L7: Cells Flashcards
Reason for different types of cells
- Transcription regulation at promoter
- Epigenetic changes
- Acetylation (activate gene transcription)/deacetylation (deactivate) of Histone
- Methylation of DNA
Components of nucleus
- Nucleolus
- Nuclear membrane (double membrane)
- Heterochromatin
- Euchromatin (active in gene transcription)
Chromatin = DNA + histone
Function of nucleolus
- ribosomal RNA synthesis and transcription (ribosomal protein imported from cytoplasm)
- Processing and assembly of ribosomes
Prominent during interphase
Rough ER function
Protein synthesis, well-developed in secretory cell
Membranous sheets, tubular network
Smooth ER function
- Calcium storage and release (sarcoplasmic reticulum)
- Lipid metabolism and detoxification
- Steroid hormone production
Golgi apparatus function
- Modifications and packaging of proteins
- Glycosylation
- Proteolysis into active form
- Sorting of protein for exocytosis - Lysosome formation
- Recycling of cell membrane
- Lipid are only for incorporation into vesicles
(Cis (forming) and trans (exit) surface)
Nucleic acid staining
Basophilic, therefore stained by basic dye (blue dye / haematoxylin dye)
Mitochondria features
- Double membrane
Outer: Permeable to many substances by non-specific channel proteins
Inner: folded into cristae, contain respiratory chain enzymes
Intermembranous space: Cytochrome C
Matrix: Citric acid cycle enzymes, fatty acid oxidation, store calcium - Circular DNA (maternal origin)
Encodes proteins for oxidative phosphorylation, mitochondrial protein encoded by nuclear genes and transported into mitochondria
Types of cytoskeleton
- Microfilament (Actin) (最細)
- Intermediate filaments (structural)
- Microtubules (地鐵路軌) (最大)
Functions of Microfilament
- Cell movement
- Cytokinesis
- Microvilli
- Stress fibres
(actin: two forms: G-actin and F-actin)
Functions of Microtubules (present in all cells except RBC)
- Intracellular transport: movement of organelles, vesicles
- Chromosome separation (by microtubules from centrosome)
- Cilia
Alpha and beta: Microtubules
Gamma: Centrosome
Functions of intermediate filament
Structural support, cell shape and rigidity
Types of intermediate filament
- Tonofilament / Cytokeratin (epithelial cells)
- Desmin filament (muscle)
- Vimentin (fibroblasts)
- Neurofilament (neurone)
- Glial filament (GFAP) (glial cells)
- Nuclear lamin
- Vimentin (fibroblasts)
- = important
Microtubule motor protein
- Kinesins (towards +ve end)
- Dyneins (towards -ve end)
(火車在路軌)
Purpose of membrane fluidity
Allow lateral diffusion for membrane protein
Breaks and tears sealed spontaneously
3 types of membrane lipids
- Phospholipid
- Cholesterol (stabilise membrane mechanically)
- Glycolipid (outer side of membrane)
Function of membrane proteins
- Transport molecules in and out
- Receptors for signalling
- Attach cells to ECM
- Attach cytoskeleton filament to cell membrane
- Enzymatic activity, cell attachment and communication
Function of membrane carbohydrates (glycocalyx)
- Antigen (Cell type and blood group)
- Histocompatibility complex
- Adhesion
4 types of endocytic vesicles
- Phagosomes (largest)
- Clathrin-coated vesicles
- Caveolae (smallest, high affinity to cholesterol)
- Uncoated vesicles
Function of exocytosis
- Secretion (from trans face of Golgi)
2. Recycling of cell membrane
What is endosome
- Sorting compartment along endocytic pathway
- Early, recycling, multivesicular, late endosome
- Fuse directly with lysosome and low pH activate lysosomal acid hydrolases
- Endosome pH affects the fate of transported ligand
Describe nuclear membrane
Two concentric membrane
Outer: continuous with ER
Inner: attached to lamins of nuclear matrix
Describe cell cycle
- G1 —> S —> G2 —> M —> G1
- G0 for non-dividing cells
- Interphase: G1, S, G2
- Regulated by cyclin dependent kinase (cdks) which is activated by cyclin
Describe mitosis
- Prophase: condensed chromosome
- Prometaphase: break down of nuclear membrane, attachments of chromosome at kinetochore to spindle microtubules
- Metaphase: Alignment at equatorial plane
- Anaphase: Separation to two poles
- Telophase: Chromatids separate from microtubules, reformation of nuclear membrane
- Cytokinesis: Cleavage into two cells by aggregation of actin-myosin belt
Describe Centrosome
- A pair of centrioles which located at spindle pole and organisation of spindle fibres
- Duplicate once each cell cycle
- Segregation of chromosome
What are lysosome
- High content of acidic hydrolytic enzyme
- Numerous in macrophage and neutrophil
- From Golgi (primary), fusion with endosome (secondary), fusion with phagosome (phagolysosome)
What are perixosomes
Contain oxidative enzyme for oxidative detoxification
Numerous in hepatocyte
Beta-oxidation to break down fatty acids
