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The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cells . The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus , and membranes of the membrane ...
The nuclear envelope is made up of two lipid bilayer membranes, an inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. Two sets of intermediate filaments provide support for the nuclear envelope. An internal network forms the nuclear lamina on the inner nuclear membrane. [7]
Illustration of a eukaryotic cell membrane Comparison of a eukaryotic vs. a prokaryotic cell membrane. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).
Phospholipid bilayers contain different proteins. These membrane proteins have various functions and characteristics and catalyze different chemical reactions. Integral proteins span the membranes with different domains on either side. [6] Integral proteins hold strong association with the lipid bilayer and cannot easily become detached. [9]
Specifically, it is the phosphodiester bonds that link the 3' carbon atom of one sugar molecule and the 5' carbon atom of another (hence the name 3', 5' phosphodiester linkage used with reference to this kind of bond in DNA and RNA chains). [3] The involved saccharide groups are deoxyribose in DNA and ribose in RNA.
These proteins take part in RNA transcription and gene regulation in the nucleoplasm. [2] Proteins located in the nucleoplasm are involved in the activation of genes that are used in the cell cycle. [8] Some nucleoporins which typically make up the nuclear pore, can be mobile and participate in the regulation of gene expression in the nucleoplasm.
RNA adopts this double helical form, and RNA-DNA duplexes are mostly A-form, but B-form RNA-DNA duplexes have been observed. [14] In localized single strand dinucleotide contexts, RNA can also adopt the B-form without pairing to DNA. [15] A-DNA has a deep, narrow major groove which does not make it easily accessible to proteins.
While the individual macromolecules are held together by a combination of covalent bonds and intramolecular non-covalent forces (i.e., associations between parts within each molecule, via charge-charge interactions, van der Waals forces, and dipole–dipole interactions such as hydrogen bonds), by definition MAs themselves are held together ...