genetica per scienze naturali a.a. 06-07 prof s. presciuttini 1. chemical composition of living...

Genetica per Scienze Naturalia.a. 06-07 prof S. Presciuttini

1. Chemical composition of living cells

Approximate chemical compositions (percent of weight) Approximate chemical compositions (percent of weight) of a typical bacterium and a typical mammalian cellof a typical bacterium and a typical mammalian cell

COMPONENT Bacteria Mammalian cells

H2O 70 70

Inorganic ions 1 1Small metabolites 3 3Proteins 15 18RNA 6 1.1DNA 1 0.25Lipids 2 5Polysaccharides 2 2

100 100

Total cell volume 2 × 10-12 cm3 4 × 10-9 cm3

Relative cell volume 1 2000


2. Four classes of macromolecules

All key components of every living cell are made of All key components of every living cell are made of macromoleculesmacromolecules. They can be classified into four main classes: . They can be classified into four main classes:

CarbohydratesCarbohydrates (sugars, starch and cellulose) (sugars, starch and cellulose) LipidsLipids (fats, oils, steroids) (fats, oils, steroids)ProteinsProteins (polypeptide chains and their assemblages) (polypeptide chains and their assemblages) Nucleic acidsNucleic acids (DNA and RNA) (DNA and RNA)

These macromolecules are made the same way in all living things, These macromolecules are made the same way in all living things, and they are present in all organisms in roughly the same and they are present in all organisms in roughly the same proportions; they make up what we visually recognize as lifeproportions; they make up what we visually recognize as life

Macromolecules are giant Macromolecules are giant polymerspolymers ( (polypoly means many; means many; mermer means units) constructed of many organic molecules called means units) constructed of many organic molecules called monomersmonomers. Some polymers are made of the same monomers, e.g. . Some polymers are made of the same monomers, e.g. cellulose, while others, e.g. proteins or nucleic acids, are made of cellulose, while others, e.g. proteins or nucleic acids, are made of a set of different monomers. Polymer chains can be linear, a set of different monomers. Polymer chains can be linear, branching or even circular.branching or even circular.


3. Functions of macromolecules

Some of the roles of macromolecules are:Some of the roles of macromolecules are: Energy storageEnergy storage CompartimentalizationCompartimentalization Structural supportStructural support CatalysisCatalysis TransportTransport Protection and defenseProtection and defense Regulation of metabolic activitiesRegulation of metabolic activities Maintenance of homeostasisMaintenance of homeostasis Means for movement, growth, and developmentMeans for movement, growth, and development HeredityHeredity

The functions of macromolecules are related to their shape and to The functions of macromolecules are related to their shape and to the chemical properties of their monomersthe chemical properties of their monomers


4. Chemical composition of biomoleculesHere is one way to think of the differences among macromolecule Here is one way to think of the differences among macromolecule classes: classes:

All carbohydrates such as wood or starch in every plant are made of just All carbohydrates such as wood or starch in every plant are made of just three chemical elements: three chemical elements: C, HC, H and and OO. (Some might also have small . (Some might also have small amounts of S and N.) amounts of S and N.)

All proteins of all organisms on earth are made of five chemical elements: All proteins of all organisms on earth are made of five chemical elements: C, H, O, N, SC, H, O, N, S. .

All nucleic acids of all organisms on earth are made of All nucleic acids of all organisms on earth are made of C, H, O, N, PC, H, O, N, P. . Here we see a uniformity of living organisms at the most elemental level. There is Here we see a uniformity of living organisms at the most elemental level. There is far less diversity in carbohydrates, which are made from just a few monomers. far less diversity in carbohydrates, which are made from just a few monomers. That is why all starches tend close-up to look alike (carrot or baobab), while That is why all starches tend close-up to look alike (carrot or baobab), while proteins look startlingly different.proteins look startlingly different.Elements such as Elements such as C, H, O, N, PC, H, O, N, P and and SS (also called macro elements) make up (also called macro elements) make up biomolecules and are therefore the largest dry weight of all living organisms. biomolecules and are therefore the largest dry weight of all living organisms. Other elements are present in small numbers but can still play important roles Other elements are present in small numbers but can still play important roles (e.g. the iron in hemoglobin, which carries oxygen, or the sodium and potassium (e.g. the iron in hemoglobin, which carries oxygen, or the sodium and potassium ions that are responsible for nerve impulses.)ions that are responsible for nerve impulses.)


5. Monomers

In living cells, a In living cells, a small setsmall set of monomers is used to create a variety of of monomers is used to create a variety of polymers. Each polymer is unique in the number and type of polymers. Each polymer is unique in the number and type of monomers used to build it. monomers used to build it.

Macromolecule Monomers

Carbohydrates monosaccharides

Lipids glycerol, fatty acids

Proteins amino acids

Nucleic acid nucleotides


6. Monomers to polymers

To qualify as a building block for polymers, each monomer must be capable of To qualify as a building block for polymers, each monomer must be capable of linking with others. When a monomer's linking with others. When a monomer's functional groupfunctional group, a specific arrangement , a specific arrangement of atoms, reacts with a functional group of another monomer, the two molecules of atoms, reacts with a functional group of another monomer, the two molecules link together with a stable link together with a stable covalent bondcovalent bond, one that will not break under normal , one that will not break under normal conditions and will not dissolve in water.conditions and will not dissolve in water.


7. Sucrose, glucose, fructose

Example:Example: Sucrose (table sugar) is composed of glucose and fructose.Sucrose (table sugar) is composed of glucose and fructose.


8. Functional groups defined

A functional group is a group of atoms of a particular arrangement that gives the A functional group is a group of atoms of a particular arrangement that gives the entire molecule certain characteristics. Functional groups are named according to entire molecule certain characteristics. Functional groups are named according to the composition of the group. For example, COOH is a carboxyl group.the composition of the group. For example, COOH is a carboxyl group.

Organic chemists use the letter "R" to indicate an organic molecule. For example, Organic chemists use the letter "R" to indicate an organic molecule. For example, the diagram below can represent a carboxylic acid. The "R" can be any organic the diagram below can represent a carboxylic acid. The "R" can be any organic molecule.molecule.


9. The seven fundamental functional groups present in biological monomers


10. Twenty aminoacids and five nitrogen bases

The total number of biologically important monomers is The total number of biologically important monomers is surprisingly small, about 40-50, from which the thousands surprisingly small, about 40-50, from which the thousands of biologically important macromolecules are constructed.of biologically important macromolecules are constructed.

In particular, the set of amino acids common to all living In particular, the set of amino acids common to all living things includes 20 total different molecules, and the set of things includes 20 total different molecules, and the set of nitrogen bases that compose DNA and RNA include 5 nitrogen bases that compose DNA and RNA include 5 total different moleculestotal different molecules


11. The 20 amino acids

The amino acids are grouped into four categories according to the properties of their side chains: nonpolar, polar, basic, and acidic. Amino acids in a subclass are chemically similar. In general, polar amino acids are hydrophilic and nonpolar amino acids are hydrophobic, and this property has a large influence on the characteristics of the protein they constitute .


12. Five different nitrogen basesNucleic acids (DNA and RNA) are linear polymers Nucleic acids (DNA and RNA) are linear polymers composed of monomers called nucleotides. The composed of monomers called nucleotides. The nucleotides are composed by a sugar, a phosphate nucleotides are composed by a sugar, a phosphate group, and an organic base. The base components group, and an organic base. The base components of nucleic acids are heterocyclic compounds with of nucleic acids are heterocyclic compounds with the rings containing nitrogen and carbon.the rings containing nitrogen and carbon.

The bases adenine, guanine, and cytosine are found The bases adenine, guanine, and cytosine are found in both DNA and RNA; thymine is found only in in both DNA and RNA; thymine is found only in DNA, and uracil is found only in RNA. Adenine DNA, and uracil is found only in RNA. Adenine and guanine are purines, which contain a pair of and guanine are purines, which contain a pair of fused rings; cytosine, thymine, and uracil are fused rings; cytosine, thymine, and uracil are pyrimidines, which contain a single ring. pyrimidines, which contain a single ring.

The bases are often abbreviated A, G, C, T, and U, The bases are often abbreviated A, G, C, T, and U, respectively. For convenience the single letters are respectively. For convenience the single letters are also used when long sequences of nucleotides are also used when long sequences of nucleotides are written out.written out.


13. Introducing metabolism

Where do the building blocks (monomers) of the macromolecules in Where do the building blocks (monomers) of the macromolecules in living cells come from? living cells come from?

METABOLISMMETABOLISM All living things must have an unceasing supply of energy and matter. The All living things must have an unceasing supply of energy and matter. The

transformation of this energy and matter within the body is called transformation of this energy and matter within the body is called metabolismmetabolism

AnabolismAnabolism Anabolism is constructive metabolism. Typically, in anabolism, small Anabolism is constructive metabolism. Typically, in anabolism, small

precursor molecules, precursor molecules, oror metabolites, metabolites, are assembled into larger organic are assembled into larger organic molecules. This always requires the molecules. This always requires the inputinput of energy of energy

CatabolismCatabolism Catabolism is destructive metabolism. Typically, in catabolism, larger organic Catabolism is destructive metabolism. Typically, in catabolism, larger organic

molecules are broken down into smaller constituents. This usually occurs with molecules are broken down into smaller constituents. This usually occurs with the the releaserelease of energy of energy


CO2

14. Polymers, monomers, metabolites

Photosynthesis

Digestion

Respiration

Anabolism

Catabolism

genetica per scienze naturali a.a. 06-07 prof s. presciuttini 1. chemical composition of living...

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