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Genomics. Lecture 3 By Ms. Shumaila Azam. Proteins. Proteins: large molecules composed of one or more chains of amino acids, polypeptides. Proteins are large, complex molecules that play many critical roles in the body.

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Lecture 3

By Ms. Shumaila Azam


  • Proteins: large molecules composed of one or more chains of amino acids, polypeptides.

  • Proteins are large, complex molecules that play many critical roles in the body.

  • They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.

  • Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains.


  • There are 20 different types of amino acids that can be combined to make a protein.

Amino acids
Amino Acids

  • Class of 20 different organic compounds containing a basic amino group

    (-NH2) and an acidic carboxyl group (-COOH).

  • The order of the amino acids is determined by the base sequence of nucleotides in the gene coding for the protein.

Amino acids1
Amino Acids

  • alanine - ala - A

  • arginine - arg - R

  • asparagine - asn - N

  • aspartic acid - asp - D

  • cysteine - cys - C

  • glutamine - gln - Q

  • glutamic acid - glu - E

  • glycine - gly - G

  • histidine - his - H

  • isoleucine - ile - I

  • leucine - leu - L

  • lysine - lys - K

  • methionine - met - M

  • phenylalanine - phe - F

  • proline - pro - P

  • serine - ser - S

  • threonine - thr - T

  • tryptophan - trp - W

  • tyrosine - tyr - Y

  • valine - val - V

The twenty amino acids (that make up proteins)each have assigned to them both three-letter (can be upper or lower case) and one-letter codes (upper case).

Amino acids2
Amino Acids

  • Sometimes it is not possible two differentiate two closely related amino acids, therefore we have the special cases:

    • asparagine/aspartic acid - asx - B

    • glutamine/glutamic acid - glx - Z

Amino acids3
Amino Acids

  • Here is list where amino acids are grouped according to the characteristics of the side chains:

    • Aliphatic - alanine, glycine, isoleucine, leucine, proline, valine

    • Aromatic - phenylalanine, tryptophan, tyrosine

    • Acidic - aspartic acid, glutamic acid

    • Basic - arginine, histidine, lysine

    • Hydroxylic - serine, threonine

    • Sulphur-containing - cysteine, methionine

    • Amidic (containing amide group) - asparagine, glutamine

How do genes direct the production of proteins
How do genes direct the production of proteins?

  • Most genes contain the information needed to make functional molecules called proteins.

  • A few genes produce other molecules that help the cell assemble proteins.

Journey gene to protein
Journey-Gene to Protein

  • It consists of two major steps:

    • Transcription and

    • Translation.

  • Together, transcription and translation are known as gene expression.

Gene expression
Gene Expression

• Each cell contains a complete copy of the organism's genome.

• Cells are of many different types and states E.g. blood, nerve, and skin cells, dividing cells, cancerous cells, etc.

• Differential gene expression, i.e., when, where, and how much each gene is expressed.

• On average, 40% of our genes are expressed at any given time.

  • Other important aspects of regulation: methylation, alternative splicing, etc.


  • A ribonucleic acid or RNA molecule is a nucleic acid similar to DNA, but

    – single-stranded;

    – ribose sugar rather than deoxyribose sugar;

    – uracil (U)replaces thymine (T) as one of the bases.


  • RNA plays an important role in protein synthesis

Classes of rna
Classes of RNA

  • Messenger RNA

  • Ribosomal RNA

  • Transfer RNA:

Messenger rna mrna
Messenger RNA (mRNA)

  • Messenger RNA (mRNA) is synthesized from a gene segment of DNA which ultimately contains the information on the primary sequence of amino acids in a protein to be synthesized. The genetic code as translated is for m-RNA not DNA. The messenger RNA carries the code into the cytoplasm where protein synthesis occurs.

Ribosomal rna rrna
Ribosomal RNA (rRNA)

  • In the cytoplasm, ribosomal RNA (rRNA) and protein combine to form a nucleoprotein called a ribosome. The ribosome serves as the site and carries the enzymes necessary for protein synthesis.

Transfer rna trna
Transfer RNA (tRNA)

Transfer RNA (tRNA) contains about 75 nucleotides, three of which are called anticodons, and one amino acid. The tRNA reads the code and carries the amino acid to be incorporated into the developing protein.

Thanks for your patience
Thanks for Your Patience

We will proceed with the transcription and translation in further classes.