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Definition
Most abundant structural protein in the body.
Structure
Triple helix composed of three α-chains
Repeating sequence: Gly–X–Y (X = proline, Y = hydroxyproline)
Types
Type I → bone, skin, tendon
Type II → cartilage
Type III → blood vessels, skin
Type IV → basement membrane
Synthesis
Occurs in fibroblasts
Requires vitamin C for hydroxylation
Functions
Tensile strength
Structural integrity
Diseases
Scurvy → defective collagen synthesis
Osteogenesis imperfecta
Ehlers–Danlos syndrome
Definition
Protein responsible for elasticity of tissues.
Structure
Rich in glycine and proline
Cross-linked by desmosine and isodesmosine
Location
Lungs
Skin
Blood vessels
Function
Allows tissues to stretch and recoil
Disease association
Cutis laxa
Emphysema (excess elastase activity)
Definition
Fibrous proteins forming intermediate filaments.
Types
Hard keratin → hair, nails
Soft keratin → skin, epithelium
Structure
α-helical coiled-coil structure
Function
Mechanical strength
Protection
Clinical relevance
Epidermolysis bullosa
Hair and nail disorders
Definition
Proteins responsible for muscle contraction.
Main proteins
Actin
Myosin
Troponin
Tropomyosin
Location
Muscle fibers
Functional unit
Sarcomere
Definition
Thin filament protein.
Forms
G-actin (globular)
F-actin (filamentous)
Function
Forms backbone of thin filament
Interacts with myosin during contraction
Definition
Thick filament protein.
Structure
Two heavy chains
Four light chains
Myosin head
ATPase activity
Actin-binding site
Function
Converts chemical energy into mechanical work
Definition
Regulatory protein complex on thin filament.
Components
Troponin T → binds tropomyosin
Troponin I → inhibitory
Troponin C → binds calcium
Clinical importance
Cardiac troponins used as markers of myocardial infarction
Theory
Sliding filament theory
Steps
Calcium release from sarcoplasmic reticulum
Calcium binds troponin C
Exposure of actin binding sites
Cross-bridge formation
ATP hydrolysis → power stroke
Energy source
ATP
Relaxation
Calcium pumped back into sarcoplasmic reticulum
Definition
Calcium-binding regulatory protein.
Structure
Binds four Ca²⁺ ions
Functions
Activates enzymes
Regulates smooth muscle contraction
Mechanism
Ca²⁺–calmodulin complex activates myosin light chain kinase
Difference from troponin
Present in smooth muscle and non-muscle cells
Troponin is absent in smooth muscle
Collagen → strength
Elastin → elasticity
Keratin → protection
Actin + myosin → movement
Troponin → Ca²⁺ control (cardiac marker)
Calmodulin → Ca²⁺ regulator in smooth muscle
Definition
Thin cytoskeletal filaments composed mainly of actin.
Diameter
~7 nm
Structure
Polymerized F-actin from G-actin subunits
Functions
Maintenance of cell shape
Cell motility
Muscle contraction
Cytokinesis
Associated proteins
Myosin
Tropomyosin
Clinical relevance
Defects affect cell movement and muscle function
Definition
Hollow cylindrical cytoskeletal structures.
Diameter
~25 nm
Composition
α-tubulin and β-tubulin dimers
Functions
Mitotic spindle formation
Intracellular transport
Cilia and flagella movement
Arrangement
9+2 structure in cilia and flagella
Drug relevance
Target of anticancer drugs (vincristine, paclitaxel)
Definition
Structural proteins maintaining lens transparency.
Major proteins
α-crystallins
β-crystallins
γ-crystallins
Functions
Transparency of lens
Refractive properties
Special feature
Extremely long half-life
Disease association
Cataract due to protein aggregation and oxidation
Definition
Infectious protein particles without nucleic acid.
Normal protein
PrPᶜ (cellular prion protein)
Pathogenic form
PrPˢᶜ (scrapie form)
Biochemical change
α-helix → β-sheet conversion
Properties
Resistant to heat and proteases
Induce misfolding of normal proteins
Group
Transmissible spongiform encephalopathies
Examples
Creutzfeldt–Jakob disease
Variant CJD
Kuru
Fatal familial insomnia
Pathology
Spongiform degeneration of brain
Neuronal loss
Clinical features
Rapidly progressive dementia
Ataxia
Myoclonus
Outcome
Always fatal
Definition
Progressive decline in physiological function with age.
Major theories
Free radical theory
Telomere shortening
Protein glycation
Biochemical changes
Increased oxidative stress
Decreased DNA repair
Accumulation of damaged proteins
Role of antioxidants
Reduce oxidative damage
Clinical relevance
Increased risk of degenerative diseases
Definition
Progressive neurodegenerative disorder causing dementia.
Key biochemical abnormalities
Amyloid-β plaque deposition
Neurofibrillary tangles (hyperphosphorylated tau)
Pathogenesis
Abnormal processing of amyloid precursor protein
Synaptic dysfunction
Neurotransmitter deficit
Acetylcholine deficiency
Clinical features
Memory loss
Cognitive decline
Biochemical hallmark
Protein misfolding and aggregation
Microfilaments → actin → movement
Microtubules → tubulin → mitosis & transport
Lens proteins → crystallins → transparency
Prions → infectious proteins
Aging → oxidative damage + telomeres
Alzheimer’s → amyloid β + tau
What are microfilaments?
Thin cytoskeletal filaments composed mainly of actin.
What is the diameter of microfilaments?
Approximately 7 nm.
What is the basic structural unit of microfilaments?
G-actin polymerized to form F-actin.
Functions of microfilaments?
Maintenance of cell shape, cell motility, muscle contraction, and cytokinesis.
What are microtubules?
Hollow cylindrical cytoskeletal structures composed of tubulin.
Which proteins form microtubules?
α-tubulin and β-tubulin dimers.
What is the diameter of microtubules?
Approximately 25 nm.
Functions of microtubules?
Mitotic spindle formation, intracellular transport, and cilia/flagella movement.
What is the structural arrangement in cilia and flagella?
9 + 2 microtubule arrangement.
Name drugs acting on microtubules.
Vincristine, vinblastine, paclitaxel.
What are the major proteins of the lens?
Crystallins.
Types of crystallins?
α-, β-, and γ-crystallins.
Why are lens proteins unique?
They have an extremely long half-life.
Function of lens proteins?
Maintain lens transparency and refractive power.
Biochemical basis of cataract formation?
Protein aggregation and oxidative modification of crystallins.
What are prions?
Infectious protein particles lacking nucleic acids.
What is the normal prion protein?
PrPᶜ (cellular prion protein).
What is the pathogenic prion protein?
PrPˢᶜ (scrapie form).
What structural change occurs in prion disease?
Conversion of α-helix to β-sheet structure.
Why are prions resistant to heat and proteases?
Due to high β-sheet content.
What are prion diseases collectively called?
Transmissible spongiform encephalopathies.
Examples of human prion diseases?
Creutzfeldt–Jakob disease, variant CJD, Kuru, fatal familial insomnia.
Characteristic pathological feature of prion diseases?
Spongiform degeneration of the brain.
Outcome of prion diseases?
Always fatal.
What is aging?
Progressive decline in physiological function with advancing age.
Major biochemical theories of aging?
Free radical theory, telomere shortening, protein glycation.
Role of free radicals in aging?
Cause oxidative damage to DNA, proteins, and lipids.
What happens to DNA repair with aging?
It decreases.
Role of antioxidants in aging?
Reduce oxidative stress and cellular damage.
What is Alzheimer’s disease?
A progressive neurodegenerative disorder causing dementia.
Key biochemical hallmarks of Alzheimer’s disease?
Amyloid-β plaques and neurofibrillary tangles.
What forms amyloid plaques?
Amyloid-β peptide derived from amyloid precursor protein.
What are neurofibrillary tangles composed of?
Hyperphosphorylated tau protein.
Which neurotransmitter is deficient in Alzheimer’s disease?
Acetylcholine.
Why is Alzheimer’s considered a protein misfolding disorder?
Due to abnormal aggregation of amyloid-β and tau proteins.
Microfilaments → actin → movement
Microtubules → tubulin → mitosis & transport
Lens proteins → crystallins → transparency
Prions → infectious proteins without nucleic acid
Aging → oxidative damage + telomere loss
Alzheimer’s → amyloid β + tau tangles
1. Microfilaments are primarily composed of:
A. Tubulin
B. Keratin
C. Actin
D. Myosin
Answer: C
2. Diameter of microfilaments is approximately:
A. 3 nm
B. 7 nm
C. 10 nm
D. 25 nm
Answer: B
3. G-actin polymerizes to form:
A. Myosin
B. Tropomyosin
C. F-actin
D. Tubulin
Answer: C
4. Microfilaments are NOT involved in:
A. Cell motility
B. Cytokinesis
C. Muscle contraction
D. Mitotic spindle formation
Answer: D
5. Microtubules are composed of:
A. Actin monomers
B. α- and β-tubulin
C. Intermediate filaments
D. Myosin heavy chains
Answer: B
6. Diameter of microtubules is:
A. 7 nm
B. 10 nm
C. 15 nm
D. 25 nm
Answer: D
7. Which structure has a 9 + 2 microtubule arrangement?
A. Centriole
B. Mitotic spindle
C. Cilia and flagella
D. Basal body
Answer: C
8. Microtubules play a major role in:
A. Apoptosis
B. Intracellular transport
C. DNA replication
D. Protein synthesis
Answer: B
9. Which anticancer drug acts by inhibiting microtubule polymerization?
A. Methotrexate
B. Vincristine
C. Cyclophosphamide
D. Doxorubicin
Answer: B
10. Major structural proteins of the lens are:
A. Collagens
B. Elastins
C. Crystallins
D. Keratins
Answer: C
11. Which crystallin acts as a molecular chaperone?
A. α-crystallin
B. β-crystallin
C. γ-crystallin
D. δ-crystallin
Answer: A
12. Lens proteins are unique because they:
A. Are rapidly degraded
B. Have very short half-life
C. Have extremely long half-life
D. Are replaced daily
Answer: C
13. Cataract formation is mainly due to:
A. Increased protein synthesis
B. Protein aggregation and oxidation
C. Increased glucose uptake
D. DNA damage
Answer: B
14. Prions are composed of:
A. DNA and protein
B. RNA and protein
C. Protein only
D. Lipoprotein
Answer: C
15. Normal cellular prion protein is designated as:
A. PrPˢᶜ
B. PrPᶜ
C. PrPβ
D. PrPα
Answer: B
16. Pathogenic prion protein differs by having increased:
A. α-helical content
B. β-sheet structure
C. Random coil
D. Disulfide bonds
Answer: B
17. Prions are resistant to:
A. Heat
B. Proteases
C. UV radiation
D. Both A and B
Answer: D
18. Human prion diseases are also known as:
A. Amyloidoses
B. Lysosomal storage disorders
C. Transmissible spongiform encephalopathies
D. Demyelinating disorders
Answer: C
19. Which is NOT a prion disease?
A. Creutzfeldt–Jakob disease
B. Kuru
C. Alzheimer’s disease
D. Fatal familial insomnia
Answer: C
20. The hallmark pathology of prion disease is:
A. Demyelination
B. Spongiform degeneration of brain
C. Plaque formation
D. Neuronal calcification
Answer: B
21. Free radical theory of aging proposes damage mainly to:
A. RNA only
B. DNA, proteins, and lipids
C. Carbohydrates only
D. Cell membrane receptors
Answer: B
22. Telomere shortening primarily affects:
A. Mitochondrial DNA
B. Ribosomal RNA
C. Chromosomal stability
D. Protein synthesis
Answer: C
23. Advanced glycation end products (AGEs) accumulate due to:
A. Lipid peroxidation
B. Non-enzymatic glycation
C. Protein phosphorylation
D. DNA methylation
Answer: B
24. With aging, DNA repair capacity:
A. Increases
B. Remains unchanged
C. Decreases
D. Is absent
Answer: C
25. Antioxidants delay aging by:
A. Increasing mutations
B. Reducing oxidative stress
C. Enhancing apoptosis
D. Inhibiting telomerase
Answer: B
26. Alzheimer’s disease is characterized by:
A. Demyelination
B. Protein misfolding
C. Glycogen accumulation
D. Lipid storage
Answer: B
27. Major component of amyloid plaques is:
A. Tau protein
B. Amyloid-β peptide
C. α-synuclein
D. Prion protein
Answer: B
28. Neurofibrillary tangles are composed of:
A. Amyloid-β
B. α-synuclein
C. Hyperphosphorylated tau
D. Actin
Answer: C
29. Amyloid-β is derived from:
A. Tau protein
B. Prion protein
C. Amyloid precursor protein
D. α-crystallin
Answer: C
30. Neurotransmitter deficiency in Alzheimer’s disease is mainly:
A. Dopamine
B. Serotonin
C. Acetylcholine
D. GABA
Answer: C
31. Microfilaments and microtubules together form part of:
A. Nuclear matrix
B. Cytoskeleton
C. Extracellular matrix
D. Basement membrane
Answer: B
32. Loss of microtubule function most directly affects:
A. Cell shape only
B. Protein synthesis
C. Mitosis
D. Glycolysis
Answer: C
33. Which protein misfolding disorder is infectious?
A. Alzheimer’s disease
B. Parkinson’s disease
C. Prion disease
D. Huntington disease
Answer: C
34. Cataract formation is accelerated by:
A. Reduced oxidation
B. Increased antioxidant activity
C. Oxidative stress
D. Increased DNA repair
Answer: C
35. Aging is associated with:
A. Increased telomerase activity
B. Reduced oxidative damage
C. Accumulation of damaged proteins
D. Enhanced DNA repair
Answer: C
36. Which cytoskeletal element is thickest?
A. Microfilaments
B. Intermediate filaments
C. Microtubules
D. Actin filaments
Answer: C
37. Alzheimer’s disease primarily affects:
A. Motor neurons
B. Sensory neurons
C. Cortical neurons
D. Spinal neurons
Answer: C
38. Which protein acts as chaperone in the lens?
A. β-crystallin
B. γ-crystallin
C. α-crystallin
D. Keratin
Answer: C
39. Prion diseases progress because:
A. Immune response destroys neurons
B. Protein induces misfolding of normal proteins
C. Viral replication occurs
D. DNA mutations accumulate
Answer: B
40. Alzheimer’s disease is NOT characterized by:
A. Memory loss
B. Cognitive decline
C. Rapid spongiform change
D. Amyloid deposition
Answer: C
41. Microtubules are absent in:
A. Cilia
B. Flagella
C. Centrioles
D. RBCs
Answer: D
42. Protein aggregation is central to:
A. Cataract
B. Alzheimer’s disease
C. Prion diseases
D. All of the above
Answer: D
43. Aging increases susceptibility to:
A. DNA damage
B. Protein oxidation
C. Degenerative diseases
D. All of the above
Answer: D
44. Tau protein normally stabilizes:
A. Microfilaments
B. Intermediate filaments
C. Microtubules
D. Actomyosin complex
Answer: C
45. Loss of tau function leads to:
A. Increased microtubule stability
B. Microtubule disassembly
C. Increased actin polymerization
D. Reduced amyloid formation
Answer: B
46. Which disease is always fatal?
A. Alzheimer’s disease
B. Cataract
C. Prion disease
D. Parkinson’s disease
Answer: C
47. Crystallin aggregation causes loss of:
A. Lens elasticity
B. Lens transparency
C. Retina function
D. Corneal curvature
Answer: B
48. Free radicals primarily damage cells by:
A. Enzyme activation
B. Oxidative stress
C. Increased ATP production
D. Gene amplification
Answer: B
49. Cytoskeletal drugs are useful in cancer because they:
A. Kill non-dividing cells
B. Inhibit mitosis
C. Increase apoptosis only
D. Reduce angiogenesis
Answer: B
50. Alzheimer’s disease belongs to which group?
A. Infectious diseases
B. Autoimmune diseases
C. Neurodegenerative diseases
D. Metabolic disorders
Answer: C
(Single best answer)
1. A patient receiving vincristine develops mitotic arrest in tumor cells. The drug acts by disrupting:
A. Microfilaments
B. Intermediate filaments
C. Microtubules
D. Actomyosin complex
Answer: C
2. A 65-year-old patient presents with progressive memory loss. Brain biopsy shows extracellular plaques composed of amyloid-β. The peptide is derived from:
A. Tau protein
B. Prion protein
C. Amyloid precursor protein
D. α-synuclein
Answer: C
3. A middle-aged individual develops rapidly progressive dementia with myoclonus. EEG shows periodic sharp waves. Most likely biochemical abnormality is:
A. Neurofibrillary tangles
B. α-helix → β-sheet protein conversion
C. Dopamine deficiency
D. Lysosomal enzyme deficiency
Answer: B
4. A newborn has normal vision at birth but develops cataract later in life due to aggregation of lens proteins. The most likely biochemical cause is:
A. Increased protein synthesis
B. Oxidative modification of crystallins
C. DNA mutation
D. Reduced ATP production
Answer: B
5. A cultured malignant cell line grows in suspension without attachment. This property depends on alteration of:
A. Contact inhibition
B. Apoptosis
C. Anchorage dependence
D. Telomerase activity
Answer: C
6. A patient with Alzheimer’s disease has deficiency of a neurotransmitter synthesized from choline. Which enzyme is targeted therapeutically?
A. Monoamine oxidase
B. Acetylcholinesterase
C. Dopamine β-hydroxylase
D. Glutamate decarboxylase
Answer: B
7. A laboratory experiment shows disruption of cytokinesis after actin depolymerization. The affected cytoskeletal element is:
A. Microtubules
B. Intermediate filaments
C. Microfilaments
D. Neurofilaments
Answer: C
8. An elderly patient shows increased oxidative stress markers and shortened telomeres. This best supports which theory of aging?
A. Genetic theory
B. Free radical theory
C. Immunological theory
D. Hormonal theory
Answer: B
9. A patient with prion disease shows resistance of the infectious agent to protease digestion. This is due to:
A. Presence of nucleic acid
B. High α-helical content
C. Increased β-sheet structure
D. Lipid coating
Answer: C
10. Loss of tau protein function in neurons primarily causes instability of:
A. Actin filaments
B. Intermediate filaments
C. Microtubules
D. Myelin sheath
Answer: C
(Choose the correct option)
A. Both A and R are true and R explains A
B. Both A and R are true but R does not explain A
C. A is true but R is false
D. A is false but R is true
1.
Assertion: Microtubules are essential for mitosis.
Reason: They form the mitotic spindle required for chromosome separation.
Answer: A
2.
Assertion: Lens proteins are susceptible to aggregation.
Reason: Lens crystallins have an extremely long half-life.
Answer: A
3.
Assertion: Prion diseases do not elicit an immune response.
Reason: Prions lack nucleic acids.
Answer: B
4.
Assertion: Alzheimer’s disease is a protein misfolding disorder.
Reason: Amyloid-β and tau proteins aggregate abnormally.
Answer: A
5.
Assertion: Aging is associated with increased oxidative damage.
Reason: Antioxidant defense mechanisms decline with age.
Answer: A
6.
Assertion: Microfilaments are thicker than microtubules.
Reason: Microfilaments have a diameter of about 7 nm.
Answer: C
7.
Assertion: Prion diseases are always fatal.
Reason: Prion proteins cause progressive neuronal degeneration.
Answer: A
What are microfilaments composed of?
Actin.
Diameter of microfilaments?
~7 nm.
Main protein of microtubules?
α- and β-tubulin.
Arrangement of microtubules in cilia?
9 + 2 pattern.
Major proteins of the lens?
Crystallins.
Which crystallin acts as molecular chaperone?
α-crystallin.
Define prions.
Infectious protein particles without nucleic acid.
Normal prion protein is called?
PrPᶜ.
Pathogenic prion form?
PrPˢᶜ.
Main biochemical change in prions?
α-helix to β-sheet conversion.
Why are prion diseases not detected by routine sterilization?
Prions are resistant to heat and proteases.
Why do cataracts increase with age?
Accumulation and oxidation of lens proteins.
Why are microtubules important targets in cancer therapy?
They are essential for mitosis.
Why is Alzheimer’s disease progressive?
Continuous accumulation of misfolded proteins.
Why is acetylcholine deficient in Alzheimer’s disease?
Loss of cholinergic neurons.
Cytoskeleton failure = loss of order
Prions prove proteins alone can be infectious
Aging is oxidative damage plus repair failure
Alzheimer’s is memory loss written in protein aggregates
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