Notes On Proteins And Nucleic Acids

Week Three Notes – Proteins and Nucleic Acids

PROTEINS
Crucial Tasks of Proteins * Defense * Antibodies attack and destroy viruses and bacteria * Movement * Motor and contractile proteins are responsible for the physical movement of the cell * Or for moving large molecules into the cell * Catalysis * Proteins function as enzymes in order to speed up chemical reactions in the body * Eg. Salivary amylase digests starch in mouth * Signaling * Proteins called peptide hormones bind to receptor cells, which activates a appropriate response * Structure * Structural proteins give the cell mechanical support * Structural proteins keep the cell flexible and in their normal shape, as well as holding together the inside and membrane of the cell * Transport * Proteins are responsible for letting molecules in and out of the cell, and for carrying compounds in the body * Hemoglobin is a transport protein that carries oxygen

Structure of Amino Acids

Most of the proteins are composed of 21 different amino acids (monomers), and all the 21 amino acids have a common backbone structure.

Amino acids * The carboxyl group is acidic * Because the 2 oxygen’s are highly electronegative * They pull electrons away from the hydrogen * Relatively easy to lose a proton * Charges on the functional group * Help amino acids to stay in solution where they can interact with each other and other solutions * Add to their chemical reactivity * Structure * A carbon is usually linked to an amino group, a carboxyl group and a R-group * Differ by the R-groups, the rest stays constant * Hydrophobic = Side chains tend to coalesce in aqueous solution * Hydrophilic = Amino acids with polar or charged side chains interact readily with water and other aqueous solutions

* The nature of the side chain influences the chemical reactivity * R-Group RARELY plays a role * Chemical behaviour of the amino acids is dependant on their size and shape rather than charge * Hydroxyl, carboxyl and sulfhydryl are the reactive functional groups

Isomers

3 types of Isomers * Structural isomers * Have the same atoms but differ in the order that they are covalently bonded * Geometric isomers * Same atoms but differ in the arrangement of the atoms around a double bond * Optical isomers * Have the same atoms but differ in the arrangement of atoms around a carbon atom that has four different groups attached * Most amino acids have optical isomers * They are identical, but cannot be superimposed * Only the “left handed” amino acid exists, because if the right handed ones are introduced into the cell, they do not function normally

Linkage of amino acids to form Proteins

Formation of a Protein * A protein is a macromolecule (a polymer) that consists of linked amino acids monomers * Complex and highly organized molecules are expected to form from simpler compounds. * Polymerization however decreases the disorder/ entropy, of the molecules involved. * Polymers are energetically much less stable than monomers * Polymerization reactions are endergonic and unspontaneous * Monomers must absorb energy in order to link together

Protein Structure

Primary Structure * Every protein has a unique sequence of amino acids * There may be 21^n possibilities, n being the length. * Eg Hemoglobin * R-groups affect the solubility and chemical reactivity, which can change the properties * When the 6th amino acid is valine instead of glutamine, the shape of t3he blood cell changes from normal to sickled

Secondary Structure * Created by hydrogen bonding * Distinctly shaped sections of proteins that are stabilized by hydrogen bonding that occurs between the carboxyl oxygen and

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