biological molecules Flashcards
what are monomers?
the smaller units from which larger molecules are made
examples of monomers
monosaccharides, amino acids, nucleotides
what are polymers
molecules made from a large number of monomers joined together
examples of polymers
polysaccharides, protein, DNA
how are polymers formed?
via a condensation reaction, which joins 2 molecules, creating a chemical bond and removing water
condensation reaction
joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
different types of bonds from condensation reactions
glycosidic (monosaccharides), peptide (amino acids), ester (fatty acids + glycerol)
hydrolysis reaction
breaks a chemical bond between two molecules and involves the use of a water molecule
what are monosaccharides
the monomers from which larger carbohydrates are made
examples of monosaccharides
glucose, fructose, galactose
disaccharides
formed by a condensation reaction between two monosaccharides
examples of disaccharides and their components
glucose+glucose=maltose+water
glucose+fructose=sucrose+water
glucose+galactose=lactose+water
polysaccharides def
a carbohydrate which contains many monosaccharides bonded together by glycosidic bonds; created by condensation reactions
examples of polysaccharides
starch, glycogen, cellulose
isomers
same molecular formula but different structure (alpha-glucose and beta-glucose)
starch
stores glucose in plants
two types of starch
amylose and amylopectin
structure of amylose
formed by a condensation reaction;
long, unbranched helix of alpha-glucose;
forms 1-4 glycosidic bonds;
coils up to form a helix (compact; stores a lot of energy-glucose)
structure of amylopectin
formed by condensation reaction;
long, branched chain of alpha-glucose;
forms straight chains of 1-4 glycosidic bonds and branches out with 1-6 glycosidic bonds (increases surface area and allows enzymes to work simultaneously and hydrolyse it back into glucose)
iodine test
add iodine dissolved in potassium iodide to sample
orange-brown–>neg result
blue-black–>pos result
glycogen
store of glucose in animals
structure of glycogen
formed from α-glucose;
more branches (1-6 gd bonds) than amylopectin (increases surface area and allows enzymes to work simultaneously and hydrolyse it back into glucose);
large and compact maximising the amount of energy it can store;
insoluble means it will not affect the water potential and cannot diffuse out of cells
cellulose
for structural strength in plant cell wall
structure of cellulose
formed from β-glucose;
each alternate glucose is inverted;
formed by many condensation reactions and 1-4 gd bonds;
creates a long, straight chain;
the chains line up parallel to each other, held in place by H bonds which are individually weak, but collectively strong (fibril)
test for reducing sugars
- add 2cm3 of food sample (must be liquid)
- add 2cm3 of benedicts reagent (copper (II) sulfate)
- heat mixture gently in water bath for 5 mins
(green/yellow/orange/brick red-positive result)
(blue- negative result)
test for non-reducing sugars
if reducing sugar is NOT PRESENT.
1. add 2cm3 of the same food sample and 2cm3 of dilute HCl
2. place in water bath for 5 mins (dilute HCl will hydrolyse the disaccharides and polysaccharides into their constituent monosaccharides)
3. add some sodium hydrogencarbonate to neutralise the test tube (benedicts reagent doesn’t work for acids)–> use pH paper to check for neutralisation
4. retest with 2cm3 of benedicts reagent and place in water bath for 5 mins
5. will change to brick-red if non-reducing sugar is present
two types of lipids
triglycerides and phospholipids
triglycerides
one molecule of glycerol with three fatty acids attached to it (ester bond);
fatty acids are tails that are hydrophobic and insoluble
saturated lipids
found in animal fats;
single bonds (C-C)
unsaturated lipids
found in plants;
contain carbon-carbon double bonds allows molecule to bend;
cannot pack together tightly and are liquid at room temperature
triglycerides properties related to its function
energy storage molecules;
metabolic water source (release water if they are oxidised);
low mass—> a lot can be stored without increasing the mass;
long hydrocarbon tails of the fatty acids contain a lot of chemical energy;
insoluble in water (doesn’t affect water potential);
bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic (the tails face inwards, shielding themselves from water with their glycerol heads)
what is a phospholipid
a lipid where one of the fatty acid molecules is replaced by a phosphate group (hydrophilic)
what is the difference between hydrophobic and hydrophilic
hydrophobic - repels water
hydrophilic - attracts water
properties of phospholipids related to its function
make up the bilayer of the cell membranes;
phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side;
the centre of the bilayer is hydrophobic so water-soluble molecules can’t easily pass through–the membrane acts as a barrier
emulsion test
- shake sample with ethanol for 1 min and pour the solution into water
- lipid will show up as a milky white emulsion layer on top
proteins
chain of amino acids
dipeptide
formed when two amino acids join together
polypeptide
when more than two amino acids join together
structure of amino acids
carboxyl group (COOH);
an amine/amino group (NH2);
and an R group (unique) attached to a central carbon atom
how are dipeptides and polypeptides formed
formed through a condensation reaction, a molecule of water is released, the bonds are called peptide bonds
primary structure of a protein
sequence of amino acids in the polypeptide chain
secondary structure of a protein
hydrogen bonds form between the amino acids in the chain;
coils into alpha-helix or beta-pleated sheet
tertiary structure of a protein
the secondary structure is coiled and folded further to form a 3D structure where H bonds, ionic bonds and a disulfide bridge maintains the structure
H bonds (tertiary structure)
numerous and easily broken
ionic bonds (tertiary structure)
form between the carboxyl and amino groups not involved in the peptide bonds;
weaker than disulfide bridge
disulfide bond (tertiary structure)
whenever two molecules of cysteine (amino acid) come close together; the S atom in one cysteine bonds to the S atom in the other cysteine
quaternary structure of a protein
the quaternary structure is the way the polypeptide chains are assembled tg
biuret test
- add a few drops of sodium hydroxide solution to make the sample alkaline
- add some copper (II) sulfate
purple-positive result
blue-negative result
enzymes
proteins that speed up chemical reactions by acting as biological catalysts
how do enzymes speed up reactions
enzymes lower the activation energy by providing alternative pathway
lock and key model
active site is a fixed shape/doesn’t change shape;
it is complementary to one substrate;
after a successful collision, an enzyme-substrate complex forms leading to reaction
induced fit model
- before reaction, enzyme active site not completely complementary to substrate/ doesn’t fit substrate
- active site shape changes as substrate binds and enzyme-substrate complex forms
- this stresses / distorts bonds in substrate leading to a reaction
how does temperature affect the rate of enzyme-controlled reactions
rate of reaction increases as particles gain more kinetic energy;
leading to more collisions;
if temperature is too high enzymes denature
how does pH affect the rate of enzyme-controlled reactions
at very acidic and alkaline pH values the shape of the enzyme is altered so that it is no longer complementary to its specific substrate
how does enzyme concentration affect the rate of enzyme-controlled reactions
there are more active sites for the substrates to bind to
however, its only applicable to a certain extent;
at some point, enzyme activity will plateau because there are too many active sites and not enough substrates
competitive inhibitors
have a similar shape to substrate;
compete with the substrate molecules to bind to the active site but no reaction takes place
what happens when there’s a higher concentration of competitive inhibitors
if there’s a higher conc of inhibitors, it will take up nearly all active sites and hardly any of the substrate will get to the enzyme
what happens when there’s a higher concentration of substrates
if there’s a higher conc of substrates, the substrates chance of getting to an active site before the inhibitor increases
increasing substrate conc increases rate of reaction
non-competitive inhibitors
they bind to the enzyme away from its active site which causes the active to change shape so the substrate molecules can no longer bind to it
what happens when you increase the substrate concentration when non-competitive inhibitors are present
non-competitve inhibitors don’t compete with the substrate molecules to bind to the active site because they are a different shape;
inhibits enzyme activity
what are DNA and RNA
types of nucleic acid
function of DNA
deoxyribonucleic acid;
used to store your genetic info (AGCT)
function of RNA
ribonucleic acid;
transfer genetic information from the DNA to the ribosomes (ACGU)
nucleotide
DNA and RNA are polymers of nucleotides
nucleotides are made from: a pentose sugar (sugar with 5 C atoms) and phosphate group (sugar-phosphate backbone and a nitrogen-containing base (ACGT)
polynucleotide structure
nucleotides join tg to form polynucleotides via a condensation reaction between phosphate group of one nucleotide and the sugar of another;
form a phosphodiester bond
DNA structure
double-helix;
composed of two polynucleotides joined tg by H bonds between complementary bases;
(a+t, c+g)
complementary base pairing
adenine pairs with thymine (2 H bonds)
guanine pairs with cytosine (3 H bonds)
equal amounts of A+T and C+G
RNA structure
a pentose sugar (sugar with 5 C atoms) and phosphate group (sugar-phosphate backbone and a nitrogen-containing base (ACGU)
RNA function
transfer the genetic code from the DNA in the nucleus to the ribosomes
difference between DNA and RNA
- deoxyribose/ribose
- thymine/uracil
- double strand/single strand
- long/short
how does DNA replicate?
semi-conservative replication
what does semi-conservative replication mean?
half of the strands in the new DNA are from the original DNA molecule;
leads to genetic continuity
semi-conservative replication (process)
- DNA helicase breaks the H bonds between bases on the two polynucleotide strands (helix unwinds)
- each original single strand acts as a template for a new strand; complementary base pairing makes free-floating DNA nucleotides are attracted to their complementary exposed bases from original template strand
- condensation reactions join the nucleotides of the new strands together catalysed by DNA polymerase; H bonds form between the bases
- each new DNA molecule contains one strand from the original DNA molecule and one new strand
semi-convervative
each replicated DNA molecule contains of the original DNA strands and one newly synthesised DNA strand
conservative
original DNA remains intact following DNA replication and the two newly-synthesised strands of DNA join together
meselson+stahl experiment
used 2 isotopes of N to show that DNA replicates using semi-conservative replication
(heavy-15);(light-14)
1. grow 2 samples of bacteria (one in lightN broth and one in heavyN broth)
2. sample of DNA taken from each batch and spun in centrifuge
3. bacteria grown in heavyN broth taken out and put in lightN broth and left for one round of DNA replication
4. DNA settled in the middle, mixture of both heavyN and lightN
ATP
adenosine triphosphate;
immediate source of energy for metabolic reactions
what is ATP made up of?
one adenine base, ribose sugar and 3 phosphate groups
where is the energy in ATP stored?
stored in high energy bonds between the phosphate groups and is released via hydrolysis reactions
how is ATP released?
ATP is broken down into ADP and Pi (inorganic phosphate); hydrolysis reaction
phosphate bond in broken down and energy is released; catalysed by ATP hydrolase
ATP hydrolysis reaction
ATP+water–>ADP+Pi (energy)
how can ATP make other compounds more reactive?
transfers energy to different compounds; the released Pi can be bonded onto different compounds to make them more reactive (phosphorylation);
happens to glucose before respiration to make it more reactive
properties of ATP
- released in small, manageable amounts so energy is wasted (cells do not overheat from wasted energy)
- small and soluble and can easily be transported around the cell
- only one bond needs to be broken to release energy (release is immediate)
- can transfer energy to another molecule by transferring one of its phosphate groups (phosphorylation)
- cannot leave the cell, always an immediate supply
is water polar or dipolar?
dipolar
5 properties of water
- metabolite
- solvent
- high specific heat capacity; buffers temperature
- large latent heat of vaporisation
- strong cohesion
where do inorganic ions occur?
in the cytoplasm and body fluids of organisms, in a range of concentrations
hydrogen ions (H+)
lowers the pH of solutions;
impacts enzyme and haemoglobin function
iron ions (Fe2+)
binds to haemoglobin to transport oxygen
sodium ions (Na+)
involved in the co-transport of glucose and amino acids
phosphate ions (PO43-)
component of DNA (forms phosphodiester bonds with deoxyribose);
involved with ATP (makes ADP more reactive)
how does the structure of ATP make it a good source of immediate energy?
the bonds between the phosphate groups have a low activation energy; this means they can be easily broken; breaking the bonds releases energy
what is the structure of ATP?
a pentose sugar (ribose), a nitrogenous base (adenine) and three inorganic phosphate groups
what is the function of ATP?
an immediate source of energy for biochemical processes and synthesis of biological molecules
