70 votes
Accepted

What is the longest-lasting protein in a human body?

Crystallin proteins are found in the eye lens (where their main job is probably to define the refractive index of the medium); they are commonly considered to be non-regenerated. So, your crystallins ...
Mowgli's user avatar
  • 1,933
51 votes
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Why are prions in animal diets not destroyed by the digestive system?

Proteases are enzymes in your digestive system that help break down food, acting like molecular-sized scissors that cut up proteins. Proteases have clefts, or subpockets, into which proteins fit, ...
Alex Reynolds's user avatar
44 votes

How do proteins 'know' where to go?

Even though this animation is very well-known and the narrator says it is "... an accurate representation of the actual DNA replication machine ...", be very careful of its visual appeal. It ...
Domen's user avatar
  • 1,929
37 votes
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Do all proteins start with methionine?

You are correct in thinking that since the translation of mRNA begins with AUG, which codes for methionine, then all proteins should contain a methionine at their N-terminus (aka start site). But, it ...
another 'Homo sapien''s user avatar
37 votes
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What is 'protein' in food?

When we say "protein" with respect to food, what is generally meant is material that contains amino acids. Every protein is, at its heart, a long string of amino acids, which then gets ...
jakebeal's user avatar
  • 6,977
33 votes

Do all humans have an identical nucleotide sequence for certain proteins, e.g haemoglobin?

It is highly unlikely that there exist any protein that is made from completely identical nucleotide sequences across the entire human population. There will certainly be regions within a gene that ...
Gen Test's user avatar
  • 431
32 votes
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Why don't membrane proteins move?

Proteins can move around the membrane. Most proteins do move within the membrane. The membrane is a liquid crystal and has fluid behaviour. Specifically, this is due to the membrane being in a gel-...
James's user avatar
  • 11.3k
29 votes
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Why are sushi proteins called "sushi"? What are the origins of this name?

Because their shape reminded researchers of rolls of Sushi (Ichinose et al, 1990): These repeats were initially called GP-I structures because they were first identified in $\beta_2$-glycoprotein I....
Jack Aidley's user avatar
  • 6,917
23 votes
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Do all humans have an identical nucleotide sequence for certain proteins, e.g haemoglobin?

Humans have many variants There is variation. The project I use to help understand this natural variation is gnomAD. Using VarMap and a slightly out of date gnomAD file, I counted 16007805 protein-...
James's user avatar
  • 11.3k
22 votes

What is the longest-lasting protein in a human body?

I like Mowgli's answer, because it is a non-obvious example. However I would also point out that there are many, many protein-based structural components in the body that we know do not regenerate due ...
Meep's user avatar
  • 2,939
20 votes
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Why is protein turnover necessary or important for cells to function?

Biology is an intricate orchestration of chemical reactions and their products. Generally, this fete is accomplished by enzymatic facilitation of certain reactions that would otherwise occur too ...
Bryan Krause's user avatar
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17 votes
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What inactivates pepsin in infants?

EDIT: Thanks a lot to @abukaj for pointing out the mistake in my answer (and to @paracetamol for asking such a beautiful question). I am rewriting my answer to incorporate the (hopefully) correct ...
another 'Homo sapien''s user avatar
16 votes
Accepted

What physical evidence exists that shows motor proteins "walking" within a cell?

Since you chose kinesins as an example class of motor proteins, I will also stick to them. In general, the movement mechanisms of kinesins are well studied and the general structure of kinesin ...
AlexDeLarge's user avatar
  • 2,868
15 votes

What is 'protein' in food?

It's a mix of all the proteins in whatever organism the food is coming from. Some (especially vegetable/grain) sources might have fairly specific proteins present because you are eating a specific ...
Bryan Krause's user avatar
  • 45.3k
14 votes

Why is glycine considered a nonpolar amino acid but a polar molecule?

The first part of your question illustrates a common confusion of beginners between the physiochemical properties of free amino acids in solution, and the properties of that part of an amino acid that ...
David's user avatar
  • 25.2k
14 votes
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Do proteins generally contain phosphorus and sulfur?

Of the 22 known proteinogenic amino acids, all contain hydrogen, carbon, nitrogen and oxygen. Some (methionine and cysteine) contain sulfur while one (selenocysteine) contains selenium. None contain ...
canadianer's user avatar
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14 votes
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What is the difference between a protein and a factor?

TLDR: As far as I know, there's no specific reason some proteins are called "factors"; it's just a matter of what name was chosen. "Protein" is a specific term meaning a long chain of amino acids. ...
Jam's user avatar
  • 1,515
14 votes
Accepted

Why can't H3O+ ions pass through aquaporins?

This question has been directly addressed by the paper The Mechanism of Proton Exclusion in the Aquaporin-1 Water Channel. I think it's a pretty good one too! I paste the abstract below: Aquaporins ...
S Pr's user avatar
  • 6,202
12 votes

What is the difference between a protein and a factor?

Short Answer There is no agreed upon naming convention for proteins - there are some rough standards because in language people usually try to convey their ideas in a way others can understand, but ...
Bryan Krause's user avatar
  • 45.3k
12 votes
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Is tyrosine hydrophobic or hydrophilic?

The answer to this question emerges from an examination of the structure of tyrosine — or, more strictly, the tyrosyl residue, which is how it exists in proteins, the concern of the question: It ...
David's user avatar
  • 25.2k
12 votes
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What is "irrational" drug/molecule design?

"Irrational" design in these papers refers to combinatorial mutagenesis, which is put forward as the alternative to "rational" protein design. Rational design involves using existing information ...
acvill's user avatar
  • 8,286
12 votes
Accepted

Does the recent concern over several papers about Aβ*56 call into question the association of Alzheimers Disease with any amyloyd beta oligomer forms?

Does the recent concern over several papers about Aβ*56 call into question the association of Alzheimers Disease with any amyloyd beta oligomer forms? From my understanding, no. alzforum.org has ...
Franck Dernoncourt's user avatar
11 votes
Accepted

Can the central dogma work in reverse?

Let’s first consider what the Central Dogma[1] actually says. It is precisely summarised in the following figure[2]: solid arrows represent transfer of information that has been observed directly; ...
Konrad Rudolph's user avatar
11 votes
Accepted

Does the term 'protein expression' refer to the production of proteins only or also their regulation?

There are no formal definitions accepted in science for ambiguous phrases such “protein expression”. If you wish to know what a particular author who uses such a shorthand phrase means you need to ...
David's user avatar
  • 25.2k
11 votes
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Arrangement of Amino Acids in the Protein alphabet

As suggested by tyersome's comment, the amino acids are grouped by their physiochemical properties. Let's add some commas: DE,KRH,NQ,ST,PGAVIL,MC,FYW aspartic ...
acvill's user avatar
  • 8,286
11 votes
Accepted

Are "antibodies" and "immunoglobulins" really the same things?

See also https://en.wikipedia.org/wiki/Immunoglobulin_superfamily What you have here is a bit of imprecise terminology, and a language problem equivalent to another familiar one: cats. A lion is both ...
Bryan Krause's user avatar
  • 45.3k
11 votes

How do proteins 'know' where to go?

This answer is specific to the "two-legged" proteins from the end of the video (motor proteins). The animation shows identical proteins moving in perfect lockstep, but really there is wide ...
benrg's user avatar
  • 211
10 votes
Accepted

By just looking at an unlabeled picture, how do you know it is a protein?

Shapes This is a common way of illustrating a protein and is often called a "protein cartoon". There are other common ways of illustrating proteins. This cartoon shows you where α helices ...
James's user avatar
  • 11.3k
10 votes

What is the longest-lasting protein in a human body?

A very interesting example are the cohesin molecules holding sister chromatids together in the oocytes (so only applicable to females, sorry!). Cohesion is established in utero, and these molecules ...
Phlya's user avatar
  • 201

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