Each organelle contains specific molecules for specific chemical reactions and cellular processes
Why organelles are so great
Compartmentalization! Incompatible chemical reactions can be separated things the cell wants to keep intact
For example, digestive enzymes can be kept away from
Why organelles are so great
Specialization! Increased efficiency of chemical rxs and cellular processes
Substrates required for chemical reactions can be clustered in one compartment and/or embedded in the organelle membrane for easy access, thus speedier rxs
Why organelles are so great
Complexity
With the help of a supportive cytoskeleton, cells can become bigger, perform more diverse functions, give rise to multicellularity
The nucleus houses the DNA and is the site of RNA synthesis
Some ribosomes float freely in the cytosol, where they make proteins that function in the cytosol
Other ribosomes are attached to the rough endoplasmic reticulum, where they synthesize proteins that will be:
embedded in a cell membrane
secreted from the cell
put inside of an organelle
The rough endoplasmic reticulum gets its name from the rough appearance of the ribosomes on its surface
The attached ribosomes grab RNA strand from nucleus and start injecting protein product directly into the lumen of the rough ER as its being translated
The smooth ER (which is “smooth” because it’s not associated with ribosomes) is where lipids such as phospholipids and fatty acids are synthesized
The Golgi apparatus receives proteins and lipids from the rough and smooth ER and:
further modifies them (e.g., by attaching a sugar molecule) and
sorts and packages them for delivery to their final locations in the membrane or outside of the cell
The Golgi apparatus is also where most of the cell’s carbohydrates are synthesized
The nucleus, ER and Golgi make up a continuous “endomembrane system” (or “secretory pathway”)– connected by vesicles –
to streamline synthesis and delivery of proteins and lipids to their final destinations
Lysosomes break down damaged or unneeded macromolecules (large molecules) into smaller components
Lysosomes form from the fusion of Golgi vescicle containing enzymes and the vesicle containing macromolecules to be broken down
Mitochondria synthesize most of the ATP (“energy currency”) used by the cell
Chloroplasts (in plant cells) capture energy from sunlight and synthesize simple sugars
The biconcave shape of a red blood cell maximizes its surface area for gas exchange and allows it to deform as it passes through the circulatory system
Long, slender extensions of the plasma membrane allow neurons to communicate with other cells
Thin, comb-like projections, called microvilli, on intestinal cells increase their absorptive surface area
Long flagellum facilities movements, packed with a lot of mitochondria to support this energy-intensive swimming function
Peroxisomes break down specific organic molecules, such as fatty acids, and synthesize other organic molecules such as cholesterol and some types of phospholipids
Cytoskeleton (the "bones of the Cell)
The cytoskeleton provides internal structural support and enables movement of substances within the cell
• 3 types
• Each type is formed from long chains of protein subunits joined together
•The cytoskeleton is DYNAMIC! (unlike bones)
Microtubules
Subunits (“Building Blocks”):
• Tubulin dimers
Microtubules
Structure:
• Hollow tube
• Directional: plus end and minus end
Microtubules
Major Microtubule Functions:
• Cell shape and support
• Vesicle transport and organellearrangement
Cell movement (by cilia, flagella)
• Cell division (chromosomesegregation)
Microtubules: vesicle transport
Motor proteins kinesin and dynein “walk” on microtubule tracks to carry cargo-filled vesicles through the cell.
Microtubules: Cell movement
Microtubules are a key part of the structures of eukaryotic cilia and flagella.
Cilia and flagella beat to either propel a cell or allow it to move fluidly across the cell surface
Microtubules are dynamic
Microtubules lengthen and shorten at their ends
Microfilaments
Subunits (“Building Blocks”):• Actin monomers
Microfilaments
Structure:
• Thin double helix of actin protein monomers
• Directional: plus end and minus end
Microfilaments
Major Microfilament Functions:
• Cell shape and support
• Cell movement (by crawling)
• Vesicle transport
• Muscle contraction
• Cell division (cytokinesis)
Microfilaments: Cell shape and support
Actin microfilaments help maintain cell shape
Lots of actin microfilaments at plasma membrane!
Microfilaments: Cell movement (by crawling)
Elongating actin filaments at the edge of the cell membrane allow crawling motion of cells
Microfilaments: Vesicle transport
Actin microfilaments work together with myosin motor proteins to carry out important functions.
Myosin motor proteins can “walk” along microfilaments carrying cargo-filled vesicles (similar to kinesin and dynein on microtubules)
Microfilaments: Muscle contraction
Interactions between actin microfilaments and myosin motor proteins are responsible for muscle contractions
Microfilaments: Cell division (cytokinesis)
Actin microfilaments play a key role in cell division.
A band of actin contracts, causing the two new cells to “pinch” apart
Intermediate Filaments
Subunits (“Building Blocks”):
• Diverse, cell - type - specific protein subunits