By• hj nabil• Hj muhd muadz• Vincent ong

Protein

protein• Proteins are biological polymers composed of

amino acids. Amino acids, linked together by peptide bonds, form a polypeptide chain. One or more polypeptide chains twisted into a 3-D shape form a protein. Proteins have complex shapes that include various folds, loops, and curves. Folding in proteins happens spontaneously.

• There are two general classes of protein molecules: globular proteins and fibrous proteins. Globular proteins are generally compact, soluble, and spherical in shape. Fibrous proteins are typically elongated and insoluble

Protein Structure Levels• Primary Structure - describes the unique order in which amino acids are

linked together to form a protein. Proteins are constructed from a set of 20 amino acids. Generally, amino acids have the following structural properties:• A carbon (the alpha carbon) bonded to the four groups below:• A hydrogen atom (H) • A Carboxyl group (-COOH) • An Amino group (-NH2) • A "variable" group or "R" group

• Secondary Structure - refers to the coiling or folding of a polypeptide chain that gives the protein its 3-D shape. There are two types of secondary structures observed in proteins:

One type is the alpha (α) helix structure. This structure resembles a coiled spring and is secured by hydrogen bonding in the polypeptide chain.

The second type of secondary structure in proteins is the beta (β) pleated sheet. This structure appears to be folded or pleated and is held together by hydrogen bonding between polypeptide units of the folded chain that lie adjacent to one another.

• Tertiary Structure - refers to the comprehensive 3-D structure of the polypeptide chain of a protein. There are several types of bonds and forces that hold a protein in its tertiary structure:

I. Hydrophobic interactions II. Hydrogen bonding III. ionic bonding IV. disulfide bridge.

Interactions called van der Waals forces also assist in the stabilization of protein structure. These interactions pertain to the attractive and repulsive forces that occur between molecules that become polarized. These forces contribute to the bonding that occurs between molecules.

• Quaternary Structure - refers to the structure of a protein macromolecule formed by interactions between multiple polypeptide chains. Each polypeptide chain is referred to as a subunit. Proteins with quaternary structure may consist of more than one of the same type of protein subunit. They may also be composed of different subunits. Hemoglobin is an example

Summary of protein structure

Protein Structure DeterminationThe three-dimensional shape of a protein is determined by its primary structure. The order of amino acids establishes a protein's structure and specific function. The distinct instructions for the order of amino acids are designated by the genes in a cell. When a cell perceives a need for protein synthesis, the DNA unravels and is transcribed into an RNA copy of the genetic code. This process is called DNA transcription. The RNA copy is then translated to produce a protein. The genetic information in the DNA determines the specific sequence of amino acids and the specific protein that is produced. Proteins are examples of one type of biological polymer.

Protein Synthesis

• Consist of;1. DNA Transcription2. DNA Translation3. Ribosomes

DNA Transcription• DNA transcription is a process that involves transcribing

genetic information from DNA to RNA. The transcribed DNA message, or RNA transcript, is used to produce proteins.

• There are three main steps to the process of DNA transcription;

1. RNA Polymerase Binds to DNA2. Elongation3. TerminationSince proteins are constructed in the cytoplasm of the cell, mRNA must cross the nuclear membrane to reach the cytoplasm. Once in the cytoplasm, ribosomes and another RNA molecule called transfer RNA work together to translate mRNA into a protein. This process is called translation

DNA Translation

• Protein synthesis is accomplished through a process called translation. After DNA is transcribed into a messenger RNA (mRNA) molecule during transcription, the mRNA must be translated to produce a protein. In translation, mRNA along with transfer RNA (tRNA) and ribosomes work together to produce proteins.

• Transfer RNA plays a huge role in protein synthesis and translation. Its job is to translate the message within the nucleotide sequence of mRNA to a specific amino acid sequence. These sequences are joined together to form a protein. Transfer RNA is shaped like a clover leaf with three loops. It contains an amino acid attachment site on one end and a special section in the middle loop called the anticodon site. The anticodon recognizes a specific area on a mRNA called a codon.

Transfer rna translation

Ribosomes• Ribosomes are typically composed of two subunits: a large subunit

and a small subunit. Ribosomal subunits are synthesized by the nucleolus. These two subunits join together when the ribosome attaches to messenger RNA (mRNA) during protein synthesis. Ribosomes along with another RNA molecule, transfer RNA (tRNA), help to translate the protein-coding genes in mRNA into proteins.

• Protein synthesis occurs by the processes of transcription and translation. In transcription, the genetic code contained within DNA is transcribed into an RNA version of the code known as messenger RNA (mRNA). In translation, a growing amino acid chain, also called a polypeptide chain, is produced. Ribosomal RNA helps to link amino acids together to produce the polypeptide chain. The polypeptide chain undergoes several modifications before becoming a fully functioning protein. Proteins are very important biological polymers in our cells as they are involved in virtually all cell functions.