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Cells - Coggle Diagram

- - - - One chromosome = one long DNA molecule + many proteins
        
        Histones: DNA coils around them to reduce length to fit into nucleus
        
        Complex of DNA + proteins = chromatin (less condensed than chromosomes)
        
        When cell is not dividing, stained chromatin appears as a diffuse mass in micrographs —> chromosomes cannot be distinguished from e/o although discrete chromosomes are present
        
        When cell prepares to divide, chromosomes form loops and coils, condensing and becoming thick enough to be distinguished under microscope as separate structures
  - - - At the lip of pore, inner and outer memb of envelope is continuous
      - Protein structure called pore complex lines each pore
        
        Regulates entry and exit of prot, RNA, and marromolecules
    - - A net-like array of protein filaments called intermediate filaments —> mechanical support of env to maintain shape of nucleus
      - Lamina and matrix help organise genetic materials so nucleus functions efficiently
    - - Framework of protein fibres extending through nuclear interior
  - - - Prot imported from cytoplasm are assembled with rRNA into small and large subunits of ribo
        
        Subunits leave nucleus by nuclear pores where they assemble into ribo
    - - Depends on species and cell repro stage
        
        Nucleolus controls cell div and lifespan
- - - - Free and bound are structurally identical; ribo can play either functions at diff times
      - Free: make prot that function within cytosol
      - Bound: make prot that insert into memb/package into organelles like lysosomes/for secretion from cell
        
        Hence cells that specialise in prot secretion have higher proportion of bound
- - - - Has impt enz that help lipid synthesis (oils, steroids, new memb p.lipids
      - Other enz help in detox of drugs and poisons (esp in liver cells)
        
        Detox usually involves adding -OH groups to drug molecules —> more soluble —> easier to flush from body
        
        Drugs induce proliferation of sER and associated detox enz —> inc. rate of detox —> inc. tolerance to drugs
        
        However, since some enz have relatively broad action, proliferation of sER in response to one drug and inc. need for higher dosage of other drugs (eg barbituate abuse can reduce effectiveness of certain antibiotics and other drugs)
      - Stores Ca2+ ions —> trigger responses in cells
        
        Eg muscle cells: sER pumps ions from cytosol to ER lumen. When muscle cell is stimulated by nerve impulse, Ca2+ rush back across ER memb back into cytosol, triggering muscle cell contraction
    - - Many cells secrete proteins that are produced by ribo attached on rER
        
        As a pp chain grows from a bound ribo, chain is threaded into the ER lumen through a pore formed by protein complex in the ER memb
        
        Folds into its functional shape
        
        Most secretory proteins are glycoproteins —> carbs are attached to prot in ER lumen by enz built into ER memb
        
        ER memb separates secretory prot from prot in cytosol (produced by free ribo)
        
        Secretory prot depart from rER in tpt vesicles that bud from a specialised region called transitional ER
      - rER grows in place by adding memb proteins and p.lipids to its memb
        
        As a pp destined to be memb prot grows from ribo, it is inserted into ER memb and anchored there by hydrophobic regions
        
        rER synthesises memb p.lipids using enz built into ER memb. The enz assemble p.lipids from precursors in the cytosol
        
        ER memb expands, but portions of it are also transferred in the form ot tpt vesicles to other components of endomemb syst —> maintain balance
    - - ER memb continuous with nuclear env i.e. space between 2 membranes of nuclear env is continuous with ER lumen
  - - - Before pdts from golgi bud off in tpt vesicles from trans face, golgi stack sorts the pdts and targets them for various parts of the cell
        
        Molecular identification tags (eg phosphate groups) are added to the pdts
        
        Tpt vesicles may also have external molecles in their memb that recognise “docking sites” on surf of organelles/on plasma memb —> targets vesicles appropriately
    - - Memb of each cisterna in a sac separates its internal space from cytosol
      - Golgi stack has distinct structural directionality; memb of cisternae on opposite sides of stack differ in thickness and molecular composition
        
        2 sides: cis and trans face
        
        Cis: located near ER
        
        Vesicles that bud from ER add their membrane and contents to lumen of cis face by fusing with golgi memb
        
        Trans: opposite side
        
        Gives rise to vesicles that pinch off and travel to other sites
        
        Pdts of ER usually modified during transit from cis to trans region
        
        Eg: glycoproteins in ER have their carbs modified, first in ER, then in golgi; golgi removes some sugar monomers and substitutes others, producing a large variety of carbs
        
        Memb p.lipids may also be altered in golgi
    - - Many polysaccharides secreted by cells are golgi pdts
      - Like secretory proteins, nonprotein golgi pdts that will be secreted depart from trans face, inside tpt vesicles that fuse and add to surf area of plasma memb, contents released via exocytosis
  - - - Lysozymes work best in acidic env found in lysosomes —> if a lysosome breaks open/leaks its contents, the enz will not be as active as cytosol has a near neutral pH
        
        However, excessive leakage from large no of lysosomes can destroy a cell by self-digestion
        
        Prot of inner surf of lysosomal memb + enz themselves are spared from destruction due to 3D shapes of these proteins protecting vulnerable bonds from enzymes
      - Hydrolytic enz and lysosomal memb are made from rER and transferred to golgi, lysosomes bud off trans face of golgi
    - - Eg: amoebas and other protists engulf and form food vacuoles via phagocytosis, lysosomes bind to vacuole to digest food, end pdts pass into cyosol and become nutrients for cell
      - Some human cells also carry out phagocytosis; eg WBCs engulf and destroy bact and foreign particles
    - - During autophagy, a damaged organelle or small amt of cytosol becomes surrounded by a dbl memb. Lysosome fuses with outer memb of vesicle. Lysozymes dismantle inner memb and enclosed materials. Resulting small organic compounds released to cytosol for reuse —> cell continually renews itself