Water, Carbohydrates, Proteins and Lipids

• It's a reactant in loads of chemcial reactions inc. hydrolysis
• It's a solvent meaning substances dissolve in it. Most biological reactions take place in solution therefore it's essential
• It transports substances e.g. glucose and oxygen around plants and animals
• It helps with temperature control because it has a high specific heat capacity and high latent heat of evaporation
• It's a habitat - many organisms can survive and reproduce in it.

1 molecule of water = 1 atom of Oxygen and 2 atoms of Hydrogen by shared electrons

The shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge.

The unshared negative electrons on the oxygen atom give it a slight negative charge

Water is a polar molecule - it has a partial negative charge and partial positive charge

The slightly negatively charged oxygen atoms attract the slightly positively charged hydrogen atoms of other water molecules.

This is called hydrogen bonding.

• Hydrogen bonds between water molecules can absorb a lot of energy so water has a high specific heat capacity - it takes a lot of energy to heat up. Specific heat capacity is the energy needed to raise the temperature of 1g of a substance by 1°C 
• Water doesn't experience rapid temperature changes - makes it a good habitat
• Takes a lot of of energy to break hydrogen bonds so water has a high latent heat of evaporation - a lot of energy is used up when water evaporates
• Water is great for cooling things due to this

Cohesion is the attraction between molecules of the same type e.g. 2 water molecules

Water molecules are very cohesive because they're polar. This helps water to flow, making it good for transportation of substances. Also helps water to be transported up plant stems in the transpiration stream.

A lot of important substances in biological reactions are ionic e.g. salt. This means they're made from one positively charged atom/molecule and one negatively charged atom/molecule. Because water is polar, the slightly positive end of a water molecule will be attracted to the negative ion and the slightly negative end of a water molecule will be attracted to the positive ion. The ions will get totally surrounded by water molecules and dissolve.

This makes it useful as important ions can dissolve in blood and then be transported around the body.

Water molecules are held further apart in ice than in liquid water because each water molecule forms 4 hydrogen bonds to other water molecules, making a lattice shape. This makes ice less dense than liquid water.

Useful for living organisms because ice forms an insulating layer on top of water - the water below doesn't freeze so organisms living in water don't freeze and can move around.

Carbohydrates are a group of substances used as energy sources and structural materials in an organism.

All carbohydrates contain carbon, hydrogen and oxygen - formula =

C_x(H₂O)_y

Three main groups:

Monosaccharides - simple sugars, monomers, soluble, can't be broken down/hydrolysed

Disaccharides - double sugars, formed from two monosaccharides, can be hydrolysed, soluble

Polysaccharides - large molecules formed from many monosaccharides, insoluble, can be hydrolysed.

Glucose is an abundant and important monosaccharide.

• 6 carbon atoms = hexose sugar.
• C₆H₁₂O₆
  
• Major energy source for most cells. Highly soluble. Main form in which carbohydrates are transported around the body of animals. Its chemical bonds contain lots of energy.
• Structure can be represented in a straight chain, ring or simplified ring.
• Two forms of glucose (structural isomers) = alpha and beta.
• Alpha = OH Below the carbon 1 (AB)
• Beta = OH Above the carbon 1 (AB)

Fructose

Hexose sugar. Very soluble. Main sugar in fruits and nectar. Sweeter than glucose

Galactose

Hexose sugar. Not as soluble as glucose. Important role in production of glycolipids and glycoproteins.

Ribose

Pentose monosaccharide. Structural isomers = ribose and deoxyribose = important consituents of RNA and DNA. The only difference between them is that ribose has 1 H atom and 1 OH group attached to carbon 2 whereas deoxyribose has 2 H atoms and no OH group.

Monosaccharides are joined together by glycosidic bonds.

During synthesis, a condensation reaction takes place - a hydrogen atom on one monosaccharide bonds to a hydroxyl (OH) group on the other, releasing a molecule of water.

Hydrolysis is the reverse of this - a molcule of water reacts with the glycosidic bond, breaking it apart.

A disaccharide is formed when two monosaccharides join together.

Maltose (malt sugar)

Glucose + Glucose - by an alpha 1-4 glycosidic bond.

Sucrose (table sugar)

Glucose + Fructose - by an alpha 1-4 glycosidic bond

Lactose (Milk Sugar)

Glucose + Galactose - by a beta 1-4 glycosidic bond. 

Polysaccharides are polymers containing many monosaccharides linked by glycosidic bonds. Formed by condensation reactions.

Mainly used as an energy store and as structural components of cells.

Major polysaccharides: starch, cellulose and glycogen.

Main energy store in plants. Usually stored as intracellular starch grains in plastids. Plastids include green chloroplasts and colourless amyloplasts. Starch is produced from glucose made during photosynthesis.When a plant needs more glucose for energy, it breaks down starch to release the glucose. It's made from two polysaccharides: amylose and amylopectin

Amylose

Long and unbranched chain. Angles of glycosidic bonds give it a coiled structure. Makes it compact so it's good for storage because you can fit more into a small space. Contains glucose molecules joined mainly by alpha 1-4 glycosidic bonds.

Amylopectin

Long and branched chain of alpha glucose. Side branches allow enzymes to break down the molecule to get at the glycosidic bonds easily so it can be released quickly. Contains glucose molecules joined by alpha 1-4 and 1-6 glycosidic bonds. Highly branched structure.

Glycogen is the main energy storage material in animals - they store excess glucose as glycogen.

Similar to amylopectin but has loads more side branches. Loads of branches means stored glucose can be released quickly, which is important for energy release in animals.

Compact molecule - stored as small granules, particularly in muscles and liver.

Less dense and more solube than starch. Broken down rapidly which indicates the higher metabolic requirements of animals compared with plants.

Major component of cell walls in plants

Made of long, unbranched chains of beta-glucose, which form rope-like microfibrils that are layered to form a network. Cellulose is very strong, and prevents cells from bursting when they take in excess water. Great tensile strength.

Structure

The glucose molecules are linked by beta 1-4 glycosidic bonds - every other glucose molecule rotates through 180 degrees so that the hydroxyl groups on each molecule are adjacent to each other.

Lipids are a diverse group of compounds that are insoluble in water but soluble in organic solvents.

The most common types of lipid are triglycerides, waxes, steroid and cholesterol.

Lipids contain carbon, hydrogen and oxygen. However, they have a higher proportion of hydrogen and a lower proportion of oxygen.

Roles

Energy source - provide twice the amount of energy as carbohydrates. Stored in adipose tissue, which has several important roles including heat insulation in mammals and protection around delicate organs. It also has a function in plasma membrane in waterproofing and waxy cuticles.

Triglycerides are not polymers because they don't consist of identical monomers. They are non-polar, insoluble and less dense than water.

Structure

3 fatty acid tails made of hydrocarbons - which are hydrophobic.

One glycerol molecule.

Esterification

Synthesis between each fatty acid and the glycerol is the formation of an ester bond. Each ester bond is formed by a condensation reaction. Triglycerides break down when the ester bonds are broken - they're broken in a hydrolysis reaction.

Saturated

DON'T HAVE DOUBLE CARBON BONDS  - they are straight. They are full of hydrogen/saturated with hydrogen atoms. Tend to form animal fats. 

Unsaturated

Not full of hydrogen so contain double bonds between carbon atoms. This creates a kink in the chain. Monounsaturated fatty acids contain 1 double bond - Polyunsaturated fatty acids contain 2 or more double bonds. 

Macromolecules.

Phospholipids are similar to triglycerides but one of the fatty acid molecules is replaced by a phosphate group.

The phosphate group is hydrophilic - attracted to water molecules

The fatty acid tails are hydrophobic - dislike interaction with water.

Triglycerides

• Energy storage molecules
• Hydrocarbon tails contain lots of chemical energy - released when broken down.
• Insoluble - don't cause water to enter cell by osmosis which would make them swell.

Phospholipids

• Make up phospholipid bilayer in cell membranes
• Hydrophilic head and hydrophobic tails form double layer with heads facing out outwards
• Bilayer centre is hydrophobic so water-soluble substacnes can't easily pass through.

Cholesterol

• Hydrocarbon ring structure attached to hydrocarbon tail - in eukaryotes, cholesterol molecules help strengthen cell membrane by interacting w/bilayer. Small size & flattened shape. Bind to hydrophobic tails causing them to pack closely together - makes membrane more rigid.

Proteins are a diverse group of large and complex polymer molecules (macromolecules), made up of long chains of amino acids.

Roles

Structural: the main component of body tissues such as muscle, skin, ligaments, hair

Catalytic: all enzymes are proteins - catalysing many biochemical reactions

Signalling: many hormones and receptors are proteins

Immunological: all antibodies are proteins

All amino acids have the same general structure - the only difference between each one is the nature of the R group. The R Group defines an amino acid.

The R group represents a side chain from the central 'alpha' carbon atom, and can be anything from a simple hydrogen atom to a more complex ring structure.

When more amino acids are added to a dipeptide, a polypeptide chain is formed.

A protein consists of one or more polypeptide chians folded into a highly specific 3D shape.

There ae up to 4 levels of protein structure: primary, secondary, tertiary and quaternary. Each of these play an important role in the overall structure and function of the protein. 

Protein shape is maintained by several types of bonds:

Hydrogen bonds

Involved in all levels of structure

Hydrophobic interactions

Between non-polar sections of the protein

Disulfide bonds

One of the strongest and most important type of bond in proteins - occur between two cysteine amino acids. Can be broken by reducing agents.

Formed from parallel polypeptide chains held together by cross-links. These form long, rope-like fibres with high tensile strength and are generally insoluble in water.

Collagen

Main component of connective tissue such as ligaments, tendons and cartilage

Keratin

Main component of hard structures such as hair, nails, claws and hooves

Silk

Forms spiders' webs and silkworms' cocoons. 

Globular proteins usually have a spherical shape caused by tightly folded polypeptide chains. They are folded so that hydrophobic groups are on the inside and the hydrophilic groups are on the outside. This makes many globular proteins soluble in water.

Transport proteins

Such as haemoglobin, myoglobin and those embedded in membranes

Enzymes

Such as lipase and DNA polymerase

Hormones

Such as oestrogen and insulin

The primary structure is simply the sequence of amino acids in its polypeptide chain.

If a single amino acid is incorrect, the whole protein can be useless.

There are two types of secondary structure: alpha helix and beta pleated sheet. Hydrogen bonds form between different amino acids in the polypeptide chain.

This makes the chain automatically coil into either the alpha helix or fold into a beta pleated sheet.

The proteins overall 3D shape is its tertiary structure. The coiled or folded chain of amino acids is often then coiled and folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

Several bonds form:

Ionic Bonds: attractions between negatively and positively charged R groups on different parts of the molecule

Disulfide Bonds: Whenever 2 molecules of cysteine come close together, the sulfur atom in one cysteine bonds to the sulfur in the other

Hydrophobic/Hydrophilic interactions: when hydrophobic R groups are close together they tend to clump together. So hydrophilic R groups are more likely to be pushed to the outside.

Some proteins have more than one polypeptide chain, and the arrangement of these is a protein's quaternary structure.

They can be influenced by ionic bonds, disulfide bonds, hydrophobic/hydrophilic interactions and hydrogen bonds.