Biochemistry Chapter 4: Non-Enzymatic Protein Functions Flashcards
Microtubule depolymerization is responsible for
separating chromosomes during anaphase of mitosis or meiosis I or II.
Rapid actin polymerization near the edge of the cellular membrane is responsible for
for cellular motility in complex eukaryotic cells.
Actin vs tubulin
Actin = microfilaments
Tubulin = microtubules
Actin is made up what subunits
G-actin = free subunit
F-actin = polymerized actin
What happen at the (+) end of an actin filament?
ATP-bound monomers are added
What happens at the (-) end of the actin filament?
ADP-bound monmers are released
Keratin is an example of
intermediate filament
properties of intermediate filaments
more flexible than actin filaments
Microtubule sub units
alpha beta tubulin dimers
Microfilaments are important for what
- cellular motility
- cell structure
- cytokinesis (cell division)
- muscle contractions
Intermediate filament functions
- provide structural support
- help cell adhere to neighbouring cells
Microtubule function
- movement of chromosomes during cell division
- intracellular transport
- neutrophil and amoeboid motility
- cilia and flagella formation
Polymerization of microtubules involves what?
GTP
Critical concentration
The critical concentration (Cc) is the minimum concentration of free tubulin dimers required for microtubule polymerization, where growth occurs if [tubulin] > Cc and shrinkage occurs if [tubulin] < Cc.
Thick filaments vs thin filaments
Thick filament
are composed primarily of myosin proteins, whose heads interact with actin filaments to generate muscle contraction through ATP hydrolysis.
thin filaments
primarily composed of actin, along with tropomyosin and troponin, and play a crucial role in muscle contraction by interacting with myosin from thick filaments.
Microfilaments vs microtubulin subunit differences
Microfilaments = monomeric units of actin.
microtubule lattices = assembled from dimeric tubulin-heterodimers.
Kinesin
- anterograde movement
- from - to +
- from center of cell to edge of cell
KICK material OUT
Dyenins
-retrograde movement
- from + to -
-from edge of cell to center of cell
-DRAG material IN
Cadherins
Cadherins are transmembrane proteins which play a primary role in cell-to-cell adhesion (remember that “C” in cadherins stands for cell-to-cell), forming adherens junctions to bind cells within tissues together.
Integrins
are transmembrane receptors that modulate cell-to-extracellular matrix interactions. Specifically, these proteins often attach the cell to collagen and fibronectin fibers
💡 What is the difference between primary and secondary active transport?
✅ Primary = Direct ATP use (e.g., pumps like Na⁺/K⁺ ATPase).
✅ Secondary = Uses ion gradients (e.g., Na⁺-glucose cotransport).
Primary Active Transport 🚀
🔹 Uses ATP directly to transport molecules against their concentration gradient.
🔹 Example: Na⁺/K⁺ ATPase (Sodium-Potassium Pump) moves 3 Na⁺ out, 2 K⁺ in, using ATP hydrolysis.
Secondary Active Transport 🔄
🔹 Uses energy from an existing ion gradient (set up by primary active transport) to move another substance against its gradient.
🔹 Indirectly depends on ATP.
🔹 Two Types:
Symport 🛤️ → Both molecules move in same direction (e.g., Na⁺/glucose cotransporter in intestines).
Antiport 🔄 → Molecules move in opposite directions (e.g., Na⁺/Ca²⁺ exchanger in heart cells).
Na+K+ ATPase is a transmembrane protein that uses one molecule of ATP to transport what and in what direction?
to transport 3 Na+ out of the cell and 2 K+ into the cell.
are intercellular junctions that function as anchors to form strong sheets of cells.
Desmosomes
intercellular junctions that provide cytoplasmic channels between adjacent cells.
Gap junctions
Intercalated discs
are specialized intercellular junctions between cardiac muscle cells that provide direct electrical coupling among cells.
are intercellular junctions that prevent the movement of solutes within the space between adjacent cells.
Tight Junctions
How to remember the difference between where to find microtubule and microfilaments
🧠 How to make this stick:
🔁 Think of it this way:
Microtubules = movement of structures
“Wavy” motion like a tail
Cilia sweeping mucus
Sperm flagellum swimming
Motor proteins walking cargo along tracks
Microfilaments = movement of the cell itself
Muscle contraction
A white blood cell crawling
A cell dividing in cytokinesis
