Cells at Work

Respiration:
Metabolic reactions and processes that convert chemical energy present in nutrients into energy form ATP. ATP is essential for powering many functions within the cell.

Cytoplasm

Mitochondria

Glycolysis: Glucose is converted into pyruvate. During this steps to ATP are produced and NADH.

Kreb's Cycle:Takes place in Mitochondrial Matrix. A series of chemical reactions that oxides Acetyl-CoA to realease stored energy in nutrients. This cycle produces: 6 NADH, 2 FADH2 and 2ATP

Oxidative Phosphorylation: Takes place in the mitochondrial membrane. This is the process in which ATP is produced as a result of transfer of electrons from NADH and FADH2 to O2. This creates an unbalance distribution of protons outside the mitochondrial matrix. This protons than rush into the mitochondrial matrix through a channel enzyme creating a proton motive force. This enzyme (ATP synthase), creates ATP as the protons are going across the membrane.

SIGNALING: Communication is key for cells. Thus, cells need to use chemical signals to talk to one another and must have specific receptors to obtain that signal.

Enzymes: Cells are very busy and in order to get work done they go through many chemical reactions. Enzymes are proteins present in the cells that act as biological catalyst. They help this reactions take place at a faster rate by lowing activation energies.

Ligands these are the signaling molecules used for cells to communicate. Ligands bind to specific receptors and can initiate a cascade of reactions within the cells. Different ligands may be responsible for different reactions.

GPCRS are the most abundant and diverse group of receptors present in cells membrane. This receptors are highly specific to one signal. GPCRs, after binding to a ligand, undergoes conformational changes and interact with a g-protein in the membrane activating it.

G protein is composed of three different sub-units. After conformational change, GDP is replaced to GTP in the alpha sub-unit. Once activated this protein diffuses along the membrane to interact with other cell membrane proteins to carry on the message. This other proteins create second messengers to initate a cascade and respond to the message.
Common 2nd Messenger : Cyclic AMP

Cytoskeleton Provides cell's structure, organization, aids with division and movement.

Michaelis-Menten is one of the best models to describe the enzymatic rate of reaction.

  • Vmax Maximun rate at which an enzyme catalyzes a reaction
  • Km: concentration of substrates at which the reaction reaches half the Vmax. Low Km number indicates high affinity. (It takes less substrate for reaction to reach half its maximun)

Microfilaments: Smallest cytoskletal structure. Composed of two intertwined strands of actin polymers. Helps to maintain cell shape and key to changing cells shape.

  • Actin filaments interact with Myocin. (Important for muscle cell).
  • Aids with movement inside the cell.
  • Cell division: Aids with cytokineses (Actin ring separates the two cells)

Intermediate Filaments: They are defined by its size rather than its monomers because there are many kinds of intermediate filaments.

  • Aids with cell shape
  • provides more stability for cell since they are less dynamic
  • Great for anchoring organelles that do not need to move (ex. Nucleus).

Microtubules:Largest cytoskeletal structure. Composed of a-tubulin and B-tubulin structures. Its imporatnt for structure and transport.

  • Transport: allow movement inside the cell. They are like railroad tracks.
  • Cell division: They help with pulling chromosome appart.
  • cell movement: Via cilia (moving fluid around the cell) and flagella structures (mobilizing the cells to different directions).

Example of Enzymes discussed: ATP Synthase, Protein kinases (add phosphate groups), Protein phosphotases (remove phosphate groups).

Enzyme Inhibition: Inhibiting enzymes is important in order to prevent enzymes from overproducing.

  • Competitive Inhibitors: Molecule that competes with subtrate for the active site of an enzyme. Does not affect Vmax but increases Km.
  • Non-competitive inhibitors: Binds to a different site of the active site changing active sites shape.
    Does not affect Km but decreases Vmax

Work at specific conditions:

  • Enzymes active site are very specific to its substrate
  • Enzymes work at specific PH
  • Enzymes work at specific temperature

If these conditions aren't met enzymes at much lower rate. Or, they can simply denature if exposed to very high temperature or different PH.
When an Enzyme is denature they lose their 3D shape conformation and essentially losing all activity.