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Cellular Organelles

by | Feb 17, 2024

  • Cell: basic functional unit of all living things bound by a plasma membrane
  • Cytoplasm: contains organelles suspended in a fluid matrix (cytosol) which consists of water and dissolved substances like proteins and nutrients
  • Organelles: Internal membrane bound bodies within the cytoplasm that serve to separate metabolic reactions and compartmentalize the cell
    • Within organelles, chemical reactions are isolated and can take place without interference/competition with other nearby reactions
  • Cell can be specialized for specific functions depending on number of specific organelles

Nucleus

  • Membrane bound organelle that contains the cell’s DNA/chromosomes
    • Nucleoli/Nucleolus: concentrations of DNA that make rRNA
  • Nuclear pores: passageways for proteins and RNA molecules on nucleus surface

Ribosomes

  • Structure: Made of ribosomal RNA (rRNA) and protein
  • Function: synthesizes protein according to mRNA sequence by assembling amino acids
  • Found in all living things, reflecting common ancestry
    • Prokaryotes have ribosomes attached to cytoplasmic surface of plasma membrane

Two types of ribosomes:

  • Attached to the Rough ER: makes proteins that are going to be exported from cell
  • Free Ribosomes: makes proteins that will be exclusively used by the cell (ex mito)

Endoplasmic Reticulum

  • Occurs in two forms: rough and smooth
  • Rough has small ribosomes attached to the ER                                                                                         
    • Synthesizes proteins using the attached ribosome
      • ER proteins, membranes, ECM, lysosome proteins; makes glycoproteins by attaching polysaccharides
    • The folded nature of the rough ER compartmentalizes the cell → increases efficiency by allowing multiple processes to happen at once and makes space for ribosomes to make proteins
  • Smooth ER does NOT have ribosomes bound to it
    • Found in liver cells and detoxifies/breaks down drugs, toxins; metabolizes carbs
    • Synthesizes lipids and steroid hormones
  • Helps transport proteins from the ribosome to other parts of the cell

Golgi Complex

  • Functions: correct folding and chemical modification of proteins and packaging in vesicles for protein trafficking               
    • Receives, modifies, ships
  • Structure: Folded membrane bound sacs (cisternae)
    • Also has vesicles attached to it to ship out proteins to membrane, lysosome, or exterior
  • Two sides to it:
    • The cis face: where all the incoming proteins go to be modified
  • The trans face: where all the modified proteins go to be “shipped out”

MITOCHONDRIA

  • Function: Site of ATP synthesis and other aerobic processes

Physical Attributes of the Mitochondria

  • Double membranes → separates metabolic processes in intermembrane space and inner membrane + increased surface area       

Contains circular mDNA, ATP synthase & own ribosomes

Cristae Intermembrane Space Inner Membrane Matrix
Convolutions of inner membrane increase surface area → better metabolic efficiency (make more ATP) Space between two membranes where protons accumulate Site of oxidative phosphorylation

Contains ETC and complexes

Separates region of high/low concentration

 Fluid material that fills space inside inner membrane

Site of Krebs Cycle and Pyruvate oxidation

Lysosomes

  • Structure: Vesicles from Golgi that contain hydrolytic enzymes (from rough ER)
  • Function: Lysosomes hydrolytic enzymes break down food (intracellular digestion), cellular debris/waste (recycle a cell’s organic materials); metabolize lipids and control apoptosis
  • Low pH is favorable to hydrolytic enzymes → any enzyme that might escape from lysosomes becomes inactive in neutral pH of cytosol

Vesicles

  • Transport Vesicles: membrane enclosed sacs that move materials between organelles and plasma membrane
    • Movement dependent on microtubules and motor proteins

Vacuole

  • Fluid-filled, membrane-bound bodies
  • Food vacuoles: stores food and often merge with lysosome whose digestive enzymes break down food
  • Contractile vacuole: collects and pumps excess water, balances H+ & water
  • Central vacuole: occupies most of interior of plant cells
    • When fully filled exert turgor (pressure) on cell wall which makes cell rigid
    • Has other functions which specializes cell for specific functions
  1. Store starch, nutrients, pigments, waste
  2. Digestion
  3. Helps plants growth by absorbing water; animal cells need nutrients to build macromolecules to grow
  4. Reduces volume of cytoplasm
  5. Act as balancers to maintain homeostasis

Centrioles/Basal Bodies

  • Act as microtubule organizing centers
  • Centrioles organize and pull replicated chromosomes apart used in cell division
    • Centrosome: contains 2 centrioles, not in plants
  • Basal bodies form and organize flagella and cilia

Peroxisomes

  • Contain enzymes that break down hydrogen peroxide (make water and oxygen), fatty acids, and amino acids
  • Many in liver and kidney cells to detoxify substances
  • In plants, found near chloroplast and modify by-products of photorespiration

Cytoskeleton

  • Network of protein fibers and internal structure of cytoplasm
  • Function: Cell support, maintain shape, motility
    • Motor proteins use ATP to act on cytoskeleton and move cell along fibers

Parts of Cytoskeleton

  • Microtubules: shape cell, guide organelle movement, separate chromosomes in cell division
    • Made of protein tubulin; organized by centrioles
    • Found in spindle apparatus + cilia and flagella
  • Microfilaments: muscle contraction (cell division), amoeboid movement, pseudopodia extension
    • Made of protein actin
    • Found in muscle cells and cells that move by changing shape (ex: phagocytes)
    • In plants allow for cytoplasmic streaming: movement of cytoplasmic materials in cell
  • Intermediate filaments: support cell shape and fix organelles in place

Flagella and Cilia

  • Motile appendages that contain microtubules and protrude from the cell membrane
  • Flagella: long, few, move snakelike
  • Cilia: short, many, move back-and-forth
  • In sperm, flagella propels them while cilia sweeps away debris

CHLOROPLASTS: REFER TO PHOTOSYNTHESIS UNIT DOWN BELOW

The Endomembrane System

  • The ER synthesizes proteins, the Golgi modifies/packages it, and then the vesicle will export them
  • To be part of EM system must be derived from ER or Golgi
    • Ex: nuclear envelope, plasma membrane, lysosomes

Extracellular Matrix/Glycolax (animal cells)

  • A large network of proteins and other molecules in animal cells
    • Molecules ex: oligosaccharides from lipids, recognition proteins, and glycoproteins
    • Has connections to cytoskeleton
  • Function: surrounds cell to provide support, structure, attachment, communication, growth, movement, & differentiation
  • Membrane Carbs: help with cell-cell recognition → interact w/ other surface molecules so cells can be sorted into tissues
    • Glycoproteins and glycolipids: have carbon chains attached