¡Descarga apuntes biología en inglés bachillerato internacional y más Apuntes en PDF de Biología solo en Docsity!
TOPIC 2 MOLECULAR BIOLOGY
Living organisms contain a vast range of chemical substances, the majority are carbon-containing compounds such as glucose, fats, and proteins. These are known as organic compounds. However, a few organic compounds are not considered organic, such as carbon dioxide, carbon monoxide, carbonates, and hydrogen carbonates. Organic compounds have a huge role within and outside of cells. CARBON
- Element, atomic nº6, has 4 electrons in its outer shell, meaning it can form 4 covalent bonds with other carbon atoms or other elements. - Methane consists of a single carbon atom and four hydrogen atoms - Carbons have 4 links Carbon-based compounds found in living organisms include: Lipids Carbohydrates Nucleic acids Proteins Living organisms are made of organic compounds called macromolecules (a very large molecules). 4 types of macromolecules:
- Carbohydrates
- Lipids
- Proteins (or parts of polypeptides showing amino acids linked by peptide bonds) o Consist of amino acids that are arranged in long chains
- Nucleic acids o Also, chains formed by nucleotides All of them contain carbon, hydrogen, and oxygen atoms. Although other elements are also present. - Nitrogen appears in proteins and nucleic acids - Phosphorus in some lipids (phospholipids) These 4 organic compounds are essential for the proper function of all living things
Macromolecules are made up of the smaller monomers o Monomers A type of small molecule, that are like building bricks, they join together (by covalent bonds to form larger structures called polymers. o Polymers a type of large molecule made up of repeating monomers Main classes of organic compounds in cells Basic structures of
Glucose hexose sugars (6 carbons) Ribose pentose sugars (5 carbons)
2. Lipids fat, oil, waxes…
Contain C, H, and O Group of organic molecules that are insoluble in water but soluble in non-polar organic solvents such as acetone EX: Common lipids include: o Triglycerides simple lipids and fats are solid at room temperature and oils are liquid at room temperature (glycerol hydrophilic and fatty acid hydrophobic) o Phospholipids a compound lipid containing a phosphate group, the main component of cell plasma membrane o Steroids derived lipids, important in membrane structure Carbohydrates and lipids (both store molecules) Carbs store glycogen… Lipids store starch… main function is energy storage Energy is stored in the molecule bonds However, when we break the bonds, we deliberate the energy
ph os ph ate b a s e s u g a r
3. Proteins
Contain C, H, O, and Nitrogen (sulfur, but it is not present in all proteins) Large organic compounds made of amino acids arranged into one or more linear chains EX: amino acids (alanine, leucine…) Proteins are formed in a condensation reaction when amino acid molecules join together, and a water molecule is removed. The R group t is like a variable that stands in for a bunch of different side chains
4. Nucleic Acids
Contain C, H, O, N and phosphorus Nucleic acids are chains of sub-units called nucleotides Nucleotides consist of base, sugar, and phosphate groups covalently bonded together If the sugar is ribose, then the nucleic acid formed is RNA if the sugar is deoxyribose, then DNA is formed
*All of these reactions require
enzymes – biological structures
Examples of anabolism by condensation
#1 Condensation example with
two alpha glucoses
Glucose + glucose = maltose condenses 2 molecules of glucose into maltose forming a glycosidic bond The bonds formed are types of covalent bonds
#2 condensation example with two amino acids
A ribosome condenses two amino acids into a dipeptide forming a peptide bond
2. Examples of catabolism by hydrolysis
A protease hydrolyses a dipeptide into two amino acids breaking the peptide bond Lactase hydrolyses Lactose into Glucose and Galactose breaking the glycosidic bond Synthesis of urea: Wöhler accidentally synthesized urea in 1828, whilst attempting to prepare ammonium cyanate. Vitalism: a theory in the past that states that only organisms can synthesize organic compounds. Then, it was discovered that they could be synthesized artificially (scientist Whöler).
2.2. WATER
Water as a coolant high-temperature damages tissues and denature proteins, causing enzymes to cease to work Water molecules and their bonds
- Made up of 2 hydrogen atoms and 1 oxygen - Polar molecules dissolve in water (hydrophilic) - Have both + and – charges acting like small magnets. - Allows the formation of H bonds between water molecules: the partially positive hydrogen atoms of one molecule are attracted to the partially negative oxygen atoms of other water molecules.
Solvent o Water can dissolve many organic and inorganic substances that have charged or polar regions o The polar attraction of large quantities of water molecules can interrupt intra-molecular forces such as ionic bonds, resulting in the dissociation/separation of the atoms Hydrophilic substances that are attracted to water (dissolve in water), including polar molecules such as glucose, and particles with + and – charges (sodium and chloride ions).
- Substances that water adheres to are also hydrophilic. Hydrophobic substances insoluble in water, do not have + and – charges, non-polar, all lipids are hydrophobic including fats and oils, dissolve in other solvents such as propanone (acetone) Transport of molecules in the blood Blood plasma consists of mainly water (95%) plus dissolved substances which it transports.
- Glucose - Polar molecules, therefore, are freely soluble - carried by the blood plasma
- Amino acids - Positive and negative charges, therefore soluble in water - R group varies can be polar, non-polar, or charged - R group determines the degree of solubility - Carried by the blood plasma
- Oxygen - Non-polar molecule - Due to the small size of an oxygen molecule, it is soluble in water, but only just a bit
- Fats = lipids - Large, non-polar molecules (insoluble in water) - They are carried in blood inside lipoprotein complexes in the plasma membrane
- Cholesterol - Hydrophobic molecules, apart from a small hydrophilic region at one end
- This is not enough to make cholesterol dissolve in water - They are carried in blood inside lipoprotein complexes in the plasma membrane Lipoprotein complex - The outer layer consists of a single layer of phospholipid molecules - hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water - The hydrophobic hydrocarbon tails face inwards and are in contact with the fats - Cholesterol molecules are positioned in the phospholipid monolayer - hydrophilic region facing outwards - Proteins are also embedded in the phospholipid layer
- Sodium Chloride - ionic compound - freely soluble in water - dissolving to form sodium ions (Na+) and chloride ions (Cl-) Thermal Water has: o a high specific heat capacity (4.2 Joules is required to raise the temperature of 1g of water by 1ºC) o higher heat of vaporization (amount of energy needed to change from liquid to a gas or vapor) the high heat of fusion (amount of energy needed to be lost to change liquid water to ice) These properties are due to many hydrogens bonds that need to be formed or broken to change the temperature or state of water Therefore, the temperature of the water remains relatively stable Water as a coolant Water is used by Leaves as a coolant. The heat lost from leaves for evaporation prevents them from overheating. If the leaves get too hot enzymes in their cells will start to denature. - It takes a lot of energy for water to change the temperature o Meaning that water has a high latent heat of vaporization
(J g-1^ oc-1) Latent heat of vapourisation (J g-1)
Melting point (oC) -182 0 Boiling point (oC) -160 100 COMPARE:
- Comparable size and weight (H 2 O = 18 dalton ; CH 4 = 16 dalton) - Comparable valence structures (both have tetrahedral orbital formations, but water is bent due to unbonded electron pairs) CONTRAST : The differences in thermal properties between water and methane arise from differences in polarity between the molecules: - Water is polar and can form intermolecular hydrogen bonds (due to high electronegativity of oxygen atom) - Methane is non-polar and can only form weak dispersion forces between its molecules (carbon has a lower electronegativity) This means water absorbs more heat before changing state (each H-bond has an average energy of 20 kJ/mol) Examples of macromolecules and their functions
Types of Monosaccharides:
- Galactose is less sweet than **_glucose
- Fructose_** is another hexose sugar, and it is commonly found in fruits and honey. It is the sweetest naturally occurring carbohydrate. Fructose is sweeter than **_glucose
- Ribose_** is a pentose sugar; it has a pentagonal ring. It forms the backbone of RNA. - Deoxyribose differs as shown in the diagram and forms the backbone of DNA. a-glucose molecules linked together Glucose + glucose = maltose Maltose is a dimer of glucose. The two glucose molecules are holding hands.
β − D − galactose + α − D − glucose The link between the two molecules is the β^ link (bond) Lactose is most commonly found in milk. The two subunits that makeup lactose are glucose and galactose. α − glucose + α − Fructose (^) = Sucrose Sucrose is also known as table sugar. The two monosaccharides that make it up are glucose and fructose. β − glucose + β − glucose = cellulose
Cellulose= β − glucose + β − glucose ( β 1 − 4 ) bond Made of β molecules linked together
- It is made by linking together β^ glucose molecules. - Condensation reactions link carbon atom 1 to carbon atom 4 on the next β (^) glucose. - The glucose subunits in the chain are oriented alternately upwards and downwards. - The consequence of this is that the cellulose molecule is a straight chain, rather than curved. - The linked molecules from bundles called cellulose microfibrils. - Hydrogen bonds link the molecules together. Identifying molecules from diagrams
The general structural formula for a fatty acid Cis-isomers Trans-isomers Very common in the nature Rare in nature-usually artificially produced to produce solid fats The hydrogen atoms are on the same side of the two carbon atoms (difference in structure) The hydrogen atoms are on different sides of the two carbon atoms (difference in structure) The double bond causes a bend in the fatty acid chain The double bond does not cause a bend in the fatty acid chain Therefore cis-isomers are only loosely packed Trans-isomers can be closely packed Triglycerides formed from cis-isomers have melting points – they usually liquid at room temperature Triglycerides formed from trans-isomers have melting points – they usually solid at room temperature HEALTH RISK OF TRANS- FATTY ACIDS The main concern is coronary heart disease (CHD). In this disease the coronary arteries
