Download A Glance on Genetics

A Glance on
Genetics - I
In this presentation……
Part 1 – Findings in Classical Genetics
Part 2 – Carbohydrates
Part 3 – Nucleotides
Part 4 – Amino Acids
Part
1
Findings in
Classical Genetics
Findings
•
•
•
•
•
•
•
•
•
•
Children resemble their parents
Genes come in pairs
Genes do not blend
Some genes are dominant whereas some are
recessive
Genetic inheritance follows rules
All cells arise from pre-existing cells
Sex cells have one set of chromosomes; body cells
have two
Specialized chromosomes determine gender
Chromosomes carry genes
Genes get shuffled when chromosomes exchange
pieces
Findings
• Evolution begins with the inheritance of gene variations
• Mendelian genetics cannot fully explain human health
and behaviour
• There are 44 autosomes and 2 sex chromosomes in
human genome, for a total of 46
• Most of the disorders in human is due to nondisjunction associated with chromosome 21
• Higher cells incorporate an ancient chromosome
• Genes can be turned on and off
• Genes can be moved between species
• Different genes are active in different kinds of cells
• Master genes control basic body plans
• Development balances cell growth and death
Findings
• A genome is an entire set of genes
• Living things share common genes
HSV Virus
Evolution levels
Level 1
– Gases
Level 2
–
–
–
–
–
N-bases
Sugars
Amino acids
Glycerin
Fatty acids
Level 3
–
–
–
–
–
Fats, lipids
Proteins
Polysaccharides
Nucleotides
Nucleic acids
Level 4
–
–
–
–
–
–
–
Energy sources
Enzymes
Construction materials
Coenzymes
Energy carriers
DNA
RNA
• Cells that possess numerous intracellular compartments enclosed by
membranes (called organelles) are called eukaryotic cells, for example,
cells of animals, plants, fungi and protists. There are certain nonmembranous organelles such as centrioles and ribosomes
• Cells that do not possess membrane bound organelles are called
prokaryotic cells. Some cells do not even the chromosomes enclosed, for
instance, bacteria
The collection of various types of molecules in a cell is termed as the
cellular pool
• Approximately, 93 percent of the cellular material is composed of carbon,
hydrogen and oxygen. The non-metal elements nitrogen, phosphorus,
chlorine and sulphur form about 2 percent of the total material in the cell
whereas iodine, fluorine, boron and selenium occur in traces. Less than 5
percent of the constituents comprise major metal elements such as
calcium, potassium, sodium and magnesium. Traces of copper, cobalt,
zinc, manganese, molybdenum, and chromium are found
• Polymerization of a large number of small molecules gives rise to
macromolecules such as proteins, nucleic acids and certain
polysaccharides
• Proteins cannot be synthesized without DNA and DNA cannot be
made without enzymes, which are proteins. This is a kind of “chickenand-egg” dogma
Flow of information to a cell
• Flow of genetic information: Genetic information
contained in DNA is transcribed into RNA, which is
translated into specific proteins
• Flow of extrinsic information: Molecules such as
hormones pass information, coming from outside to
the cell. Some of these enter the cell to influence its
activities. Others bind on to the cell surface with
certain molecules that serve as receptors. Such
binding leads to significant changes in cellular
activities. Studying the nature and action of such
molecular receptors of cell membrane is an
important line of modern research.
Part
2
Carbohydrates
Carbohydrates
• About 80 percent of the dry weight of plants is made of
carbohydrates, which is produced due to photosynthesis
• General formula for carbohydrates is CnH2nOn.
• Carbohydrates are known as saccharides or compounds
containing sugar, the simplest being monosaccharides, which
cannot be hydrolysed still further
• Monosaccharides are composed of 3 to 7 carbon atoms viz.,
trioses (C3H6O3), tetroses (C4H8O4), pentoses (C5H10O5),
hexoses (C6H12O6) and heptoses (C7H14O7)
• Hexoses and heptoses exists in both open chain and in ring
forms
Hexoses and heptoses exists in both
open chain and in ring forms
H H OH H
H H2
|
|
|
|
|
|
C –– C –– C –– C –– C –– C
||
|
|
|
|
|
O OH H OH OH OH
Glucose Open chain
Glucose Ring form
H H H
H H2
|
|
|
|
|
C –– C –– C –– C –– C
||
|
|
|
|
O OH OH OH OH
Ribose Open chain
Ribose Ring form
• Glucose, fructose and galactose are hexoses.
They are all white, crystalline, sweet-tasting
substances extremely soluble in water.
• Ribose is a pentose and glyceraldehydes and
dihydroxyacetone are trioses
• Deoxyribose that occurs in DNA is a pentose
• Compound carbohydrates can be classified into three major
groups:
– Oligosacchrides (made of few molecules of monosaccharides) such
as membranes
– Structural polysaccharides (composed of hundreds of simple sugar
molecules such as cellulose and lignocellulose of plant wall
– Food-storage polysaccharides such as starch and glycogen
• Disaccharides are composed of two monosaccharides.
– A molecule of sucrose is formed from a molecule of glucose and one
of fructose.
– Lactose or milk sugar is formed from one glucose molecule and one
of galactose
– Maltose or malt sugar is formed from two molecules of glucose
Hexokinase Glucose
Part
3
Nucleotides
Nucleotides
• Nucleotides contain carbon, hydrogen, oxygen, nitrogen and
phosphorus
• Each nucleotide is made up of a cyclic nitrogenous base, a pentose
and one to three phosphate groups
• The nitrogenous ring in nucleotides are either a purine or pyrimidine
• The pentose is either ribose or deoxyribose. The nucleotides are thus
called ribonucleotides or deoxyribonucleotides
• Examples of ribonucleotides or deoxyribonucleotides are adenylic
acid (AMP) and deoxyadenylic acid (d AMP) respectively
• A combination of the nitrogenous base with the pentose sugar is
known as a nucleoside. For instance, adenosine is a nucleoside
made of adenine and ribose
• Ribonucleotides are the basic units of RNA and deoxyribonucleotides
are basic units of DNA
Nucleotides are mono-, di-, or tri-phosphates of nucleoside. For
example, adenylic acid or adenosine monophosphate (AMP),
adenosine diphosphate (ADP) and adenosine triphosphate (ATP)
are all adenine nucleotides
Adenosine monophosphate (AMP)
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
• Likewise, other purines and pyrimidines can also form
higher nucleotides
• Sugars, amino acids and nucleotides polymerize to
produce large molecules or macromolecules
• Most important macromolecules are the
polysaccharides, proteins and nucleic acids, which
have high molecular weights and may be branched or
unbranched
• Starch, cellulose and glycogen are composed of a
single type of monosaccharides while some other like
agar are made up of more than one type of
monosachharides
Part
4
Amino Acids
Amino Acids
• Proteins are the fundamental building blocks of life
• Enzymes are proteins that are molecular machines
responsible for all the chemical transformations cells
are capable of
• Those structure that are not made of proteins are
produced by enzymes (which are proteins)
• A human contains proteins of the order of 100,000
different proteins
• Proteins are of variable length and shape
• Proteins are mixed polymers of 20 different amino
acids (or residues)
The protein backbone unit and the 20 amino acid side chains, shown with the
three and one letter abbreviations for each. Proline is an amino acid, and its N
and Ca backbone atoms are shown. Greek letters ( a, b, g, d, e, z, h) identify
the distance (number of bonds) from the central ( a) carbon atom. C=carbon,
H=hydrogen, N=nitrogen, O=oxygen, S=sulphur atoms
• Polymers of amino acids are also called peptides or polypeptides
• Polymers fold themselves to generate a shape characteristic of
each different protein
• The shape of the protein along with different chemical properties of
the 20 amino acids determine the function of the protein
• In theory, by knowing the sequence of a protein, it is possible to
infer its function
• Small or simple molecular modules are called monomers whereas
large or complex biological molecular modules are termed as
polymers
• Many monomer molecules can be joined together to form a single
and large macromolecule
• In both DNA and RNA, the linear polymers can form pair with one
another
• The nucleotides Adenine (A) and Guanine (G) are called Purines
whereas Cytosine (C) and Thymine (T) are called Pyrimidines
Purines
Adenine
Guanine
Pyrimidines
Cytosine
Uracil
Thymine
A double-ringed purine is always bonded to a single
ringed pyrimidine. G pairs with C and A pairs with T or U
• Amino acids are small molecules made of carbon,
hydrogen, oxygen and nitrogen, and in some cases
also sulphur
• They are monocarboxylic or dicarboxylic acids
bearing one or two amino groups
• The four valences of the a-carbon of an amino acid
hold respectively an amino (NH2) group, a
carboxyl (COOH) group, a hydrogen atom and a
side chain
• The side chain may be polar or non-polar
The activities of DNA Polymerase I on various
templates and primers
• A free amino group is basic; a free carboxyl group is
acidic
• Lysine and arginine are basic amino acids since they
carry two amino groups and one carboxyl group
• Glutamic acid (glutamate) and aspartic acid
(aspartate) contain one amino and two carboxyl
groups each and are classified as acidic amino acids
• Alanine, glycine, valine and phenylalanine are
neutral amino acids as they contain one amino and
one carboxyl group
The basic chemical structure of an amino acid. Carbon
atoms are black, oxygen is dark grey, nitrogen light
gray, and hydrogen white.
• Amino acid side chains differ in their physicochemical features
• Some amino acids like to be exposed to water and
hence called hydrophilic whereas the hydrophobic
amino acids tend to avoid exposure to water
• Hydrophobic amino acids tend to occur in the
interior of globular proteins whereas hydrophilic
residues are found preferentially at the surface of
the proteins
Relationships between the physiochemical
properties of amino acids
Hydrophobic
A
G
P
N
L
I
Polar
S
T
V
C
M
Acidic
D
Q
E
Y
W
F
K
H
R
Aromatic
Basic
• The genetic code consists of 61 amino acid coding
codons and three termination codons that start and
stop the process of translation
• Features of individual amino acids also play a key
role in protein secondary structure formation
• Proteins are macromolecules formed from a large
number of amino acids. They are distinct from
amino acids and small peptides in many properties
• Charge, size, or flexibility in the backbone are
only some of the other examples of amino acid
parameters
• The parameters are measured on a numeric scale
such that for every parameter there exists a table
assigning a number to each amino acid
• Taking both parameters viz., physico-chemical and
preferential occurrences together into account,
more than 200 amino acid parameters have been
published
• An amino acid, tyrosine, is converted into the
hormones thyroxin and adrenaline, as well as the
skin pigment melanin
• Glycine is involved in the formation of heme and
tryptophan in the formation of the vitamin
nicotinamide as well as the plant hormone indole3-acetic acid
• In trans-membrane proteins, the regions of the
chain that span the membrane tend to be strongly
hydrophobic
• Successive amino acids can be linked by the
formation of a peptide bond to form a linear chain
of many amino acids
• When few amino acids are joined together, the
molecule is called a peptide
• Glutamate is frequently found in a helices, Valine
has a preference for b strands and Proline is
known to be strongly avoided in helices
• Many structural proteins contain amphipatic helices,
which consist of hydrophobic, non-polar residues on
one side of the helical cylinder and hydrophilic and
polar residues on the other side, resulting in a
hydrophobic moment. Such proteins aggregate with
other hydrophobe surfaces and serve for example as
pores or channels in the cell membrane
• Some amphipatic helices are arranged as inter-twined
helices and are also called as coiled-coils or superhelices
• Generally, the sequence of an alpha helix that
participates in a coiled-coil region will display a
periodicity with a repeated unit length of 7 amino
acids, which is called a heptad repeat
• Half of the 7 amino acids denoted by a through g,
then position a and d are hydrophobic (define an
apolar stripe) while there exist electrostatic
interactions between residues at positions e and g.
They form a parallel coiled-coil of alpha helices from
two polypeptides chains holding them together