sciencesoup:

Citric Acid Cycle

The citric acid cycle (sometimes called the Krebs cycle) occurs in the mitochondrial matrix and is the third stage in the aerobic breakdown of glucose. The first, of course, is glycolysis, which creates pyruvate, NADH, and ATP. The second—which isn’t long enough to get its own post—is the linking reaction in which pyruvate is converted to Acetyl CoA. This is a coenzyme that the citric acid cycle breaks down to use later in energy production. Basically, the purpose of the linking reaction is to make pyruvate into something the cycle can use.

The main goal of the citric acid cycle is to convert bond energy (in the form of Acetyl CoA) into its reducing equivalents: i.e., to make some more NADH and FADH2, which are electron carriers. These then go through the electron transport chain and use their electron energy to create ATP. Remember, to reduce a compound is to add electrons to it—think of the mnemonic OILRIG.

So, how does the citric acid cycle do this?

Some diagrams get pretty complicated, especially when you include the enzymes responsible and the carbon compounds formed at every stage, but I’m going to break it into relatively simple steps.

  1. An enzyme joins acetyl-CoA to oxaloacetate in order to form citric acid, which is where the cycle gets its name. Then, a water molecule “attacks” the acetyl, and CoA is ejected from the cycle.
  2. Next, water is ejected and then put back in to help facilitate the reduction of NAD+ into NADH. For every turn of the cycle, 3 NADH molecules are created, and 2 molecules of CO2 are released.
  3. ADP plus a free phosphate group (denoted as “Pi”) is put into the cycle, and these are smushed together to form an ATP.
  4. Finally, FAD+ is reduced to FADH2. (FAD and NAD are both very similar coenzymes, performing the same oxidative and reductive roles in a reaction, but they’re different because they work on different classes of molecules: FAD oxidises carbon-carbon bonds, and NAD oxidises carbon-oxygen bonds)

A diagram might make it a little clearer:

image

So, let’s do a quick round-up of what’s happened:

  • Acetyl-CoA has been released as two CO2 molecules
  • 3 NAD+ were reduced to 3 NADH
  • 1 FAD+ was reduced to 1 FADH2
  • 1 ADP+Pi formed 1 ATP molecule

This isn’t the end—the main goal of citric acid cycle is to prepare the electron carriers NADH and FADH2 for the electron transport chain, where much more ATP will be made.

Onwards to the ETC!

Further resources: Khan Academy: Krebs Cycle

fuckyeahfluiddynamics:

The hummingbird has long been admired for its ability to hover in flight. The key to this behavior is the bird’s capability to produce lift on both its downstroke and its upstroke. The animation above shows a simulation of hovering hummingbird. The kinematics of the bird’s flapping—the figure-8 motion and the twist of the wings through each cycle—are based on high-speed video of actual hummingbirds. These data were then used to construct a digital model of a hummingbird, about which scientists simulated airflow. About 70% of the lift each cycle is generated by the downstroke, much of it coming from the leading-edge vortex that develops on the wing. The remainder of the lift is creating during the upstroke as the bird pulls its wings back. During this part of the cycle, the flexible hummingbird twists its wings to a very high angle of attack, which is necessary to generate and maintain a leading-edge vortex on the upstroke. The full-scale animation is here. (Image credit: J. Song et al.; via Wired; submitted by averagegrdy)

fuckyeahfluiddynamics:

The hummingbird has long been admired for its ability to hover in flight. The key to this behavior is the bird’s capability to produce lift on both its downstroke and its upstroke. The animation above shows a simulation of hovering hummingbird. The kinematics of the bird’s flapping—the figure-8 motion and the twist of the wings through each cycle—are based on high-speed video of actual hummingbirds. These data were then used to construct a digital model of a hummingbird, about which scientists simulated airflow. About 70% of the lift each cycle is generated by the downstroke, much of it coming from the leading-edge vortex that develops on the wing. The remainder of the lift is creating during the upstroke as the bird pulls its wings back. During this part of the cycle, the flexible hummingbird twists its wings to a very high angle of attack, which is necessary to generate and maintain a leading-edge vortex on the upstroke. The full-scale animation is here. (Image credit: J. Song et al.; via Wired; submitted by averagegrdy)

timemagazine:

Person of the Year runner-up: Fabiola Gianotti, Higgs boson scientist  
Finding the tiny Higgs Boson took the biggest machine in the arsenal of physics — and help from one woman obsessed with the nature of reality. Read more here.
(Photo: Levon Biss for TIME)

timemagazine:

Person of the Year runner-up: Fabiola Gianotti, Higgs boson scientist 

Finding the tiny Higgs Boson took the biggest machine in the arsenal of physics — and help from one woman obsessed with the nature of reality. Read more here.

(Photo: Levon Biss for TIME)

(via firaxa)

jtotheizzoe:

asapscience:

Science is not always as glamorous as it seems… via Twisted Doodles, Neurons Want Food

The right column is basically 99% of the take-away from grad school
AKA “WTF THIS SHIT IS HARD IT IS SUPPOSED TO JUST WORK”

jtotheizzoe:

asapscience:

Science is not always as glamorous as it seems…

via Twisted Doodles, Neurons Want Food

The right column is basically 99% of the take-away from grad school

AKA “WTF THIS SHIT IS HARD IT IS SUPPOSED TO JUST WORK”

(via danish-dino)

compoundchem:

Version 1 of ‘A Rough Guide to Spotting Bad Science’. Thanks for everyone’s suggestions earlier in the week, attempted to include as many of them as possible!
Download link here: http://wp.me/p4aPLT-ap

compoundchem:

Version 1 of ‘A Rough Guide to Spotting Bad Science’. Thanks for everyone’s suggestions earlier in the week, attempted to include as many of them as possible!

Download link here: http://wp.me/p4aPLT-ap

(via firaxa)

scifigeneration:

See-through skin
A ‘vein-viewer' works by using infrared light to image the presence of veins underneath the skin: The IR light is absorbed by the deoxygenated haemoglobin within veins. The locations of absorption and reflection are detected and the machine generates a corresponding projection using visible light. Find out more about how these devices are used in medicine in this video: http://youtu.be/lk0HMqwreIo
(via @rossexton,coolsciencegifs)

scifigeneration:

See-through skin

A ‘vein-viewer' works by using infrared light to image the presence of veins underneath the skin: The IR light is absorbed by the deoxygenated haemoglobin within veins. The locations of absorption and reflection are detected and the machine generates a corresponding projection using visible light. Find out more about how these devices are used in medicine in this video: http://youtu.be/lk0HMqwreIo

(via @rossexton,coolsciencegifs)

scifigeneration:

'One of the Greatest Discoveries in the History of Science' Hasn't Been Peer-Reviewed. Does It Matter?
Big scientific discoveries—the kind that shift our view of the world and our place within it—don’t come along very often. 
This week, though, one did. 
New data seem to offer, for the first time, direct evidence of the entities Einstein predicted in his general theory of relativity: gravitational waves. Which is a finding that, if it holds up, sheds new light on nothing less than the origins of the universe. The discovery is, according to one expert, “an amazing achievement.” It is also, according to another, “one of the greatest discoveries in the history of science”—“a sensational breakthrough involving not only our cosmic origins, but also the nature of space.”
So, basically: This is big, you guys! Einstein big! Nature-of-space big! Big Bang-big!
There’s just one small thing, though. The findings shared this week also share a significant caveat: They haven’t yet been peer-reviewed. They are discoveries that are, as far as scientific institutionalism is concerned, provisional. They’re stuck in a kind of epistemological limbo—as information that has not yet been converted into fact, and data that have not yet been codified into knowledge. Official status: truthy.
Read more.[Image: Reuters]
via theatlantic

scifigeneration:

'One of the Greatest Discoveries in the History of Science' Hasn't Been Peer-Reviewed. Does It Matter?

Big scientific discoveries—the kind that shift our view of the world and our place within it—don’t come along very often.

This week, though, one did.

New data seem to offer, for the first time, direct evidence of the entities Einstein predicted in his general theory of relativity: gravitational waves. Which is a finding that, if it holds up, sheds new light on nothing less than the origins of the universe. The discovery is, according to one expert, “an amazing achievement.” It is also, according to another, “one of the greatest discoveries in the history of science”—“a sensational breakthrough involving not only our cosmic origins, but also the nature of space.”

So, basically: This is big, you guys! Einstein big! Nature-of-space big! Big Bang-big!

There’s just one small thing, though. The findings shared this week also share a significant caveat: They haven’t yet been peer-reviewed. They are discoveries that are, as far as scientific institutionalism is concerned, provisional. They’re stuck in a kind of epistemological limbo—as information that has not yet been converted into fact, and data that have not yet been codified into knowledge. Official status: truthy.

Read more.[Image: Reuters]

via theatlantic

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