R group

Examples of R group in the following topics:

• Amino Acids

  • An amino acid contains an amino group, a carboxyl group, and an R group, and it combines with other amino acids to form polypeptide chains.
  • Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group.
  • There are 21 amino acids present in proteins, each with a specific R group or side chain.
  • The 21st amino acid, not shown here, is selenocysteine, with an R group of -CH2-SeH.
  • Amino acids have a central asymmetric carbon to which an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group) are attached.

• Protein Structure

  • Secondary structures arise as H bonds form between local groups of amino acids in a region of the polypeptide chain.
  • The R groups (the side chains) of the polypeptide protrude out from the α-helix chain and are not involved in the H bonds that maintain the α-helix structure.
  • The R groups of the amino acids in a β-pleated sheet point out perpendicular to the hydrogen bonds holding the β-pleated sheets together, and are not involved in maintaining the β-pleated sheet structure.
  • Interactions between polar, nonpolar, acidic, and basic R group within the polypeptide chain create the complex three-dimensional tertiary structure of a protein.
  • When protein folding takes place in the aqueous environment of the body, the hydrophobic R groups of nonpolar amino acids mostly lie in the interior of the protein, while the hydrophilic R groups lie mostly on the outside.

• Functional Groups

  • Functional groups are groups of molecules attached to organic molecules and give them specific identities or functions.
  • Functional groups are groups of atoms that occur within organic molecules and confer specific chemical properties to those molecules.
  • When functional groups are shown, the organic molecule is sometimes denoted as "R."
  • This carboxyl group ionizes to release hydrogen ions (H+) from the COOH group resulting in the negatively charged COO- group; this contributes to the hydrophilic nature of whatever molecule it is found on.
  • The functional groups shown here are found in many different biological molecules, where "R" is the organic molecule.

• Peptide Bonding between Amino Acids

  • Amino acids are chemical compounds consisting of a carbon atom bonded to an amine group, a hydrogen atom, a carboxylic group, and a varying side-chain (R group); it is this side chain that distinguishes each amino acid from another.
  • It occurs when the carboxylic group of one molecule reacts with the amino group of the other molecule, linking the two molecules and releasing a water molecule.
  • The amide group has three resonance forms, which confer important properties.
  • First, the stabilization afforded from the resonance structures effectively stabilizes it by 80kj/mol, making it less reactive than similar groups.
  • Peptide bonds are amide bonds, characterized by the presence of a carbonyl group attached to an amine.

• Phospholipids

  • The third carbon of the glycerol backbone is also occupied by a modified phosphate group However, just a phosphate group attached to a diacylglycerol does not qualify as a phospholipid.
  • To qualify as a phospholipid, the phosphate group should be modified by an alcohol.
  • The phosphate may be modified by the addition of charged or polar chemical groups.
  • Two chemical groups that may modify the phosphate, choline and serine, are shown here.
  • Both choline and serine attach to the phosphate group at the position labeled R via the hydroxyl group indicated in green.

• Carbohydrate Molecules

  • If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is known as an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R'), it is known as a ketose.
  • During this process, the hydroxyl group of one monosaccharide combines with the hydrogen of another monosaccharide, releasing a molecule of water and forming a covalent bond.
  • Monosaccharides are classified based on the position of their carbonyl group and the number of carbons in the backbone.
  • Aldoses have a carbonyl group (indicated in green) at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain.
  • By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group.

• Theories of Life History

  • Modern theories of life history incorporate life and survivorship factors with ecological concepts associated with r- and K-selection theories.
  • For this analysis, population biologists have grouped species into the two large categories, K-selected and r-selected, although they are really two ends of a continuum.
  • In contrast to K-selected species, r-selected species have a large number of small offspring (hence their r designation).
  • Examples of r-selected species are marine invertebrates, such as jellyfish, and plants, such as the dandelion .
  • The r- and K-selection theory, although accepted for decades and used for much groundbreaking research, has now been reconsidered.

• Molecular Analyses and Modern Phylogenetic Trees

  • The phylogenetic groupings are continually being debated and refined by evolutionary biologists.
  • For constructing an evolutionary tree from proteins, for example, the sequences are aligned and then compared. rRNA (ribosomal RNA) is typically used to compare organisms since rRNA has a slower mutation rate and is a better source for evolutionary tree construction.
  • Extensive molecular analysis using rRNA data found these animals to be protostomes, more closely related to annelids and mollusks.
  • Molecular data have also shed light on some differences within the lophotrochozoan group.
  • Some scientists believe that the phyla Platyhelminthes and Rotifera within this group should actually belong to their own group of protostomes termed Platyzoa.

• Glomeromycota

  • Glomeromycetes are an important group of fungi that live in close symbiotic association with the roots of trees and plants.
  • The first mycorrhizal gene to be sequenced was the small-subunit ribosomal RNA (SSU rRNA).
  • This gene is highly conserved and commonly used in phylogenetic studies so it was isolated from spores of each taxonomic group.

• DNA and RNA

  • Other types of RNA—like rRNA, tRNA, and microRNA—are involved in protein synthesis and its regulation.
  • Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups.
  • Each of these basic carbon-nitrogen rings has different functional groups attached to it.
  • The phosphate residue is attached to the hydroxyl group of the 5′ carbon of one sugar and the hydroxyl group of the 3′ carbon of the sugar of the next nucleotide, which forms a 5′3′ phosphodiester linkage.
  • A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups.