A Glance on A Glance on Genetics - IGenetics - I

In this presentation……

Part 1 – Findings in Classical Genetics

Part 2 – Carbohydrates

Part 3 – Nucleotides

Part 4 – Amino Acids

Part

1

Findings in Findings in Classical Classical GeneticsGenetics

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 non-

disjunction 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 non-membranous 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, bacteriaThe 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 “chicken-and-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

CarbohydraCarbohydratestes

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

NucleotidesNucleotides

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 Amino AcidsAcids

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 Cbackbone atoms are shown. Greek letters ( ) identify the distance (number of bonds) from the central ( ) 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

GuanineAdenine

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 physico-chemical 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

Acidic

Basic

Polar

Aromatic

Hydrophobic

A

G P

LIV

C

MF

W

Y

D

E

HK

R

S

N

T

Q

• 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 indole-3-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 helices, Valine has a preference for 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 super-helices

• 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