MOLECULAR BIOLOGY (PART I) Flashcards
Molecules to metabolism
2.1 Molecules to metabolism
Elements are one kind of atom. An atom is a single particle of an element, composed of a positively charged nucleus and a cloud of negatively charged electrons. Ions are atoms or groups of atoms which are charged. Molecules are groups of atoms bonded together with covalent bonds or ionic bonds. A compound is a molecule where at least two different elements are bonded.
The covalent bonds could be single, double or triple. The covalent bonds are relatively strong. Intermolecular forces are weaker bonds formed between molecules (ex. between the phospholipids in the membrane bilayer)
CARBON:
Carbon can form four covalent bonds, allowing a great diversity of compounds to exist.
The chemistry of life is based on carbon and its ability to combine with other carbon atoms to create long chains of carbon bonded with covalent bonds. The molecules which contain carbon and found in living organisms are called organic molecules.
The four basic macromolecules which are found in all living organisms are carbohydrates, proteins, lipids and nucleic acids.
METABOLISM
Metabolism is the sum of all enzyme-controlled reactions which occur in a cell or an organism. Most metabolic pathways consist of chains of reactions, where the product of one reaction becomes the reactant (substrate) of the next reaction. There are, however also cyclic metabolic pathways, where the first reactant regenerates at the end of the cycle.
ANABOLISM:
Anabolism is the synthesis of complex molecules from simpler ones. Macromolecules in living systems are produced from smaller monomers (subunits). Anabolic reactions are condensation reactions since water is produced.
CATABPLISM:
Catabolism is the breakdown of complex molecules into monomers. Catabolic reactions are hydrolysis reactions since water splits for the reaction to occur.
WATER STRUCTURE:
Life came from water. Many organisms continue to live inside water. It is the main constituent of all organisms.
Structure
It is made up of two H (hydrogen) atoms and one O (oxygen) atom. The distribution of charges in the molecule is unequal. The charge on H atoms is slightly positive (the electrons are drawn to the move electronegative O) and the O is slightly negative- the entire H2O molecule therefore is polar.
Attraction of oppositely charged poles causes them to group together. These attractive forces are called hydrogen bonds. Water by this way becomes very stable.
PROPERTIES OF WATER:
A. Water is denser than ice.
Ice floats on water
B. Colorless and transparent
C. High latent heat of vapourisation
A lot of heat energy is needed for water to evaporate from a surface. This is due to hydrogen bonds
D. High heat capacity
Water absorbs a lot of energy(heat) for only a small change in temperature
E. Cohesion
The tendency of water molecules to stick together very closely
F. Adhesion
Water being a dipole, sticks to surfaces that are polar and therefore hydrophilic
G.Universal solvent
Many substances dissolve in water due to its polarity
Transport in blood
A variety of substances are transported through blood depending on the polarity of the given substance. Sodium chloride (NaCl) is soluble in water and is transported through the blood plasma as ions (Na+ and Cl-) Glucose and amino acids are polar and can be transported dissolved into the blood plasma Oxygen is transported into the red blood cells bound in haemoglobin Cholesterol and fats are non-polar (hydrophobic) and thus must be transported as droplets together with special proteins, called lipoproteins. A monolayer of phospholipids is found surrounding the droplet.
CARBOHYDRATES:A. Monosaccharides
They have a “sweet” taste. They are named after the number of carbons they contain. I.e. pentose contains 5C, hexose contains 6C etc.
Most common monosaccharides:
GLUCOSE is a hexose
Other common hexoses: fructose (found in fruit, honey-it is part of flower nectar), galactose (found in milk as lactose)
Functions of glucose
It contains many –OH polar groups and therefore is soluble in water.
It is the energy molecule of the organism (animals). Upon oxidation it releases high amounts of energy during cell respiration.
Functions of ribose
RIBOSE is a pentose
It is part of nucleotides
It is part of RNA
As deoxyribose is part of DNA
Disaccharides
When two monosaccharides (hexoses) join together with the release of one water molecule, they form a disaccharide. This is called a CONDENSATION REACTION and it is very common in biological systems.
glucose + fructose sucrose + water
Two monosaccharides are connected by a glycosidic bond between the C1 of the first monosaccharide with the C4 of the second.
HYDROLISIS:
The opposite reaction-addition of one water molecule to break the disaccharide and give two monosaccharides is called HYDROLYSIS REACTION and occurs under special conditions (heat, acids, enzymes etc.)
Polysaccharides
Many monosaccharides combining by condensation reactions give a polysaccharide (thousands of monosaccharides are used).
PROPERTIES: The chains created may fold in space, depending on the bonding they have between their monomers, and thus occupy a smaller space which makes them ideal for storage inside cells. The size of the molecules is so large that they become insoluble in water which is also ideal for storage.
Upon hydrolysis they can be converted into smaller molecules disaccharides or finally monosaccharides.
EXAMPLE: starch + nH2O =maltose
This kind of hydrolysis takes place in the mouth with the action of the enzyme salivary amylase found in the saliva.
Examples of polysaccharides
STARCH:
Storage of energy polysaccharide for most parts of plants (in the form of grains). It is a polymer of α-D-glucose. All glycose subunits have the same orientation and thus the molecule has a helical shape. There are two forms of starch: Amylose, where only 1,4 glycosidic bonds are formed between the glucose molecules (see also figure above of how maltose is formed). Amylopectin, where also 1,6 glycosidic bonds are created giving a branched appearance to the molecule.
Examples of polysaccharides
GLYOGEN
: Storage of energy polysaccharide for animal cells (in the form of small grains). It is found mainly in liver and muscle cells. Composed of many glucose molecules also. It resembles the structure of amylopectin, with branches. There are more 1,6 bonds in glycogen than amylopectin, so it is more branched.
Examples of polysaccharides
cellulose:
Structural material, composing the cell wall of plant cells. Its structure (it makes fibrils) gives great strength (rigidity) to plant cells so that they withstand great water pressures and avoid bursting. However, it permits free entrance of water and other substances. It is made of β-D glucose monomers. The orientation of the glycose subunits alternates giving a straight appearance to the polymer. Groups of cellulose molecules are arranged in parallel with hydrogen bonds forming cross links. These structures are cellulose microfibrils, giving the molecule its tensile strength.
LIPIDS
Molecules which contain only carbon, hydrogen and oxygen. Oxygen however is in much smaller proportion here than is carbohydrates. They are completely insoluble in water.
1,Triglycerides
they are formed by the combination of one glycerol and three fatty acids. Three condensation reactions take place and three water molecules are released.
Triglycerides are used as energy stores. The energy from them is released through aerobic cell respiration. They are also used as heat/thermal insulators, since they do not conduct heat. All animals store triglycerides as solid fat. They have a layer of fat beneath their skin,
- PHOSPHOLIPIDS
These are a special category of lipids which possess a phosphate group in the place of ONE fatty acid. So a phospholipid is made of a glycerol molecule bonded with TWO fatty acids and ONE phosphate group. They are partly hydrophobic and form the basis of the membranes.
- STEROIDS:
They all have a similar structure of four fused rings in their molecule. Cholesterol, progesterone, estrogen and testosterone are all steroids.
FATTY ACIDS;Saturated:
(found in animal tissues-meat, butter, skimmed milk etc) where the hydrocarbon chain contains only single bonds between the C-C atoms=FATS→ solid in room temperature
UNSATURATED
Unsaturated=OILS→ liquid in room temperature:
Monounsaturated (olive oil)-contain one double bond in the hydrocarbon chain
Polyunsaturated (found in salmon, mackerel, egg yolk, avocado etc)-contain two or more double bonds in the hydrocarbon chain. Depending where the first double bond is from the end of the chain it is called ω-3, ω-6, ω-9 fatty acids etc.
CIS-FATTY ACIDS
Naturally existing mono- and polyunsaturated fatty acids are cis-fatty acids, that is, the hydrogens of the carbons in the double bond are on the same side. These create a bend in the hydrocarbon chain, very useful and important when lipids circulate in arteries or make up a phospholipid bilayer (in a cell membrane).
