Protein And Water

ALevel

SCIENCES

Biology-9700

Notes

Protein And Water

Protein And Water

Protein And Water


Proteins

Protein is the polymer of amino acids.

Amino Acids

The amino acid is the monomers that join together to form proteins.

Structure

Amino acid comprises of a primary carbon which is linked to carboxylic acid on one side and an amino group on the other side. The other side has a radical group that varies in different amino acids.
There are 20 different types of amino acids based on the R group they contain. This R group makes the protein acidic, basic or neutral.

Linking Of Amino Acids

Two amino acids are linked together by condensation. The bond between them is called a peptide bond.

Breaking Of Peptide Bonds

Peptide bonds can be broken down by hydrolysis.

Primary, Secondary And Tertiary Structure Of Proteins:

Amino acids are linked together to form polypeptides. These molecules can be arranged in different structural forms.

Primary Structure:

A linear chain of amino acids is called the primary structure.

The amino acids are held together by peptide bonds only.

Secondary Structure

The primary structure is folded to form a secondary structure.

The chain can be folded into ways it can either an alpha helix (3d structure) or Beta pleated sheet (twisted).

The helix has numerous hydrogen bonds between amino acids. This gives the structure stability.

Tertiary Structure

The coiling and twisting of secondary structure result in a final 3d structure called tertiary.
There are different bonds which give the structure stability.

Hydrogen bonds: Between amino acids.

Sulfide bonds: Formed between sulfur atoms present in cysteine.

Ionic bonds: Formed between R group having opposite charges.

Amino acids may be hydrophobic or hydrophilic. Based on the medium in which they are present the arrangement of amino acids is different. In a polar solvent, the hydrophilic molecules are present on the outer side while hydrophobic amino acids are present inside the protein.

Quaternary Structure

Two tertiary chains present together to make a quaternary structure.

They contain the same bond which is present in the tertiary structure.

Globular And Fibrous Proteins

There are two types of 3d structure of protein ie globular or fibrous.

Their different structure helps them in different roles they perform in the body.


Fibrous Proteins
Globular Proteins
Molecule                               
The molecules are arranged in long strands.
The molecules are coiled upon each other.
Solubility           
Insoluble
Soluble
Function            
Provide strength and stability
Perform different functions:

Transport

catalysis

Example             
Keratin
Enzymes
Hemoglobin
Myoglobin

Collagen Fiber As Fibrous Protein

Collagen is an alpha fibrous protein. It consists of 3 polypeptide chains.

Collagen molecules coils around to form collagen fibrils.

Collagen fibrils wrap around itself to form collagen fibers.

The polypeptide chains lie side by side one another and are held together by hydrogen bonds.

Function Of Collagen

Provide support and strength.

Relationship Between Structure And Function Of Collagen


Structure                                                            
Function
Explanation
Large Size Of Molecules                          
Insoluble                                       

The size of molecules is large. This makes the protein fibres insoluble in water.

This property gives it stability.

3 Chains
High Tensile Strength

The three chains of protein wound around each other gives the molecules high tensile strength.

Thus, they are difficult to break.

Glycine
Short Structure

Glycine has H as R group this makes the structure short.

The compactness of protein chains makes it stable.

Lycine
Fibres

The lycine molecule in the chain makes covalent bond with R group of other lycine molecules.

This is essential for formation of bonds between different chains.

 

Hemoglobin

Hemoglobin has a quaternary structure.

It consists of two alpha globins and two beta globins. Besides this, it also consists of an inorganic heme group.

Heme group consists of an Iron molecule. Iron holds oxygen atoms that are transported to different tissues.

Relationship Between Strucuture And Function Of Hemoglobin


Structure
Function
Explanation
Heme Group                         
Oxygen Transport                 
Each heme group consist of a iron atom. The iron binds with oxygen. 
Tertiary Structure                
Soluble
The polypeptide chains consist of both hydrophobic and hydropillic components.

Hydrophobic end are buried inside hydrophilic molecules. 
This makes the structure soluble in water.

Water

Water makes up around 80% of the total mass of the cell.  

A molecule of water consists of a positive end and a negative end. This is called a dipole.

This property of water makes it an excellent solvent.  

The hydrogen bonding between water molecules also affects its physical properties.

Below are the properties that make water an excellent compound for living organisms.

Water As A Solvent

Water has two ends. Thus, when NaCl is dissolved in water it breaks into Na+ and Cl-. Na+ makes a bond with OH- and Cl- makes a bond between H+.

In the same way, other ionic compounds can dissolve in water. Thus, water is considered as a universal solvent.

This property of water helps in the transport of a large number of molecules in living organisms.

Thermal Properties Of Water


High Specific Heat Of Capacity

As water contains a large number of hydrogen bonds it requires a lot of energy to break them. Thus, it needs a lot of energy to raise the temperature of the water. The body comprises a huge amount of water thus it makes it a stable internal environment.

High Latent Heat Of Evaporation

Water needs a high amount of heat to evaporate. This is due to a large number of hydrogen bonds. Thus, when water evaporates it absorbs a large heat from surrounding making it an efficient cooling process.

That is how the body uses sweat to cool down the temperature.

Freezing Property

Water shows an unusual behavior because the ice formed is less than water
(liquid). Thus, oceans and seas freeze in a way that ice remains at the top while the liquid water is present below it. The top layer of ice prevents heat loss from below.

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