B1.1 Carbohydrates and lipids

COMPLETE

What bonds does carbon form ?

covalent bonds ( electrons are shared )

Consequence of covalent bonds

stable molecules based on carbon can be produced

How many bonds can carbon form?

4

• 4 single covalent bonds
• 2 single and 1 double

What are the 4 major classes of carbon compounds used by living organisms ?

Hydrogen, Oxygen, Nitrogen, Phosphorus

Define monomer

Small building blocks to make polymers ( subunit )

Define polymer

Long molecules made up of many similar building blocks (monomers)

What happens in a condensation reaction?

Two molecules are linked together at the same time a smaller molecule is released ( water )

A hydroxyl group (-OH) and a hydrogen (H) is removed from the 2 molecules which allows a bond to be made to bridge the 2 molecules.

How are macromolecules constructed?

Energy is needed to construct polysaccharides, polypeptides and nucleic acids by condensation.

• Energy is supplied by ATP

What do hydrolysis reactions do?

Deconstruct macromolecules

• occur during digestion

How does digestion occur outside the cell ?

Occurs outside the cell in the gut of animals. Decomposers will release digestive enzymes into the environment around them in order to break down polymers.

What's a monosaccharide?

single sugar molecule that has between 3-7 carbons

Properties of glucose

Soluble, energy yield when oxidised, chemically stable,

Explain the chemical stability of glucose

• Very chemically stable which is useful for food storage but if stored in large quantities it causes osmosis problems. Usually converted to starch or glycogen

What are the two types of starch molecule?

amylose and amylopectin

What is amylopectin?

branched chain of alpha glucose linked by 1 - 4 glycosidic bonds but there are some 1-6 glycosidic bonds ( causes the branch )

What is amylose ?

unbranched chain of alpha glucose linked by 1-4 glycosidic bonds

• due to bond angles structure is helical rather than straight

What are the energy stores for plants and animals ?

Plants: starch
Animals: glycogen

How can glucose be removed from starch + glycogen when needed ?

A hydrolysis reaction breaks the 1-4 glycosidic bond to separate one glucose molecule from the end of the chain. This allows it to be transported or used in the cell.

• happens quicker in amylopectin as branched structure provides more ends of chains

What is the structure of glycogen ?

Same as amylopectin

• Alpha glucose molecules linked by 1-4 glycosidic bonds and branched by the 1-6 glycosidic bond
• more branched than amylopectin

Why can starch or glucose be used as storage ?

they have a large size which gives them a low solubility meaning they contribute little to the osmosis concentration

• branched structure makes them compact

Consequence of limitless addition/removal of glucose ?

Starch and glucose do not have a fixed molecular mass so molar solutions cannot be made

• concentrations have to be expressed in percentage terms

Define polysaccharide

Complex sugars that can be broken down ( carbohydrates )

What are the consequences of the strength of cellulose in the plant cell wall ?

The strength prevents plant cells from bursting even when high pressure have developed inside the cell due to osmosis.

Describe the structure of cellulose myofibrils

Cellulose is constructed in a straight chain which causes the molecules to lie parallel to each other.
Hydroxyl groups are regularly spaced along each molecule allowing hydrogen bonds to form between them.

Compare structure of alpha and beta glucose

The -OH on carbon 1 points 'up' in beta glucose and 'down' in alpha glucose

Beta glucose leads to an unbranched chain

What's the function of glycoproteins ?

Glycoproteins attach to the plasma membrane of cells with carbohydrates facing outwards. These carbohydrates serve as a distinct marker for each cell allowing other cells to recognize them. The glycoprotein will be recognized by a receptor on another cell.

What does cell to cell recognition help with ?

Helps with the organization of tissues and can allow foreign bodies or infected cells to be recognized and destroyed.

What are glycoproteins composed of ?

polypeptides with carbohydrates attached

What are the 3 possible oligosaccharides that can be present on glycoproteins ?

O, A, B

What are the consequences of receiving blood containing a different glycoprotein ?

Glycoprotein A and B must only be transfused if the person produces it themselves otherwise it will be rejected

Glycoprotein O does not cause rejection as it has the same structure as A and B with one less monosaccharide so it is not recognised as foreign.

Why are lipids said to be hydrophobic ?

Lipids are only slightly soluble in aqueous solvents. However they are not repelled by water they are just more attracted to non-polar substances.

What are the classes of commonly occurring lipids ?

Fats, Oils, Waxes, Steroids

Characteristics/ Structure of Oil:

• Melting point below 20 degrees therefore solidifies at low temperatures

Characteristics/ Structure of Fats:

• melting point between 20 and 37 degrees
• solid at room temperatures
• liquid at body temperatures

Characteristics/ Structure of Steroids:

• Molecules with a 4 ring structure

Characteristics/ Structure of Waxes:

• Melting point above 37 degrees
• liquify at high temperatures

What bonds form during the condensation reaction that results in a triglyceride ?

Three individual fatty acid molecules are linked to a singular glycerol through condensation so 3 water molecules are made.

• The links between each fatty acid and glycerol is an ester bond

When are ester bonds formed?

When an acid reacts with the hydroxyl group ( -OH ) in alcohol

Where does the reaction occur during the formation of triglycerides ?

Reaction is between the carboxyl group ( -COOH ) on the fatty acid and a hydroxyl on the glycerol.

Why are triglycerides entirely hydrophobic ?

The carboxyl and the hydroxyl groups are the hydrophilic parts of the molecules and they are entirely used up in the condensation reactions.

What do phospholipids contain?

glycerol, 2 fatty acids, and a phosphate group

Why are phospholipids both hydrophilic and hydrophobic ?

The phosphate is hydrophilic but the glycerol and fatty acids are hydrophobic

Describe the structure of a generalised fatty acid

• Unbranched chain of carbon atoms with hydrogen atoms covalently bonded ( hydrocarbon chain )
• carboxyl group ( -COOH ) at one end -> acid part
• methyl group ( -CH3) at the other end

They can have single or double bonds between carbon atoms

What's the difference between saturated and unsaturated fatty acids ?

Saturated: A fatty acid with all single bonds between carbon atoms
Unsaturated: Fatty acids that contain one or more double bonds as they contain less hydrogen than they could

Monounsaturated

fatty acid with 1 double bond

Polyunsaturated:

fatty acids with more than 1 double bond

Cis-fatty acids

Naturally occurring unsaturated fatty acids in which carbon moieties lie on the same side of the double bond.

Trans-fatty acids

Hydrogens are on the opposite side to the double bond

Characteristics of Cis fatty acids

Bend in hydrocarbon chain due to double bond

• low melting point as not closely packed together
• liquid at room temp ( oils )

Characteristics of Trans fatty acids

• straight chains
• Higher melting point
• Solid at room temperatures

How are trans fatty acids produced ?

Artificially produced by partial hydrogenation of vegetable or fish oils

• used in margarine and processed foods

What properties make triglycerides suitable for long term energy storage ?

• Chemically stable
• immiscible with water
• Release twice as much energy per gram in respiration compared to carbohydrates
• Poor heat conductors
• Liquid at room temperature

Where are triglycerides stored?

adipose tissue

Why does chemical stability mean Triglycerides are suitable for long term storage ?

Energy is not lost over time

Why does water immiscibility mean Triglycerides are suitable for long term storage ?

They naturally form droplets in the cytoplasm which do not have osmotic or other effects on the cell

Why does energy release mean Triglycerides are suitable for long term storage ?

Enough energy can be stored in half the body mass.

• Important for animals that move/fly

Why does poor heat conduction mean Triglycerides are suitable for long term storage ?

They can be used as thermal insulators in animals that need to conserve body heat

Why does liquidity at body temperatures mean Triglycerides are suitable for long term storage ?

They can act as shock absorbers

What adaptation of adipose tissue allows it to be a good insulator ?

Animals that require more thermal insulation have thick layers of subcutaneous adipose tissue

( Blubber in marine animals )

Amphipathic

A molecule that has both a hydrophilic region and a hydrophobic region.

Hydrophilic

Attracted to water

Hydrophobic

Repelled by water

Outline the amphipathic properties of phospholipids

Hydrophilic: phosphate group
Hydrophobic: 2 hydrocarbon chains

Why do phospholipids form a bi-layer in water ?

The phosphate heads are attracted to water but the tails are attracted to each other more than the water.

• This causes a double layer arrangement

Properties of steroids

• 4 fused rings of carbon atoms
• 3 cyclohexane rings
• 1 cyclopentane ring
• 17 carbon atoms in total in the rings

Why can steroids pass through the phospholipid bilayer ?

They are mostly hydrocarbon and therefore hydrophobic