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Questions tagged [biochemistry]

The study of chemistry within the scope of biology: the compounds that occur and the reactions involving them in living organisms.

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118 votes
3 answers
121k views

Why is thymine rather than uracil used in DNA?

What is the advantage gained by the substitution of thymine for uracil in DNA? I have read previously that it is due to thymine being "better protected" and therefore more suited to the storage role ...
Rory M's user avatar
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84 votes
4 answers
138k views

Death because of distilled water consumption

One of my friends said that I would die if I drank distilled water (we were using it in a chemistry experiment) I gave it a go and surprisingly did not die. I did a bit of Googling and found this ...
The-Ever-Kid's user avatar
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84 votes
2 answers
32k views

Why is the heart not in the middle of the body?

All mammals that I can think of have a high degree of bilateral symmetry (In fact, almost every animal I can think of is like this). So why is the human heart not exactly in the middle of the body? ...
DrZ214's user avatar
  • 1,421
83 votes
3 answers
22k views

Why 20 amino acids instead of 64?

This question got me thinking about amino acids and the ambiguity in the genetic code. With 4 nucleotides in RNA and 3 per codon, there are 64 codons. However, these 64 codons only code for 20 amino ...
Daniel Standage's user avatar
59 votes
10 answers
19k views

Why are there no organisms with metal body parts, like weapons, bones, and armour? (Or are there?)

Reading this question, Why are there no wheeled animals?, I wondered why no organisms seem to make use of the tensile and other strengths of metal, as we do in metal tools and constructions. I am ...
Cerberus's user avatar
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54 votes
5 answers
3k views

Human perception of time depending on age

From what I can tell and what thus far all people with whom I discussed this subject confirmed is that time appears to "accelerate" as we age. Digging a little, most explanations I found basically ...
back2dos's user avatar
  • 883
53 votes
3 answers
3k views

Can scientists create totally synthetic life?

This particular question has been of a great deal of interest to me, especially since it dives at the heart of abiogenesis.
Larian LeQuella's user avatar
50 votes
2 answers
10k views

Why does cutting onions cause tears?​

Why does cutting onions cause tears?​ From a couple of sites, I found that it is because of sulfuric acid produced by onions. But I could not find more details. What is the biochemical pathway by ...
superbug's user avatar
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44 votes
4 answers
11k views

Why are bruises not lethal?

Given the following: bruises are caused by minor trauma which breaks blood vessels beneath the skin, causing bleeding the mechanism by which bleeding stops is clotting blood clots inside the body ...
Mason Wheeler's user avatar
41 votes
5 answers
15k views

What does the human body use oxygen for besides the final electron acceptor in the electron transport chain?

My biology teachers never explained why animals need to breathe oxygen, just that we organisms die if we don't get oxygen for too long. Maybe one of them happened to mention that its used to make ATP. ...
Gordon Gustafson's user avatar
40 votes
2 answers
12k views

Why do some vegetables taste bitter?

Bitter gourd, cucumber, etc. are bitter to taste. Which chemical causes bitterness in them? I found these when I searched online: this says that it is because of calcium, while this and this talk ...
Mesentery's user avatar
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37 votes
3 answers
5k views

What does it mean to "write an image and GIF into the DNA of bacteria"?

BBC News recently published an article saying that: An image and short film has been encoded in DNA, using the units of inheritance as a medium for storing information ... The team sequenced the ...
PiratePi's user avatar
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36 votes
3 answers
61k views

Why is ATP the preferred choice for energy carriers?

Why is ATP the most prevalent form of chemical energy storage and utilization in most cells?
hello all's user avatar
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35 votes
1 answer
3k views

Why do animal cells "mistake" rubidium ions for potassium ions?

So, I was browsing the Wikipedia article for rubidium, and came across this interesting tidbit: Rubidium is not a known nutrient for any living organisms. However, rubidium ions have the same charge ...
prolyx's user avatar
  • 469
35 votes
1 answer
4k views

Ripening bananas artificially: What is the biological theory behind?

I am a resident of the tropical island of Sri Lanka, and we have a strange traditional method to ripen our banana harvest quickly. What we do is this: We dig a pit in earth that is enough to put the ...
sampathsris's user avatar
33 votes
5 answers
8k views

Why isn't Fluorine, or Neon, the final electron acceptor in cellular respiration?

I'm a Chemistry student learning about periodic trends. I know that in (many organisms') cellular respiration, oxygen serves as the final electron acceptor due to its high electronegativity. However, ...
Thomas Dang's user avatar
31 votes
3 answers
11k views

Can plants suffer from CO2 poisoning?

Is there a point where too much CO2 is bad for a plant? Basically when there is too much CO2 in the air can a plant get sick? Since plants photosynthesize and need CO2 to generate glucose and store ...
Lenkan's user avatar
  • 313
30 votes
3 answers
1k views

How, on a physical level, does ATP confer energy?

When ATP is used as the energy currency to make, say, reaction X + Y → Z happen, is what happens on a physical level down at the molecular scale that during the reaction ATP + H2O → ADP + Pi  &...
mring's user avatar
  • 1,973
28 votes
3 answers
181k views

NADH vs. NADPH: Where is each one used and why that instead of the other?

I know NADH is used in cellular respiration and NADPH is used in photosynthesis. What difference does the phosphate group make that the same one isn't or can't be used for both? Is there a greater ...
Gordon Gustafson's user avatar
28 votes
1 answer
3k views

Killing enveloped viruses with soap

Unlike non-enveloped viruses, enveloped viruses can be killed with soap, alcohol, etc. Why? Why does just having an envelope make it susceptible to soap and alcohol?
chinmai's user avatar
  • 405
28 votes
4 answers
10k views

Where does the 'C' in exhaled CO₂ mostly come from?

When a human being exhales CO₂, what is, by the numbers, the main source of carbon atoms exiting the body in this way? I mean what class of cells, or which tissues are the biggest on a pie chart of ...
mring's user avatar
  • 1,973
27 votes
7 answers
17k views

Why are there exactly four nucleobases in DNA?

Does someone know why DNA is composed of four nucleobases? In particular, is there an explanation for the number? Why four and not two, or eight?
tunnuz's user avatar
  • 373
26 votes
3 answers
4k views

Does any molecule other than DNA have a double-helical structure?

DNA is known to have a double-helical structure. Do any other molecules have this structure?
The Riddler's user avatar
26 votes
2 answers
20k views

Do all proteins start with methionine?

Start codon AUG also codes for methionine and without start codon translation does not happen. And even the ambiguous codon GUG codes for methionine when it is first. So does this mean that all ...
sreekara's user avatar
  • 769
26 votes
1 answer
4k views

Why do mints make your mouth feel cold?

Why do mints make your mouth feel cold? And specifically, why does your mouth feel so cold if you eat a few mints and then drink a glass of cold water afterwards?
rotaredom's user avatar
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26 votes
2 answers
2k views

What's the mechanism for being mentally tired?

I notice that after long tests, or long periods of critical thinking, my body and mind feel noticeably tired. Why does this happen? Are the neurons in my head not firing as quickly, or is there just a ...
Dupontrocks11's user avatar
25 votes
4 answers
164k views

What is a coupled reaction and why do cells couple reactions?

I was wondering what exactly a coupled reaction is and why cells couple them. I read the wikipedia article as well as several others, such as life.illinois.edu but I still don't get it. Could ...
Snakes and Coffee's user avatar
25 votes
1 answer
2k views

ATP cost for gene expression

How would you estimate the number of ATPs required to transcribe, export and translate a single eukariotic protein?
Gianpaolo R's user avatar
  • 3,884
25 votes
3 answers
23k views

Why is glucose our primary source of energy?

Is there any evolutionary reason for glucose being the "main" molecule used as a source of energy, beginning with glycolysis and subsequently cellular respiration (after being converted to two ...
LanceLafontaine's user avatar
24 votes
3 answers
542 views

How crowded is the bacterial cell?

I was wondering what is the protein concentration in an E. coli cell. When studying enzyme kinetics and activity in vitro, I would argue that the substrate and enzyme concentrations resemble those in ...
Gergana Vandova's user avatar
23 votes
2 answers
13k views

Is it known how the first viruses formed?

The oldest known virus is known to have infected prehistoric insects 300 million years ago. A virus is basically a parasitic strand if DNA or RNA encapsulated in a protein coat. It enters cells by "...
Jax's user avatar
  • 395
23 votes
2 answers
9k views

What is the mechanism behind "acquired" alcohol tolerance?

I can understand natural variation in alcohol dehydrogenase (ADH) in a population leading to variation in rate of inebriation (after controlling for other variables -- e.g., mass, food consumption, ...
kmm's user avatar
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22 votes
3 answers
5k views

Why does hair turn grey or white, and why does it happen later for some?

The question is pretty simple: what is happening molecularly when hair turns grey or white? I would imagine that it is due to the lack of a particular compound. I'm also interested in why some people'...
LanceLafontaine's user avatar
22 votes
1 answer
873 views

Can a human be made with ovum but without sperm?

This article says that scientists were successful in making a mouse using only a sperm and no egg (ovum). The article also states that this procedure could be applicable to humans. However, I want to ...
Mesentery's user avatar
  • 3,293
22 votes
1 answer
490 views

Evolutionary origin and exogenous cues of ~28 day infradian rhythm?

The most obvious example of an approximately monthly biological cycle is the human menstrual cycle. My questions are the following: Is it known when and where this cycle or one like it arose? What ...
Richard Terrett's user avatar
21 votes
3 answers
2k views

How is RNAse contamination in RNA based experiments prevented?

Does anyone have any suggestions to prevent RNAse contamination when working with RNA? I tend to have issues with degradation regardless of whether I use DEPC treated / RNAse free water and filtered ...
GWW's user avatar
  • 2,135
21 votes
2 answers
2k views

What inactivates pepsin in infants?

In infants, rennin helps in digestion of milk. Pepsin is also present in their stomach. Why do infants need rennin for milk digestion, at the first place? Why does pepsin not act on the milk ...
Mesentery's user avatar
  • 3,293
21 votes
1 answer
1k views

Can siRNA induce DNA methylation in mammalian cells?

Some years ago Hiroaki Kawasaki and Kazunari Taira published an article called "Induction of DNA methylation and gene silencing by short interfering RNAs in human cells" in Nature: In plants, ...
Mad Scientist's user avatar
21 votes
1 answer
1k views

Why do we feel tired if we sleep excessively?

When we eat, finally we feel full. I know which mechanism causes the sensation of being full. But when we sleep excessively we often still want more sleep. Why does this happen? Is there a mechanism ...
MySky's user avatar
  • 2,274
20 votes
2 answers
16k views

How does a plant grow before photosynthesis is possible?

During photosynthesis, a plant translates CO2, water and light into O2. I assume the carbon C is further used for the growing process. I wonder how the plant grows before the time where photosynthesis ...
Nikolaj-K's user avatar
  • 595
19 votes
3 answers
4k views

Is atmospheric nitrogen chemically necessary for life?

It is my (very basic) understanding that neither plants nor animals utilize the nitrogen in the atmosphere. Humans do not make use of atmospheric nitrogen through respiration and plants do not ...
Wyck's user avatar
  • 359
19 votes
3 answers
59k views

Why can't the brain and red blood cells use fuels other than glucose?

The question is rather straight forward: I have always been curious as to why, but cannot find an explanation online. I can imagine that the mechanism is different for each, but why does brain tissue ...
LanceLafontaine's user avatar
19 votes
1 answer
4k views

Why do humans require vitamin B12 supplementation while herbivores do not?

This question came about from reading the comments of this (very unclear) question, which the author did not properly clarify. Vegans are often recommended to take vitamin B12 supplements, as the ...
March Ho's user avatar
  • 9,452
19 votes
4 answers
23k views

Why is the brain dependent on glucose?

The strict dependence of the (human) brain on glucose has always been puzzling to me. While ketones can substitute for a portion of the brain's energy needs, it cannot substitute completely: blood ...
Roland's user avatar
  • 5,725
18 votes
3 answers
2k views

Are stable isotopes ever used in pharmaceuticals?

Carbon has two stable isotopes, C-12 and C-13. Since they both have the same electronic structure they can both make up the same molecules, but presumably they may perform different functions in ...
imrobert's user avatar
  • 454
18 votes
4 answers
9k views

Why don't antiseptic agents kill 100% germs?

I've seen innumerable antiseptic, mouthwash, handwash advertisements that claim to be able to eliminate as much as 99.9% of all germs over a surface...but why not the remaining 0.1% (i.e- why can't ...
paracetamol's user avatar
  • 1,569
18 votes
1 answer
3k views

Why are sushi proteins called "sushi"? What are the origins of this name?

Does anybody know why complement control proteins (also short consensus repeats) are called "sushi" proteins? Is there any special reason for their name?
Vii Z.'s user avatar
  • 183
18 votes
1 answer
3k views

What is the most condensed form of (stored) energy used in biology?

When considering how organisms store energy for later use, I was wondering what substance known in Biology is best for compacting the most energy in the smallest space(volume-wise). With my (limited) ...
DoubleDouble's user avatar
18 votes
1 answer
4k views

How do ants follow each other?

I was observing ants in my house.They all were going in a straight line and also some of the ants were coming back through the the same line. I took some water and rubbed the line with my finger, ...
Mesentery's user avatar
  • 3,293
18 votes
1 answer
565 views

The human brain in numbers I: neurons

Even though knowing the number of neurons in a functional unit or with the same function is not of main importance, it may be interesting to know their orders of magnitude, especially in the human ...
Hans-Peter Stricker's user avatar

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