8. B1.1 Carbohydrates and lipids

Main groups of biomolecules

• Carbohydrates

  • Monosaccharides

    • Glucose

    • Galactose

    • Fructose

    • Ribose

  • Disaccharides

    • Maltose (glu + glu)

    • Lactose (galact. + galact.)

    • Sucrose (glu +fruct.)

  • Polysaccharides

    • Starch

    • Glycogen

    • Cellulose

    • Chitin

• Proteins

  • E.g molecules

    • Enzymes

    • Antibodies

    • Peptide hormones

• Lipids

  • Triglycerides

    • Fat stored in adipose cells

  • Phospholipids

    • Lipids forming a bilayer in cell membranes

• Nucleic acids (DNA and RNA)

  • Steroids

  • Nucleotides

    • DNA

    • RNA

    • ATP

Carbon

• Carbon compounds referred to as the building blocks of life

• Carbon atoms has 4 electrons in its 2nd electron shell and can form 4 covalent bonds (borrows), allowing for a variety of stable compounds to exist

  \

Covalent bonds

A type of bond in which a pair of electrons are shared between 2 neighbouring atoms.

• Strongest bonds found in biomolecules

• Provide stability

• Only broken during specific chemical reactions with other molecules

Covalent bonds formed by carbon

Carbon can form different types of covalent bonds with other carbon atoms or other types of atoms.

Giving rise to different forms

• linear chain

• branched chain

• rings (cyclic) structures

Macromolecules

• large molecules made up of smaller molecules called monomers

• relative atomic mass of above 10,000 atomic units

Condensation / polymerisation reaction

• chemical reaction that links one monomer to another

• by-product of the reaction is water (removal)

• catalysed by enzymes

E.g triglyceride formation

• 1 glycerol, 3 fatty acids

• 3 ester bonds formed

• 3 water molecules released

E.g maltose formation

• 1 glucose, 1 glucose

• OH group on carbon-1 of one glucose attacks the -OH group on carbon-4 of the other glucose molecule

  • carbon-x, x is the position of the carbon in the compound in a clockwise direction!

• 1,4-glycosidic bond is formed

• 1 water molecule released

1. Label α-glucose on left side of eqn

2. Number the carbon atoms (6th is projected out)

3. Box up the hydroxyl group of the carbon-1 and carbon-4 atoms

4. Circle 2 H atoms and 1 O atom on the left that will form water molecule

5. Label maltose molecule

6. Add 1 water molecule on the product / right side of eqn

7. Name the bond formed

   

Hydrolysis (digestion)

• Digestion of polymers can occur in

  • all cells as they can produce enzymes

  • in the gut of animals as enzymes are secreted

  • decomposers release enzymes into their environment to hydrolyse polymers around them so that they can absorb monomers

• Hydrolysis requires water (add) and enzymes

Monosaccharides

• Single unit of carbohydrate

• Usually have 3 to 7 carbon atoms

• Classified by the no. of carbon atoms they contain

  • Pentoses (5 carbon atoms) e.g ribose

  • Hexoses (6 carbon atoms) e.g glucose, galactose, fructose

Glucose

• Hexose sugar

• Formula: C₆H₁₂O₆

• Can exist in ring form or linear

• 2 isomers

  • α-glucose (alpha-glucose)

  • β-glucose (beta-glucose)

D-glucose and L-glucose

Difference is positioning of the 3 hydroxyl groups & 1 hydrogen group

D-glucose

• RIGHT

L-glucose

• LEFT

D-glucose and L-glucose

•α-L-glucose is the mirror image of α-D-glucose.

•β-L-glucose is the mirror image of  β-D-glucose.

•*the “mirror” would be the plane of the ring, hence the oxygen and the carbon atoms do not change positions

Form and function of glucose

• solubility in water

• function an energy storage molecule

• monomer / building block for polymers / polysaccharides

Solubility of glucose

• Glucose is a polar molecule (i.e. having partial positive and negative charges)

• Present of – OH groups enables formation of hydrogen bonds with water molecules

• Hydrophilic

Energy storage

• Glucose is a respiratory substrate used by most cells for cellular respiration to produce ATP for various functions

• Energy stored in the C-C (carbon-carbon) and C-H (carbon-hydrogen) bonds of glucose

• One molecule of glucose can produce a large amt. of ATP energy

  • water and carbon dioxide are the by-products

What are the components of starch?

• 2 polysaccharides

  • amylose

  • amylopectin (major component)

  • they are both composed of alpha-glucose monomers

• Amylose and amylopectin allow more glucose molecules to be stored in a fixed volume

What are the characteristics of amylopectin?

• branched due to the presence of alpha 1-6 glycosidic bonds

Storage of starch

• in specialised plant structures (seeds, roots etc.)

• starch is compact in structure due to its coiling and branching during polymerisation

  • allows for efficient storage in a small space

• Amylose and amylopectin are relatively insoluble

  • large molecular size

  • maintain osmotic balance within organism

How is starch utilised?

1. plant in need of glucose

2. starch is broken down through hydrolysis

3. releases glucose molecules

4. glucose used as a source of energy

5. to carry out various cellular processes such as growth and photosynthesis

What is glycogen?

• primary storage form of glucose and animals and yeast

• relatively insoluble

  • large molecular size

  • helps maintain osmotic balance within an organism

• found in the liver and muscles of animals

What is the components of glycogen?

• monomer: alpha-glucose

• joined by alpha 1-4 glycosidic bonds and alpha 1-6 glycosidic bonds

• branched

  • more so than amylopectin despite being structurally similar

• compact, enabling efficiency

Where is glycogen stored and how is it utilised?

• liver

• when blood glucose levels dropped

  • break down glycogen by hydrolysis

  • release glucose molecules into the bloodstream

• muscle cells

  • store glycogen primarily to provide energy for muscle contraction during exercise

• when energy is needed

  • glycogen broken down into glucose molecules which can be used for cellular respiration (produces energy by breaking down glucose, to generate ATP)

Draw the condensation reaction to form maltose from glucose

1. label the type of glucose molecules on the left side of the equation

2. number the carbon atoms of the 2 glucose atoms on the left

3. the condensation reaction involves the hydroxyl group of carbon -4 and the hydroxyl group of carbon 1 that are closest to each other — highlight these hydroxyl groups (-OH)

4. Circle 2Hs and 1O on the left side of the equation that will form the water molecule

5. Complete the equation by adding water on the product side

6. Label the disaccharide

7. Name the bond formed

Draw the condensation reaction to form the branch point in glycogen or amylopectin

1. Label the type of glucose molecules on the left side of the equation

2. Number the carbon atoms of glucose

3. The condensation reaction involves the hydroxyl group of carbon -1 and the hydroxyl group of carbon 6 that are closest to each other — highlight these hydroxyl groups (-OH) on the left side of the equation

4. Circle 2Hs and 1O on the left side of the equation that will form the water molecule

5. Add water on the product side

6. Label the bonds (1-4, 1-6)

What is cellulose?

• complex polysaccharide that serves a structural function

• monomer: Beta-glucose

• an essential component of the plant’s cell wall

• the molecule of glucose have to be vertically flipped in an alternating pattern

  • allows the OH (hydroxyl group) on carbon01 and carbon-4 of 2 B-glucose molecules to be closer to each other