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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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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 ...
79
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4answers
102k 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 ...
79
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3answers
19k 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 ...
78
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2answers
21k 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? ...
50
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5answers
2k 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 ...
49
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2answers
8k views

Why does cutting onion cause tears?​

When I looked on 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 which onion causes tears? Also,...
48
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9answers
10k 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 ...
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3answers
2k 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.
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4answers
9k 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 ...
40
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5answers
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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. ...
39
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2answers
8k 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 ...
37
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3answers
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 ...
34
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1answer
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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 ...
31
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5answers
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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, ...
31
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3answers
6k 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 ...
30
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3answers
50k 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?
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3answers
3k 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?
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3answers
164k 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 ...
27
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4answers
8k 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 ...
27
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1answer
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?
27
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3answers
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  &...
27
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2answers
1k 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 ...
25
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4answers
142k 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 ...
25
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1answer
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?
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3answers
14k 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 ...
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6answers
12k 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?
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3answers
489 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 ...
23
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2answers
12k 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 "...
23
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1answer
542 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 ...
22
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2answers
8k 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, ...
22
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1answer
424 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 ...
21
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3answers
1k 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 ...
20
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2answers
10k 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 ...
20
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2answers
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 ...
20
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1answer
992 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, ...
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1answer
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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?
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2answers
14k 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 ...
19
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1answer
926 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 ...
18
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1answer
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) ...
18
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2answers
4k 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'...
18
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1answer
461 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 ...
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4answers
6k 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 ...
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4answers
24k views

Why do we have no enzyme to digest cellulose?

As we know, cellulose is the most abundant polysaccharide in nature. Why don't we have an enzyme to digest cellulose?
17
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1answer
3k 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, ...
17
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1answer
1k views

Are the bacteria in the stomachs of unborn babies beneficial?

Babies are born with bacteria in their stomachs. I heard on The radio that when a child is given antibiotics for the first time unique bacteria in the stomach are destroyed and cannot be replaced. Is ...
16
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4answers
37k views

Why does the oxygen produced in the photosynthesis come from water and not carbon dioxide?

In the photosynthesis equation: $$\ce{6CO2 + 6H2O ->[sunlight] C6H12O6 + 6O2}$$ The only place where we have 6 molecules of $\ce{O2}$ is in $\ce{6CO2}$. Then it reacts with $\ce{6H2O}$ to form $\...
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3answers
52k 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 ...
16
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2answers
13k views

What is the explanation for the smaller number of tRNA than codons?

Translation, or decoding, of the four-nucleotide language of DNA and mRNA into the 20–amino acid language of proteins requires tRNAs and enzymes called aminoacyl-tRNA synthetases. To participate ...
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3answers
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What happens to dextrorotatory amino acids in humans?

As indicated by this question, most of the amino acids in the human body have the L-chirality. As enzymes also have handedness, what happens to the D-amino acids that end up within the human body? Are ...
16
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1answer
27k views

What effect has changing pH and salt concentration on protein complexes?

I'm struggling to find peer reviewed literature that explains the effect of changing the pH and the salt concentration on protein/protein complexes in solution. What effect does the pH and the salt ...