Loads o’ Cell Signaling

This week was mainly focused on the concept of cell signaling and additionally cellular respiration. We first started with a diabetes and insulin packet about cell signaling. Not gonna lie, it was a little cheesy. But it had some good information buried in there.

Basically, a cell signaling pathway (3.D.2 and 3.D.3) has four essential components:

  1. The initial signal
  2. The receptor that binds the signal
  3. The signaling molecule or molecules that transmit the message
  4. The effector or effectors that result in short term or long term cellular change

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(Ignore the numbers labeled in the picture) These steps can be simplified by their names:

  1. Signaling
  2. Reception
  3. Transduction
  4. Response

Now for the deeper level. Essentially, a signaling molecule, which can be as small as estrogen or a large protein, passes through the signal-binding domain either intracellularly or extracellularly (intracellular for small signals like estrogen or extracellular for large proteins that are too large to pass through the membrane). Once the signal binds to the receptor, the receptor changes shape to accept the molecule. A quick side note– the cell can also have a second messenger for the same message. This is generally a small molecule that can travel freely through the cytoplasm or the membrane, and one released, they can interact as targets throughout the cell simultaneously. This leads to signal amplification and increased speed in signal transduction.

second-messenger
Second Messenger

ANYWAY, once the receptor receives this signal, it then sparks an enzyme within the cell to move, causing a phosphorylation cascade. The enzymes can continuously keep setting off other enzymes, each time a phosphate being added to every enzyme from ATP. Throughout this phosphorylation cascade, the signal is amplified throughout each step– to my understanding the signal is amplified to make the chances greater for the signal to be received in the fourth step. (I may be wrong though??)

phosph-cascade
A closer look at the phosphorylation cascade

Sometimes, these protein kinases must be deactivated, and this is done so through feedback inhibition. This occurs when some downstream effector inhibits an earlier step in the signal transduction. Therefore, the dynamics of speed and magnitude of the response can be slowed or stopped entirely. To my understanding, feedback inhibition is for when there are too many signals that the cell just doesn’t need in order to complete the transcription (?).  After the phosphorylation cascade comes the actual response. When the last protein kinase sends the signal within the nucleus, an inactive transcription factor becomes active and encodes DNA that the original signal sends. So yeah! That’s basically a simple version of cell signaling. What I’m still confused on is the short and long-term cellular change. What does this entail?

The last part of the week had to do with cellular respiration. This process’s goal is to make ATP that cells need all the time. In most cases, cells are in high-oxygen environments. This allows for the aerobic cellular respiration to take place. Cellular respiration generally happens in the mitochondria in our cells (go mitochondria); they take food and break it down into ATP. There are for main steps for cellular respiration: glycolysis, the link reaction, the citric acid cycle (aka Krebs), and the oxidative phosphorylation.

Glycolysis takes place in the cytoplasm. Glucose breaks down into pyruvate, and creates 2ATP and 2NADH. The pyruvate then enters the mitochondria through the link reaction.

The pyruvate molecules are decarboxylated (they lose a molecule of carbon dioxide) and 2 more NADH is also released.

Next is the citric acid cycle, which also releases COz, 2 ATP, 6 NADH and 2 FADH2. To be honest, I’m not really sure what happens besides that.

The next step is the oxidative phosphorylation, or electron transport chain. O2 is essential for this step. The chain creates 34 ATP (whoa!) and 6 H2O molecules. This is where most of the ATP is created in our cells.

cellular-respiration

So what if we don’t have any oxygen present?? Then anaerobic respiration takes place. There are two types of this; lactic acid fermentation and alcoholic fermentation. Long story short, this way doesn’t create loads of energy, but does give an extra boost of energy, for example when we sprint we first use anaerobic respiration, and then we gradually use cellular respiration.

What I’m still so confused on is oxidation and reduction. How does this play into cellular respiration? Why is it important? I would also like more clarification on NADH and FADH2– how are they created, and why? Also, I would like to talk more about how when signal transduction pathways change, they alter the cellular response. Why?

Oh! I also forgot– we briefly talked about the idea that cell signaling is a way to recognize how closely related organisms are. (3.D.1) My group concluded that his is because if cells have similar original signaling molecules and signaling pathways, they will produce DNA that is similar to each other, creating a closely relating organism.

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