Research methods in histology. Basic principles and stages of preparation of histological preparations. Structures formed by the plasma membrane Cellular conveyor during protein synthesis
In the metabolism of the body, the leading role belongs to proteins and nucleic acids. Protein substances form the basis of all vital cell structures, they are part of the cytoplasm. Proteins are extremely reactive. They are endowed with catalytic functions, that is, they are enzymes, therefore proteins determine the direction, speed and the closest coordination, conjugation of all metabolic reactions.
Rice. 13 A. Scheme of protein synthesis in a eukaryotic cell.
Rice. 13 B. Scheme of protein synthesis in a prokaryotic cell.
The leading role of proteins in the phenomena of life is associated with the richness and diversity of their chemical functions, with an exceptional ability to various transformations and interactions with other simple and complex substances that make up the cytoplasm.
Nucleic acids are part of the most important organ of the cell - the nucleus, as well as the cytoplasm, ribosomes, mitochondria, etc. Nucleic acids play an important, primary role in heredity, body variability, and protein synthesis.
The process of protein synthesis is a very complex multi-step process. It takes place in special organelles - ribosomes. The cell contains a large number of ribosomes. For example, E. coli has about 20,000 of them.
How does protein synthesis occur in ribosomes?
Protein molecules are essentially polypeptide chains made up of individual amino acids. But amino acids are not active enough to connect with each other on their own. Therefore, before they combine with each other and form a protein molecule, amino acids must be activated. This activation occurs under the action of special enzymes. Moreover, each amino acid has its own enzyme, specifically tuned to it.
The energy source for this (as well as for many processes in the cell) is adenosine triphosphate (ATP).
As a result of activation, the amino acid becomes more labile and binds to t-RNA under the action of the same enzyme.
It is important that each amino acid corresponds to a strictly specific t-RNA. She finds "her" amino acid and transfers it to the ribosome. Therefore, such RNA is called transport RNA.
Consequently, the ribosome receives various activated amino acids connected to their tRNAs. The ribosome is, as it were, a conveyor for assembling a protein chain from various amino acids entering it (Fig. 13 A and B).
The question arises: what determines the order of binding between individual amino acids? After all, it is this order that determines which protein will be synthesized in the ribosome, since its specificity depends on the order of the arrangement of amino acids in the protein. The cell contains more than 2000 specific proteins of different structure and properties.
It turns out that simultaneously with t-RNA, on which its own amino acid "sits", a "signal" from DNA, which is contained in the nucleus, enters the ribosome. In accordance with this signal, this or that protein, this or that enzyme is synthesized in the ribosome (since enzymes are proteins).
The directing influence of DNA on protein synthesis is carried out not directly, but with the help of a special intermediary, that form of RNA, which is called matrix or messenger RNA (m-RNA or i-RNA).
Messenger RNA is synthesized in the nucleus under the influence of DNA, so its composition reflects the composition of DNA. The RNA molecule is, as it were, a cast from the form of DNA.
The synthesized mRNA enters the ribosome and, as it were, transfers to this structure a plan - in what order the activated amino acids that have entered the ribosome should be connected to each other in order to synthesize a certain protein. Otherwise, the genetic information encoded in DNA is transferred to mRNA and then to protein.
The messenger RNA molecule enters the ribosome and, as it were, stitches it. That section of it that is currently in the ribosome, defined by a codon (triplet), interacts in a completely specific way with a triplet (anticodon) suitable for it in structure in the transfer RNA, which brought the amino acid into the ribosome. Transfer RNA with its amino acid approaches a specific codon of i-RNA and connects to it; to the next, neighboring plot i-RNA joins another t-RNA with another amino acid, and so on, until the entire chain of i-RNA is read and until all the amino acids are strung in the appropriate order, forming a protein molecule. And t-RNA, which delivered the amino acid to a certain site of the polypeptide chain, is released from its amino acid and leaves the ribosome. Then again in the cytoplasm, the desired amino acid can join it, and it will again transfer it to the ribosome. In the process of protein synthesis, not one, but several ribosomes, polyribosomes, are simultaneously involved.
The main stages of the transfer of genetic information: synthesis on DNA as on an i-RNA template (transcription) and synthesis in ribosomes of a polypeptide chain according to the program contained in i-RNA (translation), are universal for all living beings. However, the temporal and spatial relationships of these processes differ between pro and eukaryotes.
In organisms with a real nucleus (animals, plants), transcription and translation are strictly separated in space and time: the synthesis of various RNAs occurs in the nucleus, after which the RNA molecules must leave the nucleus, passing through the nuclear membrane (Fig. 13 A). Then, in the cytoplasm, RNA is transported to the site of protein synthesis - ribosomes. Only after that comes the next stage - translation.
In bacteria, the nuclear substance of which is not separated from the cytoplasm by a membrane, transcription and translation proceed simultaneously (Fig. 13 B).
Modern schemes illustrating the work of genes are built on the basis of a logical analysis of experimental data obtained using biochemical and genetic methods. The use of subtle electron microscopic methods allows you to literally see the work of the hereditary apparatus of the cell. Recently, electron microscopic images have been obtained, which show how, on a bacterial DNA matrix, in those areas where RNA polymerase molecules (an enzyme that catalyzes the transcription of DNA into RNA) are attached to DNA, mRNA molecules are synthesized. Strands of mRNA located perpendicular to the linear DNA molecule move along the matrix and increase in length. As the RNA strands lengthen, ribosomes join them, which, moving in turn along the RNA strand towards DNA, lead to protein synthesis.
From all that has been said, it follows that the place of synthesis of proteins and all enzymes in the cell are ribosomes. Figuratively speaking, these are, as it were, protein "factories", as if an assembly shop, where all the materials necessary for assembling a protein polypeptide chain from amino acids are supplied. The nature of the synthesized protein depends on the structure of the i-RNA, on the order of the nucleoids in it, and the structure of the i-RNA reflects the structure of the DNA, so that in the end the specific structure of the protein, i.e. the order in which the various amino acids are arranged in it, depends on the order arrangement of nucleoids in DNA, on the structure of DNA.
The stated theory of protein biosynthesis was called the matrix theory. This theory is called matrix theory because nucleic acids play, as it were, the role of matrices in which all information is recorded regarding the sequence of amino acid residues in a protein molecule.
The creation of the matrix theory of protein biosynthesis and the deciphering of the amino acid code is the largest scientific achievement of the 20th century, major step on the way to elucidating the molecular mechanism of heredity.
How to explain, briefly and clearly, what is protein biosynthesis, and what is its significance?
If you are interested in this topic, and would like to improve school knowledge or repeat gaps, then this article was created for you.
What is protein biosynthesis
First, it is worth familiarizing yourself with the definition of biosynthesis. Biosynthesis is the synthesis of natural organic compounds by living organisms.
To put it simply, it is the production of various substances with the help of microorganisms. This process plays an important role in all living cells. Do not forget about the complex biochemical composition.
Transcription and broadcast
These are the two most important steps in biosynthesis.
Transcription from Latin means “rewriting” - DNA is used as a matrix, therefore, three types of RNA are synthesized (matrix / informational, transport, ribosomal ribonucleic acids). The reaction is carried out using a polymerase (RNA) and using a large number adenosine triphosphate.
There are two main actions:
- Marking the end and start of translation by adding mRNA.
- An event carried out due to splicing, which in turn removes non-informative RNA sequences, thereby reducing the mass of matrix ribonucleic acid by 10 times.
Broadcast from Latin means "translation" - mRNA is used as a template, polypeptide chains are synthesized.
The translation includes three stages, which could be presented in the form of a table:
- First step. Initiation is the formation of a complex that is involved in the synthesis of a polypeptide chain.
- Second phase. Elongation is an increase in the size of this chain.
- Third stage. Termination is the conclusion of the above mentioned process.
Diagram of protein biosynthesis
The diagram shows how the process proceeds.
The docking point of this circuit is the ribosomes, in which the protein is synthesized. In a simple form, the synthesis is carried out according to the scheme
DNA > RNA > protein.
The first stage of transcription begins, in which the molecule is changed into a single-stranded messenger ribonucleic acid (mRNA). It contains information about the amino acid sequence of the protein.
The next stop of the mRNA will be the ribosome, where the synthesis itself takes place. This happens by translation, the formation of a polypeptide chain. After this ordinary scheme, the resulting protein is transported to different places, performing certain tasks.
Sequence of protein biosynthesis processors
Protein biosynthesis is a complex mechanism that includes the two steps mentioned above, namely transcription and translation. The transcribed stage occurs first (it is divided into two events).
After comes translation, in which all types of RNA participate, each has its own function:
- Informational - the role of the matrix.
- Transport - addition of amino acids, determination of codons.
- Ribosomal - the formation of ribosomes that support mRNA.
- Transport - synthesis of a polypeptide chain.
What components of the cell are involved in protein synthesis
As we have already said, biosynthesis is divided into two stages. Each stage has its own components. At the first stage, these are deoxyribonucleic acid, messenger and transfer RNA, and nucleotides.
In the second stage, the following components are involved: mRNA, tRNA, ribosomes, nucleotides and peptides.
What are the features of protein biosynthesis reactions in a cell
The list of features of biosynthesis reactions should include:
- Use of ATP energy for chemical reactions.
- There are enzymes that speed up reactions.
- The reaction has a matrix character, since the protein is synthesized on mRNA.
Signs of protein biosynthesis in a cell
Such a complex process, of course, is characterized by various signs:
- The first of these is that there are enzymes, without which the process itself would not be possible.
- All three types of RNA are involved, from this we can conclude that the central role belongs to RNA.
- The formation of molecules is carried out by monomers, namely amino acids.
- It should also be noted that the specificity of a protein is oriented by the arrangement of amino acids.
Conclusion
A multicellular organism is an apparatus consisting of different cell types that are differentiated - differ in structure and function. In addition to proteins, there are cells of these types, which also synthesize their own kind, this is the difference.
1. The main stages of protein biosynthesis. Genetic code
2. Regulation of gene expression
1. The main stages of protein biosynthesis. Genetic code
Protein biosynthesis in cells is a sequence of matrix-type reactions, during which the sequential transfer of hereditary information from one type of molecule to another leads to the formation of polypeptides with a genetically determined structure.
Protein biosynthesis represents the initial stage of implementation, or expression of genetic information. The main matrix processes that ensure the biosynthesis of proteins include DNA transcription And mRNA translation. DNA transcription consists in rewriting information from DNA to mRNA (messenger or messenger RNA). Translation of mRNA is the transfer of information from mRNA to a polypeptide. general characteristics The matrix synthesis reactions are given in Chapter 3. The sequence of matrix reactions in protein biosynthesis can be represented as Scheme 1.
The diagram shows that the genetic information about the structure of a protein is stored as a sequence of DNA triplets. In this case, only one of the DNA chains serves as a template for transcription (such a chain is called transcribed). The second strand is complementary to the transcribed strand and is not involved in mRNA synthesis.
The mRNA molecule serves as a template for polypeptide synthesis on ribosomes. mRNA triplets that code for a particular amino acid are called codons. Translation is carried out by tRNA molecules. Each tRNA molecule contains anticodon- a recognition triplet in which the nucleotide sequence is complementary to a specific mRNA codon. Each tRNA molecule is capable of carrying a strictly defined amino acid. The combination of tRNA with an amino acid is called aminoacyl-tRNA.
The tRNA molecule in general conformation resembles a clover leaf on a petiole. "Top of the sheet" carries anticodon. There are 61 types of tRNA with different anticodons. An amino acid is attached to the "leaf petiole" (there are 20 amino acids involved in the synthesis of the polypeptide on ribosomes). Each tRNA molecule with a certain anticodon corresponds to a strictly defined amino acid. At the same time, a certain amino acid usually corresponds to several types of tRNA with different anticodons. The amino acid covalently attaches to tRNA with the help of enzymes - aminoacyl-tRNA synthetases. This reaction is called tRNA aminoacylation.
On ribosomes, the anticodon of the corresponding aminoacyl-tRNA molecule is attached to a specific mRNA codon with the help of a specific protein. This binding of mRNA and aminoacyl-tRNA is called codon dependent. Amino acids are linked together on ribosomes by peptide bonds, and the released tRNA molecules go in search of free amino acids.
Let us consider in more detail the main stages of protein biosynthesis.
Stage 1. DNA transcription . On the transcribed DNA strand, a complementary mRNA strand is completed using DNA-dependent RNA polymerase. The mRNA molecule is an exact copy of the non-transcribed DNA chain, with the difference that instead of deoxyribonucleotides it contains ribonucleotides, which include uracil instead of thymine.
Stage 2. Processing (maturation )mRNA . The synthesized mRNA molecule (primary transcript) undergoes additional transformations. In most cases, the original mRNA molecule is cut into separate fragments. Some fragments - introns- are cleaved to nucleotides, and others - exons are fused into mature mRNA. The process of connecting exons "without knots" is called splicing.
Splicing is characteristic of eukaryotes and archaebacteria, but sometimes also occurs in prokaryotes. There are several types of splicing. Essence a alternative splicing is that the same regions of the original mRNA can be both introns and exons. Then one and the same DNA region corresponds to several types of mature mRNA and, accordingly, several different forms the same protein. Essence trans splicing consists in joining exons encoded by different genes (sometimes even from different chromosomes) into one mature mRNA molecule.
Stage 3. mRNA translation . Translation (like all matrix processes) includes three stages: initiation(Start), elongation(continued) and termination(ending).
Initiation. The essence of initiation is the formation of a peptide bond between the first two amino acids of the polypeptide.
Initially formed initiating complex, which includes: a small subunit of the ribosome, specific proteins (initiation factors) and a special initiator methionine tRNA with the amino acid methionine - Met-tRNA Met. The initiation complex recognizes the beginning of the mRNA, attaches to it, and slides to the point of initiation (beginning) of protein biosynthesis: in most cases, this start codon AUG. Between the start codon of mRNA and the anticodon of methionine tRNA, codon-dependent binding occurs with the formation of hydrogen bonds. Then the large subunit of the ribosome is attached.
When combining subunits, a complete ribosome is formed, which carries two active centers (sites): BUT – site (aminoacyl, which serves to attach aminoacyl-tRNA) and R -section (peptidyltransferase, which serves to form a peptide bond between amino acids).
Initially, Met-tRNA Met is located on BUT –section, but then moves to R -plot. On the freed BUT The –site receives aminoacyl-tRNA with an anticodon that is complementary to the mRNA codon following the AUG codon. In our example, this is Gly-tRNA Gly with the anticodon CCG, which is complementary to the GHC codon. As a result of codon-dependent binding, hydrogen bonds are formed between the mRNA codon and the aminoacyl-tRNA anticodon. Thus, two amino acids are adjacent to the ribosome, between which a peptide bond is formed. The covalent bond between the first amino acid (methionine) and its tRNA is broken.
After the formation of a peptide bond between the first two amino acids, the ribosome shifts by one triplet. As a result, translocation (movement) of the initiating methionine tRNA Met occurs outside the ribosome. The hydrogen bond between the start codon and the anticodon of the initiator tRNA is broken. As a result, free Met tRNA is cleaved off and goes in search of its amino acid.
The second tRNA, together with the amino acid (in our example, Gly-tRNA Gly), as a result of translocation, is on R -section, and BUT - the site is freed.
Elongation. The essence of elongation is the addition of subsequent amino acids, that is, the extension of the polypeptide chain. The work cycle of the ribosome during elongation consists of three steps: codon-dependent binding of mRNA and aminoacyl-tRNA to BUT – site, formation of a peptide bond between the amino acid and the growing polypeptide chain and translocation with release BUT -plot.
On the freed BUT – the site receives aminoacyl-tRNA with an anticodon corresponding to the next mRNA codon (in our example, it is Tyr-tRNA Tyr with the AUA anticodon, which is complementary to the UAU codon).
On the ribosome, two amino acids are next to each other, between which a peptide bond is formed. The link between the previous amino acid and its tRNA (in our example, between glycine and Gly tRNA) is broken.
Then the ribosome moves one more triplet, and as a result of the translocation of the tRNA that was on R -site (in our example, Gly tRNA), is outside the ribosome and is cleaved off from mRNA. BUT - the site is released, and the working cycle of the ribosome begins anew.
Termination. The essence of termination is the completion of the synthesis of the polypeptide chain.
Eventually, the ribosome reaches an mRNA codon that no tRNA (and no amino acid) matches. There are three such nonsense codons: UAA (“ocher”), UAG (“amber”), UGA (“opal”). At these mRNA codons, the working cycle of the ribosome is interrupted, and the growth of the polypeptide stops. The ribosome, under the influence of certain proteins, is again divided into subunits.
Protein modification.
As a rule, the synthesized polypeptide undergoes further chemical transformations. The original molecule can be cut into separate fragments; then some fragments are crosslinked, others are hydrolyzed to amino acids. Simple proteins can combine with a wide variety of substances to form glycoproteins, lipoproteins, metalloproteins, chromoproteins, and other complex proteins. In addition, amino acids already in the composition of the polypeptide can undergo chemical transformations. For example, an amino acid proline, which is part of the protein procollagen, oxidized to hydroxyproline. As a result of procollagen formed collagen- the main protein component of connective tissue.
Protein modification reactions are not matrix-type reactions. These biochemical reactions are called stepped.
Energy of protein biosynthesis. Protein biosynthesis is a very energy intensive process. During aminoacylation of tRNA, the energy of one bond of the ATP molecule is expended, with codon-dependent binding of aminoacyl-tRNA, the energy of one bond of the GTP molecule is consumed, when the ribosome moves one triplet, the energy of one bond of another GTP molecule is consumed. As a result, about 90 kJ / mol is spent on attaching an amino acid to a polypeptide chain. Hydrolysis of the peptide bond releases only 2 kJ/mol. Thus, during biosynthesis, most of the energy is irretrievably lost (dissipated in the form of heat).
Eukaryotic cells have a developed system of internal structures surrounded by membranes called organelles.
Each organelle has a unique composition of (glyco)proteins and (glyco)lipids and performs a specific set of functions.
Each organelle contains one or more membrane-bound compartments.
Organelles perform their functions autonomously or in groups
During endocytosis and exocytosis, transported proteins (cargo proteins) are transported between compartments through transport vesicles, which are formed by budding from the surface of the organelle and then fuse with the target membrane of the acceptor compartment.
Transport vesicles can selectively include transported material and exclude those components that should remain in the organelle from which the vesicles are formed.
Selective incorporation into vesicles is provided by signals present in the primary structure of the protein or in the carbohydrate structure
Transport vesicles contain proteins that guide them to their destinations and binding sites. Subsequently, the vesicles fuse with the acceptor site of the membrane
Membrane-bound compartments in a typical animal cell.One of the characteristic features eukaryotic cell is the presence in it of a developed system of internal structures surrounded by membranes called organelles. Eukaryotic cells are characterized by the presence of membranes that divide their internal contents into functionally different compartments, while all cells of living organisms have an outer two-layer membrane.
One of the advantages compartmentalization is that the cell has the ability to create the necessary environment to perform functions that require a certain chemical composition environment.
Illustrated structure and diversity organelle, having a membrane, which are usually present in a eukaryotic cell (in this case, in a typical animal cage). Each organelle contains one or more compartments. For example, the endoplasmic reticulum (ER) is one compartment; on the contrary, the Golgi apparatus consists of several compartments surrounded by membranes that have certain biochemical functions.
Mitochondria are characterized by two compartment, matrix and intermembrane space containing a set of specific macromolecules.
The cytosol can be considered one compartment, limited by the plasma membrane and in contact with the outer part of the membrane of all intracellular organelles. The cytoplasm consists of the cytosol and organelles. Similarly, the nucleoplasm is bounded by the inner nuclear membrane.
Each organelle contains unique set of proteins(both membrane and soluble), lipids and other molecules necessary to perform its functions. Some lipids and proteins are covalently linked to oligosaccharides. As cells grow and divide, their new components must be synthesized, which are necessary for growth, division, and the final distribution of intracellular material between two daughter cells. During cell differentiation and development, as well as in response to external factors such as stress, organelle components are synthesized.
but Components are not always formed in the organelle where they function. Typically, various macromolecules are formed at sites specially designed for their synthesis. For example, most proteins are formed on the ribosomes of the cytosol, which is the optimal environment for ribosome function and protein synthesis.
The following question arises: how the components organelle get into their places of operation? Since the early 1970s this question was central in cell biology. As shown in the figure below, there are at least eight major types of organelles, each made up of hundreds or thousands of different proteins and lipids.
exocytosis and endocytosis.
Exocytosis involves the endoplasmic reticulum (including the nuclear envelope)
and the Golgi apparatus (one stack of cisterns is shown).
Endocytosis occurs with the participation of early and late endosomes and lysosomes.
All these molecules must be transported into organelles in which they perform their functions. Most are formed in the cytosol, and therefore the question arises: how are they delivered to the corresponding organelles or exit the cell if they belong to secreted proteins? In many cases, the answer to this question is the presence of special signals in the protein molecule, usually called sorting signals or addressing signals. They are short sequences of amino acids present in the primary structure of those proteins that should not be localized in the cytosol. Each destination address of a protein molecule is associated with one or more various types signals.
Sort signals are recognized special cell systems as the protein moves towards its destination. As shown in the figure below, there are two main transport mechanisms: exocytosis (or secretory pathway) and endocytosis, in which material (cargo) is transported from the cell and into the cell, respectively.
For all newly synthesized proteins, intended for secretion from the cell, or for entry into organelles by exo- or endocytosis, there is a common entry point on the ER membrane. Signal sequences serve as signals for protein translocation across the ER membrane. In this chapter, we will look at the sorting signals that direct proteins to their destinations.
Being in EPR, the protein cannot be transported through the cytoplasm, and the only way for it to reach other organelles surrounded by membranes is vesicular transport. Transport vesicles are primarily composed of proteins and lipids and are said to "bud" from the membrane. After a vesicle has budded, it fuses with the next compartment in its path. The compartment from which the vesicle originated is usually called the donor compartment (or source compartment) and the destination (or target) compartment is usually called the acceptor compartment.
Transport vesicles directly or indirectly transfer proteins from the ER to all other compartments on the way of exo- or endocytosis. During endocytosis, vesicles form on the plasma membrane. These vesicles transport the material contained in them to endosomes, from which other vesicles are formed, carrying the material to other compartments. Thus, the composition of transport vesicles differs depending on their origin and destination compartment.
Vesicular transport creates a problem for the organelles with which the vesicles exchange. For normal functioning, a certain internal composition of organelles must be maintained. However, how can this be achieved if the vesicles change this composition all the time? The scale of the problem becomes apparent when calculating transport efficiency. Through the endocytosis pathway, the amount of membrane proteins and lipids equivalent to their total content in the plasma membrane can be transported through the organelles in less than an hour. When compared to the time it takes to synthesize a new organelle (usually one day), this speed is impressive.
Solution to this Problems related to the selectivity of the transport process. When budding, only those proteins that need to be transported pass into the vesicle. Resident proteins of the organelle do not enter the vesicle. The vesicle holds these proteins and passes them on to the next vesicle in its path. To maintain homeostasis between organelles, by its nature, vesicular transport must always be bidirectional, i.e. components of the donor compartment must not be continuously transferred to the acceptor compartment.
The contours of the cell, even at the light-optical level, do not appear to be even and smooth, and electron microscopy made it possible to detect and describe various structures in the cell that reflect the nature of its functional specialization. There are the following structures:
1. Microvilli - protrusion of the cytoplasm, covered with plasmolemma. The cytoskeleton of the microvilli is formed by a bundle of actin microfilaments, which are woven into the terminal network of the apical part of the cells (Fig. 5). Single microvilli are not visible at the optical level. In the presence of a significant number of them (up to 2000-3000), in the apical part of the cell, even with light microscopy, a “brush border” is distinguished.
2. Eyelashes - are located in the apical zone of the cell and have two parts (Fig. 6): a) outer - axoneme
b) internal - besal body
axoneme consists of a complex of microtubules (9 + 1 pairs) and associated proteins. Microtubules are formed by the protein tubulin, and the handles are formed by the protein dynein - these proteins together form the tubulin-dynein chemomechanical transducer.
Basal body consists of 9 triplets of microtubules located at the base of the cilium and serves as a matrix for the organization of the axoneme.
3. Basal labyrinth are deep invaginations of the basal plasmalemma with mitochondria lying between them. This is a mechanism of active absorption of water, as well as ions against a concentration gradient.
1. Transport low molecular weight compounds carried out in three ways:
1. Simple diffusion
2. Facilitated diffusion
active transport
simple diffusion- low molecular weight hydrophobic organic compounds (fatty acids, urea) and neutral molecules (HO, CO, O). With an increase in the concentration difference between compartments separated by a membrane, the diffusion rate also increases.
Facilitated diffusion- the substance also passes through the membrane in the direction of the concentration gradient, but with the help of a transport protein - translocases. These are integral proteins with specificity for the substances they carry. These are, for example, anion channels (erythrocyte), K channels (plasmolemma of excited cells) and Ca channels (sarcoplasmic reticulum). Translocase for HO, it is aquaporin.
Translocase mechanism of action:
1. The presence of an open hydrophilic channel for substances of a certain size and charge.
2. The channel opens only when a specific ligand is bound.
3. There is no channel as such, and the translocase molecule itself, having bound the ligand, rotates 180 in the membrane plane.
active transport is transport using the same transport protein (translocases), but against the concentration gradient. This movement requires energy.
2. Transport of macromolecular compounds across membranes
The transition of particles through the plasmalemma always occurs in the composition membrane vesicle: 1. Endocytosis: but. pinocytosis b. phagocytosis c. receptor-mediated endocytosis.
Exocytosis: but. secretion b. excretion, c. Recretion is the transfer of solids through the cell, phagocytosis and excretion are combined here.