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NEET MDS Synopsis - Lecture Notes
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📖 Biochemistry

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Sphingomyelins

Biochemistry

Sphingosine is an amino alcohol present in sphingomyelins (sphingophospholipids).  They do not contain glycerol at all.

Sphingosine is attached by an amide linkage to a fatty acid to produce ceramide. The alcohol group of sphingosine is bound to phosphorylcholine in sphingomyelin structure. .

Sphingomyelins are important constituents of myelin and are found in good quantity in brain and nervous tissues.

Essential vs. Nonessential Amino Acids

Biochemistry

Essential vs. Nonessential Amino Acids

 

Nonessential

Essential

Alanine

Arginine*

Asparagine

Histidine

Aspartate

Isoleucine

Cysteine

Leucine

Glutamate

Lysine

Glutamine

Methionine*

Glycine

Phenylalanine*

Proline

Threonine

Serine

Tyrptophan

Tyrosine

Valine
 

*The amino acids arginine, methionine and phenylalanine are considered essential for reasons not directly related to lack of synthesis. Arginine is synthesized by mammalian cells but at a rate that is insufficient to meet the growth needs of the body and the majority that is synthesized is cleaved to form urea. Methionine is required in large amounts to produce cysteine if the latter amino acid is not adequately supplied in the diet. Similarly, phenyalanine is needed in large amounts to form tyrosine if the latter is not adequately supplied in the diet.

Protein Structure and Classification
Biochemistry

Proteins are complex macromolecules composed of amino acids that perform diverse biological functions. Understanding their structure-function relationships is crucial for medical applications and biochemistry.

Levels of Protein Structure

Primary Structure

  • Linear sequence of amino acids connected by peptide bonds
  • Determines all higher levels of organization
  • Coded by DNA sequence

Secondary Structure

  • Local folding patterns stabilized by hydrogen bonds
  • Alpha helix: Right-handed spiral structure
  • Beta sheet: Extended polypeptide chains arranged side by side
  • Beta turn: Connects different secondary structural elements

Tertiary Structure

  • Three-dimensional folding of entire polypeptide chain
  • Stabilized by:
    • Hydrogen bonds
    • Disulfide bridges
    • Van der Waals forces
    • Electrostatic interactions
    • Hydrophobic interactions

Quaternary Structure

  • Assembly of multiple polypeptide subunits
  • Present only in proteins with more than one polypeptide chain
  • Examples: Hemoglobin (4 subunits), antibodies

Protein Classification

Based on Structure

  1. Fibrous Proteins

    • Elongated, insoluble
    • Structural functions
    • Examples: Collagen, keratin, elastin

  2. Globular Proteins

    • Compact, soluble
    • Functional proteins
    • Examples: Enzymes, antibodies, hormones

Based on Composition

  1. Simple Proteins

    • Composed only of amino acids
    • Examples: Albumin, globulins

  2. Conjugated Proteins

    • Contain non-protein prosthetic groups
    • Glycoproteins: Contain carbohydrates
    • Lipoproteins: Contain lipids
    • Nucleoproteins: Contain nucleic acids
    • Phosphoproteins: Contain phosphate groups
    • Metalloproteins: Contain metal ions

HORMONES

Biochemistry

HORMONES

A hormone is a chemical that acts as a messenger transmitting a signal from one cell to another. When it binds to another cell which is the target of the message, the hormone can alter several aspects of cell function, including cell growth, metabolism, or other function.

Hormones can be classified on three primary ways as following:

1.  Autocrine: An autocrine hormone is one that acts on the same cell that released it.

2.  Paracrine: A paracrine hormone is one that acts on cells which are nearby relative to the cell which released it. An example of paracrine hormones includes growth factors, which are proteins that stimulate cellular proliferation and differentiation.

3. Endocrine: An endocrine hormone is one that is released into the bloodstream by endocrine glands. The receptor cells are distant from the source. An example of an endocrine hormone is insulin, which is released by the pancreas into the bloodstream where it regulates glucose uptake by liver and muscle cells.