Genomics

Lecture 3By 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.

• 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.

Examples of protein functions

Function Description ExampleAntibody Antibodies bind to specific foreign

particles, such as viruses and bacteria, to help protect the body.

Immunoglobulin G (IgG)

Enzyme Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.

Phenylalanine hydroxylase

Messenger Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.

Growth hormone

Structural component These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.

Actin

Transport/storage These proteins bind and carry atoms and small molecules within cells and throughout the body.

Ferritin

Proteins

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

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 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 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 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

Protein

Protein

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

• It consists of two major steps:– Transcription and – Translation.

• Together, transcription and translation are known as 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.

Central Dogma

Central Dogma

RNA

• 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.

• http://www.stanford.edu/dept/humbio/chem/riboseVsDeoxyribose.html

RNA

• RNA plays an important role in protein synthesis

Classes of RNA

• Messenger RNA• Ribosomal RNA• Transfer RNA:

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)

• 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) 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

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