Meiosis, Mitosis, Reproduction...and everything else I've been to lazy to post about.

If you couldn't tell by the title of this post, I've been slacking quote bad with my biology posts (Damn you stumble upon.) These past 2 (3?) (4?) weeks we've been covering Meiosis, Mitosis, Stemcells, Cloning, Reproduction, and Genetics. Which means it's time for another series of blog posts to cover all the information. So the official topic of this post will be "How Cells Reproduce" and "How a baby is made (ish)."

How Cells Reproduce, and Make Babies. Its Magical.

Once upon a time, you were a cell. As a cell you couldn't move, breathe, talk or hear, but the one thing that you could do is reproduce, and reproduce you did. Starting as one cell and then doubling exponentially until you ended up as a body with 50-75 trillion cells. The processes that control how that original cell is made, and how a person is made from that cell are some of the most important and intricate process in biology.

Disclaimer: 

Now the first thing that I should explain is how the cell cycle and Mitosis work, as these will be necessary to understand how Meiosis (slightly more complicated than Mitosis) works, and how the baby duplicates its cells to grow in the womb. 

Mitosis & The Cell Cycle:

Since Mitosis is a circular cycle (seems redundant right?) Which means the new cycle starts right after the last cycle ended. Now that the last cell cycle has ended our newly created (cloned would be a more accurate term?) cell (let's call it Joe) enters the magical phase of G1 (not G6, G1, that song is just stupid). The G1 phase is all about...you guessed it, Growth! All that the cell does during G1 is get nice and big to prepare to duplicate its chromosomes. This happens in the next stage, aptly named Synthesis. All that happens in this stage is the chromosomes make clones of themselves going from 23 pairs of chromosomes (2 sets of 23) to 46 pairs (4 sets of 23.) From here Joe then enters phase G2, also known as.......wait for it.......wait for it.......wait......GROWTH PHASE TWO!!!!!!! During this phase the cell gets to a large enough size that it cannot efficiently remove waste from the insides, and get "food" in. Which, of course, means it's time to end interphase (the last three phases/stages) and enter...Duh Duh Duh......the Mitotic cycle!!!  

The Cell Cycle. Obviously.

This is where the action starts. The mitotic cycle consists of four separate phases: Prophase, Metaphase, Anaphase and Telophase. Prophase, the first phase, is when the chromosomes become visible (under a microscope) and the nucleolus magically dissolves. During this phase the pairs of chromosomes, due to their cloning, are in an "X" shape, where the original, and duplicate are crossed over each other. These pairs are joined to the cells by spindles attached to "Centromere's" 

"X" shape.

Then comes metaphase, where the chromosomes lined up across the center of the cell, across what as known as the metaphase plate, by the spindles attached to the centromeres. In anaphase this lining up pays off because, the pairs are then pulled apart by the centromeres to the opposite sides of the cells. In telophase the spindles disappear and the cell membrane starts to split apart into daughter cells.  When the cell enters the final stage of mitosis, and the cell cycle, cytokinesis, the cell splits into two daughter cells, each with 23 pairs of chromosomes. 

Mitosis-ness....In image form!

Meiosis & The Beginning of a Baby

When a mommy and a daddy love each other very much, (or 16 year old's want to get popular, yes I do hate MTV's programing) a baby is made. Ok, I'm joking. It's a lot more complicated than that. The process of cellular reproduction starts back when parents are just babies themselves. Creating a sort of never ending cycle of "which came first?" In order to create the cell that replicates into a baby, the parents must have sex cells (called gametes) to produce the sperm and the egg that join up and become a baby. Now, most people know that each cell has 46 chromosomes, organized into 23 pairs. But for a baby to be formed the sperm and egg have to have half that number (23 unpaired chromosomes) this happens through a process called meiosis. As Michael Rees, in his blog post "Cell's: They Reproduce." said:

  "First off, the goal of meiosis is to produce a cell with only twenty-three chromosomes so that it can share its chromosomes with another cell in order to produce a cell with unique genes that is then 

capable of developing into a baby of the species."  

Simply put, Meiosis is Mitosis with an extra division added on to the end, allowing you to get 23 individual chromosomes rather than the 23 pairs normally produced in Mitosis. Meiosis follow's the basic pattern of mitosis, but at the end, it adds in an extra division of the daughter cells. By adding that extra division at the end of the mitotic cycle,  the daughter cells of "Joe" do not get to go into synthesis, which then means that they don't double their number of chromosomes, which allows each daughter cell to get split into cells that each contain 23 individual chromosomes. Because sex cells each have 23 chromosomes they are able to combine into one cell with 23 pairs of chromosomes, which then divides by mitosis into more cells, which then create a baby. Simple right?

Photosynthesis&Respiration

So this blog post looks like its going to be a rather big project, getting two content standards to fit in one blog post....(sadly I'm doing this the night before grades are final...oh well) The aim of this post is to basically convey my understanding of photosynthesis, respiration, and how the energy produced is used. Unlike a number of my peers, rather than do the green human project, I decided, in the interest of time, just to do a flat out explanation of the two processes. So here goes.....

Photosynthesis. Or, How to make your own food.......

Essentially, photosynthesis is the process by which photoautotrophs synthesize food (sugar) from carbon dioxide (CO2) using the energy from light. Sounds mighty dang simple right? Well, it mostly is. It happens like this: In oxegenic photosynthesis (literally photosynthesis that releases oxygen) Light energy is absorbed by proteins that contain chloroplasts which contain chlorophylls (by the way, chlorophylls are green because that is the part of the light spectrum they do not use). The chlorophylls store most of the energy in the form of ATP.

Chloroplast

The next step in photosynthesis is the oxidation of H20. Energy (ADP) is used to split the hydrogen and Oxygen molecules apart. The oxygen molecules are released (they can be used in respiration), and the hydrogens are kept. When CO2 is added to the process they each lose an Oxygen, which attach to some of the hydrogen molecules, forming H2O. The remaining Hydrogen, Oxygen, and Carbon then all get combined into glucose.

---CO2 can also be converted into sugars suing a process called carbon fixation. The most common type of carbon fixation in biological life is the Calvin cycle. The Calvin cycle describes the way that light energy is used in the creation of chemical free energy, stored in glucose. The key enzyme that makes the cycle run is called RubBisCO, found in the chloroplast stroma. The Calvin cycle includes a number of regulatory functions that prevent it from being respired (look at the second half of the post) into CO2 (preventing energy (ATP) from being wasted without a net gain). For more information on the Calvin cycle, click here.-----

The glucose can then be burned through cellular respiration.

Cellular Respiration Or:how you use your food

Cellular respiration is the process by which nutrients are broken down into ADP. The first kind of respiration is called aerobic respiration. Aerobic respiration requires oxygen to break down the nutrients. It has three main stages. Glycosis, Krebs cycle, and electron transport.

1. In Glycolysis (spliting sugars), Glucose, is split into two molecules of a three carbon sugar. In the process, two molecules of ATP, two molecules of pyruvic acid and two "high energy" electron carrying molecules of NADH are produced. Glycolysis can occur with or without oxygen. In the presence of oxygen (like in aerobic respiration), glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP (fermentation).
2.  The Krebs Cycle (citric acid cycle) begins after the two molecules of the three carbon sugar produced in glycolysis are converted to a different compound (acetyl CoA). Through a series of intermediate steps, several compounds capable of storing electrons are produced along with two ATP molecules. These compounds, known as NAD (nicotinamide adenine dinucleotide...what is it with bio and big words?) and flavin adenine dinucleotide (FAD), are reduced in the process. These reduced forms carry the electrons to the next stage. The Krebs Cycle occurs only when oxygen is present but it doesn't use oxygen directly (in aerobic respiration).   
3.  Electron Transport requires oxygen directly. The electron transport "chain" is a series of electron carriers in the membrane of the mitochondria in eukaryotic cells. Through a series of reactions, the earlier mentioned electrons are passed to oxygen. In the process, a gradient is formed, and eventually ATP is produced.

Maximum ATP Yields: Prokaryotic cells can yield a maximum of 38 ATP molecules while eukaryotic cells can yield a maximum of 36. In eukaryotic cells, the NADH molecules produced in glycolysis pass through the mitochondrial membrane, which "costs" two ATP molecules.


Other kinds of cellular respiration include fermentation, where the pyruvate is converted to waste products, which when removed from the cell oxidizes the electron carriers, and anaerobic respiration wher unlike in aerobic, the oxygen is replaced by an inorganic acceptor (sulfur) is used.