Biology - Carbohydrates and lipids

Properties of carbon

Properties of carbon

• Has four outer shell electrons so it can form four bonds

• Can therefore be a component of large stable molecules

• present in all four major categories of biological molecules

• life one earth is described as “carbon based”

four major categories of biological molecules

carbohydrates

lipids

proteins

nucleic acids

what can carbon do

• bond to other carbon atoms or other atoms

• form molecules with long branched chains

• form long straight unbranched molecules

• form molecules containing cyclic single rings

• form molecules containing multiple rings

• produce tetrahedral structures

the monomers and polymers of main groups

1. carbohydrates - monosaccharides

2. lipids - fatty acids, glycerol, phosphate group

3. proteins - amino acids

4. nucleic acids - nucleotides

formation of macromolecules

formed during condensation reactions, when molecules combine together forming covalent bonds and water is removed

polysaccharides formation

condensation reaction between 2 oH groups of 2 carbohydrates forms the covalent glycosidic bond. water is removed.

polypeptides formation

condensation reaction between 2 amino acids to form a covalent peptide bond.

nucleic acid formation

joined by condensation reactions between phosphate group of one nucleotide and pentose sugar of another. forms a phosphodiester bond.

digestion of polymers

Hydrolysis reaction. Covalent bonds are broken when water is added.

general formula of monosaccharide

CnH2nOn

types of monosaccharides

triose, pentose (ribose), hexose (glucose

glucose

two types: alpha glucose (1st OH group below the ring), beta glucose (1st OH group above the ring) are isomers of eachother

properties of glucose

stable structure (strong covalent bonds), soluble in water (polar nature), easily transportable, source of chemical energy

function of carbohydrates

1. energy storage (starch and glycogen) because they are compact and insoluble

2. structural (cellulose) because it is strong and durable, insoluble and slightly elastic and chemically inert (not easily hydrolysed)

Starch

• storage polysaccharide of plants

• made of alpha glucose monomers

• constructed from amylose and amyloplectein

• amylose: unbranched helix shaped chain with 1,4 glycosidic bonds. Helix shape makes it compact and resistant to digestion

• amyloplectein: 1,4 and 1,6 glycosidic bonds creating branched molecule. branched means it can be easily hydrolysed due to the increased number of terminal glucose molecules

glycogen

• storage polysaccharide in animals and fungi

• 1,4 and 1,6 glycosidic bonds

• more branched than amyloplectein

• can get broken down quickly which supplies the higher metabolic needs of animal cells

• for example, in liver and muscle cells

cellulose

• structural carbohydrates found in cell wall of plants

• molecules are unbranched

• polymer of beta glucose so in order to form glycosidic bonds with itself it must invert itself

• alternating pattern allows hydrogen bonding to occur between strands which increases strength

• several molecules of cellulose = microfibils

role of glycoproteins

formed from combination of carbohydrates and polypeptides (classified as protein)

act as receptor molecule in: cell recognition/ identification, receptors for cell signalling, endocytosis, and cell adhesion

can act as antigens which identify as self or non-self where the non- self would trigger an immune response

Lipids forms

fats, oils, waxes, steroids

lipids characteristics

contain hydrocarbon molecules with many non-polar covalent bonds so lipids are insoluble in water

triglycerides

3 fatty acids bonded to one glycerol molecule, formed by esterification (-OH) of glycerol and (-COOH) of fatty acids (condensation reaction so three water molecules are released)

phospholipids

2 fatty acids bonded to one glycerol molecule, third fatty acid replaced by phosphate ion.

phosphate is polar so phospholipids are amphipathic

properties of triglycerides

• energy dense due to high number of ch bonds (more energy dense than carbohydrates)

• insoluble

• a lot of water is produced when respired called metabolic water and can be used as water source in for example a camels hump and birds egg

• ideal for long term storage

storage of lipids

stored in adipose tissue in animals, subcutaneous fats are below the akin and visceral fats around major organs. fat is stored in adipose cells which are specialised to contain large globules of fat and shrink when fat is respired

used as thermal insulator in for example, seals and walruses.

saturated fatty acids

all single bonds, straight molecules, so lipid molecules containing them can pack tightly together and increase melting point. usually solid at room temp which makes them useful as storage molecules in animals

unsaturated fatty acids

not all single bonds, some double bonds so there is not the max amount of hydrogen atoms, causes tail to kink and bond meaning they can not pack as tightly, so usually liquid at room temp

use of phospholipids

form basic structure of cell membranes, when placed in water the hydrophilic phosphate head orients itself towards the water and the hydrophobic tail away, forming a phospholipid monolayer. when mixed with water phospholipid bilayers are formed.

transport through phospholipid

amphipathic, small non polar molecules are soluble in the bilayer and can cross, larger non polar molecules can also cross bilayer. (eg steroid hormones)

steroid hormones

contain cholesterol (a type of lipid) hydrocarbon region of cholesterol is non-polar, allowing it to cross bilayer

eg. oestradiol and testosterone can cross lipid bilayer