Molecular Biology Primer: Understanding DNA, Proteins, and Genes - Prof. Saurabh Sinha, Study notes of Computer Science

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Lecture 2

Molecular Biology Primer

Saurabh Sinha

Heredity and DNA

• Heredity: children resemble parents
  • Easy to see
  • Hard to explain
• DNA discovered as the physical (molecular)

carrier of hereditary information

Protein functions

• “Enzymes” (catalysts)
  • Control chemical reactions in cell
  • E.g., Aspirin inhibits an enzyme that produces the “inflammation messenger”
• Transfer of signals/molecules between and

inside cells

• E.g., sensing of environment
• Regulate activity of genes

DNA

• DNA is a molecule: deoxyribonucleic acid
• Double helical structure (discovered by

Watson, Crick & Franklin)

• Chromosomes are densely coiled and

packed DNA

The DNA Molecule G -- C A -- T T -- A G -- C C -- G G -- C T -- A G -- C T -- A T -- A A -- T A -- T C -- G T -- A

Base = Nucleotide

Base pairing property

Protein

• Protein is a sequence of amino-acids

• 20 possible amino acids
• The amino-acid sequence “folds” into a 3-D

structure called protein

SRC:http://www.biologycorner.com/resources/DNA-RNA.gif Cell

From DNA to Protein: In picture

From DNA to Protein: In words

1. DNA = nucleotide sequence

• Alphabet size = 4 (A,C,G,T)

2. DNA → mRNA (single stranded)

• Alphabet size = 4 (A,C,G,U)

3. mRNA → amino acid sequence

• Alphabet size = 20

4. Amino acid sequence “folds” into 3-

dimensional molecule called protein

DNA and genes

• DNA is a very “long” molecule
  • If kept straight, will cover 5cm (!!) in human cell
• DNA in human has 3 billion base-pairs
  • String of 3 billion characters!
• DNA harbors “genes”
  • A gene is a substring of the DNA string
  • A gene “codes” for a protein

Genes code for proteins

• DNA → mRNA → protein can actually

be written as Gene → mRNA → protein

• A gene is typically few hundred base-

pairs (bp) long

Step 1: From DNA to mRNA

Transcription

SOURCE: http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm

Translation

• Process of making an amino acid sequence

from (single stranded) mRNA

• Each triplet of bases translates into one

amino acid

• Each such triplet is called “codon”
• The translation is basically a table lookup

The Genetic Code

SOURCE: http://www.bioscience. org/atlases/genecode/genecode .htm

Step 2: mRNA to Amino acid sequence

Translation

SOURCE: http://bioweb.uwlax.edu/GenWeb/Molecular/Theory/Translation/trans1.swf