Cell Respiration - Standard 9

Cell Respiration 

Throughout the past few weeks I have noticed that I have struggled a lot with understanding Cellular Respiration, and this was also evident on my most recent test. After this realization I knew I had to make extra time in my schedule to understand Cellular Respiration. I cannot simply watch a video or flip through a powerpoint to understand the material, so I have decided to type up, in my words, what cellular respiration is and how it works, and then take this information and connect it to other information.

DEFINITIONS

Oxidized - when a chemical (compound/element) is oxidized it loses electrons

Reduced - when a chemical (compound/element) is reduced it gains electrons

These play into the equation for cellular respiration: 

(C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy (ATP))

In this equation C6H12O6 becomes oxidized and becomes 6 CO2. This means that it loses electrons; This happens by Dehydrogenase which is an enzyme, and NAD+, which is a coenzyme, these transfer 1 or more protons and a pair of electrons to an acceptor. This entire first step of cellular respiration is called glycolysis, because while NAD+ is transporting electrons, the C6H12O6 is becoming pyruvic acid. This process uses 2 ATP and produces 4 ATP, so the cell gains 2 ATP from this first step alone.

The enzymes used in glycolysis and the other steps of cell respiration allow the processes to use less energy and to be done faster, and they are all created through PROTEIN SYNTHESIS!!!

Lets Review:

1st Step - Transcription from mRNA --> DNA (flashback to DNA replication)

This step occurs inside the Cell Nucleus (flashback to cell organelle projects)

First the RNA polymerase lays down corresponding RNA bases (A, U (replaces T), G, C). This creates pre-mRNA.

2nd Step - Processing 

The splicesome cuts out the introns, which is "junk DNA" or non-coding DNA. It also attaches a poly-A tail and cap. These are to protect the RNA strand from enzymes in the Cytoplasm. Instead of breaking down the important RNA information, they will break down the poly-A tail. 

2nd Step - Translation from mRNA --> Amino Acids --> peptide chain

The mRNA leaves the Nucleus through nuclear pores and enters into cytoplasm. In the cytoplasm the two pieces of a ribosome will fit together and began reading the mRNA strand from the 5'-->3' end. The strand will first enter the A or acceptor site of the ribosome. A tRNA will bind (using an enzyme) with an Amino Acid. Each different codon (3 mRNA bases) has a different Amino Acid it corresponds to. As it enters into the P site, the tRNA with the corresponding Amino Acid will begin the peptide strand. After this the mRNA will enter into the E or exit site and the process will continue until the Ribosome reads a stop codon, and will release the strand. Most of these Ribosomes are found in the Rough Endoplasmic Reticulum.

BACK TO CELL RESPIRATION:

These NAD+ are also stored energy, because they are electron carriers. This entire processes is simply moving around electrons. After NAD+ gains this electron it will be reduced to NADH. It will then transport this electron to the electron transport chain, which moves electrons through a series of small steps, rather than one gigantic step. This electron transport chain releases controlled amounts of energy for the synthesis of ATP (done by the enzyme ATP synthase). 

NEXT STEP:

Before this step can begin, Pyruvic Acid/Pyruvate must be converted to Acetyl Co A which happens by the bonding of the two carbons and co enzyme A - there are two Acetyl Co A going into the Citric Acid Cycle.

The Citric Acid Cycle takes place in the mitochondrial matrix, unlike glycolysis which takes place in the cytosol. First the two Acetyl Co A will each combine with an oxaloacetate which will form citrate. After this it breaks back down into oxaloacetate through a series of steps. This process creates NADH and FADH2 that will move electrons to the electron transport chain. The citric acid cycle or Kreb cycle will only produce 2 ATP. 

LAST STEP:

The last and final step in cell respiration is ATP Synthesis. The last two steps were known as "Substrate-level phosphorylation", however this step is known as oxidative phosphorylation. In this final phase the electrons pump protons across the inner mitochondrial membrane, then the oxygen joins with hydrogen to form water. After this the protons diffuse back into the mitochondrial matrix which causes the synthesis of 32-34 ATP.

THIS IS ME SHOWING YOU THAT I NOW UNDERSTAND CELL RESPIRATION AND CAN CONNECT IT TO OTHER THINGS WE HAVE LEARNED THIS YEAR. :)