Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Cell Recognition

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Biology

Cell recognition is a broad term. Essentially, it is one of the key ways body cells communicate with one another. Cells in the body can recognise each other, self-cells, as well as foreign material, such as bacteria, viruses, and toxins. Cell recognition is a crucial part of the immune system. The body must differentiate between self-cells, abnormal body cells, non-self material such as cells from another organism, and pathogens to identify which cells to destroy to protect the body.

This is achieved through specific complementary interactions between identifying molecules found on the surface of each cell. Each type of cell, self or non-self, can be identified by the specific molecules on its surface. These molecules include glycolipids and glycoproteins.

Proteins that are part of the phospholipid bilayer are especially useful in cell recognition. This is because proteins have highly specific tertiary and quaternary structures, and are capable of great structural variety depending on their amino acid sequence. These identifying molecules are often called antigens, especially when discussing the immune response.

The cell membrane and cell recognition

To understand how cell recognition functions in more detail, we must revisit the cell membrane structure. Every cell has a phospholipid bilayer membrane which encloses the cell's organelles and genetic material. Inside this phospholipid bilayer, molecules are necessary for cell function, including channel proteins that allow substances to pass in and out of the cell, and cholesterol, which reduces the bilayer's permeability to create a stronger concentration gradient between the inside and outside of the cell.

Crucially, each cell membrane also contains cell-identifying molecules, which are found on the outside of the phospholipid membrane and extend into the extracellular space, the space outside the cells. These identifying molecules are often called membrane carbohydrates. This is when carbohydrates are bound to molecules present in the phospholipid bilayer. It is these carbohydrate molecules that extend outwards into the extracellular space.

Cell Recognition the cell membrane and  its components StudySmarterFigure 1. The cell membrane. Source: LadyOfHats, Public domain, via Wikimedia Commons.

Membrane carbohydrates

Cell membranes contain carbohydrates, proteins, and lipids. Carbohydrates can be covalently linked to proteins in the cell membrane, forming glycoproteins, or lipids, to form glycolipids. These are known as membrane carbohydrates. These molecules mostly face the outside of the cell, extending into the extracellular space. Membrane carbohydrates are important in cell recognition.

The glyco-prefix means sugar, indicating the presence of carbohydrate molecules in the molecule.

Glycoproteins

Glycoproteins are formed when a carbohydrate molecule bonds to a protein molecule. The bond in this molecule is covalent. Glycoproteins are the most common membrane carbohydrates, with almost all membrane proteins being linked to carbohydrates.

A Covalent bond refers to two atoms sharing electrons.

These molecules have many functions in the body. In cell recognition, they protect the cell from binding to pathogens such as a virus, bacteria, or toxins. They also allow for interactions with other body cells through the binding of molecules. Glycoproteins can also act as markers for viruses to identify host cells.

An example is the CD4 glycoprotein found on T cells, which HIV specifically binds to.

The structure of a glycoprotein

Glycolipids

The binding of carbohydrates forms glycolipids to the cell membrane's lipid bilayer. A glycosidic, covalent bond joins the carbohydrate and lipid molecules. Glycolipids act as specific sites for cell recognition outside the cell surface membrane.

Glycolipids are mainly involved in cell-to-cell interactions, where the molecule will bind to a specific complementary carbohydrate or carbohydrate-binding protein on neighbouring cells. Glycolipids are also important in recognition of host cells by viruses.

Cell recognition and the immune system

Cell recognition is a crucial element in the functioning of the immune system. Cells in the body involved in immune response, such as phagocytes and lymphocytes, must identify the presence of pathogens to defend the body against them. The body has non-specific defence mechanisms, such as the action of phagocytes against pathogens, and specific defence mechanisms, such as the action of T lymphocytes and B lymphocytes. Both of these defence mechanisms use cell recognition.

Phagocytes: A type of non-specific cell that can engulf and digest foreign particles.

Lymphocytes: A white blood cell that is part of the immune system

Pathogens are organisms that cause disease.

Lymphocytes

Lymphocytes are a type of white blood cell that plays a key part in the body's immune response. There are around 10 million lymphocytes present in the body, each with different proteins on its surface that are complementary to proteins found on different pathogens; this allows them to recognise the presence of a pathogen in the body.

Lymphocytes only respond to non-self antigens. This is because lymphocytes with receptors complementary to the body's cells either die or are suppressed when a person is still a fetus.

In the fetus, lymphocytes collide almost exclusively with self-material as the body is protected from infection by the placenta. Some of these lymphocytes will have receptors complementary to the body's cells, and these lymphocytes are suppressed. Therefore, only lymphocytes that might complement non-self material are left in the body.

In the adult body, some lymphocytes, B cells to be exact, are produced in the bone marrow. These lymphocytes initially only come into contact with self-antigens. As in the fetus, any lymphocytes that show an immune response when encountering self-antigens undergo apoptosis, a programmed cell death. Therefore, no clones of these anti-self B cells will appear in the blood; only B cells that might respond to foreign antigens will be present.

Antigen-presenting cells

Antigen-presenting cells are cells that display foreign antigens on their cell surface. An important example of antigen-presenting cells is phagocytes.

Phagocytes are another type of white blood cell involved in the immune response. These cells engulf and digest pathogens using hydrolytic enzymes called lysozymes. These enzymes break down the parts of the pathogen, which can then be absorbed into the phagocyte's cytoplasm. Phagocytes can take the antigens from the broken down pathogen and display these antigens on their cell surface.

This process is crucial in triggering the cell-mediated immune response. T lymphocytes, which carry out the cell-mediated response, will only respond to antigens presented on a body cell hence it is called the cell-mediated or cellular response. Therefore phagocytes are crucial in triggering the cell-mediated immune response, where complementary T cells can bind to the presented pathogens of an antigen.

Cell recognition and organ transplants

The idea of cell recognition is important for understanding the risks associated with organ transplants in humans. Organ transplants are taken from selected donors and then given to patients. However, because transplanted organs come from a different body, the antigens on the cell surfaces of the new organ will be different from the antigens on self-cells in the body. This can cause the immune system to attack the transplanted organ and destroy it, just as it would respond to a pathogen. In other words, the transplant will be rejected.

To avoid this, doctors attempt to 'match' organ donors with patients so their tissues and antigens are as similar as possible. Often, this means selecting donors who are genetically similar to the recipient - the best matches often come from relatives. Recipients are also prescribed immunosuppressant drugs, which help prevent the immune system from reacting against the transplant.

Cell Recognition - Key takeaways

  • Cell recognition is how body cells communicate to recognise each other or recognise foreign material in the body.
  • This recognition is achieved by the presence of identifying molecules on the cell's surface membrane. These molecules have specific 3D shapes which identify the cell, toxin, or viral particle.
  • These identifying molecules are commonly membrane carbohydrates; they are molecules found in the cell membrane where a carbohydrate has bound to proteins or lipids in the cell membrane.
  • Glycoproteins are the most common form of membrane carbohydrates and are created when a carbohydrate is covalently linked to a membrane protein. Glycolipids are formed when a carbohydrate is covalently linked to a lipid in the phospholipid bilayer of the cell membrane.
  • Proteins are especially useful for identifying molecules because of their complex 3D structure, forming highly specific shapes.

  • Cell recognition is vital in the functioning of the immune system. Lymphocytes can recognise the presence of non-self material in the body due to receptors on their cell surface. Phagocytes can present the antigens of pathogens on their cell surface, triggering the cell-mediated response when interacted with by T cells.

Cell Recognition

Cell recognition is the interaction between cells in the body that allows them to distinguish self-cells from non-self material, as well as identify abnormal body cells.

Each cell in the body has identifying molecules, such as glycolipids and glycoproteins, on their cell surface. These molecules have specific structures which identify them as belonging to the body. Different cells can bind to each other using these molecules and interact.

Cell recognition is important in the immune system. Cells must be able to distinguish between self-material and non-self material, which may include pathogens and toxins. If cells involved in the immune response can identify non-self material, then they will be able to target pathogens and destroy them before they can significantly harm the body.

Cell recognition proteins are found on cell surface membranes. They extend into the extracellular space and identify cells as either self or non-self with their specific tertiary structure.

Phagocytes engulf the dead cells and digest them via lysozymes (hydrolytic enzymes).

Final Cell Recognition Quiz

Question

What are immune cells in the body able to identify?

Show answer

Answer

Lymphocytes are able to recognize pathogens, non-self materials (eg cells from a different organism of the same species), toxins, and abnormal body cells such as cancer cells.

Show question

Question

How do cells recognise each other?


Show answer

Answer

Cells can recognize each other via identifying molecules on their cell surface membranes. These molecules have specific 3D structures which may or may not be complementary to identifying molecules on other cells.

Show question

Question

Why are proteins useful in cell recognition?


Show answer

Answer

Proteins are able to form highly specific shapes due to their tertiary and quaternary structures. They can therefore form many different shapes and allow for detailed differentiation in cell recognition.

Show question

Question

Why might an organ transplant be rejected?


Show answer

Answer

Transplanted organs have different identifying molecules, or antigens, on their cell surface to self-cells, identifying them as foreign material. When the immune system identifies these foreign cells it attacks the transplant in the same way it would a pathogen.

Show question

Question

How do doctors prevent transplanted tissues from being rejected?


Show answer

Answer

Doctors will try to ‘match’ organ donors closely with patients so that their cells are as similar as possible, usually taking organs from relatives, as they are genetically related. Doctors will also prescribe immunosuppressants to prevent the immune system from attacking the transplanted organ.

Show question

Question

What are membrane carbohydrates?


Show answer

Answer

Membrane carbohydrates are molecules found on the cell surface membrane, where carbohydrates are covalently linked to molecules in the cell membrane to form identifying molecules or receptors.

Show question

Question

What are glycoproteins?


Show answer

Answer

Glycoproteins are molecules made up of a carbohydrate covalently bonded to a protein. These molecules are involved in cell recognition.

Show question

Question

What is an example of a glycoprotein?


Show answer

Answer

An example of a glycoprotein is the CD4 receptor found on helper T cells.

Show question

Question

An example of a glycoprotein is the CD4 receptor found on helper T cells.


Show answer

Answer

Glycolipids are molecules made up of a carbohydrate covalently bonded to a lipid. The bond in this molecule is called a glycosidic bond. These molecules are involved in cell recognition.

Show question

Question

What is the most common type of membrane carbohydrate?


Show answer

Answer

The most common type of membrane carbohydrate is glycoproteins. Most of the proteins in the cell membrane are linked to a carbohydrate.

Show question

Question

What are the body's specific defense mechanisms?


Show answer

Answer

Specific defense mechanisms in the body are the action of T lymphocytes in the cellular response and B lymphocytes in the humoral response.

Show question

Question

Why do lymphocytes only recognize non-self material?


Show answer

Answer

In the fetus, lymphocytes only collide with self-material. Any lymphocytes that fit the antigens of self-material either die or are suppressed, so only lymphocytes that respond to non-self material are matured and present in the body. This is also the same for B cells in the bone marrow, where any cells that show an immune response against self-antigens undergo programmed cell death.

Show question

Question

What are antigen-presenting cells?


Show answer

Answer

Antigen-presenting cells are cells that display foreign antigens on their cell surface.

Show question

Question

What is an example of an antigen-presenting cell?


Show answer

Answer

An example of an antigen-presenting cell is a phagocyte.

Show question

Question

Why is the cell-mediated response called the cell-mediated response?


Show answer

Answer

T cells only respond to antigens that are presented on a body cell, such as on antigen-presenting phagocytes or infected body cells.

Show question

Question

What type of molecule is an antibody?

Show answer

Answer

An antibody is a protein, specifically an immunoglobulin or globular glycoprotein.

Show question

Question

How are antibodies produced?

Show answer

Answer

Antibodies are synthesized by B cells and plasma cells in the humoral immune response. They are synthesized in response to the presence of non-self material in the body, such as a pathogen or pollen.

Show question

Question

What is the structure of an antibody?


Show answer

Answer

An antibody is made up of four chains, two shorter light chains ad two longer heavy chains. These chains are connected by disulfide bridges. The variable region of the antibody is found at the top of the Y shape, and the constant region is found at the button of the Y shape.

Show question

Question

Where is the antigen-binding site on an antibody?


Show answer

Answer

The antigen-binding site is found at the two ends of the antibody’s Y shape, at the end of the variable region. The antigen-binding site is located at the ends of both the light and the heavy chains.

Show question

Question

Why are the variable and constant regions named as they are?


Show answer

Answer

The constant region is called constant because it is the same on every antibody, while the variable region is called variable because it has a specific shape that changes depending on the cell that has produced it.

Show question

Question

What is agglutination?


Show answer

Answer

Agglutination is when antibodies bind to multiple antigens, causing non-self cells or particles to clump together in one place. This makes it easier for phagocytes to engulf and destroy foreign material as they are all in one centralized place.

Show question

Question

How do antibodies neutralise toxins?


Show answer

Answer

Antibodies can neutralize some toxins by binding to them. This forms an antibody-toxin complex.

Show question

Question

What is the antigen-antibody complex?


Show answer

Answer

The antigen-antibody complex is the name given to when an antibody binds to a specific complementary antigen.

Show question

Question

How do antibodies stimulate phagocytosis?


Show answer

Answer

Antibodies can act as chemical markers which stimulate phagocytes to move towards them and the agglutinated antigens.

Show question

Question

How does the structure of an antibody make agglutination possible?


Show answer

Answer

Antibodies have two antigen-binding sites rather than one. This means antibodies can attach to two antigens at once, so can hold two cells or particles together at once.

Show question

Question

What are monoclonal antibodies?


Show answer

Answer

Monoclonal antibodies are a specific, single type of antibody, where all antibodies are identical to one another. This is because they are clones of one another and are produced by the same B cell.

Show question

Question

What are the uses of monoclonal antibodies?


Show answer

Answer

Monoclonal antibodies can be used to treat diseases such as cancer. They can also be used to diagnose diseases or conditions, such as HIV.

Show question

Question

How can monoclonal antibodies be used to treat cancer?


Show answer

Answer

Monoclonal antibodies can bind directly to specific cancerous cells. Once bound, they can either act directly by blocking chemical signals that promote cancerous growth or deliver targeted medication attached to the antibodies.

Show question

Question

How can monoclonal antibodies be used for diagnosing diseases?


Show answer

Answer

Monoclonal antibodies are used in the ELISA test, which can diagnose a range of diseases, including HIV.

Show question

Question

What are the 3 main functions of antibodies?

Show answer

Answer

Agglutination, marking and toxin neutralisation. 

Show question

Question

What is the definition of a monoclonal antibody?

Show answer

Answer

Monoclonal antibodies are a specific, single type of antibody, where all antibodies are identical to one another.

Show question

Question

How are monoclonal antibodies produced in the immune response?

Show answer

Answer

Monoclonal antibodies are synthesized by one type of B cell in response to stimulation of B cells by helper T cells.

Show question

Question

How can monoclonal antibodies be produced for clinical use?


Show answer

Answer

Monoclonal antibodies for medical use can be manufactured using mice. In this method, mice are exposed to some non-self material, which causes their B cells to produce antibodies. These B cells are then fused with cancer cells so they divide rapidly, forming hybridoma cells, from which antibodies can be extracted.

Show question

Question

What is a hybridoma cell?


Show answer

Answer

A hybridoma cell is a hybrid cell used for antibody production. It is made by fusing antibody-producing lymphocytes with human cancer cells.

Show question

Question

What is the advantage of using hybridoma techniques to manufacture antibodies?


Show answer

Answer

Hybridoma techniques can produce many antibodies because of the use of cancer cells, which divide rapidly. This means very large quantities of antibodies can be produced for use in research and medicine.

Show question

Question

What is direct monoclonal antibody therapy?


Show answer

Answer

Direct monoclonal antibody therapy is the practice of giving patients monoclonal antibodies that are complementary to antigens on cancer cells. The monoclonal antibodies bind to these antigens, blocking the chemical signals which stimulate their uncontrolled growth.

Show question

Question

What is indirect monoclonal antibody therapy?


Show answer

Answer

Indirect monoclonal antibody therapy involves attaching radioactive or cytotoxic drugs to monoclonal antibodies specific to cancer cells. When introduced into the patient's bodies, the monoclonal antibodies attach to cancer cells and kill them.

Show question

Question

How are antibodies used in pregnancy tests?


Show answer

Answer

Antibodies on the testing strip of pregnancy tests bind to the hormone human chorionic gonadotropin (hCG), which is produced by the placenta during pregnancy. These antibodies are attached to a colored particle. Once bound, the hCG-antibody-color complex moves up the testing strip and is trapped by another antibody, forming a colored line that indicates a positive test.

Show question

Question

What are the advantages and disadvantages of indirect monoclonal antibody therapy?


Show answer

Answer

The advantage of indirect monoclonal antibody therapy is that it is specific, so only a small dose needs to be used, which makes treatments relatively cheap. The disadvantage is that indirect monoclonal antibody therapy uses radioactive and cytotoxic drugs, which may cause unpleasant side effects in patients.

Show question

Question

What are the advantages of direct monoclonal antibody therapy?


Show answer

Answer

The advantages of direct monoclonal antibody therapy are that it does not use toxic drugs and so is unlikely to cause side effects, that it is specific so only a small dose needs to be used, and that it is relatively cheap as a treatment.

Show question

Question

What is informed consent?


Show answer

Answer

Informed consent involves making patients aware of the full risks and benefits of their treatment options before giving their consent to any medical procedures.

Show question

Question

What are the ethical issues with the use of monoclonal antibodies on patients?


Show answer

Answer

Monoclonal antibodies can cause severe side effects in some patients, for example in the treatment of multiple sclerosis. Patients should always be fully informed of the risks of using monoclonal antibodies before consenting to treatment.

Show question

Question

What is the disadvantage of using hybridoma techniques to manufacture antibodies?


Show answer

Answer

Hybridoma techniques use mice to manufacture antibodies. Mice cannot give consent to treatment and may experience pain in the process of manufacture, such as during surgeries.

Show question

Question

What does the immune system do?

Show answer

Answer

The immune system keeps the body safe using cells, organs, and proteins.

Show question

Question

What are pathogens?

Show answer

Answer

Bacteria.

Show question

Question

How do pathogens spread?

Show answer

Answer

Bodily fluids.

Show question

Question

What makes up the immune system?


Show answer

Answer

White blood cells, bone marrow, antibodies, the spleen, the thymus, and the lymphatic system.

Show question

Question

What cells does the bone marrow make?


Show answer

Answer

The bone marrow makes red and white blood cells and platelets.

Show question

Question

What do white blood cells do?


Show answer

Answer

Create T cells.

Show question

Question

What does humoral immunity do?


Show answer

Answer

It uses memory cells and antibodies to destroy pathogens.

Show question

60%

of the users don't pass the Cell Recognition quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.