Energy!

This post has the most monstrous image I’ve made to date.  I hope it will become more popular and useful than my current heavy hitters the cell and even Louis Pasteur’s experiment of spontaneous generation, which I’ve seen make the top ranks of both Google and Bing image search!

In this image, I’ve covered energy as it passes from the sun in the form of light to the chloroplast of plants. In the chloroplasts, there are structures called thylakoids where the magic happens. This is where photosynthesis takes place in two parts, 1) light-dependent reactions and, 2) Calvin Cycle.

The waste products here are eliminated and the useful products are then sent to the mitochondria.  The first step is 1) glycolysis, followed then by 2) the Krebs cycle (also called the Citric Acid Cycle) under aerobic conditions OR, 2) fermentation (under anaerobic conditions)

There’s a LOT of stuff that happens here. These are the basics.  This stuff can get extraordinarily complicated–the guy the Krebs cycle is named for won a Nobel prize for his work!

I’ve never, personally seen an image that attempted to go from the sun to photosynthesis to cellular respiration but I tried to keep it as simple as possible. That said, if you feel something’s missing, its probably because it is. Some steps weren’t explicitly mentioned for simplicity’s sake.

One final note: ATP gives you a burst of energy. If you need energy to do anything for longer than about a minute and a half, you want sugar. Sugars provide longer-lasting energy.  ATP (which makes up about a half-pound of your total body weight) doesn’t store, in other words, it gets used shortly after it’s made. ATP actually gets recycled over 1,000 times a day by humans!

Click for full size

Mitosis

The M phase of the cell cycle is the process known as mitosis. Some scientists classify cytokinesis as separate from mitosis, but still in the M phase. Mitosis is split into 4 distinct phases plus cytokinesis.

Prophase is the longest phase of mitosis. Chromatin condenses to form chromosomes, centrioles move to the poles, spindles form, the chromosomes attach to the spindle fibers at the centromere and the nuclear envelope breaks down.

Metaphase is usually brief. Chromosomes line up across the center of the cell and microtubules connect the centromere of each chromosome to the two spindles at the poles.

Anaphase is the next phase. The spindles split the sister chromatids and when they reach the poles and stop moving, anaphase is over.

Telophase if the final phase. The distinct, condensed chromosomes disperse, the nuclear envelope reforms around the chromosomes, and the spindles break apart.

Cytokinesis is the last step of cell division. This involves the division of cytoplasm and the cell membrane pinches shut, separating the two daughter cells.

This Krispy Kreme illustration is actually a great example of what this looks like:

Click through to see it full size.

Cell Division – An Intro

When cells grow, the run into a problem.  As the cell grows in size, their surface area to volume ratio changes.  As it turns out the higher the volume is in relation to the surface area, the more difficult it becomes to diffuse enough material into the cell.  Think of a city with 1 road.  As the town grows, the main road doesn’t change much.  Sure you may be able to add in a few extra lanes, but the town can grow rapidly in every direction but the road can only grow a little bit.  So when before a cell gets too big to function properly, the cell divides.

In order for both of the daughter cells (the new cells) to be able to survive and work properly, the cell needs to do a little prep work.  In eukaryotes like your venus fly trap, a wild capybara, and even you & me the process of dividing is commonly called mitosis.  More accurately, however, the process is called the M stage of the cell cycle.  In the M stage, two things occur, 1) mitosis, in which the cell’s chromosomes are divided and 2) cytokinesis, in which a cell’s cytoplasm divides in half.  (In prokaryotes, like amoeba, cell division is usually referred to as asexual reproduction, but it is still the same process.)  The actual prep work of division, though, occurs in the rest of the cell cycle.

The Cell Cycle

The cell cycle can be easily broken into two parts: 1) cell division, and 2) interphase.  A great deal happens in both of these parts of the cycle, so we’ll look at them separately.  Today I give you interphase.  Cell division will be in my next post.

Cellular Respiration

Heterotrophs need to obtain energy from consuming autotrophs.  Remember autotrophs turn light energy into chemical energy, which is stored as the sugar glucose.  The process of releasing energy by breaking down glucose and other food in the presence of oxygen is called cellular respiration.

Cellular respiration is not exactly, but can be roughly viewed as, the reverse process as photosynthesis.  Oxygen and glucose combine to breakdown and reassemble as carbon dioxide, water, and energy.

6O2 + C6H12O6 -> 6CO2 + 6H2O + ATP

oxygen + glucose -> carbon dioxide + water + energy

This process is simplified of course.  There’s a whole confusing mess of glycolysis, ATP, and NADH which the average high school bio teacher would want you to know, but honestly it’s overkill (…it’s not even in our state standards…).

Now there are cases when cells don’t get enough oxygen.  In this case, the cells produce nasty waste products that they remove from their body.  Some microorganisms, such as yeast, produce alcohol in the absence of oxygen.  This is called alcoholic fermentation.  Other organisms, such as yourself, produce lactic acid in the absence of oxygen.  Fittingly, this is called lactic acid fermentation.  Fermentation is vital in our food system.  Production of alcohol is quite the large business throughout the world; as is production of foods such as yogurt and pickles which utilize lactic acid.

One last point of overkill: the Krebs cycle and electron transport chain.  Unless you go to college for Biology, you have no need for this… and honestly, I went to college for Biology and I don’t have a use for it, short of torturing students with it if I was an evil person.

Photosynthesis

Previously you read about autotrophs and heterotrophs.  The difference being in the way they obtain energy.  Plants are autotrophs, and today I’d like to focus on how plants get the energy they need.

Plants need the following things to get energy to live:

• Water (H2O)
• Carbon Dioxide (CO2)
• Sunlight

The process of converting H2O and CO2 in the presence of sunlight into energy is called photosynthesis.

In order for the water to get to the leaves of a plant where photosynthesis takes place, it is absorbed from the surrounding ground through roots and is brought up through tissue like your blood vessels.

The carbon dioxide is absorbed my the leaf directly through openings (or pores) on the under side of the leaf.

Light-absorbing molecules called pigments capture sunlight for the plant.  The primary pigment in plants is called chlorophyll.  Chlorophyll gives plants their green color because it absorbs reds and blues and reflects green!

Chlorophyll is housed in organelles called chloroplasts.  This is where photosynthesis takes place.

The equation for synthesis looks like this:

6CO2 + 6H2O (in the process of light) -> C6H12O6 + 6O2

carbon dioxide (in) + water (in) -> glucose (used for energy) + oxygen (out)

(That’s the same oxygen we need to breathe!!!)

All that happens in plants which are pretty fascinating, even if they aren’t furry and cuddly!

Energy

Every organism needs energy to live.  But where does that energy come from?  Let’s find out…

There are two types of organisms: autotrophs, which make their own food, and heterotrophs, which must consume food from an outside source.

Most autotrophs convert light energy from the sun into usable energy.  These are the only types of autotrophs you need to be concerned with for now.  Your typical autotroph would be any plant, a grass, a tree, a shrub.  Unicellular organisms can be autotrophs too!

Examples of heterotrophs include animals, such as yourself or a lion, as well as fungi plus some unicellular organisms like some protists or bacteria.

Energy comes in many forms.  We already mentioned light energy from the sun.  There’s also heat energy and other types like the electricity that powers your television.

The type of energy that cells can best use is chemical energy.  Specifically it’s in the form of a chemical called ATP.  Really the only thing you need to know is that ATP is like a fully charged battery.  A bond is broken and energy is released. That turns ATP into ADP.  Or you can think of it like this A3P =>release of energy => A2P.  ADP is like a battery waiting to be recharged.

ADP + Engery stored = ATP

For some reason this seems to really trip people up.  If you have any questions, drop me a comment or a tweet @AmoebaMike.