This is an efficient way for the cell to rapidly change the abundance levels of specific proteins in response to the environment. Because proteins are involved in every stage of gene regulation, the phosphorylation of a protein depending on the protein that is modified can alter accessibility to the chromosome, can alter translation by altering transcription factor binding or function , can change nuclear shuttling by influencing modifications to the nuclear pore complex , can alter RNA stability by binding or not binding to the RNA to regulate its stability , can modify translation increase or decrease , or can change post-translational modifications add or remove phosphates or other chemical modifications.
All of these protein activities are affected by the phosphorylation process. The enzymes which are responsible for phosphorylation are known as protein kinases. The addition of a phosphate group to a protein can result in either activation or deactivation; it is protein dependent. Another example of chemical modifications affecting protein activity include the addition or removal of methyl groups.
Methyl groups are added to proteins via the process of methylation; this is the most common form of post-translational modification. The addition of methyl groups to a protein can result in protein-protein interactions that allows for transcriptional regulation, response to stress, protein repair, nuclear transport, and even differentiation processes.
Methylation on side chain nitrogens is considered largely irreversible while methylation of the carboxyl groups is potentially reversible. Methylation in the proteins negates the negative charge on it and increases the hydrophobicity of the protein. Methylation on carboxylate side chains covers up a negative charge and adds hydrophobicity. The addition of this chemical group changes the property of the protein and, thus, affects it activity.
The addition of an ubiquitin group to a protein marks that protein for degradation. Ubiquitin acts like a flag indicating that the protein lifespan is complete. These proteins are moved to the proteasome, an organelle that functions to remove proteins to be degraded. Ubiquitin Tags : Proteins with ubiquitin tags are marked for degradation within the proteasome. Privacy Policy. Skip to main content. Microbial Genetics. Search for:.
Protein Modification, Folding, Secretion, and Degradation. Key Terms intron : a portion of a split gene that is included in pre-RNA transcripts but is removed during RNA processing and rapidly degraded moiety : a specific segment of a molecule spliceosome : a dynamic complex of RNA and protein subunits that removes introns from precursor mRNA.
Denaturation and Protein Folding Denaturation is a process in which proteins lose their shape and, therefore, their function because of changes in pH or temperature. Learning Objectives Discuss the process of protein denaturation. The body strictly regulates pH and temperature to prevent proteins such as enzymes from denaturing. Some proteins can refold after denaturation while others cannot. Chaperone proteins help some proteins fold into the correct shape.
Key Terms chaperonin : proteins that provide favorable conditions for the correct folding of other proteins, thus preventing aggregation denaturation : the change of folding structure of a protein and thus of physical properties caused by heating, changes in pH, or exposure to certain chemicals.
Protein Folding, Modification, and Targeting In order to function, proteins must fold into the correct three-dimensional shape, and be targeted to the correct part of the cell.
Learning Objectives Discuss how post-translational events affect the proper function of a protein. Key Takeaways Key Points Protein folding is a process in which a linear chain of amino acids attains a defined three-dimensional structure, but there is a possibility of forming misfolded or denatured proteins, which are often inactive.
Proteins must also be located in the correct part of the cell in order to function correctly; therefore, a signal sequence is often attached to direct the protein to its proper location, which is removed after it attains its location.
Protein misfolding is the cause of numerous diseases, such as mad cow disease, Creutzfeldt-Jakob disease, and cystic fibrosis. Regulating Protein Activity and Longevity A cell can rapidly change the levels of proteins in response to the environment by adding specific chemical groups to alter gene regulation.
Learning Objectives Explain how chemical modifications affect protein activity and longevity. Key Takeaways Key Points Proteins can be chemically modified by adding methyl, phosphate, acetyl, and ubiquitin groups. Protein longevity can be affected by altering stages of gene regulation, including but not limited to altering: accessibility to chromosomal DNA for transcription, rate of translation, nuclear shuttling, RNA stability, and post-translational modifications.
Denaturation and degradation of proteins are key steps in the processing of proteins in the cell. They are extremely important cellular processes. In the denaturation of protein, the protein loses its biological activity because the biological function is directly dependent on its structure.
However, degraded proteins can still have a secondary or tertiary structure. Overview and Key Difference 2. What is Denaturation of Protein 3. What is Degradation of Protein 4. Similarities Between Denaturation and Degradation of Protein 5. Denaturation is the process in which the protein losses its quaternary structure, tertiary structure, and secondary structure present in the native state. But the primary structure of proteins remains intact.
It can be achieved by the application of external stresses, compounds such as strong acid or base, a concentrated inorganic salt, an organic solvent alcohol, chloroform and radiation or heat. If the proteins in the cell get denatured, it results in the disruption of cell activity, possibly cell death. In protein denaturation, the protein loses its biological function. The denatured proteins can have a wide range of characteristics such as conformational changes, loss of solubility, and aggregation due to exposure to hydrophobic groups.
Denatured proteins lose their 3D structure; therefore, they cannot function, as mentioned earlier. Proper protein folding helps globular or membrane proteins to do their job correctly.
And these interactions are stabilized by van der Waals interactions, hydrophobic packing, and disulfide bonding, in addition to the same hydrogen bonding that helps to determine secondary structure. And then quaternary structure just describes the different interactions between individual protein subunits. So you have the folded-up proteins that then come together to assemble the completed, overall protein.
And the interaction of these different protein subunits are stabilized by the same kinds of bonds that help to determine tertiary structure. So all of these levels of protein structure help to stabilize the folded-up, active confirmation of a protein.
So why is it so important to know about the different levels of protein structure and how they contribute to conformational stability? Well, like I said, a protein is only functional when they are in their proper conformation, in their proper 3D form. And an improperly folded or degraded, denatured, protein is inactive.
So in addition to the four levels of protein structure that I just reviewed, there is also another force that helps to stabilize a protein's conformation. And that force is called the solvation shell. Now, the solvation shell is just a fancy way of describing the layer of solvent that is surrounding a protein.
So say I have a protein who has all these exterior residues that are overall positively charged. And picture this protein in the watery environment of the interior of one of our cells, then the solvation shell is going to be the layer of water right next to this protein molecule.
And remember that water is a polar molecule, so you have the electronegative oxygen atom with a predominantly negative charge leaving a positive charge over next to the hydrogen atoms. The same is true for each of these water molecules. So now, as you can see, the electronegative oxygen atoms are stabilizing all the positively charged amino acid residues on the exterior of this protein.
So as you can see, the conformational stability of a protein depends not only on all of these interactions that contribute to primary, secondary, tertiary, and quaternary structure, but also what sort of environment that protein is in. And all of these interactions are very crucial for keeping a protein folded properly, so that it can do its job. Now, what happens when things go wrong? How does a protein become unfolded and thus inactive? Well, remember that this is called denaturation.
And this can be done by changing a lot of different parameters within a protein's environment, including changing the temperature, the pH, adding chemical denaturants, or even adding enzymes.
So let's start with what happens if you alter the temperature around a protein. And we can use the example of an egg when we put it into a pot of boiling water, because an egg, especially the white part, is full of protein, and this pot of boiling water is representing heat. And remember that heat is really just a form of energy. So when you heat an egg, the proteins gain energy and literally shake apart the bonds between the parts of the amino acid chains.
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