Cytology

Question 1

What are the three main destinations of proteins modified in the Golgi apparatus?

Answer 1

• Secretory Vesicles
• Lysosomes
• Constitutive Pathway

Question 2

What is the function of secretory vesicles?

Answer 2

• Act as a storage mechanism for proteins and other products
  
  • Mature vesicles fuse with the membrane space in response to a signal and release into the extracellular space
    
    • Pancreatic Acinar Cells
      
      • Certain digestive enzymes

Question 3

Golgi Apparatus Structure

Answer 3

• Structure:
  
  • Series of stacked, flattened, membrane limited cisternae and tubular extensions
  • Stacked cisternae are polarized
    
    • Side receiving vesicles is termed the cis Golgi
    • Middle cisternae are termed the medial Golgi
    • Cisternae from which proteins are transported from are termed the trans Golgi

Question 4

Smooth Endoplasmic Reticulum (SER)

Answer 4

• Tubular in Structure
• Functions:
  
  • Lipid and Steroid Metabolism (should be first thing you think of)
    
    • Membrane Recycling and Formation
  • Detoxification
    
    • Prominent in Liver Cells
  • Glycogen Metabolism
  • Sarcoplasmic Reticulum
    
    • Calcium

Question 5

Describe the structure and function of the nuclear envelope.

Answer 5

• Two membranes
  
  • Outer nuclear membrane
    
    • Continuous with the RER
    • Ribosomes commonly attached the the cytoplasmic surface
    • Perinuclear space is continuous with the lumen of the RER
  • Inner nuclear membrane
    
    • Distinct from the ER in that it is able to bind chromatin and lamins
  • Nuclear lamina- formation of lamins (specialized intermediate filaments) attached to the inner membrane that represents the skeleton of the nucleus
  • Nuclear pores
    
    • Allow communication between the nucleus and cytoplasm
    • 70-80 nm openings with a complex structure of protein spokes projecting into the lumen of the pore to the central plug
      
      • Allows free passage of small molecules <9 nm
      • Large particles actively transported

Question 6

Describe the structure and function of the cell nucleus.

Answer 6

• Nucleus is a large membrane limited organelle - 5-10 micrometers
  
  • Contains the genome in eukaryotes (chromatin)
  • Contains machinery for DNA replication and RNA transription and processing
  • Contains one or more nucleoli
  • Surrounded by a double membrane called the nuclear envelope

Question 7

Describe the structure and function of peroxisomes.

Answer 7

• Structure:
  
  • Small membrane bound organelles - 0.5 micrometers
• Function:
  
  • Contain oxidative enzymes and catalase
    
    • Used to converse ethanol to acetaldehyde
    • Used to oxidize very long chain fatty acids
  • Catalase degrades hydrogen peroxide produced as part of the oxidation reactions

Question 8

Describe the structure of membrane proteins.

Answer 8

• Structure (2 Types)
  
  • Integral
    
    • Embedded into hydrophobic core
    • Transmembran proteins
  • Peripheral
    
    • Not embedded in hydrophobic core
    • Attach either to integral proteins or hydrophilic heads of the membrane lipids

Question 9

Describe the structure of biological membranes.

Answer 9

• Composed of lipids, proteins, and carbohydrates
• Thin 7nm
• Lipid Bilayer
  
  • Amphipathic
    
    • Uncharged hydrophobic tails (associate w/ each other at the center)
    • Polar hydrophilic heads (face outwards towards aqueous environment)
  • Spontaneously form bilayer in aqueous environment
  • Hydrophobic center acts as anchor for membrane proteins that can move within the bilayer
• Highly permeable only to small uncharged molecules

Question 10

Golgi Apparatus Function

Answer 10

• Posttranslational Modification of Proteins
  
  • Glycosylation/Deglycosylation (Adding and removal of sugars)
  • Adding and Removal of Sulfate
  • Adding and Removal of Phosphate
• Sorting and Packaging of Proteins
  
  • Secretory Vesicles
  • Lysosomes
  • Constitutive Pathway

Question 11

What are the three types of lysosomes? Differentiate between each of them.

Answer 11

• Primary Lysosomes
  
  • Have not yet received substrates for digestion
• Secondary Lysosomes
  
  • Result from fusion of primary lysosomes with their target
• Lipofuscin Granules (Residual Bodies)
  
  • Senescent lysosomes w/ undigestible material
    
    • Found in adrenal cortex

Question 12

Describe the structure and function of actin filaments.

Answer 12

• Important role in cell movement, shape, and organelle transport
• Exists in 2 forms
  
  • G-actin
    
    • soluble monomeric globular protein
  • F-actin (Thin filaments)
    
    • Polymerization of G-actin filament into a double stranded helical filament
      
      • Occurs head to tail creating polarity
    • Form a thin sheath beneath the cytoplasm = cortex
      
      • Resist cell deformation, transmit forces, and restrict the movement of organelles
      • Reinforces the plasma membrane and restricts lateral motion of some integral proteins
    • Interacts with myosin to generate force and movement
      
      • Myosin = motor protein associated with thin filaments

Question 13

List the three major types of cytoskeletal filaments.

Answer 13

1. Actin
2. Microtubules
3. Intermediate

Question 14

Describe the function of ribosomes.

Answer 14

• Ribosomes catalyze protein synthesis
  
  • Exist as either:
    
    • Free Ribosomes
      
      • Contribute to the majority of synthesis of cellular proteins
        
        • Except those synthesized by RER Ribosomes
      • Synthesize 80% of mitochondrial proteins
    • Mitochondrial Ribosomes
      
      • Synthesize 20% of mitochondrial proteins
    • RER Ribosomes
      
      • Synthesize proteins in Golgi Apparatus, Lysosomes, Secretory Granules, and Plasma Membrane

Question 15

Describe the structure and function of the nucleolus.

Answer 15

• Is a small area inside the nucleus where rRNA is processed and assembled into ribosomal subunits
  
  • Contains 3 distinct regions
    
    • Fibrillar Centers
      
      • Contain DNA loops with rRNA genes and transcription factors
    • Dense fibrillar component (pars fibrosa)
      
      • Contains ribosomal genes that are being translated and large amounts of RNA
    • Granular component (pars granulosa)
      
      • Site for ribosome assembly and is made of densely packed clusters of pre-ribosomal particles

Question 16

Differentiate between euchromatin and heterochromatin.

Answer 16

• Euchromatin
  
  • Contains transcriptionally active DNA
    
    • Loosely packed
  • Appears lightly stained
  • Prominent in metabolically active cells
• Heterochromatin
  
  • Contains transcriptionally inactive DNA
    
    • Tightly packed
  • Appears dark when stained
  • Prominent in metabolically inactive cells

Question 17

What is a Polysome?

Answer 17

A polymer or ribosomes attached to a single mRNA molecule.

Question 18

Describe the strucure and function of intermediate filaments.

Answer 18

• Intermediate in thickness
  
  • Strong, but flexible
  • Exhibit no polarity
• Provide mechanical support for cells
  
  • Form bundles between the plasma membrane and the nucleus
    
    • Spread tensile forces
    • Maintain cell architecture
    • Act as a cocoon when cell is damaged
    • Anchor ion channels

Question 19

What is the function of lysosomes?

Answer 19

• Involved in digesting material taken up from outside the cell
• Degradation of senescent organelles
  
  • Low pH and hydrolytic enzymes
• Mannose-6-phosphate is the signal that directs proteins from the trans Golgi to the lysosome

Question 20

Describe the structure of ribosomes.

Answer 20

• RNA/protein particles
  
  • 15-25 nm in size
  • Consist of a large and small subunit
    
    • Each subunit consists of one or more rRNA and many specialized proteins

Question 21

Describe the three types of transport membrane proteins.

Answer 21

• Channel Proteins
  
  • Form “pores” that allow passage of small molecules by passive diffusion
• Carrier Proteins
  
  • “Drag” other molecules across membrane by hiding them in the cleft of the protein
• Pumps
  
  • Use ATP to pump ions against a concentration gradient

Question 22

Describe the higher order structures formed by microtubules.

Answer 22

• Include cilia, flagella, centrioles, and microtubules-organizing centers
  
  • Core of cilia and flagella
    
    • Formed by the axoneme which is compose of 9 doublets and a central pair of microtubules
      
      • Dynein arms attached to A-tubule of each doublet interact with the B-tubule of the next doublet by walking along it bending the axoneme
  • Base of cilia and flagella
    
    • Centriole/basal body
      
      • 9 triplets of microtubules NO central pair
  • Microtubule organizing center (MTOC)
    
    • Found in most cells except neurons and erythrocytes
    • Consists of two centrioles
      
      • Which again are formed by 9 triplets of microtubules

Question 23

Describe the structure of the endoplasmic reticulum.

Answer 23

• Series of membrane-formed anastomosing tubules and cisternae
• Subdivided into SER (tubules) and RER (cisternae)

Question 24

Describe the structure and function of microtubules.

Answer 24

• Stiff, non-branching, cylindrical polymers made of two polymerized globular proteins alpha-tubulin and beta-tubulin
  
  • Polymerized side to side and head to tail creating polarity (plus end and minus end)
  • Have two types of motor proteins (ATP
    
    • Dyneins
      
      • Move towards minus end
      • Involved in beating of cilia and flagella
    • Kinesins
      
      • Move towards plus end
• Functions
  
  • Organelle and vesicle movement
    
    • e.g. movement of materials along the axon of a neuron
  • Formation of mitotic spindle and chromosome movement (Mitosis and Meiosis)
  • Beating of cilia and flagella

Question 25

Rough Endoplasmic Reticulum (RER)

Answer 25

• Ribosomes bound to its surface
• Formed mostly of Cisternae
• Functions:
  
  • Synthesis of proteins for Golgi apparatus, lysosomes, plasma membrane, and exportation out of the cell

Question 26

Describe the constitutive pathway?

Answer 26

• Pathway by which proteins that are not destined for lysosomes or secretory granules are sorted into small vesicles that are transported directly to the plasma membrane
  
  • Example: integral membrane proteins and proteins secreted continuously (collagen)

Question 27

What are lamins and what makes them distinct?

Answer 27

Lamins are specialized intermediate filaments the disassemble during mitosis and reassemble when mitosis ends

Question 28

Describe the structure and function of the mitochondria.

Answer 28

• Function to produce ATP through oxidation of pyruvate and fatty acids
  
  • Are also “sensors” of cell health and initiate apoptosis
  • Regulate concentration of certain ions like Ca2+ role shared with SER
• Display a variety of shapes
  
  • Spheres, Rods, Elongated Filaments, and Spirals
• Variety of sizes
  
  • 1-5 micrometers
• Two membranes
  
  • Outer mitochondrial membrane
    
    • Porous (anion channels)
  • Inner mitochondrial membrane
    
    • Thinner than outer membrane
    • Highly folded cristae
      
      • Steroid-producing cells may have tubulovesicular appearance (these cells are very active)
    • Contain many of the enzymes involve in energy production
• Intermembrane space
  
  • pH and ionic composition similar to cytoplasm
  • Location of Cytochrome C
    
    • Initiates apoptosis
• Matrix
  
  • Contains soluble enzymes
    
    • Krebs cycle
    • DNA transcription
  • Mitochondrial DNA
  • Mitochondrial ribosomes
  • rRNA, mRNA, tRNA
  • Electron dense granules
    
    • Store Ca2+

Question 29

Explain are two of the common severe disorders caused by abnormal function of peroxisomes?

Answer 29

• Zellweger Syndrome
  
  • Congenital disease
    
    • Caused by mutation of the proteins responsible for proper transport of peroxisomal enzymes from the cytoplasm
      
      • Peroxisomes thus lack the necessary enzymes
  • Affects brain development
    
    • improper formation of the myelin sheath
  • No Cure
    
    • Patients die before 6 months of age
• Adrenoleukodystrophy
  
  • Inherited X-linked disorder
  • Disrupts oxidation of very long chain fatty acids
    
    • Lipids accumulate in brain and adrenals
  • Results in progressive brain damage (dementia), failure of adrenal glands, and death

Question 30

List the major types of intermediate filaments and where they are found in the body.

Answer 30

• Lamins - Nucleus
• Keratins - Epithelial Cells
• Vimentin - Connective Tissue
• Desmin - Muscle Cells
• Glial Fibrillary Acidic Protein - Nervous System
• Neurofilaments - Neurons

Question 31

Describe the three functions of membrane proteins.

Answer 31

• Functions (3 Types)
  
  • Transport
    
    • Selectively allow charged and polar molecules to cross membrane
  • Receptors
    
    • Bind w/ specific molecules that results in a transformational change serving as a signaling cascade
  • Structural
    
    • Serve to attach the cell to its surroundings
      
      • Link to the cytoskeleton and extracellular proteins