B1.1- Carbohydrates and lipids

Explain the importance of the carbon atom

• Carbon forms covalent bonds:

  • a type of bond in which electrons are shared between two neighboring atoms

  • Considered a stable bond therefore its presence gives stability to molecules

• A carbon atom can form four bonds

  • Allows for the formation of many different molecules

State an example of a chain form carbon molecule

Fatty acid molecule

State an example of a ring structure form carbon molecule

Glucose

State an example of a branched structure form carbon molecule

Glycogen (polymer of glucose)

Define monomer

Individual subunit that can be linked together to form a longer chain (polymer)

Define polymer

Large molecule (macromolecule) made by combining smaller compounds (monomer)

State the four classes of macromolecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Define condensation reaction

Polymerisation reaction in which two or more molecules combine to form a larger molecule and water is released

Describe the formation of a polymer of glucose through condensation reactions

• Glucose is a monosaccharide

• The -OH group on carbon 1 of one glucose molecule attaches to the -OH group on carbon 4 of the other glucose molecule.

• This results in the formation of a covalent bond between the two glucose molecules- called 1,4-glycosidic bond, and the release of a molecule of water

• In the glycosidic bond, an oxygen atom is shared between the two glucose molecules that are joined together

• This joining of two glucose molecules together forms maltose, which is a disaccharide molecule, as it is composed of two monosaccharides bonded together chemically

• The joining of more than two glucose molecules forms the polysaccharide molecules, as it is composed of multiple monosaccharides bonded together chemically

List examples of pulysaccharides

• Starch

• Glycogen

• Cellulose

Define hydrolysis

A chemical reaction in which a water molecule is used to break down large molecules by breaking the covalent bonds between the monomers that make up a polymer.

Describe an example of the hydrolysis of a molecule

Hydrolysis of disaccharide sucrose

• The -OH group of the water molecule will attach to one of the monosaccharides

• -H of the water molecule will attach to the other monosaccharide

• This breaks the glycosidic bond that was present in the disaccharide

• The molecule is broken down to its constituent monosaccharides: glucose and fructose.

Define monosaccharides

Fundamental biological molecules that serve as a source of energy for cells and are involved in various cellular processes

List examples of monosaccharides with the number of carbon atoms they contain

• Pentoses- 5 carbon atoms (eg: ribose)

• Hexoses- 6 carbon atoms (eg: glucose, galactose in dairy, fructose in fruits)

Describe isomerism exhibited by glucose monosaccharide

• The molecule of glucose can be either one of two: an alpha glucose molecule or a beta-glucose.

• Alpha-glucose molecules have the -OH group on the first carbon atom oriented downwards

• Beta-glucose molecules have the -OH group on the first carbon atom oriented upwards

Explain the solubility of glucose

• Glucose is polar because of its molecular structure

  • It contains several -OH polar functional groups

  • The oxygen atom present in the glucose ring has a partial negative charge, therefore C-H groups linked to it have a partial positive charge, difference in charge throughout a molecule contributes to polarity

• Polarity of the structure cause it to be soluble

Explain the stability of a glucose molecule and why that is relevant to different cells

• Cyclic molecule

• -OH groups situated in the axial regions of the molecule

• The glucose molecule is therefore stable

• Cellulose polysaccharides in plant cell walls are stable due to this and help maintain the structure of the cell

• The stability of the glucose molecule is also useful in animals, as energy can therefore be stored through the use of the polysaccharides starch and glycogen

Describe the process of oxidation in glucose that forms ATP

• Oxidation is when a molecule experiences a loss of electrons from an atom or molecule

• This can happen through the addition of oxygen to a molecule or the loss of hydrogen or loss of electrons to another molecule or ion

• During oxidation of glucose, the six carbon molecule is broken down by using electrons to oxygen

• This reaction produces water, carbon dioxide, and energy

Define starch

The polysaccharide that serves as the main energy store in plants

Compare and contrast the two types of startch

• Amylose:

  • Linear polysaccharide made up of glucose monomers

  • Linked together through alpha-1,4 glycosidic bonds

  • Has a coiled structure

  • is typically composed of between 300 and 3000 glucose subunits

• Amylopectin

  • Highly branched polysaccharide made up of glucose monomers

  • Linked together through alpha-1,4 glycosidic bonds and alpha-1,6-glycosidic bonds

  • Has complex 3-dimensional structure

Explain the suitability of starch as an energy storage molecule

• Compact:

  • Starch is a compact structure due to its coiling (Amylose) and branching (Amylopectin)

  • This allows for efficient energy storage in smaller space

• Large:

  • Due to starch usually having a large size

  • water molecules find it difficult to surround and dissolve

  • Making starch insoluble, good for energy storage

Define glycogen

A branched polysaccharide that serves as the primary energy storage molecule in humans

Describe the structure of glycogen

• Linear chains of glucose are linked together through both alpha-1,4 glycosidic bonds (forming a backbone)

• And alpha-1,6 glycosidic bonds occurring every 8-12 glucose units, causing frequent branching and therefore allowing glycogen to be highly compact

Explain the relative ease of adding and removing alpha-glucose monomers by condensation and hydrolysis to build or mobilize energy storage molecules

• Through condensation reactions, when energy needs to be stored, alpha glucose molecules are joined together, releasing water molecules. This process is catalysed by enzymes such as glycogen synthase

• Through hydrolysis reactions, when energy is needed, enzymes like glycogen phosphorelase break these glycosydic bonds by adding water. The process happens quickly due to the branched structure, which allows for multiple glucose molecules to be released simultaneously.

Describe the structure of cellulose

• Formed from beta-glucose molecules

• Due to the beta-glucose molecules having the ability to alternate in orientation, a unique structure of a long, straight chain can be formed

• Those chains can be grouped into bundles called microfibrils

• The microfibrils are held together by hydrogen bonding that occurs between adjacent cellulose molecules

• Hydrogen bonds between chains create a strong and stable lattice structure, giving it a lot of tensile strength

Define glycoproteins

Proteins that have one or more carbohydrates attached to them.

Explain the role of glycoproteins in cells

• Cell recognition

  • They act as markers on the surface of cells

  • This allows them to identify each other and interact appropriately

• Receptors

  • They act as receptors on the surface of cells

  • Allowing them to receive signals from other cells or molecules in the environment

• Ligands

  • They bind to specific receptors on other cells to initiate signalling pathways

• Structural support

  • They contribute to the structural integrity of cells and tissues

Explain an example of glycoproteins functioning in terms of cell recognition

• The ABO blood group system is based on the presence of specific glycoproteins on the surface of red blood cells

• These glycoproteins are called A and B antigens

• Individuals can have one, two, both, or neither of these antigens in their red blood cells. This is what determines blood types

• Compatibility of blood types is based on recognition and interaction of specific glycoproteins on the surface of red blood cells

• When incompatible types are mixed, the immune system can recognise the other glycoproteins as foreign molecules and attack

• This leads to clumping of red blood cells

• This may lead to organ failure and death

Define lipids

A diverse group of non-polar molecules that are characterised by their low solubility in water

Define triglycerides

A type of liquid molecule composed of three fatty acid chains attached to a glycerol

List types of fats and thier state at room temperature

• Triglycerides: solid

• Oil: liquid

• Wax: solid

Outline the formation of triglycerides

• One glycerol molecule undergoing condensation reaction with three fatty acid molecules

• Each time a fatty acid molecule joins the glycerol molecule, a water molecule is released

• The bond that forms between the glycerol and fatty acid is called an ester bond

Outline the formation of phospholipid molecule

• Through condensation reaction, two fatty acids join a molecule of glycerol that is modified with glycerol phosphate molecule

• A water molecule and a phospholipid molecule are produced

Describe the general structure of a fatty acid

Hydrocarbon chain ranging from 4 to 35 carbons long, with carboxyl functional group at the end

Explain the structure of saturated fatty acids

• There are no carbon-carbon double bonds

• Each carbon atom in the hydrocarbon chain is bound to 4 atoms

• This allows the fatty acids to pack tightly together

• More energy would be required to pull the molecules apart

• HIgher melting point is a result of this

• Solid at room temperature

Explain the structure of saturated fatty acids

• There is one or more carbon-carbon double bond

• Kinks or bends in the fatty acid chain are introduced

• These kinks prevent the fatty acid molecules from being packed closely together

• Less energy would be required to pull the molecules apart

• Lower melting point is a result of this

• Liquid at room temperature

Define monounsaturated fats

Fats that have one double bond in their hydrocarbon chain, causing on kink/bend in the chain, making it difficult for molecules to pack together tightly, resulting in a liquid state at room temperature, having a low melting point

Define polyunsaturated fats

Fats that have two or more double bonds in their hydrocarbon chain, causing multiple kinks/bends in their hydrocarbon chain, making it even more difficult for molecules to pack together, resulting in a liquid state at room temperature, have an even lower melting point

Describe the arrangement of cis unsaturated fatty acids

• Hydrogen atoms attached to the double bond are located on the same side of the molecule

• This creates a bend or kink in the molecule, causing it to have a less linear structure

Describe the arrangement of trans unsaturated fatty acids

• Hydrogen atoms attached to the double bond are located on different sides of the molecule

• This creates a more linear structure

• Results in a molecule that is less flexible and more rigid

Explain how triglycerides in adipose tissue is used for energy and thermal insulation

• They intake a lot of energy in the form of food

• Fat is an important source of energy as it stores much of it

• After consumption and digestion, it is stored in adipocytes as liquid droplets

• It can then be broken down into ATP when energy is needed

• In addition to their role as an energy reserve, they also serve as effective thermal insulators to help regulate body temperature and to protect the organism’s body from the cold

Explain the formation of the phospholipid bilayer membrane

• Composed of a bilayer of phospholipid molecules arranged in a specific orientation.

• A phospholipid consists of a negatively charged phosphate head and hydrocarbon tail

• Phosphate head readily interacts with water molecules (is hydrophilic)

• Hydrocarbon tail consists of long non-polar fatty acid chains that repel water molecules (hydrophobic)

• Phospholipids are considered to be amphipathic molecules as they present both hydrophilic and hydrophobic properties

• When placed in an aquatic environment, hydrophilic tails orient themselves toward each other as they are more attracted to each other than to the water molecules

• Spontaneously, a bilayer is formed

Define steroids

A group of naturally occurring hormones that play a vital role in regulating a wide range of physiological functions in the body

List examples of steroids

• Oestradiol (signalling, female reproductive development)

• Testosterone (signalling, male reproductive development)

• Cholesterol (providing the bilayer with stability and flexibility)

Outline how signalling steroids are able to pass through the phospholipid bi-layer

• As steroids are hydrophobic molecules,

• They are capable of passing through the phospholipid bilayer of cells

• Allowing cells to have a faster response to the presence of these steroids

• Allowing the signal to occurs more efficiently