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Here is a thorough exam-ready summary of the PDF (Lectures 3 & 4 - Cytology: Cell Structures & Cytoskeleton):
Cytology Lectures 3 & 4 - Final Exam Summary
Course: Cytology and Embryology | Geomedi, 2026 | Dr. Giorgi Berishvili
LECTURE 3: Cell Structures
1. Eukaryotic Cell Compartments
- Eukaryotic cells isolate reactions within membrane-enclosed compartments (organelles)
- Molecules are concentrated inside organelles to optimize biochemical reactions
2. Cytosol
- = liquid part of cytoplasm (surrounds organelles); NOT the same as cytoplasm (which includes organelles)
- Gel-like: water, ions, molecules, enzymatic complexes
- Site of protein synthesis and degradation
- Contains ~10 billion protein molecules in an animal cell
- Constantly in motion
3. Nucleus
- Command center - houses genomic DNA; site of gene expression & RNA synthesis
- Size: 1-10 µm diameter; ~10% of average somatic cell volume
- Exceptions:
- RBCs and platelets: no nucleus
- Skeletal muscle & osteoclasts: many nuclei (syncytia)
- Liver cells: may have 2 nuclei (endomitosis)
Nuclear Components:
| Structure | Function |
|---|---|
| Nuclear envelope | Double lipid bilayer enclosing nucleus |
| Perinuclear space | 20-40 nm gap between inner & outer membranes |
| Outer membrane | Continues into rough ER |
| Inner membrane | Associated with nuclear lamina (intermediate filaments) |
| Nuclear pore complexes (NPCs) | Mediate transport; built from nucleoporins (Nups); at least 456 individual Nup molecules from ~34 distinct proteins |
| Nuclear lamina | Protein meshwork of intermediate filaments supporting inner membrane |
Nuclear Transport:
- Particles up to 9 nm pass by passive diffusion (amino acids, nucleotides, small proteins, water)
- Larger molecules: active transport via receptor, powered by GTP and ATP hydrolysis
4. Chromatin
- Complex of DNA + associated proteins
- Human DNA: 2 m long, 3.2 billion base pairs, 23 pairs of chromosomes
- Wrapped around 8 histone proteins → nucleosome
- Nucleosomes connected by linker DNA, stabilized by H1 linker histone
- Chromosomes become visible as discrete structures during cell division under light microscopy
Chromatin Types:
| Type | Packing | Transcription |
|---|---|---|
| Euchromatin | Loosely packed | Transcriptionally ACTIVE |
| Heterochromatin | Densely packed | Transcriptionally SILENT |
5. Karyotype
- Representation of all chromosomes during cell division
- Humans: 22 pairs of autosomes + 1 pair of sex chromosomes (XX = female, XY = male)
- Diploid cells: both homologous chromosomes present
- Haploid cells: gametes (sperm & egg) - half the chromosome number
- Karyotyping detects: indels and aneuploidy
6. Chromosomal Territories
- Chromosomes occupy distinct, non-overlapping territories during interphase
- Positioning determined by interactions with nuclear lamina and nuclear matrix
- Influenced by chromatin type and gene activity
- Important for gene expression, DNA replication, and genomic integrity
7. Nucleolus
- Most prominent basophilic structure in nucleus
- Function: transcription, processing, and assembly of ribosomal RNA (rRNA) + ribosomal subunits
- ~50% of all RNAs produced in cell are rRNAs
- Three zones:
- Fibrillar Centers (FC) - contain rDNA; site of initial rRNA transcription
- Dense Fibrillar Component (F) - accumulated rRNAs
- Granular Component (G) - assembled ribosomal subunits
8. Other Nuclear Structures
| Structure | Function |
|---|---|
| Barr body | Condensed inactive X chromosome (seen in females) |
| Cajal bodies | Ribosome & spliceosome biogenesis, telomere maintenance |
| PML bodies | Genome maintenance |
| GEM bodies | Nuclear organization |
9. Mitochondria
- Elongated organelles, 0.5-1 µm in diameter
- Double membrane: outer membrane + inner membrane folded into cristae
- Oxidative phosphorylation occurs at inner membrane (cristae)
- Two compartments: matrix (innermost) + intermembrane space
- Only organelle (besides nucleus) with its own DNA (mtDNA)
- mtDNA: double-stranded, circular, ~5 copies per mitochondrion, 37 genes
- mtDNA inherited maternally
- Defects accumulate over time - potentially contribute to aging
- Cells with high energy demand (e.g., cardiac muscle) have many mitochondria
ATP/Energy:
- ATP (adenosine triphosphate) = main chemical energy currency
- Most ATP produced by oxidative phosphorylation from ADP in mitochondria
10. Endoplasmic Reticulum (ER)
| Type | Features | Functions |
|---|---|---|
| Rough ER (RER) | Studded with ribosomes | Protein synthesis |
| Smooth ER (SER) | No ribosomes | Lipid & steroid biosynthesis, detoxification, storage |
- Connected to Golgi and nucleus via transport vesicles
11. Golgi Apparatus
- Receives proteins from RER via transport vesicles
- Composed of flattened membrane sacs (cisternae) in curved/crescent arrangement, near nucleus
- Functions: processing, modification, sorting of proteins & lipids; formation of lysosomes; packaging into secretory granules for exocytosis
12. Lysosomes
- Spherical, 0.05-0.5 µm in diameter
- ~40 hydrolytic enzymes (proteases, nucleases, phosphatases)
- Highly acidic (H+ import)
- Most abundant in phagocytic cells (macrophages, neutrophils)
- Also involved in autophagy (fuse with autophagosomes to recycle cellular components)
13. Peroxisomes
- Small membrane-enclosed vesicles
- Contain catalases and peroxidases - break down H₂O₂ and ROS
- Breakdown of fatty acids for energy
- Membrane proteins from ER; enzymes enter directly from cytosol
- Part of the endomembrane system (along with ER, Golgi, endosomes, lysosomes)
14. Ribosomes
- Human ribosomes: small 40S + large 60S subunits
- Composed of 4 rRNA + ~80 ribosomal proteins
- Small subunit: decodes mRNA
- Large subunit: catalyzes peptide bond formation
- Undergo association/dissociation each translation cycle
Polyribosomes:
| Type | Location | Products |
|---|---|---|
| Free ribosomes | Cytosol | Proteins for use inside cell (no post-translational modification) |
| ER-bound ribosomes | RER | Membrane proteins & secreted proteins (post-translational modification) |
15. Proteasome
- Large (26S) multi-subunit (33 subunits) protein complex
- Recognizes proteins tagged with ubiquitin (ubiquitination) for destruction
- Unfolds protein, feeds into inner cylinder, chops into short peptides
- Dysfunction linked to: neurodegeneration, immunopathologies, cancer, aging
16. Cytoplasmic Inclusions
| Inclusion | Description |
|---|---|
| Lipid droplets | Lipid aggregates enclosed by phospholipid monolayer; adipocytes have one large droplet |
| Glycogen granules | Glucose polymer aggregates (no membrane); energy source |
| Pigment deposits | Melanin, lipofuscin, hemosiderin |
LECTURE 4: Cytoskeleton
Overview
- Enables: shape maintenance, mechanical interaction with environment, coordinated movements
- Network of protein filaments + associated proteins (girders, ropes, motors)
- Highly dynamic - continuously reorganized in response to cell division, shape changes, environmental stimuli
Three Major Components
1. Microtubules
- Hollow cylinders, 25 nm diameter, made of 13 parallel protofilaments
- Most rigid of the three filaments; rupture when stretched
- Dynamic in cytoplasm; rigid (axonemes) in cilia/flagella
Assembly:
- Built from α and β tubulin heterodimers
- Growth at (+) end; GTP bound to incoming tubulin provides energy
- Dynamic instability - constantly switches between growth and shrinkage
- Regulated by Ca²⁺, Mg²⁺, and microtubule-associated proteins (MAPs)
Centrosome (MTOC):
- Principal microtubule organizing center (MTOC)
- Built around two centrioles, each with 9 microtubule triplets
- Surrounded by matrix containing γ-tubulin ring (starting point for MT growth)
- Duplicates during DNA replication → forms mitotic spindle
Motor Proteins:
| Motor | Direction |
|---|---|
| Kinesins | Move toward (+) end |
| Dyneins | Move toward (-) end |
- Both are dimers with 2 ATPase heads (bind microtubule) + 1 tail (binds cargo)
Functions:
- Maintain cell shape and polarity
- Tracks for cytoplasmic component movement
- Chromosome movement during mitosis
- Move cilia and flagella
2. Actin Filaments (Microfilaments)
- Helical polymers of actin, 5-7 nm diameter
- Flexible and dynamic
- Most concentrated in the cortex (layer just beneath plasma membrane)
- Motor: Myosin family
Assembly:
- G-actin (globular) monomers assemble (need K⁺ and Mg²⁺) into F-actin (filamentous) double-stranded helix
- ATP-bound monomers added at (+) end; ADP-bound monomers dissociate from (-) end
- Treadmilling: monomers move through filament from (+) to (-) end
- Actin-binding proteins cross-link filaments into actin bundles or actin networks
Actin-Myosin Contraction:
- Myosin has ATPase head (binds actin) + tail (attaches to cargo)
- Head rotation pulls cargo along actin track
- Responsible for muscle contraction
Functions:
- Mechanical strength for plasma membrane
- Transport of organelles, vesicles (cytoplasmic streaming)
- Cell surface changes during endocytosis
- Form microvilli (stable, stiff structures)
- Small contractile bundles in most animal cells
- Temporary structures at leading edge of crawling cells
- Contractile ring during cytokinesis (cell division)
3. Intermediate Filaments
- Ropelike fibers, ~10 nm diameter (between micro- and microtubules)
- Very flexible and strong; deform under stress but do NOT rupture
- Most stable of the three - confer mechanical stability
- Network throughout cytoplasm, around nucleus, to cell periphery
- Only filament found INSIDE the nucleus (lamins)
Assembly:
- Many different fibrous protein subunits
- Form coiled dimers → antiparallel tetramers → non-polar assembly
Types and Functions:
| Type | Location |
|---|---|
| Keratins | Epithelial cells |
| Vimentins | Connective tissue, mesenchyme; Desmin in muscle; GFAP in glia |
| Neurofilaments | Nerve cells |
| Lamins | Inside nuclear envelope |
Functions:
- Strengthen cell and tissue structure
- Maintain cell shape and elasticity
- Maintain nuclear shape
Quick Comparison Table: Cytoskeleton Filaments
| Feature | Microtubules | Actin Filaments | Intermediate Filaments |
|---|---|---|---|
| Diameter | 25 nm | 5-7 nm | ~10 nm |
| Structure | Hollow cylinder, 13 protofilaments | Double-stranded helix | Ropelike fiber |
| Subunit | α/β tubulin | G-actin | Various fibrous proteins |
| Polarity | Yes (+/-) | Yes (+/-) | Non-polar |
| Motor | Kinesin, Dynein | Myosin | None |
| Stability | Dynamic | Dynamic | Stable |
| Energy | GTP | ATP | None |
| Key function | Mitosis, cilia, intracellular transport | Muscle contraction, cell movement, endocytosis | Mechanical strength |
| Found in nucleus? | No | No | Yes (lamins) |
Key "must-remember" facts for exams:
- Nuclear pores allow passive diffusion up to 9 nm; larger molecules need active (GTP/ATP-powered) transport
- mtDNA has 37 genes, is circular, double-stranded, maternally inherited
- Nucleolus = site of rRNA transcription and ribosome assembly
- Proteasome recognizes ubiquitin-tagged proteins
- Kinesin = (+) end direction; Dynein = (-) end direction
- Actin treadmilling = monomers flow from (+) to (-) end
- Intermediate filaments = only type non-polar and found inside nucleus
- Barr body = inactive X chromosome in females
Give me MCQ type questions from this pdf
Here are 40 MCQ-style questions based on the PDF content, covering all major topics:
MCQ Practice Questions
Cytology Lectures 3 & 4 - Cell Structures & Cytoskeleton
SECTION A: Nucleus & Nuclear Components
1. Which of the following cells contains NO nucleus?
- A) Hepatocyte
- B) Osteoclast
- C) Skeletal muscle cell
- D) Red blood cell ✅
2. The nuclear envelope is separated by a perinuclear space of what width?
- A) 5-10 nm
- B) 20-40 nm ✅
- C) 50-100 nm
- D) 100-200 nm
3. The outer membrane of the nuclear envelope continues into which structure?
- A) Smooth ER
- B) Golgi apparatus
- C) Rough ER ✅
- D) Lysosome
4. Molecules up to what size can pass through nuclear pore complexes by passive diffusion?
- A) 2 nm
- B) 5 nm
- C) 9 nm ✅
- D) 15 nm
5. Nuclear pore complexes are constructed from transmembrane proteins called:
- A) Lamins
- B) Histones
- C) Nucleoporins (Nups) ✅
- D) Tubulins
6. The nuclear lamina is made of which type of protein filaments?
- A) Actin filaments
- B) Microtubules
- C) Intermediate filaments ✅
- D) Collagen fibers
7. How many individual Nup molecules are present in a nuclear pore complex?
- A) At least 100
- B) At least 234
- C) At least 456 ✅
- D) At least 600
8. Active transport through nuclear pore complexes is powered by:
- A) NADH oxidation
- B) GTP and ATP hydrolysis ✅
- C) Na⁺/K⁺ gradient
- D) Passive osmosis
SECTION B: Chromatin & Chromosomes
9. Human DNA is wrapped around how many histone proteins to form a nucleosome?
- A) 4
- B) 6
- C) 8 ✅
- D) 10
10. Which histone stabilizes the linker DNA between nucleosomes?
- A) H2A
- B) H3
- C) H4
- D) H1 ✅
11. Euchromatin differs from heterochromatin in that it is:
- A) Densely packed and transcriptionally silent
- B) Loosely packed and transcriptionally active ✅
- C) Found only in the nucleolus
- D) Associated only with sex chromosomes
12. The human genome contains how many base pairs?
- A) 1.6 billion
- B) 2.3 billion
- C) 3.2 billion ✅
- D) 4.8 billion
13. A Barr body represents:
- A) An extra autosome
- B) An active X chromosome
- C) A condensed, inactive X chromosome ✅
- D) A segment of heterochromatin in males
14. Gametes (sperm and egg) are:
- A) Diploid
- B) Triploid
- C) Haploid ✅
- D) Tetraploid
15. Karyotyping is used to detect:
- A) Protein folding errors
- B) RNA splicing defects
- C) Indels and aneuploidy ✅
- D) Mitochondrial mutations
SECTION C: Nucleolus & Other Nuclear Structures
16. The nucleolus is the site of:
- A) DNA replication
- B) mRNA splicing
- C) rRNA transcription and ribosome subunit assembly ✅
- D) Protein ubiquitination
17. What percentage of all RNAs produced in the cell are rRNAs?
- A) 10%
- B) 25%
- C) 50% ✅
- D) 75%
18. Which zone of the nucleolus contains assembled ribosomal subunits?
- A) Fibrillar Centers (FC)
- B) Dense Fibrillar Component (F)
- C) Granular Component (G) ✅
- D) Nuclear lamina
19. Cajal bodies are involved in:
- A) Lipid synthesis
- B) Ribosome & spliceosome biogenesis and telomere maintenance ✅
- C) Protein degradation
- D) ATP production
SECTION D: Mitochondria
20. Which of the following statements about mitochondrial DNA (mtDNA) is TRUE?
- A) It is linear and single-stranded
- B) It contains over 1000 genes
- C) It is inherited from both parents equally
- D) It is circular, double-stranded, and contains 37 genes ✅
21. Oxidative phosphorylation in mitochondria takes place at:
- A) The outer mitochondrial membrane
- B) The intermembrane space
- C) The inner membrane (cristae) ✅
- D) The mitochondrial matrix
22. How many copies of mtDNA does each mitochondrion contain (approximately)?
- A) 1
- B) 5 ✅
- C) 23
- D) 37
23. Mitochondria are inherited:
- A) From the paternal parent only
- B) Equally from both parents
- C) From the maternal parent only ✅
- D) They are synthesized de novo each generation
SECTION E: ER, Golgi, Lysosomes & Peroxisomes
24. Rough ER differs from smooth ER because it:
- A) Is found only near the nucleus
- B) Lacks a membrane
- C) Is studded with ribosomes ✅
- D) Produces steroids
25. The Golgi apparatus is composed of flattened membrane-bound sacs called:
- A) Vesicles
- B) Cisternae ✅
- C) Cristae
- D) Lacunae
26. Lysosomes contain approximately how many hydrolytic enzymes?
- A) 5-10
- B) 20-25
- C) 40 ✅
- D) 100
27. Which cells are MOST abundant in lysosomes due to their phagocytic activity?
- A) Hepatocytes and neurons
- B) Macrophages and neutrophils ✅
- C) Red blood cells and platelets
- D) Adipocytes and fibroblasts
28. Peroxisomes break down hydrogen peroxide using which enzymes?
- A) Proteases and nucleases
- B) Lipases and amylases
- C) Catalases and peroxidases ✅
- D) Kinases and phosphatases
29. Which of the following is NOT part of the endomembrane system?
- A) Golgi apparatus
- B) Lysosomes
- C) Mitochondria ✅
- D) Peroxisomes
SECTION F: Ribosomes & Proteasome
30. Human ribosomes consist of which two subunits?
- A) 30S and 50S
- B) 40S and 60S ✅
- C) 20S and 40S
- D) 50S and 70S
31. Free ribosomes in the cytosol produce proteins that:
- A) Are secreted outside the cell
- B) Are inserted into membranes
- C) Are used inside the cell without post-translational modification ✅
- D) Are transported to the Golgi
32. The proteasome recognizes proteins marked for destruction by:
- A) Phosphorylation
- B) Glycosylation
- C) Acetylation
- D) Ubiquitination ✅
33. Proteasome dysfunction is implicated in all of the following EXCEPT:
- A) Neurodegeneration
- B) Cancer
- C) Aging
- D) Lipid droplet accumulation ✅
SECTION G: Cytoskeleton
34. Which cytoskeletal filament is the MOST rigid?
- A) Intermediate filaments
- B) Actin filaments
- C) Microtubules ✅
- D) Lamins
35. Microtubules are hollow cylinders made of how many parallel protofilaments?
- A) 9
- B) 11
- C) 13 ✅
- D) 15
36. Growth of microtubules occurs at which end?
- A) (-) end
- B) (+) end ✅
- C) Both ends simultaneously
- D) Growth is non-polar
37. Which motor protein moves toward the MINUS end of a microtubule?
- A) Kinesin
- B) Myosin
- C) Dynein ✅
- D) Actin
38. The centrosome contains a matrix with which protein that serves as the starting point for microtubule growth?
- A) α-tubulin ring
- B) β-tubulin ring
- C) γ-tubulin ring ✅
- D) Dynein ring
39. In actin filament dynamics, "treadmilling" refers to:
- A) Rapid depolymerization of the entire filament
- B) Simultaneous growth at both ends
- C) Monomers moving through the filament from (+) to (-) end ✅
- D) Cross-linking of actin into bundles
40. Which intermediate filament type is found INSIDE the nuclear envelope?
- A) Keratins
- B) Vimentins
- C) Neurofilaments
- D) Lamins ✅
Answer Key (Quick Reference)
| Q | A | Q | A | Q | A | Q | A |
|---|---|---|---|---|---|---|---|
| 1 | D | 11 | B | 21 | C | 31 | C |
| 2 | B | 12 | C | 22 | B | 32 | D |
| 3 | C | 13 | C | 23 | C | 33 | D |
| 4 | C | 14 | C | 24 | C | 34 | C |
| 5 | C | 15 | C | 25 | B | 35 | C |
| 6 | C | 16 | C | 26 | C | 36 | B |
| 7 | C | 17 | C | 27 | B | 37 | C |
| 8 | B | 18 | C | 28 | C | 38 | C |
| 9 | C | 19 | B | 29 | C | 39 | C |
| 10 | D | 20 | D | 30 | B | 40 | D |
Good luck on your exam! These 40 questions cover every major topic from both lectures. Focus especially on the cytoskeleton comparison table, nuclear transport size limits, organelle functions, and mtDNA facts - those are classic exam targets.
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