2.1.2 Biological Molecules

What type of molecule is water?

polar molecule

What is a polar molecule?

a molecule in which the charges are unevenly distributed

How are charges distributed on a water molecule?

The oxygen end is delta negative as hydrogen's electrons are pulled towards it. This leaves the hydrogen molecules being delta positive.

How are hydrogen bonds formed in water molecules?

The delta positive hydrogens are electrostatically attracted to the delta negative oxygen atoms, allowing hydrogen bonding to occur

How would we describe the way water molecules stick together

They are cohesive

List the 6 properties of water that make it important to life

Liquid, density, solvent, cohesion/surface tension, high specific heat capacity and high latent heat of vaporisation

Why is water a liquid at room temp and why is this important?

Water is a liquid at room temp due to its polarity and the hydrogen bonds. This is important as it means water can provide habitats, be an effective transport medium and be a reaction medium

Why is the density of water an important property?

When water is below 4C, due to its polar nature the water molecules align themselves differently and form a structure that is less dense than liquid water. This means that aquatic organisms have a stable environment in which to live during the winter

Why is it important that water is a good solvent?

As water is polar, the water molecules surround themselves around the charged parts of the solute and help break it apart. This means that molecules and ions can be transported easily whilst dissolved in water

Why is water cohesive and why is it important that is is cohesive and displays surface tension?

Hydrogen bonding between molecules pulls them towards each other and therefore causes water to be cohesive. Similarly at the surface, the water contracts as it is more attracted to the water molecules beneath than the air molecules above. This helps organisms like pond skaters

Why is water's high specific heat capacity important?

There are many hydrogen bonds within water molecules and so this means it requires a lot of energy to break them. Therefore water acts as a thermal buffer as its temperature is stable, helping enzyme function and animals in their habitats

Why is water's high heat of vaporisation important?

There are many hydrogen bonds within water molecules and so a relatively large amount of heat is required to make water evaporate. This means water can cool both plants and humans through sweat and transpiration.

What is a monomer?

A small molecule which binds to many other identical molecules to form a polymer

What is a polymer?

a long molecule consisting of many smaller molecules called monomers

What is a condensation reaction?

When two molecules are covalently joined together by oxygen with the removal of water. It is anabolic

What is a hydrolysis reaction?

A covalent bond is broken by adding a molecule of water. It is catabolic

What key chemical elements make up a carbohydrate?

Carbon, hydrogen and oxygen

What key chemical elements make up lipids?

Carbon, hydrogen and oxygen

What key chemical elements make up proteins?

Carbon, hydrogen, oxygen, nitrogen and sulphur

What key chemical elements make up nucleic acids?

Carbon, hydrogen, oxygen, nitrogen and phosphorus

List 4 functions of a carbohydrate

Energy source, energy store, structure and forming parts of larger molecules

What is the general formula for a monosaccharide?

CnH2nOn

What is a monosaccharide?

single sugar molecule

List the 3 different types of monosaccharides

Triose sugars (3 carbons), pentose sugars (5 carbons) and hexose sugars (6 carbons)

What types of monosaccharides form ring structures in water?

Pentose and hexose

What type of sugar is ribose and what is the formula?

pentose monosaccharide - C5H10O5

What is the function of ribose?

Used as a component of RNA and ATP

What type of sugar is glucose and what is the formula?

hexose monosaccharide - C6H12O6

What are the two variations of glucose, and how can we remember them?

Alpha glucose and beta glucose - ABBA hydroxyl on Carbon 1

What are the properties of alpha glucose

It is an energy source, and a component of starch and glycogen which act as energy stores

What are the properties of beta glucose

It is an energy source, and a component of cellulose which provides structural support in plant walls

What is a disaccharide?

two monosaccharides joined together

What is a polysaccharide?

Polymers of monosaccharides, consisting of thousands of monosaccharides

How do disaccharides form?

A condensation reaction between two monosaccharides resulting in a glycosidic (covalent) bond, or the breakdown of polysaccharides

How are disaccharides broken down

A hydrolysis reaction breaks the glycosidic bond by adding water

What is lactose made of?

alpha glucose + beta galactose

What is maltose made of?

alpha glucose + alpha glucose in a 1-4 glycosidic bond

What is sucrose made of?

glucose + fructose in a 1-2 glycosidic bond

What type of sugar is sucrose and why?

Sucrose is a non-reducing sugar because the carbons are locked in the bond so the reducing group is unavailable

What is starch made up of

amylose and amylopectin

What is amylose

A long unbranched helical chain of alpha glucose with 1-4 glycosidic bonds

What is amylopectin?

A long, branched chain of alpha glucose. The chains contain 1-4 glycosidic bonds and the branches contain 1-6 glycosidic bonds

What shape do alpha polysaccharides make and why?

Helical structures due to the angle of the 1-4 glycosidic bond

What is the function of starch, and is it soluble or insoluble?

Stored in chloroplasts and plant storage organs, and can be broken down into glucose to be respired. It is insoluble.

What is a glycosidic bond?

a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

What is the structure of glycogen?

Glycogen is a highly branched polymer of alpha glucose consisting of many 1-4 glycosidic bonds in the main chain, and 1-6 glycosidic bonds in the branches.

What properties does glycogen have

Glycogen's many branches make it an energy dense, compact molecule as there are lots of glucose monomers concentrated in one area. Glycogen's branches also mean there are lots of free ends so it can be hydrolysed easily. Finally it is insoluble.

What is the structure of cellulose?

Long, unbranched chains of beta glucose with many 1-4 glycosidic bonds

How do beta glucose monomers join together?

Every other beta glucose monomer is flipped 180 degrees so the OH groups are closer

How do cellulose molecules fit together

They bundle together and make microfibrils

What is a microfibril (cellulose) and how do they work?

Bundles of straight unbranched cellulose molecules lie parallel to form microfibrils. They are held together by hydrogen bonds between the OH groups in neighbouring chains to make a strong structure

What happens when microfibrils join?

They form macrofibrils which then join to form strong, insoluble fibres

What is the energy storage molecule in plants?

Starch

What is the energy storage molecule in animals?

glycogen

Give 2 similarities between glycogen and starch

Both are long chains than can be broken off to use in respiration, and both are insoluble so don't affect the water potential of the cell

How is glycogen different from amylopectin?

Glycogen is more highly branched than amylopectin

Are lipids soluble in water?

No, they are hydrophobic

What are the 3 main types of lipids?

Triglycerides, phospholipids and steroids

What is the structure of a triglyceride?

glycerol + 3 fatty acids

What is a fatty acid?

hydrocarbon chain with a carboxyl group at one end

What is an essential fatty acid?

fatty acids that the body needs but cannot make

What is glycerol?

A three-carbon alcohol with a hydroxyl group attached to each carbon

What part of the fatty acid chain is polar

The carboxyl head is polar and so is hydrophillic; the tail is hydrophobic

What do the properties of trigylcerides depend on?

The nature of the fatty acid chain

If a triglyceride has a saturated fatty acid chain, what does this mean?

No C-C double bonds so is less fluid and has a higher melting point

If a triglyceride has a monounsaturated fatty acid chain, what does this mean?

It has one C-C double bond so is more fluid and has a lower melting point

If a triglyceride has a polyunsaturated fatty acid chain, what does this mean?

It has multiple C-C double bonds so is even more fluid and has an even lower melting point

Why do some fatty acid chains have 'kinks' in them?

They have a double bond so they cannot pack tightly together

How is a triglyceride formed?

Through esterification. When 3 fatty acid chains are linked to the glycerol backbone through a condensation reaction to form an ester bond

Why are triglycerides not polymers?

Separate triglycerides are not held together by covalent bonds

What does the ester bond in a triglyceride connect?

When the hydroxyl group from the glycerol bonds with the carboxyl group of the fatty acid

Give 3 functions of triglycerides

Energy store, thermal insulator and organ protection

Why are triglycerides good energy stores?

They have a high calorific value and are insoluble so don't affect the water potential

What are phospholipids made of?

A phosphate head (with glycerol combined) and two fatty acid tails.

Are phospholipids hydrophobic or hydrophilic?

both - they have a polar head (hydrophilic) and a hydrophobic tail

Why are phospholipids used in membranes?

Membranes contain a phospholipid bilayer, where the hydrophilic heads stick out and the hydrophobic tails point inwards.

How does the nature of the fatty acids in a phospholipid affect the membrane fluidity?

They may be unsaturated or saturated depending on the environment, as colder environments need unsaturated molecules and warmer environments need saturated

Why are lipids (in general) important in respiration?

They can be respired directly ie don't need to be converted into glucose

What is the structure of cholesterol?

A small molecule made of 4 carbon based rings

What is the function of cholesterol?

Helps regulate the strength and fluidity of the membrane

What are steroid hormones made from, and why is this important?

They are made from cholesterol, and since they are a lipid it means they can pass through the phospholipid bilayer into the cell to reach the target

What is the structure of an amino acid?

Amino group on the left, central carbon with hydrogen attached, R group attached to the central carbon and then a carboxylic acid on the right at the end

How are amino acids linked?

Covalently by peptide bonds in a condensation reaction

What is a peptide bond?

A carbon from a carboxyl group on one molecule joined to the nitrogen of an amino group on another molecule

How are amino acids broken down?

hydrolysis

What is a dipeptide and a polypeptide?

A dipeptide is two amino acids joined together, and a polypeptide is multiple amino acids joined together

What are the four levels of protein structure?

primary, secondary, tertiary, quaternary

What is the primary structure of a protein?

The sequence in which the amino acids in a polypeptide chain are joined

What is the secondary structure?

The structure resulting from coiling or folding of the amino acids in a polypeptide, held together by hydrogen bonds

What are the two types of secondary structure?

Alpha helix and beta pleated sheet

Describe an alpha helix

A single helix held together by hydrogen bonds between the oxygen of the C-O group and the hydrogen of the N-H of another amino acid

What keeps the shape of an alpha helix regular?

The hydrogen bonds

Describe a beta sheet

The polypeptide chains zigzags back and forward forming a sheet of antiparallel strands, held together by hydrogen bonds

Why does pH affect the secondary structure?

H+ and OH- ions interfere with the hydrogen bonding

What is the tertiary structure of a protein?

Further folding into a 3D shape as a result of bonding between amino acids within the polypeptide ie it can contain both beta pleated sheets and alpha helices

Where are the hydrophobic interactions found within the tertiary structure of a protein?

They orient themselves towards the centre to avoid the water

Where are the hydrophilic interactions found within the tertiary structure of a protein?

They orient themselves out from the centre to be close to the water

Where are the ionic bonds in the tertiary structure of a protein?

Positively charged R-groups bond together

Why do some amino acids have disulfide bridges, and give a example?

They help keep the shape due to the stronger covalent bonds - proteins in harsh environments eg insulin have these

What is the quaternary structure of a protein?

two or more polypeptide chains joined