biology - biological molecules

covalent bonding

atoms share a pair of electrons in their outer shells

ionic bonding

ions with opposite charges attract each other - electrostatic attraction

hydrogen bonding

electrons within a molecule not evenly distributed - one region more negatively charged = polar

what do polymers usually contain?

carbon, hydrogen, oxygen and nitrogen

condensation reaction

joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

hydrolysis reaction

breaks a chemical bond between two molecules and involves the use of a molecule of water

what is metabolism?

all the chemical processes that take place in living organisms

why is carbon often used in polymers?

carbon atoms can bond with each other to form a carbon sequence - a backbone

what is a monomer?

the smaller units from which larger molecules are made

examples of monomers

monosaccharides, amino acids and nucleotides

2 isomers of glucose

alpha and beta glucose

what is a reducing sugar?

a sugar that can donate electrons to another chemical

what is the test for reducing sugars?

add 2 cm3 of the food sample to a test tube

add 2cm3 Benedict’s reagent to test tube

heat for 5 minutes in water bath

what is the positive result when testing for reducing sugars?

colour change:

green and yellow = low concentration

orange = medium

brick-red = high

glucose + glucose

maltose

glucose + galactose

lactose

glucose + fructose

sucrose

what is the bond formed when monosaccharides bond?

glycosidic bond

what is an example of a non-reducing sugar?

sucrose

what is the test for non-reducing sugars?

add 2cm3 of food sample and 2cm3 hydrochloric acid to a test tube

heat for 5 minutes - HCl will hydrolyse any disaccharide present

slowly add sodium hydrogencarbonate solution to test tube - neutralise HCl

heat with 2cm3 Benedict’s reagent for 5 minutes

what is the positive result when testing for a non-reducing sugar?

Benedict’s reagent will turn orange-brown

what is a property of all polysaccharides?

insoluble - suitable for storage

where is starch found?

plants - in the form of small grains

what is the test for starch?

place sample into a spotting tile

add 2 drops of iodine

what is the positive result when testing for starch?

colour changes from orange to blue-black

what is starch made up of?

amylose and amylopectin

structure of amylose

1,4 glycosidic bonds

unbranched chain

coiled, very compact

structure of amylopectin

1,4 and 1,6 glycosidic bonds

branched - hydrolysed quickly to release energy

properties of starch

insoluble - doesn’t affect water potential of cell

large, compact

branched - hydrolysed quickly to form alpha glucose which can be used in respiration

what type of glucose is glycogen and starch made up of?

alpha glucose

what bonds are in glycogen?

1,4 and 1,6 glycosidic bonds

properties of glycogen

main storage molecule of animal cells

highly branched = rapidly hydrolysed

compact

insoluble - doesn’t affect water potential of cells

what type of glucose is cellulose made up of?

beta glucose

structure of cellulose

straight, unbranched chains - run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent chains

cellulose molecules group together to form microfibrils - arrange in parallel groups called fibres

what is the purpose of cellulose?

major component of plant cell walls - provides rigidity, prevents cell bursting due to osmotic pressure caused by entry of water, makes cell turgid

2 types of lipids

triglycerides and phospholipids

roles of lipids

phospholipids in cell surface membrane - contribute to flexibility and transfer of lipid-soluble substances

source of energy

waterproofing

insulation

protection

structure of triglycerides

three fatty acid chains and glycerol head - each fatty acid forms an ester bond with glycerol during condensation reaction

what does an unsaturated triglyceride have?

at least one carbon carbon double bond

how does the structure of triglycerides relate to their properties?

high ratio of energy-storing carbon-hydrogen bonds = good energy source

low mass to energy ratio = good storage molecules

insoluble in water = doesn’t affect water potential of cells

structure of phospholipids

hydrophilic phosphate head, glycerol backbone, 2 hydrophobic fatty acid tails

how does the structure of phospholipids relate to their function?

polar = in an aqueous environment they form a bilayer within cell-surface membranes

phosphate heads help to hold at the surface of the cell-surface membrane

structure allows them to form glycolipids by combining with carbohydrates in the cell-surface membrane = important in cell recognition

what are the similarities between the two types of lipids?

contain carbon, hydrogen and oxygen

insoluble in water

soluble in organic solvents

all contain ester bonds

what are the differences between the two types of lipids?

t = 3 fatty acid chains, p = 2 fatty acid chains

p = hydrophilic phosphate head

what is the test for lipids?

add 2cm3 of sample and 5cm3 ethanol to test tube

shake tube to dissolve any lipid

add 5cm3 water and shake

what is the positive result when testing for lipids?

milky-white emulsion

how many amino acids occur in all living organisms?

20

what is the structure of an amino acid?

amino group: N-H-H

carboxyl group: COOH

hydrogen atom: H

R group

what is the bond between amino acids in polypeptides?

peptide bond (between carbon of one AA and nitrogen of other AA)

what is the primary structure of proteins?

polypeptide chain - peptide bonds between amino acids

what is the secondary structure of proteins?

alpha helix or beta pleated sheet

contains hydrogen bonds

what is the tertiary structure of proteins?

further folded, 3D

bonds = disulfide bridges, ionic bonds, hydrophobic-hydrophilic

what is the quaternary structure of proteins?

more than 1 polypeptide chain

may also contain a prosthetic group (non-protein)

give an example of a protein that has a tertiary structure

enzymes

give an example of a protein that has a quaternary structure

haemoglobin - 4 polypeptide chains and 4 haem (iron) groups

what is the test for proteins?

place sample in test tube and add Biuret solution (sodium hydroxide solution + copper II solution)

what is the positive result when testing for proteins?

colour change from blue to violet

what type of proteins are enzymes?

globular

what are enzymes?

biological catalysts

what is the purpose of enzymes?

lower activation energy of reactions

where on the enzyme does the substrate bond?

active site

what is formed when a substrate binds to an active site?

enzyme-substrate complex

explain the induced fit model of enzyme action

the active site changes shape to fit the substrate

explain the lock and key theory

the substrate fits the active site perfectly - complementary shapes

what factors affect enzyme action?

temperature, pH, enzyme concentration, substrate concentration

how do we measure the progress of an enzyme-catalysed reaction?

formation of the products of the reaction and the disappearance of the substrate

explain the effect of temperature on enzyme action

* a rise in temperature increases the kinetic energy of molecules - the molecules move around more rapidly and collide with each other more often = more enzyme-substrate complexes
* temperature rise also causes the bonds in the enzyme molecule to break - active site changes shape, substrate no longer fits = less or no enzyme-substrate complexes formed
* enzyme finally denatures - no longer works

explain the effect of pH on enzyme action

a change in pH alters the charges on the amino acids that make up the active site of the enzyme - the active site changes shape and the substrate no longer fits, enzyme-substrate complex can’t be formed

explain the effect of enzyme concentration on the rate of reaction

* once an active site on an enzyme has acted on a substrate, it is free to repeat the procedure on another substrate molecule = enzymes work efficiently at low concentrations
* as long as there is an excess of substrate, an increase in the amount of enzyme leads to a proportionate increase in the rate of reaction

explain the effect of substrate concentration on the rate of enzyme action-

* if the concentration of enzyme is fixed and substrate concentration is slowly increased, the rate of reaction increases in proportion to the concentration of substrate
* when there is an excess of substrate the rate of reaction plateaus

competitive inhibitors

* they have a molecular shape similar to the substrate = they occupy the active site - block it
* the difference between the concentration of the inhibitor and the concentration of the substrate determines the effect on enzyme activity

non-competitive inhibitors

* attach themselves to the enzyme at the binding site (not the active site) - the inhibitor alters the shape of the active site so the substrate can no longer bind

what does DNA stand for?

deoxyribonucleic acid

what are nucleotides made up of?

* pentose sugar
* phosphate
* a nitrogen-containing base

what are the 5 bases called?

pyrimidine bases = cytosine, thymine and uracil

purine bases = adenine and guanine

what is the bond called that is formed between two nucleotides?

phosphodiester bond

what is the structure of RNA (ribonucleic acid)?

* single polynucleotide chain
* pentose sugar a ribose sugar
* bases = adenine, guanine, cytosine and uracil

who discovered the structure of DNA?

Watson and Crick

what is the structure of DNA?

* pentose sugar - deoxyribose
* bases - adenine, thymine, guanine, cytosine
* made up of 2 polynucleotide strands - double helix
* strands joined together by hydrogen bonds

what are the base pairings?

adenine with thymine - 2 hydrogen bonds

cytosine with guanine - 3 hydrogen bonds

what is the function of DNA?

the hereditary material responsible for passing information from cell to cell and generation to generation

how is DNA adapted to carry out its functions?

* a very stable structure which normally passes from generation to generation without significant change
* 2 strands are joined only with hydrogen bonds - allow them to separate during DNA replication and protein synthesis
* large = carries an immense amount of genetic information

what is DNA replication called and why?

semi-conservative replication - double helix made up of one new strand and one old strand

describe the process of semi-conservative replication

* DNA helicase breaks the hydrogen bonds linking the base pairs of DNA
* double helix unwinds
* each exposed polynucleotide strand acts as a template - free complementary nucleotides bind by specific base pairing
* DNA polymerase joins nucleotides

describe the structure of ATP

* adenine
* ribose sugar
* 3 phosphates

how does ATP store energy?

the bonds between phosphate groups are unstable so have a low activation energy = easily broken, release a considerable amount of energy

what is the equation for the hydrolysis of ATP?

ATP + H2O --→ ADP+ Pi

what enzyme is used during the synthesis of ATP?

ATP synthase

what is the role of ATP?

immediate energy source - hydrolysis of ATP to ADP a single reaction

which processes is ATP used in?

* metabolic processes - build up polymers
* muscle contraction
* active transport

what type of molecule is water?

polar - oxygen atom slightly negative, hydrogen atom slightly positive, the positive pole of one water molecule attracted to the negative pole of another water molecule

what are the properties of water?

* high specific heat capacity
* high latent heat of vaporisation
* cohesion - water molecules stick together (e.g. in xylem)

what is the importance of water to living organisms?

* water the main constituent of all organisms
* water used in hydrolysis reactions
* chemical reactions take place in an aqueous medium
* water used in photosynthesis

how is water used as a solvent?

water dissolves other substances: gases, wastes, inorganic ions, enzymes

what are other important features of water?

* evaporation cools organisms and allows them to control their temperature
* not easily compressed so provides support
* transparent - aquatic plants can photosynthesise

where are inorganic ions found?

in organisms where they occur in solution in the cytoplasm of cells and in body fluids, as well as part of larger molecules

iron ions

found in haemoglobin where they play a role in the transport of oxygen

phosphate ions

form a structural role in DNA molecules and a role in storing energy in ATP molecules

hydrogen ions

important in determining the pH of solutions and therefore the functioning of enzymes

sodium ions

important in the transport of glucose and amino acids across plasma membranes