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 in animals and yeast

• relatively insoluble

  • large molecular size

  • helps maintain osmotic balance within an organism

• found in the liver and muscles of animals

What are 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

STRUCTURE:

• the molecule of glucose have to be vertically flipped (rotated 180 degrees) in an alternating pattern

  • allows the OH (hydroxyl group) on carbon-1 and carbon-4 of 2 B-glucose molecules to be closer to each other

    • H2O molecule is removed, leaving just one O in the middle

  • allowing the B-1, 4 glycosidic bond is formed

• a straight chain

  • due to alternating orientations of beta-glucose molecules

  • allows the cellulose molecules to form long, unbranched chains

  • grouped into bundles called microfibrils 

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

FUNCTION:

• As a result of the cross-linking of cellulose by hydrogen bonds, these microfibrils have high tensile strength

• This tensile strength is critical for its function in plants, where it forms an essential component of the cell wall

What are glycoproteins?

• proteins that have one or more carbohydrates attached to them.

• found embedded in cell membranes (plasma membrane)

• carbohydrate portion of the glycoprotein faces the exterior of the cell

• it serves 4 functions

• Cell-cell recognition

• Receptors

• Ligands

• Structural support

How does glycoproteins play a part in cell-cell recognition?

• Glycoproteins on cell membranes are known as antigens

• act as markers on the surface of cells, allowing them to identify each other and interact appropriately. 

• They are important for immune response

• The immune system recognises the body’s cells “self” via antigen-receptor interactions

• The immune system can also identify foreign pathogens “non-self” by antigen-receptor interactions

  • e.g immune cells recognise and attack foreign cells that display different glycoproteins on their surface, such as viruses or bacteria.

Definition of Antigens: An antigen is any molecule, including proteins, lipids, or glycoproteins, that the immune system can react to.

What is the role of glycoproteins in ABO blood groups?

• Blood types are categorised by the type of glycoproteins (antigens) on the cell membrane of red blood cells

• A and B antigens have an impact on blood transfusion

• When incompatible blood types are mixed, the immune system will recognise the other glycoproteins (antigens) as foreign molecules and attack.

  • Antibodies (Plasma) vs. Antigens (RBC Surface): Your blood plasma contains antibodies against the antigens not present on your red blood cells.

  • Type A: Contains A-antigens and anti-B antibodies.

  • Type B: Contains B-antigens and anti-A antibodies.

  • Type AB: Contains both antigens and no antibodies (universal recipient).

  • Type O: Contains no antigens but has both anti-A and anti-B antibodies (universal donor)

  • E.g When incompatible blood is introduced (e.g., Type B blood into a Type A person), the anti-B antibodies immediately bind to the foreign B-antigens. This immune response causes hemolysis (destruction of RBCs) and agglutination (clumping), forming clumps of blood that blocks blood vessels, which may be fatal.

    

What are the types and properties of lipids?

• Lipids = fats (mainly made of C, H and O)

• Fats are liquid at body temperature (37 ℃) but solid at room temperature (20 ℃) 

• Whereas oils are liquid at both body temperature and room temperature

• Waxes having melting points above 37 ℃ 

• Cholesterol is another type of lipid

• Steroids have a typical 4 ring structure

Properties

• non-polar

• can dissolve in non-polar solvents

What are the essential structural features of fatty acids?

How are triglycerides and phospholipids formed?

What are the different saturation levels of lipids and how do they come about?

Saturated fatty acids

• Function: pack closer to each other, fats made of these chains to have a higher melting point

Unsaturated fatty acids

• Function: cannot pack closer to each other, fats made of these chains to have a lower melting point

Unsaturated have diff isomers:

• cis isomers

  • hydrogen atoms are nearly always on the same side of the double bond

• trans isomers

  • hydrogen atoms are on opposite sides of the double bonds

What are the consequences of lipid contents in our diet? (meh)

• Diets rich in lipids

  • may result in obesity

  • increases risk of Type II diabetes and high blood pressure

• Diets low in lipids

  • insufficient energy from fatty acids

    • the body uses amino acids from proteins for respiration instead of using them to build muscles and other tissues 

    • Prolonged low-energy diet results in proteins from muscles being broken down into amino acids for energy

What are the functions of lipids in storing energy?

• lipids are normally used for long-term energy storage. 

• The lipids that are used are fats (solid)

• They are stored in specialized groups of cells called adipose tissue. 

• Adipose tissue is located immediately beneath the skin and also around some organs including the kidneys. 

Why?

• Lipids are chemically stable, so energy is not lost over time

• Lipids are more efficient than carbohydrates for long-term energy storage

  • The amount of energy released in cell respiration per gram of lipids is double the amount released from a gram of carbohydrates.

    • requires less mass for the same amount of energy which is essential for animals such as birds and bats that fly

    • Storing lipids is important for animals that hibernate or have to survive long unfavourable seasons 

    • Plants store lipids for energy in seeds and fruits

• Fats are hydrophobic—less likely to associate with water in adipose tissue—while glycogen will be associated with water, increasing its overall mass

What are the non-energy storage related functions of lipids? (meh)

Provide thermal insulation

• As lipids are poor conductors of heat, used as heat insulators. 

• This is the reason for much of our stored fat being in sub-cutaneous adipose tissue next to the skin. 

Increase buoyancy

• e.g blubber in seals as lipids are less dense

Shock absorber

• when fats is liquid at body temp

• reason why adipose tissue around the kidneys and some other organs. 

Metabolic water

• is water produced from respiration of lipids

• Lipids contain a lot of hydrogen (in the C – H bonds)

• During respiration oxygen is combined with hydrogen to produce metabolic water

• Supplies water

• e.g camel humps

Ability of non-polar steroids to pass through the phospholipid bilayer

• the inner region of the phospholipid layer is hydrophobic —> non-polar

Steroids structure

• Four fused rings of carbon atoms

• Few polar groups, so most steroids are non-polar

Cholesterol

• is a steroid

• In the phospholipid bilayer: Functions to control the fluidity of the membrane

Hormones

• are steroid in nature

• E.g. testosterone and estrogen (estradiol)

• Hence they are non-polar (hydrophobic)

What happens when they pass through?