Lecture 9: Cells 2 Flashcards Preview

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- describes mitochondria and chloroplasts



- found in both plant and animal cells
- Where Respiration takes place (energy comes from ATP)
- Have two membranes (outer and inner)
- The inner membrane is folded to generated cristae. This increases the SA to fill membranes with proteins that are required for generation
- The matrix has cytric acid cycle takes place (like cytoplasm of cell). You'll also find DNA, RNA and ribosomes



- not found in animals (mostly plants)
- Responsible for photosynthesis
- Have outer membrane and an inner membrane
- Stacks of membranes sit inside and are called thylakoids
- Cytoplasm of the chloroplast is called the stroma (where carbon fixaition takes place- converts CO2 into sugar)
- Never find DNA and RNA inside the Golgi or ER (only outside). But, Chloroplass have RNA and RNA and ribosomes inside
- Gave rise to idea of endosymbiotic organelles


Endosymbiotic Organelles

- Mitochondria and chloroplasts are descendants of bacteria. Bacteria was taken up by eukaryotic cell via phagocytosis
- Double membrane (likely taken up by endocytosis)
- Own genome
- Own ribosomes more
similar to Eubacteria
- Genes more similar to
eubacterial genes
- Lipids come from ER through a unique system;
Unique machinery for protein import



- you need structure inside in order for cell to keep shape (since membrane is very flexible)
- This is a cytoskeleton
- Very crowded inside cell
- Almost entire space is taken up


Cytoskeleton Filaments

• Actin filaments (smallest)
• Intermediate Filaments
• Microtubules (largest)


Actin filaments

- exists in cells as monomers and filaments
- there are many proteins
that regulate polymerization
and depolymerization
- When they polymerize, there is protein to protein interaction (non covalent)
- They have a polarity when they polymerize (neg end and pos end)
- form very long bundles


Actin in Gut cells

- Cortically stabilizes the cell to make sure they look rectangular and can extend fingers (full of actin which increase SA so a lot of food can be taken up)


Actin and Myosin

- interact to cause movement
- When myosin “head” attaches to actin and moves, the actin filament slides
- myosin can move in one direction
- can hydrolyze one ATP


Actin and Myosin contraction

- Coiled-coil tail domains of myosin II can interact to form antiparallel bipolar complexes.
- These may contain many myosin molecules, as in thick filaments of skeletal muscle, or as few as 2 myosins.
- Myosin heads can move along actin filaments in only one direction.
- Antiparallel actin filaments can “contract”.


Examples of movement caused by actin-myosin

• Cytokinesis in animals
- Actin-myosin
interactions pinch
membrane in two
• Cytoplasmic streaming
in plants
- Actin-myosin interactions
move cytoplasm around
- Cytoplasmic streaming (need to remove contents around cytosol which is mediated by actin myosin contraction)



- As for actin, there are many
proteins that regulate growth
or shrinkage of MTs
- alpha and beta tubulin bind together to form tubulin monomer
- Has polarity to it
- Then microtubules emirate from nucleus and go to cell periphery


Microtubules; organization

- organize the cell
- they organize the transport of things from nucleus to periphery
- Basically highway of cell because they have two types of motors (actin has one) they move in opposite directions
- Gave kinesis and dyenin (walk in opposite directions)



- has tail, stalk and then head
- "walks" along a microtubule track



- walks in opposite direction to kinesin


CiIia & Flagellum

- formed by microtubules
• Cilia (single celled eukaryotes), move only backwards and forwards (found in throat and lungs, and oviduct in women where egg is moved)
• Flagellum (found in sperm cells)(also found in bacteria, but have a different structure)


Microtubule doublet

Called 9+2 (because 9 microtubule doublet around the edge, then two doublets in the middle)
- tightly bound to each other
- dynein connects the microtubule doublets together (only can slide up and down)
- When ATP is added, the sliding causes bending


Intermediate filaments

- form rope like structures in cells that provide mechanical strength to cells (coiled coils of keratins) or nucleus (lamins)
- Cannot polymerize
- Not many regulatory proteins
- No plus or minus end
- Make cells more structurally stable
- Provide structure to nucleus (always round)
- Basically connect cells (as shown in picture)


Coiled Coils

- arise when two α-helices have hydrophobic amino acids at every 4th position (one complete turn 3.6 amino acids)
- Fibrous structural proteins consist mainly of α-helices arranged as coiled coils, such as the keratins in hair and feathers.


Extracellular Matrix (ECM)

- used to stabilize cells
- contain many collagen fibrils, each made up of collagen proteins


Collagen Proteins

- consist of three polypeptide chains that wind around each other
- found in gelatin
- important for muscle attachment


Cell- Cell Adhesion

• Cells can interact with the environment:
- In cell recognition, one cell specifically binds to another cell of a certain type. This can lead to phagocytosis, DNA exchange, sperm-egg fusion
- In cell-cell adhesion, cells stably bind to each other.
- Evolutionary came from phagocytosis


Tight junction

- ensures no food cannot enter body without going through the cells (no food is stuck between cells)
- a tight junction forms a watertight seal between epithelial cells


Gap junctions

- allows separation of different membrane domains
- Separates apical side (transport glucose) and basolaterial side (side facing bloodstream with glucose carrier proteins)
- creates channels that connect animal cells
- allow diffusion of small things like ions (due to low molecular weight)
- Ex in the heart (have pacemaker cells that are connected to neurons to receive contraction signal, release Ca through gap junctions)