comprises the nuclear envelope?
What comprises the nuclear envelope?
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What differentiates kinocilium from stereocilium?
What differentiates kinocilium from stereocilium?
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How does the axoneme originate?
How does the axoneme originate?
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Which type of integral membrane protein is primarily responsible for transmitting signals in response to external stimuli?
Which type of integral membrane protein is primarily responsible for transmitting signals in response to external stimuli?
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What role do basal bodies play in relation to cellular structures?
What role do basal bodies play in relation to cellular structures?
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What function is a canal (channel) protein NOT typically responsible for?
What function is a canal (channel) protein NOT typically responsible for?
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Which of the following integral membrane protein types is involved in energy-consuming processes?
Which of the following integral membrane protein types is involved in energy-consuming processes?
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Which type of membrane transport mechanism does NOT require energy?
Which type of membrane transport mechanism does NOT require energy?
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Which integral membrane protein type would be most closely related to immune reactions?
Which integral membrane protein type would be most closely related to immune reactions?
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What type of integral membrane protein provides structural support and facilitates interactions between the cytoskeleton and extracellular matrix?
What type of integral membrane protein provides structural support and facilitates interactions between the cytoskeleton and extracellular matrix?
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Which type of integral membrane protein can act as a catalyst for biochemical reactions within the membrane?
Which type of integral membrane protein can act as a catalyst for biochemical reactions within the membrane?
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What is the main role of constitutive proteins in the plasma membrane?
What is the main role of constitutive proteins in the plasma membrane?
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Where does transcription occur within the cell?
Where does transcription occur within the cell?
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What is the initial form of mRNA before post-transcriptional modifications?
What is the initial form of mRNA before post-transcriptional modifications?
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What signifies the target destination of an amino acid during protein synthesis?
What signifies the target destination of an amino acid during protein synthesis?
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Which component interacts with the translocator during the process of signal peptide transfer?
Which component interacts with the translocator during the process of signal peptide transfer?
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During translation, what reads the genetic code of the mRNA?
During translation, what reads the genetic code of the mRNA?
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Which option correctly describes the nature of codons in the genetic code?
Which option correctly describes the nature of codons in the genetic code?
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What happens to the signal peptide after it performs its function?
What happens to the signal peptide after it performs its function?
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What is formed as a result of the translation process?
What is formed as a result of the translation process?
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What is the role of the nuclear localization signal in the transport of proteins to the nucleus?
What is the role of the nuclear localization signal in the transport of proteins to the nucleus?
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Which export mechanism is utilized for moving RNA and ribosomal subunits from the nucleus to the cytoplasm?
Which export mechanism is utilized for moving RNA and ribosomal subunits from the nucleus to the cytoplasm?
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What distinguishes the nucleolus from other cellular structures?
What distinguishes the nucleolus from other cellular structures?
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Which component of the nucleolus contains the DNA that holds rRNA genes?
Which component of the nucleolus contains the DNA that holds rRNA genes?
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What is the main function of the granular material in the nucleolus?
What is the main function of the granular material in the nucleolus?
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How are histones and lamin-like nuclear proteins transported to the nucleus?
How are histones and lamin-like nuclear proteins transported to the nucleus?
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Which part of the nucleolus is associated with ribosomal genes during transcription?
Which part of the nucleolus is associated with ribosomal genes during transcription?
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A nucleus can contain multiple nucleoli. What is the primary reason for this?
A nucleus can contain multiple nucleoli. What is the primary reason for this?
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What type of intermediate filament is vimentin categorized as?
What type of intermediate filament is vimentin categorized as?
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Which of the following structures is considered a microtubule organizing center?
Which of the following structures is considered a microtubule organizing center?
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How many globular dimeric tubulins make up each microtubule within a centriole?
How many globular dimeric tubulins make up each microtubule within a centriole?
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What composition is found in each triplet of microtubules within a centriole?
What composition is found in each triplet of microtubules within a centriole?
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What kind of cytokeratins are present in epithelial cells?
What kind of cytokeratins are present in epithelial cells?
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What role do centrioles play during cell division?
What role do centrioles play during cell division?
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Which of these types is NOT classified under intermediate filaments?
Which of these types is NOT classified under intermediate filaments?
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What connects cells in desmosomes?
What connects cells in desmosomes?
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Study Notes
Main Title: Histology
- Main topic is Histology
- Subtitle: The Ultrastructure of Cell
- Lecturer: Prof. Yeşim ULUTAŞ UĞUR M.D
Plasma Membrane (Cell Membrane)
- Essential for cell viability
- Dynamic structure
- Organized as a bilayered lipid
- Contains two electron-dense (dark) and one electron-lucent (light) layers
- 8-10 nanometers thick
- Contains embedded integral membrane proteins
- Has attached peripheral membrane proteins
- Defined as a modified fluid-mosaic model
Components of Plasma Membrane
- Cholesterol
- Protein
- Phospholipid
- Glycoprotein (forms glycocalyx)
- Glycolipid (forms glycocalyx)
- Hydrophobic (central) and hydrophilic parts
Glycocalyx
- Acts as a receptor
- Lipid rafts are areas with high concentrations of cholesterol & glycosphingolipids
- Lipid rafts facilitate protein movement within the membrane
- Lipid rafts support intercellular communication (signaling)
Integral Membrane Protein Types
- Receptor
- Linker
- Pump
- Canal (channel)
- Enzyme
- Constitutive protein
Transport Types at the Plasma Membrane
- Simple diffusion
- Structures constructed by proteins (voltage-gated, ligand-gated, mechanically gated channels)
- Mechanisms functioning through mobile molecules (passive transport (glucose), active transport (ion pumps))
- Endocytosis (taking into cytoplasm): pinocytosis (water & small molecules), phagocytosis (large molecules & structures), receptor-mediated (by binding to specific ligand)
- Exocytosis (giving out of cytoplasm): constitutive (works continuously), regulated (works only when needed)
Endocytosis at the Plasma Membrane
- Pinocytosis & phagocytosis are clathrin-independent
- Receptor-mediated endocytosis is clathrin-dependent
- A coated vesicle is formed
- Receptor interacts with clathrin via ADAPTIN
- DYNAMIN is the enzyme of the act
Exocytosis at the Plasma Membrane
- Sorting & packing in the Golgi apparatus
- Cargo is coated by a "coatomer"
- Targeting provided by COP I or COP II.
Transcytosis
- Diagram shows the process involves endocytosis, passing through the cell, and exocytosis, involving vesicle formations.
Endosome
- Early endosome: constructed by fusion of plasma membrane-originated vesicles, located near the plasma membrane, sorts internalized proteins, environment isn't acidic.
- Late endosome: acidic environment, located near Golgi apparatus & nucleus.
Lysosome
- Originates from endosomal structures
- Contains enzymes for degrading or destroying
- Lysosome-specific membrane proteins & lysosomal enzymes are added to the endosomal structure
- Endosomes & lysosome have mannose-6-phosphate receptors
- Mannose-6-phosphate is added to cargo before leaving Golgi apparatus
Lysosomal Membrane
- Cholesterol, lysobisphosphatidic acid
- Proton (H+) pumps
- Transport proteins
- LIMP (lysosomal integral membrane protein)
- LAMP (lysosome-associated membrane protein)
- LGP (lysosomal membrane glycoprotein)
Proteasome
- Ubiquitin added to cargo to target proteasome
- Contains ATP-dependent protease complexes
- Degrades abnormal proteins
- Recycles short-lived normal regulatory proteins for reuse
Peroxisome (microbody)
- Provides detoxification (hydrogen peroxide is toxic)
- Contains oxidative enzymes (peroxidases)
- Surrounded by membrane
- Provides fatty acid degradation
Endoplasmic Reticulum
- Granular endoplasmic reticulum (GER)
- Smooth endoplasmic reticulum (SER)
- Protein synthesis occurs in granular endoplasmic reticulum & ribosomes
- GER-containing cytoplasm is defined as ergacytoplasm
- Organized as membrane-limited continuous stacks
- Stacks have spaces called cisternae
Granular Endoplasmic Reticulum
- Cytoplasmic surfaces of cisternae contain ribosomes
- Ribosomes are protein synthesizing factories
- A single ribosome has small & large subunits
- Each subunit has ribosomal RNA (rRNA)
- A group of ribosomes is defined as a polysome
- Ribosomes are attached to Messenger RNA (mRNA) threads
- GER is continuous with the outer leaflet of the nuclear envelope
- Ribosomes can also be found freely within the cytoplasm
- Ribosomes bind to mRNA
- Peptide synthesis occurs
Post-translational Modification
- Within GER cisterna modifications occur through enzymes (folding by chaperons, glycosylations)
- After modifications, products move towards Golgi apparatus
Transport between GER & Golgi Apparatus
- Transport between GER & Golgi apparatus is provided by coatomers
- Anterograde transport is from GER towards Golgi apparatus (COP II)
- Retrograde transport is from Golgi apparatus backwards to GER (COP I)
- Cargo dissociates from its coatomer when it reaches its target
- Abnormal protein is carried back by COP I.
Free Ribosomes
- Some functional cytoplasmic elements are produced by free ribosomes residing within cytoplasmic matrix
Smooth Endoplasmic Reticulum (SER)
- Lacks ribosomes
- Stacks are tube-shaped
- Prominent in steroid-synthesizing cells, involved in lipid & glycogen metabolism; detoxification
- Neutralizes toxic substances by conjugation
- Named as sarcoplasmic reticulum in skeletal & cardiac muscles
- Stores calcium
- Regulates intracytoplasmic calcium concentration
Golgi Apparatus
- Organized as membranous stacks
- A polarized organelle
- GER-facing side is called cis-Golgi network (CGN)
- Cargo-releasing side is called trans-Golgi network (TGN)
- Between them is the medial-Golgi network
- Transport vesicles transfer cargo between cisternae
- Well-developed in secretory cells
- Functions of Golgi Apparatus: sorting & packing, secretion, membrane addition, post-translational modifications, adding phosphate/sulfate groups.
Mitochondrion
- Produces energy (ATP)
- Can be stained & displayed by Janus Green (vital dye)
- Divides & proliferates; its division cycle isn't synchronized with the cell cycle.
- Changes location & shape
- Acidophilic staining pattern
- Erythrocytes lack mitochondria
- Mitochondrion's evolution: aerobic bacteria, own genome, ribosomes, some constitutive proteins by itself, closed-type circular DNA, rRNA & tRNA provide translation of mRNA, via its DNA produces 13 self-enzymes, other mitochondrial proteins produced by free ribosomes.
Mitochondrial Membranes
- Outer & inner membranes
- Space between is intermembrane space
- Medium enclosed by inner membrane is matrix
- Inner membrane surrounds the matrix
- Transport traffic between mitochondrial membranes, needs energy & chaperon proteins.
- TOM complex: translocase of outer mitochondrial membrane
- TIM complex: translocase of inner mitochondrial membrane
Outer Mitochondrial Membrane
- Smooth membrane
- Contains canals (channels) named porins
- Porins are open to large uncharged molecules
- Contains receptors for proteins & polypeptides to be carried into the intermembrane space
- Has enzymes
Inner Mitochondrial Membrane
- Thinner than outer membrane
- Has folds defined as cristae
- Cristae extend towards matrix
- Cristae increase surface area; tubular-shaped in steroid-synthesizing cells; impermeable to ions
- Cardiolipin (a phospholipid) provides impermeability function
Inner Mitochondrial Membrane proteins
- Respiratory electron transport chain extends towards the matrix
- Contains tennis racket-shaped structures defined as elementary particles
- Elementary particles contain enzymes and provide ATP synthesis via oxidative phosphorylation.
Intermembrane Space of Mitochondrion
- ATP produced at inner membrane is used at intermembrane space
- Contains enzymes: cytochrome c (initiates apoptosis), kinases
Mitochondrial Matrix
- Contains matrix granules (calcium stores)
- Contains enzymes of citric acid cycle (Krebs) & beta oxidation of fatty acids
- Contains mitochondrial DNA, tRNA, & ribosomes
- Matrix reactions produce CO2 & NADH
- Functional configurations: orthodox (Cristae prominent, enlarged matrix, low oxidative phosphorylation) and condense (Cristae not prominent, condensed matrix, wide intermembrane space, high oxidative phosphorylation)
Cytoskeleton
- Microfilament
- Intermediate filament
- Microtubule
Microfilament
- Actin is the microfilament
- Actin has globular (ball-like) & filamentous (thread-like) forms
- When there is no need, it is in globular form within cytoplasm
- When in need, it polymerizes and changes into its filamentous form
- Filamentous actin is polarized structure
- Rapidly-growing end is called as positive end
- Slow-growing end is called as negative end.
Microfilament-Associated Proteins
- Actin-binding proteins
- Actin-bundling proteins
- Actin-severing proteins
- Actin-capping proteins
- Actin cross-linking proteins
- Actin motor proteins
Microfilament
- Mostly located near plasma membrane
- Form a terminal web immediately beneath apical cell surface to construct & stabilize cell shape
- Intracytoplasmic attachment point of junctional units
- Via polymerization provides movement of the cell.
Intermediate Filament
- Acts as cytoskeleton
- NOT polarized
- Specific to tissue
- Provides linkage between cytoplasm & extracellular environment (desmosomes).
- Intermediate Filament Types:
- Type 1 & Type 2: Acidic & basic cytokeratins (epithelial cells)
- Type 3: Vimentin (fibroblasts), Desmin (myocytes)
- Type 4: Neurofilaments
- Type 5: Lamins
- Type 6: Beaded-filaments
Intermediate Filament-Associated Proteins
- In links between neighboring cells, cells & extracellular matrix (desmosomes)
Centriole
- Found as two short sticks arranged at an angle of 90 degrees to each other
- Made up of 9 microtubule triplets
- Centriole pair is located within "pericentriolar material"
- Together, they are termed centrosome or microtubule-organizing center (MTOC)
- Centrioles give rise to basal bodies, sources of cilia & flagella
- Centrioles form mitotic & meiotic spindles during cell division
- Each microtubule within a centriole is composed of 13 globular dimeric tubulins
- Each microtubule triplet has 3 types of microtubules (A, B, & C)
- Neighboring microtubules share common parts
- A microtubule is a complete ring; B & C are incomplete, half moon-shaped
- They share some part of their neighbors' rings
- Basal Bodies & CilioGenesis: Cilium formation ("ciliogenesis")
- Basal bodies are involved in ciliogenesis
- Kinocilium is a movable process of the cell.
- Stereocilium is a non-moveable process of the cell & does not contain axoneme.
- Cilium has 2 central separated & 9 peripheral conjoined paired microtubules
- Structure is called as axoneme
- Axoneme originates from A & B microtubules of basal body.
Nucleus, Nucleolus, Nuclear Envelope
- Nucleoplasm: Material within the nuclear envelope excluding chromatin & nucleolus.
- Nucleolus: Not surrounded by a membrane. rRNA genes are found; site where ribosome production is initiated; rRNA synthesis takes place; ribosomal subunits are produced; can be more than one per nucleus. - Nucleolus Parts: Fibrillar center (DNA-containing rRNA genes), Fibrillar material (pars fibrosa) (Ribosomal genes are in the process of transcription), Granular material (pars granulosa) (site of ribosomal subunits formation) -The nucleolar content is totally called as nucleolonema
- Nucleolus is the site where the cell cycle is controlled
- Inclusion: remnants of metabolic activity, pigment granules (surrounded by plasma membrane), lipofuscin pigment, lipid droplets, glycogen granules, hemosiderin, crystalline inclusions
- Cytoplasmic matrix: electrolytes, metabolites, RNA, proteins
- Nuclear envelope: separates cytoplasm from nucleoplasm; composed of two membranes; perinuclear cisternal space is between outer & inner membranes, continues with GER cisternae; selective barrier – Nuclear Pores: Nuclear pore complex (NPC) is a cylinder (with 8 proteins-nucleoporins) through which ribosome subunits pass while moving into the cytoplasm.
- Outer nuclear membrane: structure is similar to endoplasmic reticulum membrane; has ribosomal docking proteins at the cytoplasmic face; polyribosomes are attached to these dockers
- Inner nuclear membrane: nucleoplasmic face is supported by intermediate filament network ("nuclear fibrous lamina"); lamina contains nuclear lamins & lamin-associated proteins; which are involved in DNA replication & transcription; during cell division lamina is disrupted, but reformed after the event.
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