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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Determining if a specific proline is cis or trans in the protein?

While peptide bonds usually adopt the trans conformation, peptide bonds to proline can exist in either cis or trans conformation. The isomerization between cis and trans is slow, and has been shown to ...
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2k views

Molecularly, why can you straighten or perm hair?

I'm aware that hair can be curly because of the disulfide bond interactions in between cysteine amino acids in alpha-keratin filaments. However, I'm curious as to the biochemistry involved in ...
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180 views

What is the origin of “melting” in molecular genetics?

I'm reading some papers about prokaryotic transcription mechanisms, and I've come across a term I haven't heard before: DNA melting or promoter melting. After reading a bit, it's pretty clear that ...
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183 views

Decreasing the alcohol proof and faster in hangover, why?

My russian friend says that the USSR agents used/use the trick that they offered the victim first vodka and then last wine. I have noted that this puts you faster to hangover: decreasing the alcohol ...
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804 views

Basic Amino Acid Residue Binding Mechanism to DNA

I understand that many protein DNA binding domains bind to DNA via basic residues such as Arginine and Lysine. But what is the mechanism used to bind to DNA and where on the DNA would these residues ...
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4k views

Does consuming sodium benzoate (preservative E211) cause problems during pregnancy?

There seems to be strong evidence to support the claim that sodium benzoate (E211) causes hyperactivity in young children, e.g. Bateman et al. (2004) and McCann et al. (2007). This leads me to ...
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82 views

What are the lifetimes of cellular components on organelle or molecular level?

I was thinking that even though I know how generally the cell works, I don't really have a feeling of how volatile it is. I want to know what is the lifetime/turnover rate of different constituents of ...
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1k views

Very high 260/230 absorbance ratio of an RNA sample

After my most recent RNA extraction, the RNA samples had very high 260/230 absorbance ratios, (ranging from 5 to 25). I've never gotten numbers like this and I know the ratio is supposed to be ~2 in ...
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683 views

Why is absorbance at 280 nm for protein solution going up when I measure repeatedly?

I have been measuring my protein solutions' concentrations by diluting them in water 20 fold with a final volume of 100 uL and then measuring the absorbances of these solutions in 96 well plates with ...
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290 views

$S_{0.5}$ vs $K_m$ values in enzyme kinetics

What is the difference between $S_{0.5}$ values and $K_m$ values in enzyme kinetics?
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123 views

Can jellyfish improve Black Sea environment?

According to this study, cited by many popular science magazines, jellyfish and other, smaller animals can contribute to the vertical ocean stir as much as currents do. Black Sea chemistry and ...
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508 views

Why insects are so energy-efficient while flying?

Why are insects so energy-efficient while flying? Is it because of their light weight and aerodynamics or due to very efficient biochemical transformations (food->energy)?
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107 views

Is fluoride toxic, and how worried should I be about it?

A recent flurry of "fluoride is bad!" posts are appearing on my social network news feeds. Usually I can simply ignore them after a brief look, but this one, stemming from a recent article in The ...
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175 views

Can PCR tubes be made of different materials than plastic?

Does it matter if I replace the PCR tube (usually made of plastic) with another material like aluminum, glass, or something similar?
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2k views

Does ethanol destroy RNase?

I've gotten conflicting advice on this: some people believe one can remove RNase contamination simply by spraying the bench, pipettes, gloves, etc. with ethanol. Others think ethanol does not destroy ...
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3answers
121 views

Finding a template/oligo combination for my first PCR experiment

I'm an information technology engineer. I love biology so I research biological topics and have an interest in PCR. That's why I have decided to create a PCR machine. Everything is done now and I ...
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250 views

Diffusion of Hypotonic solution into solution with glucose and starch

Cell walls are selectively permeable to ions and organic molecules. Sometimes the selectivity is passive and a reflection of the physical laws governing diffusion. We can do simple experiments that ...
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148 views

What does it mean for a distribution to be “consistent with a two rate-limiting stochastic steps”?

I'm reading a study (full text here) that examine the dynamic of nuclear translocation of a transcription factor in budding yeast, in response of calcium stress. They found that it occurs in bursts, ...
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663 views

Isotype control antibodies in Flow Cytometry

In a Flow Cytrometry, one can add an Isotype Control Antibody to allow another antibody to bind more specific to the cells. My question is, how can the Isotype Control Antibody add specificity to the ...
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300 views

What are the units of enzyme activity?

I was looking at this graph of turnip peroxidase activity and I saw that they use units of 1/sec for enzyme activity. What does this unit intuitively represent and how is it calculated?
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266 views

Signaling through G protein Coupled Receptors?

There are two different cell lines but we do not know that these cell lines have Gs or Gi proteins, associated with their G-protein coupled receptors. If we wants to know about this. Can we design a ...
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719 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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82 views

Photosynthesis regulation

I read about the regulation of Calvin cycle by thioredoxin which activates key enzymes essentially by converting disulphide linkages on inactive enzymes into sulfhydryls. Another regulatory mechanism ...
5
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238 views

What causes humans to be sleepy?

Is there a hormone or group of hormones that regulates when we feel sleepy late at night, or in the morning? Or is sleepiness caused by some other non-hormonal mechanism? (e.g. pure psychological, ...
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45 views

How do rodenticides with delayed effect work?

Most modern rodenticides are claimed to cause death no earlier than several days after ingestion. That's quite strange - once a chemical was ingested it will be absorbed in the digestive system and ...
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80 views

In which way would the yeast cell cope with the excess amount of methionine in the growth media?

I guess that when there is surplus of methionine in the cell it is incorporated in the TCA cycle as a succinyl CoA, with cysteine as a by-product. But now the cell has the surplus of cysteine. What ...
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3answers
227 views

Biological Pathway of Lipid Hypothesis

I've read a lot on both sides of the debate of low carb vs low fat diets trying to make some sense of what is being proposed. The lipid hypothesis runs roughly along the lines that we have lots of ...
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169 views

Are quaternary protein monomers unique to a particular protein complex?

I know that quaternary protein structures are formed exclusively via non-covalent bonds. My biochemistry professor discussed a viral capsid that is essentially one quaternary structure with 240 ...
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334 views

How to Design an siRNA Experiment?

I'm going to undertake an siRNA experiment soon, but I have only read about them. I want to address the role an enzyme plays in processing a protein. From what I understand, I will need to pick two ...
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655 views

How does water buffer a sudden drop in temperature?

A property of water is that it is slow to heat and cool. According to my biology book, some energy from an increase in temperature would spent breaking hydrogen bonds, so that temperature does not ...
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1answer
950 views

What causes adenosine build up in the brain when awake?

Adenosine is an important hormone in sleep regulation. It is postulated that when a person is awake, there is a build up of adenosine in the brain, which inhibits the neurons in the brain, and ...
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1answer
326 views

Using ion-exchange chromatography to purify DNA from a cell extract - Is DNA more negatively charged then RNA?

When applying this method we have a glass or plastic column of resin which is positively charged. Then we pour cell extract into the column in order to capture the negatively charged particles which ...
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303 views

In biosynthesis of cysteine and methionine, where does the sulfur come from?

Methionine and Cysteine are the two amino acids containing sulfur. According to wikipedia, cysteine is built from methionine. However, the wikipedia also claims that methionine is synthesized from ...
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90 views

What makes a metal safe to use for an artificial joint?

What determines if a metal is suitable for transplantation such as in the hip? What I am most interested in however is why might some metals be toxic to animals once in the body?
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214 views

What is the molecular basis of hangovers?

Well, most of us have experienced the wonderful feeling of the dreaded hangover. How does it work exactly? I imagine it has something to do with dehydration but what are the underlying mechanisms? ...
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2k views

DNA as an acid? [duplicate]

Possible Duplicate: Does DNA react in all of the ways most other acids do? Even if DNA is made up of nucleotide bases, it is said to be an acid. Why is this?
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237 views

If proteins have an overall charge, how do membrane proteins traverse through the hydrophobic region of the plasma membrane?

These two concepts seem almost contradictory, proteins have a net negative charge due to the amino acids in them each having a small negative charge, yet membrane proteins are able to exist traversing ...
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89 views

Why isn't there any repulsive force between Na+ and K+ disrupting thier roles in transmembrane voltage/ action potentials

Pretty self explanatory question. I have a basic grasp on the "How" and "Why" of Reversal/Action Potential in and between neurons, but this question lingers.
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101 views

Effect of testosterone hormone on cell signalling and behaviour?

A steroid, testosterone was injected in female body which led to development of secondary sexual characters but these characters were not developed over night (Response was very slow). What could be ...
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86 views

Stability of helical strands of DNA?

The DNA molecules contain phosphate groups involved in $3'\rightarrow 5'$phosphodiester linkages. These groups, in the bonded state with deoxyribose, contain 1 negative charges ($\ce{3'-PO4^{-}-5'}$). ...
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97 views

Why don't amino acids get linked in the functional groups of acidic and basic amino acids?

There are 'acidic' and 'basic' amino acids like aspartate and histidine. When protein is synthesized with those amino acids, what ensures that the to-be-assembled amino acids will not bond to the ...
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1answer
4k views

Does mixing alcoholic drinks really make you more drunk?

There is plenty of anecdotal evidence ("beer after wine and you'll feel fine, wine after beer will make you feel queer") that mixing alcoholic drink types leads to a stronger effect, but I can't find ...
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59 views

Effect of steroid hormone on specific cells?

As steroid hormones can pass through the plasma membrane by simple diffusion because they are lipid derived hormones, it means that they are capable of passing through every cell of our body, BUT why ...
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1answer
79 views

What is an irreversible reaction?

There are reactions with large Delta G negative values. Why these reactions are irreversible? As in: out of 10 steps of Glycolysis, 3 are irreversible steps. I need an explanation for why they are ...
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1answer
132 views

How does ethanol interact with insulin?

I know that ethanol increases insulin secretion--could someone explain why? All I have found till now is experimental data analyses. I am interested in mechanism of alcohol consumption.
4
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1answer
78 views

Question about Monofunctional glycosylases

I am learning about Base excision repair mechanism. I understand the main idea how glycosylases are working, but I am trying to understand this with much more details. I found a paper where they are ...
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2answers
79 views

Why isn't the phosphoglycerate kinase reaction of the glycolysis pathway irreversible?

Step 7 of the glycolysis pathway is the conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate by the action of the enzyme phosphoglycerate kinase, resulting in the production of 2 ATP ...
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103 views

Topology of closed circular DNA

Why are covalently closed circular plasmid DNAs naturally found in an underwound state ? Is it because this makes it easier for the DNA replication machinery to access and unwind DNA ? Or is it ...
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1answer
3k views

Is there a difference between NADH and NADH2?

I've been reading a lot about the oxidative dissimilation etc, and often I see different sources use NADH and NADH2 in the same reactions. One source uses NADH and another uses NADH2 in the exact same ...
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314 views

Why are enzyme-catalysed reactions slower at lower substrate concentration?

Suppose I'm using 200 nmoles of enzyme and 2 mmoles of substrate. The enzyme should be saturated but if I use 50 mmoles of substrate, the reaction will be faster. Why? I just can't get it! Even at ...