What Are Proteins?

Proteins are among the iii macronutrients that are essential for the structure and function of cells. They accept diverse biological functions in the body including structure, storage, transportation, protection, hormone and enzyme activeness. The smallest unit of a protein is called an amino acid. 2 amino acids joined together is called a dipeptide, three is a tripeptide, four is a tetrapeptide, five is a pentapeptide and movement than v is called a polypeptide. Polypeptides that are l amino acid units long or more is called a poly peptide.

Know the ix Essential Amino Acids

At that place are 20 amino acids that brand up proteins. Nine of them are essential. The nine can be memorized using the mnemonic: "High protein intake left Larry'south muscles very tightly toned" i.due east. –

  1. High: Histidine
  2. Poly peptide: Phenylalanine
  3. Intake: Isoleucine
  4. Left: Leucine
  5. Larry's: Lysine
  6. Muscles: Methionine
  7. Very: Valine
  8. Tightly: Threonine
  9. Toned: Tryptophan

Know All twenty Amino Acids and their Abbreviations

The tabular array below shows you a listing of all 20 amino acids and their 3 and one-letter abbreviations.

The xx amino acids

Notice that with the exception of tyrptophan, they end with the "ine" or "ic" (you may likewise come across glutamic and aspartic acid given as glutamate and aspartate respectively). You should besides notice that in most cases, the 3-letter abbreviations are the same as the offset three letters of the amino acid east.m. alanine = ala. Similarly, in most cases, the one-alphabetic character abbreviation is the same as the first letter of the alphabet of the amino acid e.g. alanine = A. However, there are some exceptions, e.g. –

  • Asparagine: Asn, North
  • Retentiveness tool: Retrieve that ends with an "N" sound
  • Arginine: Arg, R
  • Retentivity tool: The beginning two messages sounds like "R"
  • Aspartic acrid: Asp, D
  • Memory tool: Pronounce information technology as "aspar-Dick" acid to call back the D
  • Glutamic Acrid: Glu, Eastward
  • Memory tool: The combined abbreviations spells "gluE"
  • Glutamine: Gln, Q
  • Memory tool: Pronounce information technology as "Q-tamin" with an "north" at the end
  • Isoleucine: Ile, I
  • Retention tool: "so" was isolated from "isole" leaving "Ile"
  • Lysine: Lys, K
  • Retention tool: "K" is side by side to "50"
  • Phenylalanine: Phe, F
  • Retention tool: The ane-letter abridgement sounds like the first letter of the alphabet of the amino acid
  • Tryptophan: Trp, W
  • Pronounce it as "T-W-iptophan" to remember the W
  • Tyrosine: Tyr, Y
  • Memory tool: Remember of theY as resembling a "neck-necktie" to remind yous of "tyrosine"

Creating abbreviations for amino acids is necessary to simplify writing of amino acids sequences. For example a sequence of amino acids containing histidine, lysine, arginine, tryptophan and alanine would be written as: his-lys-arg-trp-ala, or H-Grand-R-W-A. consider if you had to write a sequence that was 20,000 amino acids long. Can y'all see how cumbersome writing out the unabridged name would be?

The Structure of Amino Acids

Now, let'due south have a look at the structure of amino acids and proteins start with amino acids. An amino acid contains an amino group, a carboxylate grouping, an R group which distinguishes one amino acrid from another, and a carbon called an alpha carbon on which a hydrogen and the R group is continued.

Structure of an alanine. Source: 2016 Pearson Instruction, Inc

Amino acids are divided into basically 2 groups. They are either non-polar or polar. Not-polar amino acids are hydrophobic (h2o-antisocial) significant that they cannot deliquesce in h2o. Polar amino acids are are hydrophillic (water-loving) and can therefore dissolve in h2o. Polar amino acids may be one of three types, i.e. basic, acidic or neutral. Notice that this spells "BAN" to help y'all think.

Of the xx amino acids 9 are not-polar. The number nine should remind yous of cats since they have "nine lives". Besides, retrieve that cats hate water to retrieve that these amino acids are hydrophobic. Three amino acids are polar-basic, two are polar-acidic and six are polar neutral. If you think the time, iii minutes to vi (3-2-6), yous volition call up the amino acids that are "BAN".

Non Polar Amino Acids

Source: 2016 Pearson, Inc.

Note: The numbers at the bottom of each amino acid represents its isoelectric point. This is the pH at which the amino acid is neutral.

Memory tool: LIMP And Fiveery Wet Yardrumpy Feline

Polar Basic Amino Acids

Polar basic amino acids have an extra amine grouping which is attached to the side chain. Since only one of the charged groups can be neutralized by the acrid group, the amino acrid is left with a net positive charge.

Source: 2016 Pearson, Inc.

Memory tool: We become our basic training from Home, Kindergarten and Reality

Polar Acidic Amino Acids

Polar acidic amino acids are take an extra carbonyl group which is fastened to the side chain. Since only one of the charged groups can be neutralized by the amino group, the amino acrid is left with a cyberspace negative charge.

Memory tool: The only amino acids ending with "ate" or "ic".

Source: 2016 Pearson, Inc.

Polar Neutral Amino Acids

These amino acids are polar (able to interact with water) due to differences in electronegativity in the OH, SH and C-O bonds. This happens because O and  S "hogs" electrons causing information technology to become negatively charged and the H positively charged. However, the groups are still neutral overall, since the atoms have an equal amount of electrons and protons.

Source: 2016 Pearson, Inc.

Memory tool: Remember that water has a neutral taste. Therefore let'south use a mnemonic that has to practice with water: Youthful Swimmers Ne'er Quit Tough Competitions.

Forming Peptide Bonds

Amino acids join together to course long bondage called polypeptide chains. Each amino acid is joined at a peptide bond. This is the outcome of a condensation reaction involving the loss of two hydrogen and an oxygen atom (H2O).

Peptide bond

The resulting peptide has an N-terminus at the amino terminate and a C-terminus at the carbonyl cease. Amino acid sequences are written from left to right from the N to the C terminus.

Rigidity of Peptide Bonds

Peptide bonds are restricted to a single plane, that is, they are not able to rotate inside the bond. Instead, rotation occurs at the blastoff carbon. This restriction is due to the fact that electrons in the bond are delocalized (non restricted to a single bond) making it possible for the C-N bond to be a double bond and hence rigid, given the inflexible nature of double bonds.

How to Proper noun Peptides

Drop the "ine" or "ate" and replace with "yl". Leave the terminal (C-last) amino acrid unchanged due east.grand.

  1. Alanine-proline = alanylproline
  2. Serine-histidine-glycine = serinylyhistidylglcyine
  3. Lysine-methyonine-tyrosine-alanine = lysylmethyonyltyrosylalanine

Structure of Proteins

Proteins have four bones structural levels. These are primary, secondary, tertiary and fourth. The structure of proteins play a key role in determining their functional properties. See my article on functional properties of proteins.

Primary

Secondary

Secondary structure of protein is the construction formed due to hydrogen bonding within the aforementioned peptide chain or across peptide chains. The two common types of secondary structures are alpha-helix and beta-pleated sheets. Structures that are neither alpha-helix or beta-pleated sheets are called random coils. Alpha helices have a spring-like advent due to hydrogen bonding between the oxygen atom in the C=O bond and the hydrogen in the N-H bond four amino acids away.

Alpha helix. Source: 2016 Pearson, Inc.
Beta-pleated sheet. Source: 2016 Pearson Inc.

Beta-pleated sheets consist of lengths of polypeptides running along side each other and connected by hydrogen bonds. The sheets can exist acquired by a bend in the same polypeptide chain or may be due to interaction across different polypeptide chains. Beta-sheets are and so chosen considering they form a zig-zag pleat-like construction.

The polypeptide strands may run in either a parallel or anti-parallel management. You can tell the management past looking at the ends to find the C and N-terminals. If the terminals of both strands line up, they are moving in an antiparallel direction. Nevertheless, if they are on the opposite sides, they are parallel. You lot tin also tell if the strands are running parallel or anti-parallel by counting the number of atoms in the hydrogen-bonded rings. Strands that are running parallel will accept exactly 12 atoms in the rings while those that are running antiparallel will have 10 and 14 atoms alternating in the rings.

Tertiary

The tertiary structure of protein is caused by different forces of attraction and repulsion betwixt amino acids in the polypeptide chain causing it to twist and bend resulting in a specific shape. These forces may exist a combination of hydrophillic interaction with water, salt bridges (ionic bonds), disulfide bonds andhydrophobic interactions.

These bonds can be disrupted in a procedure called denaturation where the protein loses its shape. This can occur due to rut, agitation, and the presence of alcohol and acids. A proficient example of estrus denaturation is seen when egg is fried. You tin can see denaturation occurring before your eyes as the transparent albumin turns white and the whole egg becomes solid. When we swab our hands with alcohol, we impale bacteria by denaturing proteins in the bacteria. When we whip egg-white it turns to a foam due to denaturation. An example of acid denaturation is seen in the production of cheese and yogurt. The presence of lactic acrid produced by bacteria, causes the casein in the milk to coagulate.

Fourth

Quaternary structures consist of two or more 3rd protein structures, called sub-units working together. They are held together by the same forces every bit required in third structures. Well-nigh biologically active proteins are in the quaternary class. An instance is hemoglobin shown in the prototype beneath. Hemoglobin consists of 4 different sub-units.

Source: Wikimedia commons

Big Ideas

  1. Proteins are made upward of amino acids
  2. In that location are twenty amino acids, nine of which are essential
  3. Amino acids are either polar or non-polar
  4. Polar amino acids are either basic, acidic or neutral
  5. Proteins consist of four structural levels – primary, secondary, tertiary and fourth

Reference: Timberlake, KC. 2016. General, organic, and biological chemistry – Structures of life (5th edition). Boston, MA:Pearson Inc.

Courtney Simons

Administrator

Courtney Simons is a food science professor. He holds a BS caste in food science and a Ph.D. in cereal scientific discipline from North Dakota Land University.