Carbohydrates are versatile molecules in cells, serving as energy storage and structural support. Glucose powers cells, while glycogen and starch store energy in animals and plants. Cellulose and chitin provide structure in plant cell walls and arthropod exoskeletons.
Beyond energy and structure, carbohydrates play crucial roles in cell recognition and communication. They form the glycocalyx on cell surfaces, mediate cell adhesion, and determine blood types. Glycosylation modifies proteins, influencing their function and stability.
Energy Storage and Structural Support
Carbohydrates as Energy Reservoirs
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- Carbohydrates serve as primary energy storage molecules in living organisms
- Glucose functions as the main energy source for most cells
- Glycogen acts as a short-term energy storage in animals, primarily found in liver and muscle tissues
- Starch serves as the primary energy storage molecule in plants, consisting of amylose and amylopectin
- Excess carbohydrates convert to fat for long-term energy storage
Structural Support in Plants and Animals
- Cellulose provides structural support in plant cell walls, contributing to plant rigidity and strength
- Chitin forms exoskeletons in arthropods (insects, crustaceans) and cell walls in fungi
- Proteoglycans contribute to cartilage structure in animals, providing cushioning and flexibility in joints
- Glycosaminoglycans form essential components of connective tissues, including hyaluronic acid in synovial fluid
Extracellular Matrix Components
- Extracellular matrix consists of a complex network of carbohydrates and proteins
- Glycoproteins, such as fibronectin and laminin, facilitate cell adhesion and signaling
- Proteoglycans contribute to the hydration and structural integrity of the extracellular matrix
- Hyaluronic acid maintains tissue hydration and acts as a lubricant in joints
- Collagen, the most abundant protein in the extracellular matrix, provides tensile strength to tissues
Cell Recognition and Communication
Carbohydrates in Cell Surface Recognition
- Cell surface carbohydrates function as recognition molecules for cell-cell interactions
- Lectins, carbohydrate-binding proteins, mediate cell adhesion and signaling
- Sialic acids play crucial roles in cell recognition and immune system function
- Heparan sulfate proteoglycans facilitate growth factor signaling and cell-matrix interactions
- Selectins mediate leukocyte rolling and adhesion during inflammation
Glycocalyx Structure and Function
- Glycocalyx forms a carbohydrate-rich layer on the cell surface
- Consists of glycoproteins, glycolipids, and proteoglycans
- Protects cells from mechanical and chemical damage
- Regulates the passage of molecules through the cell membrane
- Participates in cell-cell recognition and adhesion processes
Blood Group Antigens and Immune Recognition
- ABO blood group antigens consist of specific carbohydrate structures on red blood cell surfaces
- A antigen contains N-acetylgalactosamine, B antigen contains galactose, and O lacks both
- Rh factor, another blood group antigen, determines Rh-positive or Rh-negative blood types
- Blood group antigens play crucial roles in blood transfusion compatibility and immune responses
- Antibodies against non-self blood group antigens can cause agglutination and hemolysis
Glycosylation in Protein Modification
- Glycosylation involves the addition of carbohydrate chains to proteins or lipids
- N-linked glycosylation occurs on asparagine residues in the endoplasmic reticulum
- O-linked glycosylation takes place on serine or threonine residues in the Golgi apparatus
- Glycosylation influences protein folding, stability, and function
- Aberrant glycosylation patterns associate with various diseases (cancer, autoimmune disorders)