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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.
• 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
Example
Antibody
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
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alanine arginine asparagine aspartic acid cysteine glutamine glutamic acid glycine histidine isoleucine leucine lysine methionine phenylalanine proline serine threonine tryptophan tyrosine valine -
ala arg asn asp cys gln glu gly his ile leu lys met phe pro ser thr trp tyr val -
A
R
N
D
C
Q
E
G
H
I
L
K
M
F
P
S
T
W
Y
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.