B1.1_Carbohydrates_and_lipids_SL

B1.1 Carbohydrates and lipids

Form and function - Molecules

• In what ways do variations in form allow diversity of function in carbohydrates and lipids?
• How do carbohydrates and lipids compare as energy storage compounds?

Carbon Molecules

B1.1.1—Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Carbon atoms can form 4 covalent bonds

B1.1.1—Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Covalent bond: a very stable chemical bond in which electrons are shared between two neighbouring atoms.

B1.1.1—Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Carbon can form up to 4 covalent bonds with other carbon atoms or other non-metallic elements

Covalent bonds can be single, double or triple

B1.1.1—Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Fatty acid: a linear molecule

Glucose: a ringed molecule

Glycogen: a branched molecule with multiple rings

B1.1.2—Production of macromolecules by condensation reactions that link monomers to form a polymer

Macromolecules or polymers are large molecules that are made up of smaller building blocks called monomers.Monomers are individual subunits that can be linked together to form longer chains or polymers.

B1.1.2—Production of macromolecules by condensation reactions that link monomers to form a polymer

Formation of polymers by condensation reactions

Condensation: polymerisation reaction in which two molecules join together. One molecule loses a hydroxyl group (−OH) and the other loses a hydrogen atom (−H), forming a water molecule and resulting in formation of a new covalent bond.

B1.1.3—Digestion of polymers into monomers by hydrolysis reactions

Break down of polymers by hydrolysis reactions

Hydrolysis: chemical reaction in which water molecules are used to split larger polymer down into its individual monomers (by breaking down the covalent bonds). It is the reverse reaction for the condensation.

Carbohydrates

B1.1.4 Form and function of monosaccharides

Carbohydrates are macromolecules composed of C, O and H. They are essential to life.

Monosaccharides

Simple

Disaccharides

Carhohydrates

Oligosaccharides

Complex

Polysaccharides

B1.1.4 Form and function of monosaccharides

Monosaccharide: simplest form of a carbohydrate, consisting of a single sugar unit that cannot be broken down into smaller molecules by hydrolysis.

According to the number of C, they are classified into:

• Pentoses: 5 C atoms
• Ribose
• Deoxyribose
• Hexoses: 6 C atoms
• Glucose
• Fructose
• Galactose

Ribose

Deoxyribose

B1.1.4 Form and function of monosaccharides

Properties and uses of glucose Structure

Different isomers depending on the position of the hydroxyl group of the carbon linked to the O atom

Glycogen, Starch Cellulose

B1.1.4 Form and function of monosaccharides

Properties and uses of glucose Solubility and transport

Glucose is a polar molecule due to: - OH groups - partial negative and positive charges It is, therefore, soluble in water and can easily be transported in blood, phloem...

B1.1.4 Form and function of monosaccharides

Properties and uses of glucose Chemical stability

The –OH groups situated in the axial regions of the molecule, minimise the electrostatic repulsions within it, making glucose stable.

Storage in glycogen and starch

Structural stability of cellulose

B1.1.4 Form and function of monosaccharides

Properties and uses of glucose Oxidation

Oxidation: chemical reaction that involves the loss of electrons from an atom or molecule. During cellular respiration, glucose, in the presence of O2, is oxydised, broken down into CO2 and H2O. In this process, energy is produced in the form of ATP.

B1.1.5—Polysaccharides as energy storage compounds

Starch: Storage of glucose in plants

Amylopectin

Amylose

Linear: alpha-1,4-glycosidic bonds Branched: alpha-1,6-glycosidic bonds

300 - 3,000 glucose units 2,000 - 200,000 units

B1.1.5—Polysaccharides as energy storage compounds

Glycogen: Storage of glucose in animals (muscle and liver)

30,000 units of glucose Branches every 8 to 12 units

B1.1.4 Form and function of monosaccharides

Research skills – Using search engines and libraries effectively

Click on the image and explore molecules in MolView. You can rotate the 3D structure and find more information in the Tools tab. Search for the monosaccharides studied. Look also for disaccharides (e.g. lactose) and polysaccharides (e.g. glycogen)

B1.1.4 Form and function of monosaccharides

Research skills – Using search engines and libraries effectively

1. Which element is represented in: - Red? - Grey? - Black? 2. What is lactose made of? 3. Can you find 1,4 and 1,6 bonds in the glycogen molecule? (note that only a small part of the glycogen molecule is represented)

B1.1.5—Polysaccharides as energy storage compounds

Polysaccharides are compact in structure due to coiling and branching during polymerisation, which allows for efficient storage in a small space

Due to their large size, they are relaively insoluble in water, which helps to maintain the osmotic balance

B1.1.5—Polysaccharides as energy storage compounds

Relative ease of adding or removing alpha-glucose monomers by condensation and hydrolysis to build or mobilize energy stores

B1.1.6—Structure of cellulose related to its function as a structural polysaccharide in plants

Cellulose Beta-glucose molecules alternate in orientation forming a straight line, resulting in long chains that can be grouped into bundles (microfibrils). Microfibrils are held together by hydrogen bonds between adjacent cellulose molecules. This results in a strong an rigid structure that forms the cell wall in plant cells, providing tensile strength.

B1.1.7—Role of glycoproteins in cell–cell recognition

Glycoproteins: proteins with carbohydrates attached

Receptors. E.g., insulin receptor

Cell-cell recognition (markers). E.g., immune cells; ABO antigens

Ligands. E.g., immune cells

Structural support. E.g., extracellular matrix

B1.1.7—Role of glycoproteins in cell–cell recognition

ABO antigens

Lipids

B1.1.8—Hydrophobic properties of lipids

Lipids: substances that dissolve in non-polar solvents but are only sparingly soluble in aqueous solvents

Fats

Triglycerides

Oils

Saponifiable

Waxes

Esters of alcohol and fatty acids

Phospholipids

Lipids

Steroids

Non-saponifiable

B1.1.8—Hydrophobic properties of lipids

Lipids: substances that dissolve in non-polar solvents but are only sparingly soluble in aqueous solvents

B1.1.8—Hydrophobic properties of lipids

Lipids with high melting points are solid at room temperature, whereas those with low melting points are liquid

Triglicerydes Waxes Steroids

B1.1.9—Formation of triglycerides and phospholipids by condensation reactions

Triglicerydes

Ester bond

B1.1.9—Formation of triglycerides and phospholipids by condensation reactions

Phospholipids

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Faty acids Saturated Unsaturated

Double bonds cause kinks Prevent packing tightly ↓Melting point Liquid oils at room temperature

Straight linear shape Allows packing tightly ↑Melting point Solid fats at room temperature

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Saturated fatty acids found in:

• beef, pork and poultry
• whole milk, cheese, butter and cream
• coconut and palm oil

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Monounsaturated fatty acids found in:

• olive oil (oleic acid)
• macadamia nuts (palmitoleic acid)

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Polyunsaturated fatty acids found in:

• soybean oil and other vegetable oils (linoleic acid)
• fatty fish, e.g. salmon (alpha-linolenic acid)

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

B1.1.11—Triglycerides in adipose tissues for energy storage and thermal insulation

Functions of lipids:

• Long term energy storage: triglicerydes in adipose tissues
• Thermal insulation: triglicerydes in animals adipose tissues
• Structural: phospholipids in cell membranes
• Hormonal signalling: steroids
• Protection against physical injury: triglicerydes in adipose tissue around organs in animals

https://mmegias.webs.uvigo.es/02-english/a-imagenes-grandes/adiposo_blanco.php

B1.1.11—Triglycerides in adipose tissues for energy storage and thermal insulation AND B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Long term energy storage: fats provide 9 kcal/g when consumed through respiration

Fat stored in adipocites is used as energy source and to generate heat, and maintain constant body temperature, in endothermic animals

Seeds fats/oils (mainly unsaturated fatty acids) and use the energy for germination

B1.1.11—Triglycerides in adipose tissues for energy storage and thermal insulation AND B1.1.5—Polysaccharides as energy storage compounds

Energy storage: Fats vs Carbohydrates

B1.1.11—Triglycerides in adipose tissues for energy storage and thermal insulation

Thermal insulation

B1.1.12—Formation of phospholipid bilayers as a consequence of the hydrophobic and hydrophilic regions

Phospholipids are amphipathic molecules

B1.1.13—Ability of non-polar steroids to pass through the phospholipid bilayer

Steroids: non-polar organic molecules with 4 different carbon-based rings

Provides stability and flexibility to the phospholipid bilayer

Cholesterol

Hormones (signalling molecules) that play key roles in the development of male and female reproductive development

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Thinking skills – Experimenting with new strategies for learning

Linking questions

• How can compounds synthesized by living organisms accumulate and become carbon sinks?
• What are the roles of oxidation and reduction in biological systems?