Bio questions... aquaporins vs carrier proteins

[Ame535]

Hi,
Please help me with these questions,

1) When do we use aquaporins and when do we use carrier proteins? Which one require ATP? Are they both integral proteins?

2) What's the difference between crossing over and independent assortment? Do they only occur in Meiosis? Also what stages?

3) What's the difference between binding site and an active site on an enzyme?

Thanks in advance.

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[FeralisExtremum]

1. Aquaporin is more of a channel protein, specific to water. Water just moves in and out of it according to the gradient. Unlike a carrier protein it doesn't change conformation - picture it as kind of just a tube. It is integral, and doesn't require ATP. A carrier protein will bind a substance and then change shape to transfer it across the membrane. It is integral. Some of them require ATP (active transport). Some don't, and just work via facilitated diffsion.

2. Crossing over and independent assortment are both only during meiosis. Crossing over refers to the homologous chromosome pairs swapping pieces of genetic information, resulting in genetic variation in the gametes. Crossing over occurs during Prophase I. Independent assortment refers to the separation of the homologous chromosome pairs during Anaphase I - specifically it says that the way one pair of homologues chromosomes separates is completely independent of how each of the others will separate (e.g. if your first chromosome pair separated so that your mom's chromosome went to the left and your dad's to the right, this doesn't change how the second chromosome pair will separate - your mom's could go to the right or the left, each separation is considered its own separate isolated event).

3. The active site of the enzyme is where the substrate binds and usually some conformational change takes place. "Binding site" is kind of vague - it could refer to the active site, but some enzymes may have other binding sites (allosteric enzymes) where other molecules could bind and affect the enzyme shape and function.

 

[Ame535]

Thank you @FeralisExtremum, you are the best!

 

[Ame535]

I have another question I hope you help me with
What's the difference between point and frameshift mutation also to which of these do nonsense, missense and silent mutations belong?

Thank you.

 

[FeralisExtremum]

A point mutation is a broad term for a mutation involving a single nucleotide. This could mean one nucleotide being turned into a different nucleotide, or it could mean the insertion or deletion of a nucleotide. If a nucleotide is deleted or inserted, it will cause a frameshift mutation because the reading frame has been moved. This is a bit hard to describe in words so here is a visual of a frameshift mutation:

Notice how all the codons after the insertion/deletion are now read completely differently. Frameshifts are usually detrimental. It's worth pointing out that you can have a frameshift involving more than one nucleotide being inserted or deleted, however if you add or remove 3 nucleotides (or a multiple of 3) then it's technically not a frameshift anymore (because the codons are still read correctly but an entire amino acid will have been added or removed). So a point mutation can cause a frameshift mutation, or not, it depends on if the specific point mutation was an insertion/deletion or just a substitution of one nucleotide for another.

Nonsense, missense, and silent mutations describe the functional effect that a mutation has on the actual protein that is encoded.
-In a nonsense mutation, an existing codon is changed to a stop codon, resulting in the protein being cut short early. Usually detrimental to the function of the protein.
-In a missense mutation, a codon is changed in a way that results in a different amino acid being used than the one that should be there. Depending on the protein and amino acid change, this can have little to no effect, or a severe effect on the function of the protein.
-In a silent mutation, the codon is changed but due to the redundancies in codons (there are multiple codons for some amino acids), the same amino acid gets incorporated as normal. The function of the protein remains unaltered.

The above mutations can be the result of a point mutation where a nucleotide is changed and a different codon ends up being made than normal. A frameshift mutation could technically cause the above, but would do so on a much larger scale (since most if not all of the codons after a frameshift will be changed to something other than what they should be). So a frameshift could end up causing a nonsense mutation, or a consecutive series of missense mutations, or both.

 

[Ame535]

Thank you.