2- MOLECULAR BIOLOGY
Water
● Formula → H2O
● Type of bonding → covalent (electrons are shared)
● Structure:
● Electrons aren't shared equally because oxygen is ‘stronger’, this makes the molecule slightly
more nega ve.
● Polar molecules are overall neutral, but there are slightly charged regions.
● Hydrogen bonding → when the oxygen from a H2O molecule is a racted to a hydrogen atom
from another H2O molecule but can’t share any other electrons.
● It happens because oxygen is nega ve and hydrogen is posi ve, only between two neighbouring
molecules and only in polar molecules.
● Cohesion → the ability of water molecules to s ck together.
● Surface tension → the tension o ered by a water system’s surface for small objects to oat.
● Adhesion → the ability of water molecules to s ck to another surface or solu on.
● Water is known as a ‘universal solvent’ because it can dissolve any molecule as long as it’s polar.
● Example: lipids cannot dissolve in water.
● Why is it important? Because if water wasn’t a solvent, many molecules couldn’t be transported
through transport systems.
Thermal proper es of water
● High speci c heat → a large amount of heat required to raise the temperature of water, it
prevents temperature uctua ons.
● High latent heat → high energy required to change state, important for thermoregula on.
● How’s life in a frozen pond possible?
- The ice on the top layer oats because its density is lower than water’s.
- The lower layer doesn’t freeze because the top ice sheet acts as an insulator.
- The ice is transparent so sunlight can pass and reach aqua c plants, photosynthesis
produces oxygen which is then used for respira on by other living organisms.
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, Organic molecules
● → compounds that contain Carbon which make up living organisms.
● There are four categories:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
● They all come as monomers which then chain together to form polymers.
● Condensa on → when two monomers join to form a polymer and a water molecule is released.
● Hydrolysis → when a polymer’s bonds are broken by a water molecule to form monomers.
Carbohydrates
● Made up by Carbon, Hydrogen and Oxygen atoms.
● Monomers: monosaccharides.
- Called ‘triose, pentose, hexose, heptose’ etc… based on the number of carbon atoms.
● Polymers: polysaccharides → disaccharides (2 monomers), trisaccharides, pentasaccharides…
● E.g. glucose is a carbohydrate monomer (monosaccharide) with 6 Carbon atoms → hexose.
● Since carbohydrates are polar molecules, they are o en soluble in water.
● Isomers: two monosaccharides with the same chemical formula but di erent structures.
● E.g. glucose and fructose are isomers.
● There are 2 types of glucose:
1. Alpha-glucose
2. Beta-glucose
● The only thing that changes is the posi on of
the H and OH groups in Carbon atom n.1 →
they’re switched.
● Condensa on of glucose → water is released from Carbon atoms in posi ons 1 and 4, this is
called 1-4 glycosidic bond.
● Two glucoses join together to form Maltose (C12H22O11).
● C6H12O6 + C6H12O6 = C12H24O12 - H2O = C12H22O11
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, ● Other monosaccharides:
- Ribose → C5H10O5 (pentose found
in RNA).
- Deoxyribose → C5H10O4 (pentose
found in DNA).
● Test for sugars → Benedict’s test.
Disaccharides
● Lactose = glucose + galactose
● Maltose = glucose + glucose
● Sucrose = glucose + fructose
Polysaccharides
● → a chain of 2 or more monosaccharides joined together by glycosidic bonds.
● STARCH:
- Storage molecule in plants.
- Formed by more than two alpha-glucose molecules joined together by 1-4 glycosidic
linkage.
- A chain of amylose and amylopec n (starch= amylose + amylopec n).
- Amylose → a linear chain of alpha-glucose units.
- Amylopec n → chains of alpha-glucose units cross linked to each other.
- Can be stored because it’s insoluble in water, while a single glucose unit would be
soluble.
- Compact molecule.
● GLYCOGEN:
- Storage molecule in animals.
- Also formed by alpha-glucose units joined together by 1-4 glycosidic linkage.
- More compact than starch.
● CELLULOSE:
- Formed by more than two beta-glucose molecules joined together by 1-4 glycosidic
linkage.
- Found in plants’ cell walls.
- To provide strength and structure.
- Chains of monosaccharides are cross linked (like amylopec n).
● CHITIN:
- Main component of arthropods' exoskeleton (e.g. insects).
- Chain of Glucosamine molecules (glucose with nitrogen).
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Water
● Formula → H2O
● Type of bonding → covalent (electrons are shared)
● Structure:
● Electrons aren't shared equally because oxygen is ‘stronger’, this makes the molecule slightly
more nega ve.
● Polar molecules are overall neutral, but there are slightly charged regions.
● Hydrogen bonding → when the oxygen from a H2O molecule is a racted to a hydrogen atom
from another H2O molecule but can’t share any other electrons.
● It happens because oxygen is nega ve and hydrogen is posi ve, only between two neighbouring
molecules and only in polar molecules.
● Cohesion → the ability of water molecules to s ck together.
● Surface tension → the tension o ered by a water system’s surface for small objects to oat.
● Adhesion → the ability of water molecules to s ck to another surface or solu on.
● Water is known as a ‘universal solvent’ because it can dissolve any molecule as long as it’s polar.
● Example: lipids cannot dissolve in water.
● Why is it important? Because if water wasn’t a solvent, many molecules couldn’t be transported
through transport systems.
Thermal proper es of water
● High speci c heat → a large amount of heat required to raise the temperature of water, it
prevents temperature uctua ons.
● High latent heat → high energy required to change state, important for thermoregula on.
● How’s life in a frozen pond possible?
- The ice on the top layer oats because its density is lower than water’s.
- The lower layer doesn’t freeze because the top ice sheet acts as an insulator.
- The ice is transparent so sunlight can pass and reach aqua c plants, photosynthesis
produces oxygen which is then used for respira on by other living organisms.
fiti ti fl fl ti ff ti titi titi tt ti tifl
, Organic molecules
● → compounds that contain Carbon which make up living organisms.
● There are four categories:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
● They all come as monomers which then chain together to form polymers.
● Condensa on → when two monomers join to form a polymer and a water molecule is released.
● Hydrolysis → when a polymer’s bonds are broken by a water molecule to form monomers.
Carbohydrates
● Made up by Carbon, Hydrogen and Oxygen atoms.
● Monomers: monosaccharides.
- Called ‘triose, pentose, hexose, heptose’ etc… based on the number of carbon atoms.
● Polymers: polysaccharides → disaccharides (2 monomers), trisaccharides, pentasaccharides…
● E.g. glucose is a carbohydrate monomer (monosaccharide) with 6 Carbon atoms → hexose.
● Since carbohydrates are polar molecules, they are o en soluble in water.
● Isomers: two monosaccharides with the same chemical formula but di erent structures.
● E.g. glucose and fructose are isomers.
● There are 2 types of glucose:
1. Alpha-glucose
2. Beta-glucose
● The only thing that changes is the posi on of
the H and OH groups in Carbon atom n.1 →
they’re switched.
● Condensa on of glucose → water is released from Carbon atoms in posi ons 1 and 4, this is
called 1-4 glycosidic bond.
● Two glucoses join together to form Maltose (C12H22O11).
● C6H12O6 + C6H12O6 = C12H24O12 - H2O = C12H22O11
ti ti ft ff ti
, ● Other monosaccharides:
- Ribose → C5H10O5 (pentose found
in RNA).
- Deoxyribose → C5H10O4 (pentose
found in DNA).
● Test for sugars → Benedict’s test.
Disaccharides
● Lactose = glucose + galactose
● Maltose = glucose + glucose
● Sucrose = glucose + fructose
Polysaccharides
● → a chain of 2 or more monosaccharides joined together by glycosidic bonds.
● STARCH:
- Storage molecule in plants.
- Formed by more than two alpha-glucose molecules joined together by 1-4 glycosidic
linkage.
- A chain of amylose and amylopec n (starch= amylose + amylopec n).
- Amylose → a linear chain of alpha-glucose units.
- Amylopec n → chains of alpha-glucose units cross linked to each other.
- Can be stored because it’s insoluble in water, while a single glucose unit would be
soluble.
- Compact molecule.
● GLYCOGEN:
- Storage molecule in animals.
- Also formed by alpha-glucose units joined together by 1-4 glycosidic linkage.
- More compact than starch.
● CELLULOSE:
- Formed by more than two beta-glucose molecules joined together by 1-4 glycosidic
linkage.
- Found in plants’ cell walls.
- To provide strength and structure.
- Chains of monosaccharides are cross linked (like amylopec n).
● CHITIN:
- Main component of arthropods' exoskeleton (e.g. insects).
- Chain of Glucosamine molecules (glucose with nitrogen).
ti ti ti ti
