Biology- B1.1: Carbohydrates and Lipids

carbon

• building blocks of life

• forms 4 covalent bonds

• can form numerous stable compounds

carbon-carbon bond

• strong and stable

• longer the c-c chain, the stronger the molecule

• found in chain form, ring form, branch form

macromolecules

large molecules made up of smaller molecules called monomers

condensation reaction

• specific monomers join together to form a macromolecule

• polymerisation reaction

  • two monomers join together

  • one releases the hydroxyl group (OH)

  • the other releases the hydrogen atom (H)

  • giving water and a disaccharide

condensation of glucose molecules

• 2 glucose molecules join together to form maltose

• OH group of Carbon-1 and H atom of carbon-4 are released

• resulting bond that links glucose molecules together is called a 1-4 glycosidic bond

hydrolysis reaction

• process of breaking down macromolecules into monomers (reverse of condensation)

  • OH group of water joins to one of the monosaccharides and the H atom joins to the other to break them into individual monomers

monosaccharides

• simplest form of a carb and can’t be broken down into simpler means by hydrolysis

• fundamental biological molecules that:

  • serve as a source of energy for cells

  • are involved in various cellular processes

types of monosaccharides

• classified by number of carbon atoms

  • pentose: 5 C atoms-ribose

  • hexose: 6 C atoms- glucose, fructose, galactose

properties of glucose

• most common monosaccharide found in nature

• soluble (polar)

• stable

• can be oxidised

• 2 isomers (alpha-glucose and beta-glucose)

  • OH group below in alpha and above in beta

  • different isomers form different polysaccharides

starch

• composed of alpha-glucose molecules

• serves as storage for glucose in plants

• 2 types: amylose and amylopectin

  • amylose: linear, 1-4 glycosidic bonds, coiled

  • amylopectin: highly branched, 1-4 glycosidic bonds with occasional 1-6 glycosidic bonds that create branches, major component (80%-85%)

glycogen

• composed of alpha-glucose molecules

• serves as storage for glucose in animals

• stored mainly in the liver and muscle cells

  • branched, highly compact, coiled

  • 1-4 glycosidic bonds, occasional 1-6 glycosidic bonds every 8-12 glucose molecules

cellulose

• composed of beta-glucose molecules

• essential components of plants cell walls

  • forms a straight chain

  • long chains grouped into bundles called microfibrils

  • strong structure due to how chains are cross-linked

  • hydrogen bonds make the cellulose rigid due to forming a strong and stable lattice

glycoproteins

• proteins that have one or more carbohydrates attached to them

• found in many cellular structures, including the extracellular matrix, cell membranes and secreted proteins.

roles of glycoproteins

• cell-cell recognition

• receptors

• ligands

• structural support

ABO blood groups

• based on the presence of specific glycoproteins on the surface of red blood cells

• called A and B antigens

• presence or absence of antigens determines an individuals blood type

hydrophobic properties of lipids

• non-polar molecules

• low solubility in water

• insoluble in aqueous solutions (hydrophobic nature causes them to repel)

• lipids dissolve in non-polar solvents

triglycerides

• composed of 3 fatty acid chains and a glycerol molecule

• can be found in food and synthesised by the liver

• solid at room temperature

• used for thermal insulation inside animals

formation of triglycerides

• formed by condensation of 1 glycerol molecule and 3 fatty acid molecules

• each time fatty acid joins to glycerol, a water molecule is released

• called an ester bond

phospholipids

• formed by condensation of a modified glycerol molecule with a phosphate group and 2 fatty acids

• a water molecule is released and is called an ester bond

saturated fatty acids

• straight, linear shape because there are no double bonds between carbon atoms

• solid at room temperature as the straight shape allows atoms to be tightly packed

unsaturated fatty acids

• have one or more double bonds, causing them to have a bend/kink

• bends prevent fatty acid atoms from being packed tightly, therefore is a liquid at room temperature

• monounsaturated or polyunsaturated

monounsaturated fats

• 1 double bond in their chain so only 1 bend

• examples: oleic acid found in olive oil, palmitoleic acid found in macadamia nuts

polyunsaturated fats

• 2 or more double bonds in their chains so multiple bends

• examples: linoleic acid found in vegetable oils and alpha-linolenic acid found in fatty fish

degree of unsaturation of fatty acids

• more double bonds, lower melting point

• double bonds disrupt the regular packing, making it easier to break bonds

CIS unsaturated fatty acids

• hydrogen atoms attached to the carbon atoms around the double bond are located on the same side of the molecule

• creates a bend or a kink in the molecule, which causes the molecule to have a less linear structure

TRANS unsaturated fatty acids

• the hydrogen atoms attached to the carbon atoms around the double bond are located on opposite sides of the molecule

• creates a more linear structure and results in a molecule that is less flexible and more rigid

• made industrially and are unhealthy

lipid storage in plants

• Plants store fats or oils as a source of energy in many of their seeds, primarily as unsaturated fatty acids

• energy from the stored fat is used by the germinating seedling to grow

endotherms

animals that rely on metabolic reactions to generate heat to maintain a constant internal body temperature

lipid usage in endotherms

• important source for energy

• stored in adipocytes as liquid droplets and can be broken down into ATP- used to power cellular processes

structure of phospholipids

• hydrophilic head and hydrophobic tail (amphipathic molecules)

• head: phosphate and glycerol molecule (polar)

• tail: 1 unsaturated and 1 saturated fatty acid (non-polar)

phospholipid bilayer

• phospholipids oriented in a special way

• when placed in water, head faces the aqueous solution, tail faces away from the solution

• orient themselves this way

steroids and the phospholipid bilayer

• steroids are naturally occuring hormones

• they are hydrophobic

• steroids can pass through the bilayer and are an important component of it:

  • cholesterol provides it with stability and flexibility

  • some play a role in signalling