Carbohydrates

Large Molecules

Monomer (-OH) + Monomer (-H) → Polymer + H2O(l)

Condensation: monomers (e.g. amino acids) join to form polymers (e.g. proteins)

Glycosidic bond forms when two carbohydrate monomers join together

Hydrolysis: break down of a polymer; reverse reaction

Polymers are also called macromolecules (e.g. starch, proteins, triglyceride)

Carbohydrates

Organic molecules in which C, H and O bind together in the ratio Cx(H2O)y

Serve as an energy source important for the brain and cellular respiration

Plants produce carbohydrates by using energy from sunlight

6CO2 + 6H2O + energy (from sunlight) → C6H12O6(carbohydrate) + 6O2

Animals eat plant materials to obtain the produced carbohydrates

They can then be used in animal metabolism to release energy

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

Monosaccharides

Triose (3 carbons)

Product of respiration and photosynthesis

Pentose (5 carbons)

- Ribose

- Deoxyribose

Found in RNA and DNA

nucleic acids

Hexose (6 carbons)

- Glucose

- Fructose

- Galactose

Source of energy in respiration

Main energy source in brain

Found in sweet-tasting fruits

Disaccharides (two sugar residues)

Sucrose (glucose + fructose)

Transport carbohydrates in plants

Maltose (glucose + glucose)

Formed from digestion of starch

Lactose (glucose + galactose)

Carbohydrates found in milk

Polysaccharides (many sugar residues)

Starch (alpha-glucose)

Main storage of carbohydrates 

- in plants

Glycogen (alpha-glucose)

- in humans and animals

Cellulose (beta-glucose)

Important component of the plant cell wall

Starch

Consists of amylopectin and amylose (both are made of α-glucose)

Amylopectin is branched via 1,6-glycosidic bonds

Amylose forms a stiff helical structure via 1,4-glycosidic bonds

Both are compact molecules → starch can be stored in small space

The ends are easily broken down to glucose for respiration

Does not affect water potential as it is insoluble

Readily hydrolysed by the enzyme amylase found in the gut and saliva

Major carbohydrate used in plants

Found as granules (chloroplast)

Each granule contains amylopectin combined by a larger amount of amylose

Commonly used sources are corn (maize), wheat, potato, rice

Glycogen

Branched, storage, polymer of glucose linked via glycosidic bonds

Found in skeletal muscle and in the liver

Chains are linked by alpha-1,4-linkage, branches are linked by alpha-1,6-linkages

Glycogen is broken down to glucose by glycogenolysis (glycogen phosphorylase)

Major site of daily glucose consumption (75%) is the brain via aerobic pathways

Most of the remainder is utilized by erythrocytes, skeletal muscle, and heart muscle

Glucose is obtained from diets or from amino acids and lactate via gluconeogenesis

Storage of glycogen in liver are considered to be main buffer of blood glucose levels

Cellulose

Polysaccharide consisting of long beta-glucose chains

Linked together by hydrogen bonds to form microfibrils

Structural function is a important component of plant cell walls

Its tensile strength helps plant cells in osmosis //cell does not burst in dilute solutions

Proteins

Structure

Proteins are polymers of amino acids

Proteins are made up by different combinations of 20 amino acids

They have a general structure:

The difference between different amino acids is found in the R-group

When two amino acids join together, they release -H and -OH groups highlighted in red below

Peptide bond is formed between alpha-carbon and nitrogen

Condensation reaction

Primary structure of a protein

Sequence of amino acids

Joined together by covalent peptide bonds

Secondary structure

Hydrogen bonds between amino acids

Made of a combination of alpha-helices and beta-pleated sheets

Proportion of α-helix and β-sheet depends on sequence (primary structure)

Tertiary structure

Complex globular shape

Folding and twisting of polypeptides (H-bond)

Polypeptides contain many peptide bonds

Quaternary structure

Several polypeptide chains //several tertiary structures combined

Haemoglobin has 4 polypeptide chains

Collagen has 3 polypeptide chains, twisted around each other

Globular proteins are soluble and has folded chains

Fibrous proteins are insoluble and long, thin, twisted chains

Same amino acid sequence → same shape always

Bonds Found in Proteins

Hydrogen bonds

Between R-groups are easily broken, but are numerous

The more bonds, the stronger the structure

Disulphide bonds

Between sulphur-containing amino acid cystine

Strong bonds found in skin and hair

Denaturation

Destruction of tertiary structure, can be done by heat

Protein structure is lost and cannot reform → dysfunctional

Absorption and Function

Absorption of proteins in the digestive tract

Proteins are taken in as food

They are broken down in the digestive tract into their individual amino acids

Amino acids are recombined in the body to form different proteins

Good food sources include beans, milk, cheese, fish, meat

Several substances are composed of proteins with distinct functions

Keratin, collagen are main components in hair, muscles, tendons, skin

Enzyme amylase digests starch

Haemoglobin transports O2 in the blood stream

Insulin regulates glucose storage

Lipids

Easily dissolved in organic solvents but not in water

Triglycerides (fats and oils)

Serves as an energy reserve in plant and animal cells

Consists of 3 fatty acids linked by ester bonds to glycerol

Excess energy available from food/photosynthesis is stored as triglycerides

Can be broken down later to yield energy when needed

Fats and oils contain twice as many energy stored per unit of weight as carbohydrates

Triglycerides (TG) are also called triacylglycerides (TAG)

Saturated fatty acids

-COOH group without double bonds in the carbohydrate chain

May cause blockage of arteries which can lead to strokes and heart attacks

High melting point / solid at room temperature (fats) / typical animal fats

Unsaturated fatty acids

-COOH group with double bonds in the carbohydrate chain

Low melting point / liquid at room temperature (oils)

Found in plants

Phospholipids

Formed by replacing one fatty acids in a triglyceride with a phosphate group

Phosphate is polar / hydrophilic / does mix with H2O

Fatty acid tails remain non-polar / hydrophobic / insoluble, does not mix with H2O

Form a ball called a micelle when placed in a polar solution (e.g. water)

Cells & Molecules

Cell Division

Cell Types

Cell Ultrastructure

Enzymes

Gene Technology

Genes, DNA, RNA

Large Molecules

Plasma Membrane

Respiration

Content

Large Molecules

Carbohydrates

Monosaccharides

Disaccharides (two sugar residues)

Polysaccharides (many sugar residues)

Starch

Glycogen

Cellulose

Proteins

Lipids