Cell and Organelles

Question 1

Tissues vs. organs

Answer 1

• Tissues – group of cells with similar properties that perform specific function
o Epithelium
o Connective tissue proper
 Specialized – cartilage, bone, fat, blood
o Nerve
o Muscle
• Organs – structures comprised of different tissues that collectively carry out specific function

Question 2

plasma membrane structure and function

Answer 2

•	Plasma Membrane Structure – Fluid Mosaic Model
o	Unit membrane – phospholipid bilayer
o	Asymmetrical
o	Fluid
•	Plasma Membrane Function
o	Separate
o	Barrier
o	Transport/exchange
o	Constancy
o	Recognition

Question 3

phospholipid bilayer

Answer 3

o Amphipathic
 Nonpolar fatty acid hydrocarbon tails
 Polar charged head groups
o Asymmetrical
o Glycocalyx striated border = glycocalyx + microvilli
 Glycocalyx – carbohydrate chains that vary at the surface of the membrane

Question 4

cholesterol

Answer 4

– necessary ingredient for membranes
o Cholesterol stiffens the membrane and reduces the permeability
 Can be temporary or permanent
o Impairment in neuronal membranes indicated in Alzheimer’s and Autistic spectrum disorders
o Essential component of myelin
o Required for brain growth, differentiation, preservation
o Keeps membrane architecture stable
 Failures in homeostasis contribute to progressive neurodegeneration
 Participates in membrane raft microdomain composition – sites of protein signaling clusters

Question 5

proteins

Answer 5

o Peripheral – noncovalent interactions; changing the salt concentration of environment can affect these proteins
o Integral – stronger interactions
o Transmembrane

Question 6

membrane transport - endocytosis

Answer 6

 Fluid-phase pinocytosis – cell membrane invaginates to form a pit
 Receptor-mediated endocytosis
 Phagocytosis – extension of pseudopodia from the cell that engulf particles and then internalize the material
 Clathrin-mediated endocytosis – energy dependent and highly regulated
• Receptor-mediated endocytosis
• Sequestration of receptors
• Synaptic vesicle recycling
• Co-opted by viruses for host entry
 Intracellular Clathrin-coated vesicles
• Mediate protein transport
• Mediate lipid transport

Question 7

membrane transport - exocytosis

Answer 7

 Fusogenic proteins – energy dependent; fuse with outer membrane to excrete products extracellularly
 Increase in Ca+

Question 8

Malfunctioning Clathrin-coated pits

Answer 8

o Huntington’s Disease
 Nerve cells in brain waste away resulting in altered cellular physiology and peripheral pathologies
 Genetic defect that presents in middle age
 Presentation – uncontrolled movements and loss of balance
 Late stages – loss of mobility, can’t talk/swallow, poor memory
o Familial Hypercholesterolemia – unable to remove LDL “bad cholesterol”; high levels in blood
 Genetic – autosomal dominant, familial condition
 Coronary disease at early age
• Atherosclerosis (narrowing arteries)
• Angina
 Histopathology
• Narrowing of arteries
• Atherosclerosis – plaque deposits with lipid core and fibrous cap

Question 9

nucleus and nuclear envelope

Answer 9

• Nucleus – “brain” of the cell; controls eating, movement, and reproduction
• Nuclear Envelope
o 2 parallel membranes
o Fibrous lamina made of lamins A, B, C provide skeleton framework for the nuclear envelope

Question 10

myoclonic epilepsy associated with ragged-red fibers (MERRF)

Answer 10

o Presentation – myoclonic seizures, ataxia, muscle weakness
o Histopathology
 Massive subsarcolemmal
 Proliferation of dysfunctional mitochondria

Question 11

endoplasmic reticulum

Answer 11

– site of translation of mRNA into proteins
o	Rough ER
	Segregate proteins NOT destined for cytosol
	Post-translational modification
o	Smooth ER
	Synthesize phospholipids
	Neutralize noxious substances
	Steroid synthesis
	Muscle cell contraction

Question 12

golgi apparatus

Answer 12

o Finishes post-translational modifications
o Packages and concentrates
o Addresses proteins for delivery
 Packages proteins in specific way depending on where they are destined to go

Question 13

lysosomes

Answer 13

o Intracellular digestion and turnover of cellular components

Question 14

Tay-Sachs

Answer 14

o	Early and late onset
o	Presentation 
	Hypotonia and muscle weakness
	Impaired thinking
	Blindness and deafness
o	Histopathology
	GM2 gangliosidosis
	Accumulation in lysosomes

Question 15

peroxisomes

Answer 15

o Oxidize organic substances with catalase
 H2O2 decomposed to H2O and O2 via catalase
 Degrade ethyl alcohol, drugs, toxic molecules
 Beta-oxidation of long fatty acid chains

Question 16

Zellweger’s syndrome

Answer 16

– cerebrohepatorenal syndrome
o High levels of long chain fatty acid and bile acid intermediates
o Presentation – seizures; eye defects
o Histopathology – low catalase in peroxisomes

Question 17

proteasomes

Answer 17

– only removes proteins that have been tagged with ubiquitin
o Digest specific proteins targeted for destruction with the aid of ubiquitin (Ub)
o Ub is conjugated to targeted proteins through ATP-dependent, enzymatic pathway
o Ub-activating enzyme (E1) transfers Ub to Ub-conjugating enzyme (E2), then Ub is covalently transferred to the targeted substrate protein
o Altered Ub enzymatic pathway contributes to several diseases

Question 18

ubiquitin-dependent proteolysis impacts

Answer 18

o Cell cycle progression
o Transcription
o Receptor endocytosis
o Signal transduction

Question 19

cervical cancer

Answer 19

o 3rd most common form of cancer in women
o Healthy cells are transformed by oncogenic form of HPV (16 and 18)
o Early cancer – no signs or symptoms
o Late cancer – bloody vaginal discharge; pelvic pain
o Caused by: dysregulated Ub-dependent proteolysis – HPV cellular machinery promotes ubiquitination (removal) of cell’s tumor suppressor protein (p53)
o Histopathology
 Squamous cell carcinoma epithelial lining
 Adenocarcinoma glandular tissue
 Cancer cells obliterate the normal epithelial structure

Question 20

cytoskeleton

Answer 20

o	Function – structural Proteins that provide shape for a cell
o	Components
	Microtubules
	Actin and myosin
	Intermediate filaments

Question 21

microtubule structure and function

Answer 21

o 24 nm diameter
o Heterodimer of alpha and beta tubulin
o Polymerize into spiral of 13 units per turn
o Polymerization is asymmetrical and calcium dependent – growing end (+) and subtracting end (-)
• Microtubule Function – intracellular transport of organelles

Question 22

actin structure and arrangements

Answer 22

o 5-7nm diameter
o Thin filament with globular subunits arranged as a double helix
 Polymerization is Ca+ dependent
• Actin Arrangements
o Paracrystalline array with myosin
o Cell cortex – thin sheath beneath cell membrane
o Organelles – cytoplasmic streaming
o Cytokinetic apparatus – separates daughter cells
o Scattered in the cytoplasm

Question 23

sickle cell anemia

Answer 23

o Presentation – fatigue, shortness of breath, dizziness, headaches
o Histopathology
 Defective hemoglobin
 Distorted RBC bears sickle shape
 Actin/spectrin cytoskeleton locks; RBC is less deformable
 Sickle cells obstruct the microcirculation

Question 24

intermediate filaments

Answer 24

– can be used to identify cancer based on presence of certain types of intermediate filaments
o	10-12nm
o	Keratin – epithelium
o	Vimentin – embryonic mesenchyme
o	Desmin – smooth muscle and Z disks
o	Glial (GFAP) – astrocytes

Question 25

duchene’s muscular dystrophy

Answer 25

o Presentation – muscle weakness; apparent lack of coordination; progressive crippling, fixations (contractures) of the muscles around joints; loss of mobility
o Histopathology
 Disrupted dystrophin gene
 Abnormal dystrophin cannot anchor cytoskeletal elements to plasma membrane
 Lack of structural support leads to permeable membrane and intracellular pressure rises resulting in cell “exploding”

Question 26

mitosis

Answer 26

o Interphase – duplicate centrosomes and centrioles
o Prophase – mitotic spindle MOC (mitotic operating center) migration
o Metaphase – chromosomes migrate to center upon the MOC arriving at midline of cell
 Microtubules grow to reach the chromosomes in center
o Anaphase – chromatids migrate to opposite poles
 Microtubules break down in order to pull
o Telophase and Cytokinesis – cell divides
 Intermediate filaments involved