Edexcel a level biology topic 1

carbohydrates

molecules which only consist of hydrogen carbon and oxygen,

they are three types of chains,

monosaccharides

disaccharides

polysaccharides

Monosaccharides

Single sugar molecules

such as glucose it contains 6 carbon atoms and there is alpha or beta glucose

ribose

monosaccharide

its a pentose sugar used in RNA.

DNA contains an isomer of ribose called deoxyribose.

disaccharides

maltose- two glucose molecules

sucrose- fructose and glucose

lactose- glucose and galactose

polysaccharides

long chains of monosaccharides

such as glycogen and starch which are made up of alpha glucose

cellulose made up beta glucose.

Both formed via condensation

glycogen

made up of 1-4 and 1-6 glycosidic bonds, it contains a lot of energy branches so it can be hydrolysed and energy can be release quickly.

its also compact so storing it is much easier

starch

stores two polysaccharides

amylose-is an unbranched molecule made up of 1-4 glycosidic bonds, it is also coiled and very compact so it can store a lot of energy

amylopectin- branches and made up of both 1-4 and 1-6 glycosidic bonds, so enzymes are able to digest the branched chains so it is made for quick energy release, it is compact however not as compact as amylose

cellulose

long, unbranched beta glucose monomers, joined by 1-4 glycosidic bonds.

contains microfibrils and microfibres held together by hydrogen bonds

lipids

saturated lipids c-c single bonds and are found in animals

unsaturated made up of c=c double bonds and are found in animals, they have a lower melting point compared to saturated lipids, because of the weaker intermolecular forces and branched hydrocarbons aren't as compact so they have more kinks.

properties of lipids

they're water proof/hydrophobic

compact and release energy quicker than carbs.

non polar

thermal insulation

triglycerides

made up of 3 fatty acids, one glycerol and are joined by ester bonds which are formed in the condensation reaction.

They're used as energy reserves in both plant and animals.

protiens

they contain an anime group and a carboxyl group.

theyre joined by a peptide bond in condensation reaction

primary structure-is the linear sequences of the amino acids

secondary structure-formed by folding by folding the polypeptide chains in alpha or beta helix, it only contains hydrogen bonds.

tertiary structure-3d folding of the secondary structure into a complex shape, joined by either hydrogen or ionic bonding

quaternary-3d arrangement of more than one polypeptide

fibrous proteins

Very little teritary/quaternary structure - mainly secondary structure.

Occasional cross-linkages which form microfibres for tensile strength

Insoluble

Used for structural purposes

such as collagen high tensile strength from hydrogen bonds, collagen forms structure of the bones the cartilage and connective tissues

globular protien

complex tertiary/quaternary structure

forms colloids in water

many uses e.g hormones

e.g haemoglobin which is water soluble, consisting of 4 polypeptide chains.

DNA and protein synthesis

DNA nucleotide contains a deoxyribose, phosphate group and the organic base A,T,C,G.

Pyrimidines-single ring structure, uracil, cytosine and thymine

purines-adenine and guanine

pyrimidines are smaller with only one nitrogen containing ring, whereas purines have more than one.

transcription

hydrogen bonds break via dna helicase and the dna uncoils.

one of the dna strands acts as a template making mRNA this is antisense strands, the coding strand is the sense strand, which has the same nucleotide sequence as the stand being synthesised.

free floating nucleotides line up on the template strand by complimentary base pairing, and adjacent molecules are joined together by phosphodiester bonds, thus forming the molecule RNA, which is catalysed by RNA polymerase.

mRNA the moves out of the nucleus via the nuclear pore, into the ribosomes ready for the next stage of protein synthesis.

Translation

mRNA attaches on the ribosomes on the rough endoplasmic reticulum.

a tRNA molecule, which has the specific amino acid binding site, binds to the mRNA via its anticodon.

Hydrogen bonds form between the anticodon of the tRNA and the codon of mRNA.

a second tRNA molecule binds to the mRNA and the two amino acid forms a peptide bond

a third tRNA joins and the first one leaves the ribosomes.

this process has repeated thus leading the formation of the polypeptide chains until the stop codon has reached the mRNA.

enzymes

they're biological catalysts, increasing the rate of reaction by lowering the activation energy pathway., including both anabolic and catabolic reactions.

the active site is the area of the enzymes where only the substrate binds, meaning enzymes are specific where the substrate binds to.

However when an enzyme and substrate forms a complex, the structure of the enzyme is distorted so that it fits the substrate complex, known as the induced fit model.

inhibitors

used to slow down a chemical reaction, there are two types competitive inhibition and non competitive inhibition.

competitive inhibition- when the inhibitor competes with the substrate molecule for the active site, therefore preventing it from binding, it can be reversed by increasing the substrate concentration.

non competitive inhibition- where the inhibitor doesn't bind the active site, yet binds to the allosteric site, this changes shape of the enzyme which decrease the reaction rate.Increasing substrate does not decrease the rate of reaction.

inorganic ions

they're required for plant growth.

nitrate ions-required to make DNA and amino acids

calcium ions- required for calcium pectate for the middle lamellae of the plants

phosphate ions- required to make ATP and ADP, also DNA and RNA.

magnesium ions- needed to produce chlorophyll

Water

polar molecule due the uneven distribution of the charge, so metabolic reactions can occur.

high specific latent heat- a lot of energy is required to change the temperature, therefore no temperature fluctuations which can be dangerous for animals that live in the rivers.

maximum density- ice is less dense than water, which is an insulating layer in colder regions, where on the top layer of the ice has been melted off.